CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of Provisional U.S. Patent Application No. 62/712,109, filed July 30, 2018, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

[0002] Light-emitting diode (LED) light sources ( e.g ., LED light engines) are often used in place of or as replacements for conventional incandescent, fluorescent, or halogen lamps, and the like. LED light sources may comprise a plurality of light-emitting diodes mounted on a single structure and provided in a suitable housing. LED light sources are typically more efficient and provide longer operational lives as compared to incandescent, fluorescent, and halogen lamps. In order to illuminate properly, an LED driver control device (e.g., an LED driver) may be coupled between an alternating-current (AC) source and the LED light source for regulating the power supplied to the LED light source. The LED driver may regulate either the voltage provided to the LED light source to a particular value, the current supplied to the LED light source to a specific peak current value, or may regulate both the current and voltage.

[0003] LED light sources are typically rated to be driven via one of two different control techniques: a current load control technique or a voltage load control technique. An LED light source that is rated for the current load control technique is also characterized by a rated current (e.g, approximately 350 milliamps) to which the peak magnitude of the current through the LED light source should be regulated to ensure that the LED light source is illuminated to the appropriate intensity and color. In contrast, an LED light source that is rated for the voltage load control technique is characterized by a rated voltage ( e.g ., approximately 15 volts) to which the voltage across the LED light source should be regulated to ensure proper operation of the LED light source. Typically, each string of LEDs in an LED light source rated for the voltage load control technique includes a current balance regulation element to ensure that each of the parallel legs has the same impedance so that the same current is drawn in each parallel string.

[0004] The light output of an LED light source can be dimmed. Different methods of dimming LEDs include a pulse-width modulation (PWM) technique and a constant current reduction (CCR) technique. Pulse-width modulation dimming can be used for LED light sources that are controlled in either a current or voltage load control mode/technique. In pulse-width modulation dimming, a pulsed signal with a varying duty cycle is supplied to the LED light source. If an LED light source is being controlled using the current load control technique, the peak current supplied to the LED light source is kept constant during an on time of the duty cycle of the pulsed signal.

However, as the duty cycle of the pulsed signal varies, the average current supplied to the LED light source also varies, thereby varying the intensity of the light output of the LED light source. If the LED light source is being controlled using the voltage load control technique, the voltage supplied to the LED light source is kept constant during the on time of the duty cycle of the pulsed signal in order to achieve the desired target voltage level, and the duty cycle of the load voltage is varied in order to adjust the intensity of the light output. Constant current reduction dimming is typically only used when an LED light source is being controlled using the current load control technique. In constant current reduction dimming, current is continuously provided to the LED light source, however, the DC magnitude of the current provided to the LED light source is varied to thus adjust the intensity of the light output. Examples of LED drivers are described in greater detail in commonly-assigned U.S. Patent No. 8,492,987, issued July 23, 2010, and U.S. Patent Application Publication No. 2013/0063047, published March 14, 2013, both entitled LOAD CONTROL

DEVICE FOR A LIGHT-EMITTING DIODE LIGHT SOURCE, the entire disclosures of which are hereby incorporated by reference. SUMMARY

[0005] A load control device is described herein for controlling an amount of power delivered to an electrical load. The load control device may comprise a load regulation circuit, a load sense circuit and a control circuit. The load regulation circuit may be configured to control a magnitude of a load current conducted through the electrical load to control the amount of power delivered to the electrical load across a power range. The load regulation circuit may comprise a transformer and an output inductor located on a secondary side of the transformer. The load regulation circuit may further comprise a winding magnetically coupled to and electrically isolated from the output inductor. The load regulation circuit may be configured to generate a sense signal via the winding and the sense signal may be indicative of a voltage developed across the output inductor. The load sense circuit may be configured to generate, based on the sense signal, a load current feedback signal that indicates a magnitude of the load current conducted through the electrical load. The control circuit may be configured to generate, during at least a first portion of the power range, at least one drive signal based on the load current feedback signal. The at least one drive signal may be used to control the load regulation circuit to adjust an average magnitude of the load current conducted through the electrical load. The load current feedback signal may be generated using different techniques based on the operational characteristics of the electrical load.

In one example technique, the sense signal may be integrated and filtered to derive the load current feedback signal. In another example technique, the sense signal may be used in conjunction with an input power of the load control device and an efficiency parameter of the load control device to derive the load current feedback signal. In yet another example technique, values derived from the foregoing two techniques may be blended together to obtain the load current feedback signal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Fig. 1 is a simplified block diagram of an example load control device, such as, a light-emitting diode (LED) driver for controlling the intensity of an LED light source.

[0007] Fig. 2 is a simplified schematic diagram of a forward converter and a load sense circuit of an example LED driver. [0008] Fig. 3 is a diagram of simplified waveforms illustrating the operation of the LED driver of Fig. 2 when the forward converter is operating in a continuous mode of operation ( e.g ., near a high-end intensity).

[0009] Fig. 4 is a diagram of simplified waveforms illustrating the operation of the LED driver of Fig. 2 when the forward converter is operating in a discontinuous mode of operation (e.g., near a low-end intensity).

[0010] Figs. 5-7 are simplified example flowcharts of load current measurement procedures that each may be executed by a control circuit of a load control device for determining a magnitude of a load current conducted through an electrical load.

DETAILED DESCRIPTION

[0011] Fig. 1 is a simplified block diagram of an example load control device, e.g, a light- emitting diode (LED) driver 100, for controlling the amount of power delivered to an electrical load, such as, an LED light source 102 (e.g, an LED light engine), and thus the intensity of the light source. The LED light source 102 is shown as a plurality of LEDs connected in series but may comprise a single LED or a plurality of LEDs connected in parallel or a suitable combination thereof, depending on the particular lighting system. The LED light source 102 may comprise one or more organic light-emitting diodes (OLEDs). The LED driver 100 may comprise a hot terminal H and a neutral terminal that are adapted to be coupled to an alternating-current (AC) power source (not shown).

[0012] The LED driver 100 may comprise a radio-frequency interference (RFI) filter circuit

110, a rectifier circuit 120, a boost converter 130, a load regulation circuit 140, a control circuit 150, a current sense circuit 160, a memory 170, a communication circuit 180, and/or a power supply 190. The RFI filter circuit 110 may minimize the noise provided on the AC mains. The rectifier circuit 120 may generate a rectified voltage VRECT. The boost converter 130 may receive the rectified voltage VRECT and generate a boosted direct-current (DC) bus voltage VBUS across a bus capacitor CBUS. The boost converter 130 may comprise any suitable power converter circuit for generating an appropriate bus voltage, such as, for example, a flyback converter, a single-ended primary-inductor converter (SEPIC), a Cuk converter, or other suitable power converter circuit. The boost converter 120 may operate as a power factor correction (PFC) circuit to adjust the power factor of the LED driver 100 towards a power factor of one.

[0013] The load regulation circuit 140 may receive the bus voltage VBUS and control the amount of power delivered to the LED light source 102 across a power range. For example, the load regulation circuit may control the intensity of the LED light source 102 between a low-end ( e.g ., minimum) intensity LLE (e.g., approximately 0.1-5%) and a high-end (e.g, maximum) intensity LHE (e.g, approximately 100%). An example of the load regulation circuit 140 may be an isolated, half bridge forward converter. An example of the load control device (e.g, LED driver 100) comprising a forward converter is described in greater detail in commonly-assigned ET.S. Patent No. 9,253,829, filed February 2, 2016, entitled LOAD CONTROL DEVICE FOR A LIGHT-EMITTING DIODE LIGHT SOEIRCE, the entire disclosure of which is hereby incorporated by reference. The load regulation circuit 140 may also comprise, for example, a buck converter, a linear regulator, or any suitable LED drive circuit for adjusting the intensity of the LED light source 102.

[0014] The control circuit 150 may be configured to control the operation of the boost converter 130 and/or the load regulation circuit 140. An example of the control circuit 150 may be a controller. The control circuit 150 may comprise, for example, a digital controller or any other suitable processing device, such as, for example, a microcontroller, a programmable logic device (PLD), a microprocessor, an application specific integrated circuit (ASIC), or a field-programmable gate array (FPGA). The control circuit 150 may generate a bus voltage control signal VBUS-CNTL, which may be provided to the boost converter 130 for adjusting the magnitude of the bus

voltage VBUS. The control circuit 150 may receive a bus voltage feedback signal VBUS-FB from the boost converter 130, which may indicate the magnitude of the bus voltage VBUS.

[0015] The control circuit 150 may generate at least one drive signal such as drive signals

VDRI, VDR2. The drive signals VDRI, VDR2 may be provided to the load regulation circuit 140 for adjusting the magnitude of a load voltage VLOAD generated across the LED light source 102 and/or the magnitude of a load current ILOAD conducted through the LED light source 120, for example, to control the intensity of the LED light source 120 to a target intensity LTRGT, which may range from the low-end intensity LLE to the high-end intensity LHE. The control circuit 150 may adjust an operating frequency fop and/or a duty cycle DCINV (e.g, an on time TON) of the drive signals VDRI, VDR2 to adjust the magnitude of the load voltage VLOAD and/or the load current ILOAD. Near the high-end intensity LHE, the load regulation circuit 140 may operate in a continuous mode of operation (e.g, as will be described in greater detail below). Near the low-end intensity LLE, the load regulation circuit 140 may operate in a discontinuous mode of operation (e.g, as will be described in greater detail below).

[0016] The control circuit 150 may receive one or more sense signals from the load regulation circuit 140. For example, the load regulation circuit 140 may generate first and second sense signals VSENSEI, VSENSE2. The control circuit 150 may receive the first sense signal VSENSEI from the load regulation circuit 140 and may be configured to determine an input power PIN of the load regulation circuit 140 in response to the bus voltage feedback signal VBUS-FB and the first sense signal VSENSEI. The LED driver 100 may also comprise a load sense circuit 160 that receives the second sense signal VSENSE2 and generates a load voltage feedback signal VV-LOAD and/or a load current feedback signal VI-LOAD. The load voltage feedback signal VV-LOAD may have a magnitude representative of a magnitude of the load voltage VLOAD while the load current feedback signal VI- LOAD may have a magnitude representative of an average magnitude IAVE of the load current ILOAD. The control circuit 150 may generate a filter control signal VFC for controlling the load sense circuit 160 (e.g, for controlling a portion of the load sense circuit 160). For example, the control circuit 150 may use the filter control signal VFC to control the generation of the load current feedback signal VI-LOAD. The control circuit 150 may be configured to receive the load voltage feedback signal VV-LOAD and/or the load current feedback signal VI-LOAD.

[0017] The control circuit 150 may control the drive signals VDRI, VDR2 to adjust the magnitude of the load current ILOAD to a target load current ITRGT to thus control the amount of power delivered to the electrical load to a target power level (e.g, to control the intensity of the LED light source 102 to the target intensity LTRGT) in response to the first sense signal VSENSEI, the voltage feedback signal VV-LOAD, and/or the load current feedback signal VI-LOAD (e.g, using a control loop). The control circuit may be configured to determine the average magnitude IAVE of the load current ILOAD using different techniques, for example, based on where the target power level falls within the power range of the lighting source 120 ( e.g ., based on where the target intensity LTRGT falls within the intensity range of the LED light source 120). When the target power level is greater than a first power threshold (e.g., when the target intensity LTRGT is greater than a first threshold intensity LTHI such as a high threshold intensity, which may be approximately 60%), the control circuit 150 may be configured to determine the average magnitude IAVE of the load current ILOAD using a first load current measurement technique. For example, when using the first load current measurement technique, the control circuit 150 may calculate the average magnitude IAVE of the load current ILOAD using the input power PIN of the load regulation circuit 140, the magnitude of the load voltage VLOAD (e.g, as determined from the load voltage feedback signal VV-LOAD), and an efficiency h (e.g, a predetermined efficiency parameter) of the load regulation circuit 140. When the target power level is less than a second power threshold (e.g, when the target intensity LTRGT is less than a second threshold intensity LTH2 such as a low threshold intensity, which may be approximately 40%), the control circuit 150 may be configured to determine the average magnitude IAVE of the load current ILOAD using a second load current measurement technique. For example, when using the second load current measurement technique, the control circuit 150 may determine the average magnitude IAVE of the load current ILOAD from the load current feedback signal VI-LOAD.

[0018] When the target power level is less than or equal to the first power threshold and greater than or equal to the second power threshold (e.g, when the target intensity LTRGT is between the first threshold intensity LTHI and the second threshold intensity LTTK), the control circuit 150 may be configured to use both of the first and second load current measurement techniques to determine the average magnitude IAVE of the load current ILOAD. For example, the control circuit 150 may be configured to appropriately mix the average magnitude IAVE of the load current ILOAD determined using the first measurement technique and the average magnitude IAVE of the load current ILOAD determined using the second load current measurement technique to determine the average magnitude IAVE of the load current ILOAD (e.g, as will be described in greater detail below). The load regulation circuit 140 may transition between the continuous and discontinuous modes of operation at an intensity that is greater than the first threshold intensity LTHI to prevent the control circuit 150 from using the second load current measurement technique to determine the average magnitude IAVE of the load current ILOAD when the load regulation circuit is operating in the continuous mode.

[0019] The control circuit 150 may be coupled to the memory 170. The memory 170 may store operational characteristics of the LED driver 100 ( e.g ., the target intensity LTRGT, the low-end intensity LLE, the high-end intensity LHE, etc.). The communication circuit 180 may be coupled to, for example, a wired communication link or a wireless communication link, such as a radio- frequency (RF) communication link or an infrared (IR) communication link. The control circuit 150 may be configured to update the target intensity LTRGT of the LED light source 102 and/or the operational characteristics stored in the memory 170 in response to messages (e.g., digital messages) received via the communication circuit 180. The LED driver 100 may be configured to receive a phase-control signal from a dimmer switch for determining the target intensity LTRGT for the LED light source 102. The power supply 190 may receive the rectified voltage VRECT and generate a direct-current (DC) supply voltage Vcc for powering the circuitry of the LED driver 100.

[0020] Fig. 2 is a simplified schematic diagram of a forward converter 240 (e.g, the load regulation circuit 140) and a load sense circuit 260 (e.g, the current sense circuit 160) of an example LED driver 200 (e.g, the LED driver 100 shown in Fig. 1). The LED driver 200 may also comprise a control circuit 250 for controlling the forward converter 240 to adjust a present intensity LPRES of an LED light source 202 in response to the load sense circuit 260. The control circuit 250 may receive a bus voltage feedback signal VBUS-FB that may indicate a magnitude of a bus voltage VBUS received by the forward converter 240. For example, the bus voltage feedback signal VBUS-FB may be generated by a resistive divider including resistors R204, R206.

[0021] As shown in Fig. 2, the forward converter 240 may comprise a half-bridge inverter circuit including two field effect transistors (FETs) Q210, Q212 for generating a high-frequency inverter voltage VINV from the bus voltage VBUS. The control circuit 250 may generate at least one drive signal (e.g, drive signals VDRI, VDR2) for rendering the FETs Q210, Q212 conductive and non-conductive. The drive signals VDRI, VDR2 may be coupled to gates of the respective

FETs Q210, Q212 via a gate drive circuit 214 (e.g, which may comprise part number L6382DTR, manufactured by ST Microelectronics). The forward converter 240 may comprise a transformer 220 and the inverter voltage VINV may be coupled to the primary winding of the transformer 220 through a DC-blocking capacitor C216 (e.g, which may have a capacitance of approximately 0.047 pF), such that a primary voltage VPRI may be generated across the primary winding.

[0022] The forward converter 240 may comprise a current sense circuit 218 (e.g, including a sense resistor R219) coupled in series with the half-bridge inverter (e.g, in series with the first FET Q210 and the second FET Q212). The current sense circuit 218 may generate a first sense signal VSENSEI in response to a sense current ISENSE conducted through the sense resistor R219 (e.g, conducted through the half-bridge inverter). The control circuit 250 may receive the first sense signal VSENSEI and may be configured to determine the magnitude of the sense current ISENSE of the forward converter 240 in response to the first sense signal VSENSEI. The control circuit 250 may use the magnitude of the sense current ISENSE to determine an input power PIN of the forward

converter 240. For example, the control circuit 250 may use the magnitude of the bus voltage VBUS (e.g, which may be determined from the bus voltage feedback signal VBUS-FB and/or stored in the memory 170) to calculate the input power PIN, e.g, PIN = VBUS TSENSE.

[0023] The secondary winding of the transformer 220 may generate a secondary

voltage VSEC and may be coupled to the AC terminals of a rectifier bridge 224 (e.g, a full-wave diode rectifier bridge) for rectifying the secondary voltage generated across the secondary winding. The positive DC terminal of the rectifier bridge 224 may be coupled to the LED light source 202 through an output inductor L226 (e.g, an energy storage inductor, which may be located on the secondary side of the transformer and may have an inductance of approximately 400 mH), such that an inductor current IL226 may be conducted through the output inductor L226 and a load

voltage VLOAD may be generated across an output capacitor C228 (e.g, which may have a capacitance of approximately 3 pF). The transformer 220 may provide electrical isolation between the line voltage input of the LED driver 200 (e.g. , the hot terminal and the neutral terminal N) and the LED light source 202.

[0024] The control circuit 250 may be configured to pulse-width modulate (PWM) the drive signals VDRI, VDR2 to control the present intensity LPRES of the LED light source 202 towards a target intensity LTRGT, which may range from the low-end intensity LLE to the high intensity LHE. The control circuit 250 may be configured to adjust respective duty cycles DCi, DC2 of the drive signals VDRI, VDR2 to adjust the present intensity LPRES. Near the high-end intensity LHE, the load regulation circuit 240 may operate in a continuous mode of operation. The continuous mode of operation may refer to a mode in which the inductor current IL226 may be continuous (e.g, the inductor current IL226 may be continuously above zero amps). Near the low-end intensity LLE, the load regulation circuit 140 may operate in a discontinuous mode of operation. The discontinuous mode of operation may refer to a mode in which the inductor current IL226 may be discontinuous (e.g, the inductor current IL226 may reach approximately zero amps during at least a portion of an operating period of the drive signals VDRI, VDR2).

[0025] The control circuit 250 may receive a load-voltage feedback signal VV-LOAD and/or a load-current feedback signal VI-LOAD from the load sense circuit 260. The load sense circuit 260 may generate the load-voltage feedback signal VV-LOAD and/or load-current feedback signal VI-LOAD in response to a second sense signal VSENSE2 received from the load regulation circuit 240. For example, the second sense signal VSENSE2 may be generated across a winding 230 magnetically coupled to the output inductor L226 of the load regulation circuit 140 and may be representative of the magnitude of an inductor voltage VL226 generated across the output inductor. The winding 230 may be electrically isolated from the output inductor L226, and as such the load sense circuit 260 (and thus the line voltage input of the LED driver 200) may be electrically isolated from the load regulation circuit 240 (and thus the LED light source 202).

[0026] When the target intensity LTRGT of the LED light source 202 is greater than a first threshold intensity LTHI (e.g, approximately 60% of a maximum intensity of the lighting load), the control circuit 250 may be configured to determine the average magnitude IAVE of the load current ILOAD from the load-voltage feedback signal VV-LOAD using a first load current measurement technique. The load sense circuit 260 may comprise a peak detect circuit 270 for generating the load-voltage feedback signal VV-LOAD from the second sense signal VSENSE2. When the FETs Q210, Q212 of the load regulation circuit 240 are non-conductive, the output inductor L226 is electrically coupled in parallel with the LED light source 202, and the magnitude of the inductor voltage VL226 may be approximately equal to the load voltage VLOAD. When the FETs Q210, Q212 of the load regulation circuit 240 are non-conductive ( e.g ., when the magnitude of the inductor voltage VL226 may be approximately equal to the load voltage VLOAD), a capacitor C272 may be configured to charge through a diode D274 and the winding 230 to the peak magnitude of the second sense signal V SENSE2. Because of the orientation of the diode D274, a negative voltage VNEG (e.g., voltage having a negative polarity) may be generated at the junction of the capacitor C272 and the diode D274. The negative voltage VNEG may be received by an inverting amplifier 275 (e.g, an operational amp inverter), which may generate a positive voltage VPOS (e.g, a voltage having positive polarity). The positive voltage VPOS may be filtered by a resistor-capacitor (RC) filter circuit comprising a resistor R276 (e.g, having a resistance of approximately 12.1 1<W) and a capacitor C278 (e.g, having a capacitance of approximately 1000 pF). The load-voltage feedback signal VV-LOAD may be generated at the junction of the resistor R276 and the capacitor C278 and may have a magnitude (e.g, a DC magnitude) that is representative of the magnitude of the load voltage VLOAD. The control circuit 250 may calculate the average magnitude IAVE of the load current ILOAD using the input power PIN of the forward converter 240 (e.g, determined from the magnitude of the bus voltage VBUS and the first sense signal VSENSEI), the magnitude of the load voltage VLOAD determined from the load-voltage feedback signal VV-LOAD, and an efficiency h of the forward converter 240, e.g, IAVE = (h PIN) / VLOAD, where h PIN may represent the output power POUT of the load control device.

[0027] When the target intensity LTRGT of the LED light source 202 is less than a second threshold intensity LTH2 (e.g, approximately 40% of the maximum intensity of the lighting load), the control circuit 250 may be configured to determine the average magnitude IAVE of the load current ILOAD from the load-current feedback signal VI-LOAD using a second load current measurement technique. The load sense circuit 260 may comprise an integrator circuit 280 and a filter circuit 282 (e.g, such as a boxcar filter circuit) for generating the load-current feedback signal VI-LOAD. The integrator circuit 280 may integrate the second sense signal VSENSE2 and may generate an integrated signal VINT, which may be approximately equal to or may be a scaled version of (e.g, a percentage of) the inductor current IL226. For example, the integrator circuit 280 may comprise an operational amplifier integrator. Since the magnitude of the inductor voltage VL226 may be a function of the derivative of the inductor current IL226, the integral of the second sense signal VSENSE2 may be approximately equal to or may be a scaled version of ( e.g . , a percentage of) the inductor current IL226, where the scaling factor may be dependent upon a number of factors including the inductance of the output inductor L226, the number of turns of the winding 230, and/or the values of the components of the integrator circuit 280.

[0028] The average magnitude IAVE of the load current ILOAD may be approximately equal to the average magnitude IAVE of the inductor current IL226. The filter circuit 282 may be configured to filter the integrated signal VINT to generate the load-current feedback signal VI-LOAD, which may have a DC magnitude that is representative of the average magnitude IAVE of the load current ILOAD. The filter circuit 282 may operate to improve the performance of the load control device in various ways. For example, when the forward converter 240 is operating in the discontinuous mode (e.g., near the low-end intensity LLE), the load current ILOAD and/or the inductor current IL226 may reach

approximately zero amps during at least a portion of the operating periods of the drive signals VDRI, VDR2 (e.g, the inductor current IL226 and/or the load current ILOAD may comprise one or more pulses in the discontinuous mode). The pulses of the load current ILOAD (e.g, and thus pulses of the inductor current IL226) may be far apart and the average magnitude IAVE of the integrated signal VINT may be so small that the control circuit 250 may not able to appropriately sample and/or measure the average magnitude IAVE of the integrated signal VINT. The filter circuit 282 may be configured to filter (e.g, only filter) the integrated signal VINT during a filter window time period TFW (e.g, a time window) around the pulses of the inductor current IL226. The filter circuit 282 may comprise a controllable switching device (e.g, a controllable switch 284) that may be rendered conductive and non-conductive in response to a filter control signal VFC generated by the control circuit 250. This way, the control circuit 250 may control the controllable switch 284 to selectively couple the integrated signal VINT to a filter (e.g, an RC filter) comprising a resistor R286 (e.g, having a resistance of approximately 510 W) and a capacitor C288 (e.g, having a capacitance of

approximately 0.47 pF). The load-current feedback signal VI-LOAD may be generated at the junction of the resistor R286 and the capacitor C288.

[0029] Since the control circuit 250 is generating the drive signals VDRI, VDR2, which cause the generation of the pulses of the inductor current IL226, the control circuit 250 may generate the filter control signal VFC to render the controllable switch 284 conductive and non-conductive in coordination with the drive signals VDRI, VDR2. For example, the control circuit 250 may drive the filter control signal VFC high ( e.g ., towards the supply voltage Vcc) to render the controllable switch 284 conductive at approximately the same time as driving either of the drive

signals VDRI, VDR2 high. The control circuit 250 may maintain the filter control signal VFC high for filter window time period TFW, which may be at least as long as the length of each pulse of the inductor current IL226 (e.g., at least as long as the length of each pulse of the load current ILOAD). At the end of the filter window time period TFW, the control circuit 250 may drive the filter control signal VFC low (e.g, towards zero volts) to render the controllable switch 284 non-conductive. The capacitor C288 may charge when the controllable switch 284 is conductive and may maintain the magnitude of the load-current feedback signal VI-LOAD substantially constant when the controllable switch 284 is non-conductive. As a result, the magnitude of the load-current feedback signal VI-LOAD may indicate an average magnitude IWIN of the load current ILOAD during (e.g, only during) the filter window when the filter control signal VFC is high. The control circuit 250 may be configured to calculate the average magnitude IAVE of the load current ILOAD based on the average magnitude IWIN of the load current ILOAD during the filter window and a present duty cycle DCsw of the filter control signal VFC, e.g., IAVE = DCsw IWIN.

[0030] The filter control signal VFC may be used to reset the integrator circuit 280 at the end of the filter window when the magnitude of the filter control signal VFC is high. For example, the filter control signal VFC may be coupled to the integrator circuit 280 via an inverter circuit 289, which may be configured to generate an inverted signal VINV. When the filter control signal VFC is driven low (e.g, towards circuit common) at the end of the filter window, the inverted signal VINV may be driven high to reset the inverter circuit 280.

[0031] When the target intensity LTRGT of the LED light source 2020 is less than or equal to the first threshold intensity LTHI and greater than or equal to the second threshold intensity LTH2, the control circuit 250 may be configured to use both of the load-voltage feedback signal VV-LOAD and the load-current feedback signal VI-LOAD to determine the average magnitude of the load current ILOAD. For example, the control circuit 150 may be configured to appropriately mix the average magnitude of the load current ILOAD determined from the load-voltage feedback signal VV-LOAD, and the average magnitude of the load current ILOAD determined from the load-current feedback signal VI-LOAD ( e.g ., as will be described in greater detail below) to derive an estimated average magnitude of the load current ILOAD.

[0032] Fig. 3 is a diagram of simplified waveforms illustrating the operation of the LED driver 200 when the forward converter 240 is operating in the continuous mode of operation (e.g., near the high-end intensity LHE). The drive signals VDRI, VDR2 may be characterized by an operating frequency fop and an operating period TOP. During each period of the drive signals VDRI, VDR2, the control circuit 250 may drive one of the drive signals VDRI, VDR2 high (e.g, towards the supply voltage Vcc) for an on-time TON (e.g, between times ti and t2 in Fig. 3) to render the respective FET Q210, Q212 conductive for the on-time at different times (e.g, the FETs Q210, Q212 are conductive at different times). The control circuit 250 may then drive signal VDRI, VDR2 low for the remainder of the period (e.g, between times t2 and t3 in Fig. 3). During the next period of the drive signals VDRI, VDR2, the control circuit 250 may drive the other one of the drive signals VDRI, VDR2 high for the on-time TON (e.g, between times t3 and t ₄ in Fig. 3) to render the respective FET Q210, Q212 conductive for the on-time.

[0033] When the high-side FET Q210 is conductive, the bus voltage VBUS may be coupled across the series combination of the capacitor C216 and the primary winding of the transformer 220 allowing the capacitor C216 to charge, such that the primary voltage VPRI has a magnitude of approximately half of the magnitude of the bus voltage VBUS. Accordingly, the magnitude of the primary voltage VPRI across the primary winding of the transformer 220 may be equal to

approximately half of the magnitude of the bus voltage VBUS (e.g, VBUS/2). When the low-side FET Q212 is conductive, the capacitor C216 may be coupled across the primary winding, such that the primary voltage VPRI may have a negative polarity with a magnitude equal to approximately half of the magnitude of the bus voltage VBUS.

[0034] When either of the high-side and low-side FETs Q210, Q212 are conductive, a secondary voltage VSEC may be developed across the secondary winding of the transformer 220. Because the secondary winding of the transformer 220 is coupled to the output inductor L226 and the LED light source 202 through the rectifier bridge 224, the secondary voltage VSEC may be produced across the series combination of the output inductor L226 and the LED light source 202 when either of the FETs Q210, Q212 are conductive. At this time, the magnitude of the inductor voltage VL226 may be at a peak magnitude VL-PK and the magnitude of the output inductor current IL226 conducted by the output inductor L226 may increase with respect to time as shown in Fig. 3. When the FETs Q210, Q212 are non-conductive, the output inductor L226 may be coupled in parallel with the LED light source 202 and the magnitude of the inductor voltage VL226 may have a negative peak magnitude -VL-PK. In addition, the magnitude of the inductor current IL226 may decrease in magnitude with respective to time when the FETs Q210, Q212 are non-conductive.

Since the forward converter 240 is operating in the continuous mode, the magnitude of the inductor current IL226 does not reach zero amps (e.g, the magnitude of the inductor current IL226 is continuously above zero amps during respective operating periods of the drive control signals VDRI, VDRZ). In the continuous mode, the operating period TOP of the drive signals VDR may be equal to a minimum operating period TMIN. The inductor current IL226 may be characterized by a peak magnitude IL-PK and an average magnitude IL-AVG. The control circuit 250 may increase and/or decrease the on-time TON of the drive control signals VDRI, VDR2 (e.g, and the duty cycle DCINV of the inverter voltage VINV) to respectively increase and decrease the average magnitude IL-AVG of the output inductor current II, and thus respectively increase and decrease the intensity of the LED light source 202.

[0035] Near the high-end intensity LHE (e.g, when the forward converter 240 is operating in the continuous mode of operation), the control circuit 250 may determine the average magnitude of the load current ILOAD from the load-voltage feedback signal VV-LOAD using the first load current measurement technique. When the FETs Q210, Q212 are rendered non-conductive (e.g, at times t2 and t ₄ in Fig. 3), the capacitor C272 of the peak detect circuit 270 may charge to the peak magnitude of the second sense signal VSENSE2 for generating the load-voltage feedback signal VV-LOAD across the capacitor C278. When either of the FETs Q210, Q212 are conductive, the capacitor C278 may maintain the magnitude of the load-voltage feedback signal VV-LOAD substantially constant (e.g, between times t3 and t ₄ ). The control circuit 250 may sample (e.g, periodically sample) the magnitude of the load-voltage feedback signal VV-LOAD and calculate the average magnitude of the load current ILOAD.

[0036] Fig. 4 is a diagram of simplified waveforms illustrating the operation of the LED driver 200 when the forward converter 240 is operating in the discontinuous mode of operation ( e.g ., near the low-end intensity LLE). The control circuit 250 may generate the drive signals VDRI, VDR2 with the operating period TOP (e.g., the same operating period as in Fig. 3), but with a smaller length for the on-time TON (e.g, compared to the on-time in Fig. 3).

[0037] When either of the high-side and low-side FETs Q210, Q212 are conductive, the magnitude of the inductor voltage VL226 may be at the peak magnitude VL-PK and the magnitude of the output inductor current IL226 conducted by the output inductor L226 may increase with respect to time (e.g, between times ti and t2 and/or between times t ₄ and ts). When the FETs Q210, Q212 are non-conductive, the magnitude of the inductor voltage VL226 may be at the negative peak

magnitude -VL-PK, and the magnitude of the inductor current IL226 may decrease in magnitude with respective to time until the magnitude of the inductor current IL226 reaches approximately zero amps (e.g, between times t2 and t3 and/or between times ts and to). Since the forward converter 240 is operating in the discontinuous mode, the magnitude of the inductor current IL226 may be at approximately zero amps for the remainder of the present operating period TOP (e.g, between times t3 and t ₄ and/or between t ₆ and t7). At the beginning of each period, the output inductor L226 may conduct a pulse of current (e.g, a triangular pulse), as shown in Fig. 4. Because the pulses of current may be spaced apart by larger amounts as the present intensity LPRES is decreased towards the low-end intensity LLE, the average magnitude IL-AVG of the inductor current IL226 may become very small (e.g, much smaller than the peak magnitude IL-PK of the inductor current IL226).

[0038] Near the low-end intensity LLE (e.g, when the forward converter 240 is operating in the discontinuous mode of operation), the control circuit 250 may determine the average magnitude of the load current ILOAD (e.g, from the load-current feedback signal VI-LOAD) using the second load current measurement technique. The integrator circuit 280 of the load sense circuit 260 may integrate the second sense signal VSENSE2 to generate the integrated signal VINT, which may be equal to or may be a scaled version of the inductor current IL226 as shown in Fig. 4. Since the average magnitude IL-AVG of the inductor current IL226 may be very small (e.g., close to approximately zero amps) near the low-end intensity LLE, the control circuit 250 may be configured to generate the filter control signal VFC to enable the filter circuit 282 to filter (e.g, only filter) the integrated signal VINT during filter window time periods TFW around the pulses of the inductor current IL226. The control circuit 250 may generate the filter control signal VFC in coordination with the drive signals VDRI, VDR2. For example, the control circuit 250 may generate the filter control signal VFC as a pulse-width modulated signal having a period equal to or similar as the operating period TOP of the drive signals VDRI, VDR2. The control circuit 250 may drive the magnitude of the filter control signal VFC high at approximately the same time or slightly before the time at which either of the drive signals VDRI, VDR2 is driven high (e.g, at times ti and t ₄ in Fig. 4). For example, the filter window time periods TFW of the filter control signal VFC may each be approximately equal to twice the on-time TON of the drive signals VDRI, VDR2. In addition, the filter window time periods TFW of the filter control signal VFC may each be longer than twice the on-time TON of the drive signals VDRI, VDR2, for example, up to approximately the minimum operating period TMIN of the drive signals. The control circuit 250 may drive the magnitude of the filter control signal VFC low at the ends of the filter window time periods TFW (e.g, at times t3 and te in Fig. 4). When the filter control signal VFC is high, the filter circuit 282 may be configured to filter the integrated signal VINT to generate the load-current feedback signal VI-LOAD. When the filter control signal VFC is low (e.g, between times t3 and t ₄ ), the capacitor C288 of the filter circuit 280 may maintain the magnitude of the load-current feedback signal VI-LOAD substantially constant (e.g, the magnitude of the load-current feedback signal VI-LOAD between times t3 and t ₄ may be substantially similar to the magnitude of the load-current feedback signal VI-LOAD between times ti and t2). The control circuit 250 may sample (e.g, periodically sample) the magnitude of the load-current feedback signal VI-LOAD to determine the average magnitude of the load current ILOAD.

[0039] Fig. 5 is a simplified example flowchart of a first load current measurement procedure 500 that may be executed by a control circuit of a load control device (e.g, the control circuit 150 of the LED driver 100 and/or the control circuit 250 of the LED driver 200) for controlling an electrical load (e.g, an LED light source, such as the LED light source 202). For example, the control circuit 250 may execute the first load current measurement procedure 500 to determine an average magnitude of a load current conducted through the electrical load ( e.g ., the load current ILOAD described herein) using a first load current measurement technique. The load control device may comprise a load regulation circuit (e.g., the load regulation circuit 140 and/or the forward converter 240), which may in turn comprise an output inductor. The output inductor may be magnetically coupled to a winding for generating a sense voltage that may be used to generate a load-voltage feedback signal. The load-voltage feedback signal may have a magnitude

representative of the magnitude of a load voltage generated across the electrical load (e.g, the load- voltage feedback signal VV-LOAD).

[0040] The control circuit may execute the first load current measurement procedure 500, for example, periodically at 510 (e.g, when a target power level of the electrical load is above a high threshold). In addition, the first load current measurement procedure 500 may be executed as part of another load current measurement procedure. At 512, the control circuit may determine the magnitude of the bus voltage VBUS. For example, the control circuit 250 may determine the magnitude of the bus voltage VBUS from the bus voltage feedback signal VBUS-FB at 512. In addition, the control circuit 250 may recall a target bus voltage (e.g, for controlling the bus voltage control signal VBUS-CNTL) from memory at 512 to use as the magnitude of the bus voltage VBUS. At 514, the control circuit may determine the magnitude of the sense current ISENSE. (e.g. , shown in Fig. 2). For example, the control circuit 250 may determine the magnitude of the sense current ISENSE at 514 from the first sense signal VSENSEI generated by the current sense circuit 218 when the second FET Q212 is conductive. At 516, the control circuit may calculate the input power PIN of the load control device using the determined magnitude of the bus voltage VBUS and the determined magnitude of the sense current ISENSE, e.g, PIN = VBUS TSENSE.

[0041] At 518, the control circuit may calculate the output power POUT of the load control device using the calculated input power PIN and an efficiency h of the power regulation circuit. For example, the efficiency h may be a predetermined value stored in memory (e.g, the memory 170).

At 520, the control circuit may determine the magnitude of the load voltage VLOAD, e.g, by sampling and processing (e.g, scaling) the load-voltage feedback signal VV-LOAD. At 522, the control circuit may calculate the magnitude of the load current ILOAD using the calculated output power POUT and the determined load voltage VLOAD, e.g, ILOAD = POUT/VLOAD, before the first load current measurement procedure 500 exits.

[0042] Fig. 6 is a simplified example flowchart of a second load current measurement procedure 600 that may be executed by a control circuit of a load control device (e.g, the control circuit 150 of the LED driver 100 and/or the control circuit 250 of the LED driver 200) for controlling an electrical load (e.g, an LED light source, such as the LED light source 202). For example, the control circuit 250 may execute the second load current measurement procedure 600 to determine an average magnitude of a load current of the electrical load (e.g, the load current ILOAD described herein) using a second load current measurement technique. The load control device may comprise a load regulation circuit (e.g, the load regulation circuit 140 and/or the forward converter 240) which may in turn comprise an output inductor. The output inductor may be magnetically coupled to a winding for generating a sense voltage that may be used to generate a load-current feedback signal. The load-current feedback signal may have a magnitude representative of the magnitude of a load current conducted through the electrical load (e.g, the load-current feedback signal VI-LOAD).

[0043] The control circuit may execute the second load current measurement procedure 600, for example, periodically at 610 (e.g, when a target power level of the electrical load is below a low threshold). In addition, the second load current measurement procedure 600 may be executed as part of another load current measurement procedure. At 612, the control circuit may drive a filter control signal (e.g, the filter control signal VFC) high to enable a filter circuit (e.g, a boxcar filter circuit) to adjust the magnitude of the load-current feedback signal. At 614, the control circuit may wait for a time period (e.g, the filter window time period TFW as shown in Fig. 4), before driving the filter control signal low to disable the filter circuit from adjusting the magnitude of the load-current feedback signal at 616. At 618, the control circuit may determine the average magnitude of the load current ILOAD, e.g, by sampling and processing (e.g, scaling) the magnitude of the load-current feedback signal VI-LOAD.

[0044] Fig. 7 is a simplified flowchart of a third load current measurement procedure 700 that may be executed by a control circuit of a load control device (e.g, the control circuit 150 of the LED driver 100 and/or the control circuit 250 of the LED driver 200) for controlling an electrical load ( e.g ., an LED light source, such as the LED light source 202). For example, the control circuit may execute the third load current measurement procedure 600 to determine an average magnitude of a load current of the electrical load (e.g., the load current ILOAD described herein) using multiple load current measurement techniques (e.g, using the first and second load current measurement procedures 500, 600 shown in Figs. 5 and 6). The load control device may comprise a load regulation circuit (e.g, the load regulation circuit 140 and/or the forward converter 240).

[0045] The control circuit may execute the third load current measurement procedure 700, for example, periodically at 710. For example, if the present intensity LPRES of the LED light source is greater than a first threshold intensity LTHI (e.g, approximately 60% of a maximum intensity of the LED light source) at 712, the control circuit may determine the average magnitude of the load current ILOAD using a first load current measurement technique at 714, for example, by executing the first load current measurement procedure 500 (e.g, as shown in Fig. 5). If the present intensity LPRES of the LED light source is less than a second threshold intensity LTH ₂ (e.g, approximately 40% of the maximum intensity of the LED light source) at 716, the control circuit may determine the average magnitude of the load current ILOAD using a second load current measurement technique at 718, for example, by executing the second load current measurement procedure 600 (e.g, as shown in Fig. 6).

[0046] If the present intensity LPRES of the LED light source is less than or equal to the first threshold intensity LTHI at 712 and greater than or equal to the second threshold intensity LTH ₂ at 716 (e.g, if the present intensity LPRES of the LED light source is between the first threshold

intensity LTHI and the second threshold intensity LTH2), the control circuit may use both of the first and second load current measurement techniques and combine the values (e.g, scaled versions of the values) determined from the first and second load current measurement techniques to determine the average magnitude of the load current ILOAD. For example, the control circuit may determine a first value ILOADI for the average magnitude of the load current ILOAD using the first load current measurement technique at 720, and determine a second value ILOAD2 for the average magnitude of the load current ILOAD using the second load current measurement technique at 722. At 724, the control circuit may determine a scaling factor a for calculating the average magnitude of the load current ILOAD. For example, the first and second values ILOADI, ILOAD2 may be blended (e.g, linearly blended) together between the first and second threshold intensities LTHI, LTH2. The scaling factor a may represent a percentage distance of the present intensity LPRES between the first and second threshold intensities LTHI, LTH2, e.g. ,

a = (LPRES - LTH2) / (LTHI - LTH2).

At 726, the control circuit may calculate the average magnitude of the load current ILOAD based on two components derived using the first and second load current measurement techniques and by applying the scaling factor a to those components, e.g. ,

ILOAD = a · ILOADI + (1 - a) ILOAD2

where a · ILOADI and (1 - a) ILOAD2 may represent respective portions of ILOADI, ILOAD2 used to calculate the average magnitude of the load current ILOAD. After determining the average magnitude of the load current ILOAD at 714, 718, or 726, the third load current measurement procedure 700 may exit.

[0047] Although described with reference to an LED driver, one or more embodiments described herein may be used with other load control devices. For example, one or more of the embodiments described herein may be performed by a variety of load control devices that are configured to control of a variety of electrical load types, such as, for example, a LED driver for driving an LED light source (e.g., an LED light engine); a screw-in luminaire including a dimmer circuit and an incandescent or halogen lamp; a screw-in luminaire including a ballast and a compact fluorescent lamp; a screw-in luminaire including an LED driver and an LED light source; a dimming circuit for controlling the intensity of an incandescent lamp, a halogen lamp, an electronic low- voltage lighting load, a magnetic low-voltage lighting load, or another type of lighting load; an electronic switch, controllable circuit breaker, or other switching device for turning electrical loads or appliances on and off; a plug-in load control device, controllable electrical receptacle, or controllable power strip for controlling one or more plug-in electrical loads (e.g, coffee pots, space heaters, other home appliances, and the like); a motor control unit for controlling a motor load (e.g, a ceiling fan or an exhaust fan); a drive unit for controlling a motorized window treatment or a projection screen; motorized interior or exterior shutters; a thermostat for a heating and/or cooling system; a temperature control device for controlling a heating, ventilation, and air conditioning (HVAC) system; an air conditioner; a compressor; an electric baseboard heater controller; a controllable damper; a humidity control unit; a dehumidifier; a water heater; a pool pump; a refrigerator; a freezer; a television or computer monitor; a power supply; an audio system or amplifier; a generator; an electric charger, such as an electric vehicle charger; and an alternative energy controller ( e.g ., a solar, wind, or thermal energy controller). A single control circuit may be coupled to and/or adapted to control multiple types of electrical loads in a load control system.