BACKGROUND [0002] High-voltage power sources are well-known in the art. For example, Figure 1 illustrates a conventional high voltage power source. The configuration and operation of the Figure 1 conventional high-voltage power source is now briefly discussed. Thereafter, some disadvantages of the Figure 1 conventional high-voltage power source are described.

[0003] Turning now to Figure 1, a conventional high-voltage power source circuit 100 is schematically illustrated. As can be seen from Figure 1, a number of the circuits of the power source circuit 100 are powered by a low- voltage power circuit 104. A circuit 101 is provided for each channel of high- voltage output. The variable high-voltage output 110 of each circuit 101 is controlled nominally by an analog input voltage control signal 103 provided to a variable high-voltage power source circuit 106 of that circuit 101. The analog input voltage control signal 103 for each circuit 101 is provided to the variable high-voltage power source for the circuit 101 from a microprocessor 102 via a digital-to-analog converter (DAC) 118.

[0004] For each circuit 101, the current in the high-voltage output signal of the variable high-voltage power source circuit 106 is measured by an analog current sense circuit 114 (typically comprised of high-gain current sense amplifier components), as a function of a voltage drop across a current sense resistance 108.

The analog sense circuit 114 generates an analog current sense signal nominally

indicative of the current of the high-voltage output signal of the variable high- voltage power source circuit 106.

[0005] A"tracking"power supply circuit 112 operates on the output of the variable high-voltage power source circuit 116 to generate a low-voltage power signal, which is used to power the analog current sense circuit 114 and tracks the output of the variable high-voltage power source circuit 106.

[0006] The current sense output of the current sense circuit 114 is provided to an analog isolation barrier circuit 116, also powered by the tracking signal from the tracking power supply 112. The analog isolation barrier circuit 116 voltage-translates the analog current sense signal, and the thus-translated analog current sense output is provided to a ground-referenced analog-to-digital converter (ADC) 120. The digital output of the ADC 120 is then provided to microprocessor 102.

[0007] A significant disadvantage of conventional high-voltage power sources, such as are illustrated in Figure 1, is the high cost of providing a variable high-voltage power source for each channel of high-voltage output.

Furthermore, while such circuits are typically timely in responding to commands for increasing output voltage, they are typically not timely in responding to commands for decreasing output voltage. A further disadvantage of the Figure 1 circuit 100 is the error in current sense results associated with the analog voltage translation performed by the analog isolation barrier circuit 116.

SUMMARY [0008] A circuit generates a plurality of channels of high-voltage output signals from the substantially constant bulk power source output signal of a high- voltage power source that is powered by a low-voltage power source. The circuit includes a plurality of high-voltage regulators, each high voltage regulator corresponds to a particular one of the channels. Each high-voltage regulator regulates the bulk power source output signal based on an input control voltage signal for that channel (e. g., provided from a microprocessor) to generate a regulated high-voltage output signal for that channel.

[0009] The regulated high-voltage output signal has voltage level corresponding to a level of the input control voltage signal for that channel. The high-voltage regulator circuit also generating a high-voltage tracking power signal for that channel having a voltage level within a predetermined range of the regulated high-voltage output signal. Furthermore, each channel has associated with it a current sensor. The current sensor for a particular channel is powered by the high-voltage tracking power signal for that channel and generates an output high-voltage digital current sensing signal for that channel that corresponds to the current in the regulated high-voltage output signal for that channel.

[0010] An isolation barrier is provided for each channel. Each isolation barrier translates the voltage level of the output high-voltage digital current sensing signal for that channel to a low-voltage level.

BRIEF DESCRIPTION OF FIGURES [0011] Figure 1 schematically illustrates a prior art variable power supply circuit with current sensing.

[0012] Figure 2 schematically illustrates a variable power supply circuit in accordance with an embodiment of the invention.

[0013] Figure 3 schematically illustrates an embodiment of the high voltage regulator and current sense power circuit 208 of the Figure 2 circuit 200.

[0014] Figure 4 schematically illustrates an embodiment of the current sense and isolation barrier circuit 213 of the Figure 2 circuit 200.

[0015] Figure 5 schematically illustrates an alternate embodiment of the Figure 3 embodiment.

[00161 Figure 6 schematically illustrates an alternate embodiment of the Figure 4 embodiment.

[0017] Figure 7 schematically illustrates an alternate embodiment of an isolation barrier circuit.

DETAILED DESCRIPTION [0018] In accordance with one aspect of the invention, an improved high- voltage power supply circuit (with current sensing) is provided. An embodiment of the improved high-voltage power supply circuit is illustrated in Figure 2.

[0019] Turning now to Figure 2, the improved high-voltage power supply circuit 200 includes a circuit 201 for each channel of high-voltage output. In particular, for each channel of high-voltage output, the corresponding circuit 201 includes a high voltage regulator circuit 208 that operates on the high-voltage output signal of the single fixed DC high-voltage power source 204 to generate a variable high voltage power signal 209. (Depending on the number of channels of high-voltage output, more than one fixed DC high-voltage power source may be employed.) As with the prior art circuit 100 shown in Figure 1 and discussed in the Background, the analog control voltage (in this case, analog control voltage 203) is provided from a DAC (in this case, DAC 218) based on a command from a microprocessor (in this case, microprocessor 202).

[0020] The current in the high-voltage output signal 209 of the variable high-voltage power regulator circuit 208 is measured by a current sense circuit 214, as a function of a voltage drop across a current sense resistance 210. The analog current sense circuit 214 employs the high voltage output signal 209 as a reference voltage, instead of ground or zero volts. As a result, the accuracy of the current sense circuitry 214 output is substantially unaffected by large changes in the high voltage output signal 209 that would otherwise result from common mode voltage differences between the tracking signal and amplifier components of the analog current sense circuit 214.

[0021] Now, a particular circuit embodiment 300 of the high voltage power regulator circuit 208 is described with reference to Figure 3. Then, a particular embodiment of the current sense circuit 214 is described with reference to Figure 4.

[0022] Turning now to Figure 3, the circuit 300 operates on a"bulk source"input high-voltage signal BLKSRC 301 from the high-voltage power source 204 and a control voltage VCNTO 303 based on analog control voltage

signal 203 from the DAC 218. As output, the circuit 300 provides signal TRKREFO 316, which is the regulated high-voltage output (also used as the "tracking reference", or ground, for the current sensing circuitry). The circuit 300 also provides as output the tracking power source signal TRKPWRO 314 to power the current measurement circuitry--approximately five volts above TRKREFO 316. Finally, the circuit 300 provides signal VSNSO 318, which is the high-voltage sensing amplifier output--a voltage proportional to the regulated high-voltage output TRKREFO 316.

[0023] The operation of the Figure 3 circuit embodiment 300 is now described. There are two current sources 302,308 operating to regulate the output voltage TRKREFO 316. The top current source 302 is a sourcing circuit comprised of six high-voltage MOSFET transistors, each of which share an equal voltage drop from the high-voltage source signal BULKSRC 301 to the regulated output TRKREFO 316. The number of high-voltage MOSFET transistors may be adjusted based on the desired total voltage drop from the high-voltage source signal BULKSRC 301 to the regulated output TRKREFO 316. More than one such MOSFET transistor is employed to distribute the high-voltage load. In other examples, other devices such as IGBT or BIMOSFET transistors are employed. The current through the top current source 302 is controlled by the current steering circuit 304, which provides for an"idling current"or"quiescent current"to maintain a DC bias in the current source 302, and also to keep the tracking voltage regulator 320 in conductive mode so that the regulated output TRKREFO 316 remains available. Additionally, the current steering circuit 304 controls the gate voltages of MOSFETS of the top current source 302 to increase or decrease the current through the top current source 302.

[0024] The bottom current source 308 is commanded to increase the amount of current through it whenever the regulated output TRKREFO 316 is above the target voltage set by the control voltage VCNTO 303. Conversely, the bottom current source 308 is commanded to decrease the amount of current through it whenever the regulated output TRKREFO 316 is below the target voltage set by the control voltage VCNTO 303. As the current through the

bottom current source 308 is reduced, the current steering circuit also increases the current through the top current source 302, causing more current to be sourced to the regulated high-voltage output signal TRKREFO 316. The regulated high-voltage output signal TRKREFO 316 will increase until brought into balance such that the high-voltage sensing amplifier output VSNSO 318 is equal to the control voltage VCNTO 303. Additionally, VSNSO 318 is used by the microprocessor to monitor the high-voltage tracking signal TRKREFO 316.

[0025] The control properties of the circuit 300 are determined at least in part by the values of the resistor 320 and capacitor 322 of the integrator circuit 310. In both the top current source 302 and the bottom current source 304, transient suppressor diodes are employed to protect the MOSFET transistors from being subjected to excessive voltages.

[0026] Turning now to Figure 4, the embodiment schematically illustrated therein is now described. As discussed above with respect to Figure 3, TRKREFO 316 is the regulated high-voltage output signal of the voltage regulator circuit 300, and TRKPWRO 314 is a reference voltage output of the voltage regulator circuit 300 that is, in one embodiment, five volts above TRKREFO 316. The current in the TRKREFO 316 signal flows through a resistor 402 operating as the current sense resistor 210 (Figure 2) and, thus, the voltage across the resistor 402 is proportional to the current in the TRKREFO 316 signal.

[0027] In some examples, an operational amplifier 404 (e. g., part number TLC27L7C) operates to translate (reference) the voltage across the resistor 402 to 2.5 volts above the TRKREFO 316 signal. The 2.5 V reference is from a voltage reference source circuit 406 (e. g., part number LT1004). The output voltage range from the resistor 402 is from OVto 2.5V over the range of measured currents, matching the input range of the analog-to-digital converter (ADC) 408 (e. g., part number AD7714). A twenty-four bit result is provided in the ADC 408 result register in two's complement form (where negative numbers represent negative currents).

[0028] Now, with further reference to Figure 4, two other input signals are described. As described above with reference to Figure 2, these input signals are

provided by the microprocessor 202 via the isolation barrier 216, and are utilized by the current sense circuitry 300 to configure the operation thereof. DATA IN 410 is an input to the ADC 408 for binary, serial data from the microprocessor 202, for controlling the ADC 408. CONCLK 414 is employed to clock the serial data into DATA IN 410. For even more flexibility, other signals may be provided. For example, a select line (not shown) from the microprocessor 202 may be employed to select a particular channel for operation. As another example, a signal (not shown) may be provided to put the current sensing circuit 400 in a sleep mode when, for example, the channel is not in use.

[0029] The twenty-four bit result from the (ADC) 408 is transmitted serially through a high voltage capacitor 419 (which is part of isolation barrier 420), thereby translating the logic levels referenced to TRKREFO 316 to a normal ground level associated with the microprocessor 202. The output signal CONV-DAT 421, contains digital data from the ADC 408.

[0030] Figure 5 schematically illustrates an alternate circuit embodiment 1300 of the high voltage power regulator circuit 208, and Figure 6 schematically illustrates an alternate circuit embodiment 1400 of the current sense circuit 214.

[0031] Turning now to Figure 7, an alternate circuit embodiment 700 of the isolation barrier 420 is schematically illustrated. The read data from the ADC 408 is indicated by reference numeral 702, while the TRKREFO 316 signal is indicated by reference numeral 704. The converted data output signal is indicated by reference numeral 706. The read data 702 is provided through a capacitor 708. The capacitor 708 and resistors 712,714,716 and 718 are all associated with node A and are collectively characterized by a time constant TCA that, in one example, is high enough not to significantly alter the read data 702.

[0032] The reference signal 704 is provided through a capacitor 710. The capacitor 710 and resistors 720,722,724 and 726 are all associated with node B and are collectively characterized by a time constant TCB. The impedance of the combination of capacitor 708 and resistors 712,714,716 and 718 is substantially the same (e. g., within about 5%) as the impedance of the combination of capacitor 710 and resistors 720,722,724 and 726. The diodes 728 and 730

protect the comparator 736 should the signals input to the comparator 736 go above a particular voltage (in one example, above +12V). Similarly, the diodes 732 and 734 protect the comparator 736 should the signals input to the comparator 736 go below a particular voltage (in one example, below ground).

[0033] In one example, the voltage on the positive input 738 of the comparator 736 is slightly below 6V (i. e., half of 12V) and the voltage on the negative input 740 of the comparator 736 is slightly above 6V. The amount by which the inputs are below and above 6V depends on the value of the resistor 716 for the positive input 738 and on the value of the resistor 722 for the negative input 740. These voltage offsets create a threshold for the comparator 736, which improves noise rejection. That is, the threshold is a nominal voltage difference between the inputs 738 and 740 of the comparator 736 when the read data 702 and the tracking reference signal 704 are not present. The threshold is further a function of the time constants TCA and TCB, in such a way that the signal on the positive input 738 does not drop below the signal on the negative input 740 before the converted data output signal 706 is transmitted.