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Title:
PROTECTION CIRCUIT IN TRIAC APPLICATIONS
Document Type and Number:
WIPO Patent Application WO/2013/027121
Kind Code:
A1
Abstract:
A circuit is disclosed that includes a transistor configured to control energy entering into the circuit from a power supply. A capacitor is coupled to the transistor to store the energy that enters the circuit, and a protection circuit is provided to prevent undesired conduction of the transistor due to coupling of step voltage changes in the power supply voltage to the gate electrode of the transistor.

Inventors:
CHUI SIEW YONG (SG)
Application Number:
IB2012/001880
Publication Date:
February 28, 2013
Filing Date:
July 25, 2012
Export Citation:
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Assignee:
MARVELL WORLD TRADE LTD (BB)
CHUI SIEW YONG (SG)
International Classes:
H02H9/00; G05F1/56
Foreign References:
US3506905A1970-04-14
DE2054858A11972-05-10
Attorney, Agent or Firm:
KERN, John, S. (277 South Washington Street Suite 50, Alexandria VA, 22314, US)
Download PDF:
Claims:
WHAT IS CLAIMED IS:

1. A circuit, comprising:

a transistor configured to control energy entering the circuit from a power supply, a capacitor coupled with the transistor to store the energy that enters the circuit; and

a protection circuit configured to counteract a voltage change of the transistor tha t is caused by a step voltage change in the power supply.

2. The circuit of claim 1 , further comprising:

a control circuit configured to control the transistor based on the energy stored on the capacitor.

3. The circuit of claim 1 , wherein the transistor is a depletion mode transistor,

4. The circuit of claim 1, wherein the transistor is a metal-oxide-semiconductor- fieid-effeci-transistor ( OSFET).

5. The circuit of claim 4t wherein the protection circuit is coupled to a gate terminal of the transistor to counteract a gate voltage change on the gate terminal of the transistor caused by the step voltage change in the power supply,

6. The circuit of claim 5, wherein the transistor is a first transistor, and the protection circuit further comprises:

a second transistor configured to discharge the gate terminal of the first transistor in response to the step voltage change in the power supply.

7. The circuit of claim 6, wherein the protection circuit further comprises:

a resistor defining a time constant for the protection circuit to be operative,

8. The circuit of claim 1 , wherein the protection circuit is configured to operate independent of the stored energy on the capacitor.

9. A method, comprising:

storing energy that enters into a circuit via a transistor that controls the energy entering the circuit from a power supply;

receiving a step voltage change in the power supply, the step voltage change causing a voltage change on the traiisisior; and

counteracting the voltage change on the transistor by a protection circuit.

10. The method of claim 9. wherein storing the energy that enters into the circuit vis the transistor that controls the energy entering the circuit from the power suppiy comprises:

controlling the transistor to charge a capacitor, and maintain a voltage on the capacitor.

11. The method of claim 9, wherein storing the energy that enters into the circuit vis the transistor that controls the energy entering the circuit from the power supply comprises:

storing the energy that enters into the circuit via a depletion mode transistor.

12. The method of claim 9, wherein storing the energy that enters into the circuit via the transistor that controls the energy entering the circuit from the power supply comprises:

storing the energy that enters into the circuit via a metal -oxide-semi conductor- field-effect-transistor (MOSFET).

13. The method of claim 12, wherein the step voltage change in the power supply causes a gate voltage change on a gate terminal of the transistor

1 . The method of claim 13, wherein counteracting the voltage change on the transistor by the protection circuit comprises:

discharging the gate terminal of the transistor in response to the step voltage change.

1 5. The method of claim 14, wherein discharging the gate terminal of the transistor in response to the step voltage change comprises:

discharging the gate terminal of the transistor for a time duration defined based on a resistor.

16. The method of claim 9, wherein counteracting the voltage change on the transistor by the protection circuit comprises:

counteracting the voltage change on the transistor by the protection circuit that operates independent of the stored energy.

17. An electronic system, comprising:

a rectifier configured to receive and rectify a AC power supply and generate a rectified power supply; and

a circuit comprising:

a transistor configured to control energy enteri g the circuit from the rectified power suppiy; a capacitor coupled with the transistor to store the energy that enters the circuit; and

a protection circuit configured to counteract a voltage change of the transistor that is caused by a step voltage change in the rectified power supply.

18. The electronic system of claim 17. wherein the circuit further comprises:

a controi circuit configured to control the transistor based on the energy stored on the capacitor.

19. The electronic system of claim 17, further comprising:

a dimmer configured to stop the AC power supply for a dimming angle in an AC cycle to cause the step voltage change.

20. The electronic system of claim 17, wherein the transistor is a metal-oxide- semiconductor-fieid-efiect-transistor (MOSFET).

21. The electronic system of claim 20, wherein the protection circuit is coupled to a gate terminal of the transis tor to counteract a gat e voltage change on the gate terminal of the transistor caused by the step voltage change in the power supply.

22. The electronic system of claim 21 , wherein the transistor is a first transistor, and the protection circuit further comprises:

a second transistor configured to discharge the gate terminal of the first transistor in response to the step voltage change in the power supply; and

a resistor defining a time constant for the protection circuit to be operative,

23. The electronic system of claim 17, wherein the protection circuit is configured to operate independent of the stored energy on the capacitor.

Description:
PROTECTION CIRCUIT IN TRIAC APPLICATIONS

INCORPORATIO BY REFERENCE

{00011 This present disclosure claims the benefit of U.S. Provisional Application

No. 61/525,639. "Protection Circuit for UHV Device in TRIAC Applications" filed on August 19, 201 1, which is incorporated herein by reference in its entirety.

BACKGROUND

{0002] The background description provided herein is for the purpose of generally presentin the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure

{0003 j Many electrical and electronic devices are controlled by dimmers to change output characteristics of the devices. In an example, a dimmer is used to change Sight output from a lighting device. In another example, a dimmer is used to change rotation speed of a fan. IMMMX

J0004] Aspects of the disclosure provide a circuit. The circuit includes a transistor configured to control energy entering the circuit from a power supply, a capacitor coupled with the transistor to store the energ that enters the circuit, and a protection circuit configured to counteract a voltage change of the transistor that is caused by a step voltage change in the power supply. In an embodiment, the protection circuit is configured to operate independent of the stored energy on the capacitor.

{0005j Further, in an example, the circuit includes a control Circuit configured to control the transistor based on the energy stored on the capacitor.

{0006] in an embodiment, the transistor is a depletion mode transistor, such as a depletion mode metal-oxide-semiconductor-field-eiTect-transistor (MOSFET). Then, the protection circuit is coupled to a gate terminal of the transistor to counteract a gate voltage change on the gate terminal of the transistor caused by the step voltage change in the power supply. [0007] According to an aspect of the disclosure, the transistor is a first transistor and the protection circuit includes a second transistor configured to discharge the gate terminal of the first transistor in response to the step voltage change in the power supply. Further, the protection ci cuit includes a resistor defining a time constant for the protection circuit to be operative,

[0008] Aspects of the disclosure provide a method. The method includes storing energy that enters i to a circuit via a transistor that, controls the energy entering the circuit from a power supply, and receiving a step voltage change in the power supply. The ste voltage change causes a voltage change on the transistor. The method includes counteracting the voltage change on the transistor by a protection circuit In an embodiment, the protection circuit operates independent of the stored energy.

[0009] Aspects of the disclosure provide an electronic system. The electronic system includes a rectifier and a circuit. The rectifier is configured to receive and rectify an AC power supply and generate a rectified power supply. The circuit includes a transistor configured to control energy entering the circui from the rectified power supply, a capacitor coupled with the transistor to store the energy that enters the ci cuit, and a protection circuit configured to counteract a voltage change of the transistor that is caused by a ste voltage change in the rectified power supply. The electronic system can include other components, such as a dimmer, a transformer, and the like,

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Various embodiments of this disclosure that are proposed as examples will be described in detail with reference to the following figures, wherein like numerals reference like elements, and wherei :

[0011] Fig. 1 shows an electronic system 100 according to an embodimen t of the disclosure;

[0012] Fig. 2 shows waveforms for a power supply according to an embodiment of the disclosure;

[0013] Fig. 3 shows a flowchart outlining a process 300 according to an embodiment of the disclosure; and

[0014] Figs. 4A-4B show waveforms according to an embodiment of the disclosure. DETAILED DESCRIPTION OF EMBODIMENTS

J0015j Fig. I shows an electronic system 1 00 coupled to an energy source 101 according to an embodiment of the disclosure. The electronic system 100 includes a rectifier 103 and a circuit 1 10 coupled together as shown in Fig. 1 ,

[0016] The energy source 101 provides electric energy to the electronic system 100, In the Fig. 1 example, the energy source 101 is an alternating current (AC) voltage supply to provide an AC voltage VAC, such as 1 1 0V AC supply voltage, 220V AC supply voltage, and the like. In addition, the energy source 1 includes suitable elements to adjust the provided electric energy. For example, the energy source .101 includes a dimmer .102 to suitably adjust the amount of electric energy provided to the electronic system 1 0.

{0017] In an embodiment, the dimmer 102 is a phase angle based dimmer. In an example, the AC voltage supply has a sine wave shape, and the dimmer 102 is a forward-type triode for alternating current (TRIAC) dimmer 102 having an adjustable dimming angle 0. within [0, %]. Even' time the AC voltage V A C crosses zero, the forward-type TRIAC dimmer 1 2 stops firing charges for a dimming angle a. Thus, in each cycle [0, 2κ), when the phase of the AC voltage V A C IS within [0, ] or iz+ ), the TRIAC voltage VTRI A C output front the forward-type TRIAC dimmer 10:2 is zero; and when the phase of the AC voltage V A c is within a, it] or [iz+a, 2it], the TRIAC voltage VIS .' follows the AC voltage VAC- Generally, [0, «} and [π, π+ ] are- referred to as non-conduction angle. Similarly, [α. π] and [π+ , 2π] are referred to as conduction angle.

10018] According to another embodiment of the disclosure, the electronic system 100 includes a dimmer (not shown). The dimmer in the electronic system 100 can be similarly configured as the dimmer 102 in Fig. 1 ; the description has been provided above and will be omitted here for clarity purposes.

}0019 j Accordi ng to an embodiment of the disclosure, the electronic system 100 is suitably coupled with the energy source 101. In an example, the electronic system 100 includes a power cord that can. be manually plugged into a wall outlet (not shown) on a power grid. In another example, the electronic system 100 is coupled to the energy source 101 via a switch (not shown). When the switch is switched on, the electronic system 100 is coupled to the energy source 101, and when the switch is switched off, the electronic system 100 is decoupled from the energy source 101 . [0020] The rectifier 103 rectifies the received AC voltage to a fixed polarity, such as to be positi e, in the Fig. 1 example, the rectifier 103 is a bridge rectifier 103. The bridge rectifier 103 receives the AC voltage, generates a rectified voltage VRE C T, and provides the rectified voltage VKK C T to other components of the electronic system 100, such as the circuit 1 10 and die like, to provide electric power to the electronic, system 100.

[0021) In an embodiment, the circuit 110 is implemented on a single integrated circuit (!C) chip, in another embodiment, the circuit 1 10 is implemented on multiple IC chips. The electronic system 100 can include other suitable components, such as a transformer (not shown), a light bulb (not shown), a plurality of light emitting diodes (LEDs) (not shown), a fan (not shown), another circuit (not shown), and the like, that are suitably coupled with the circuit. 1 10. In an example, the circuit 110 provides control signals to control the operations of the other components, in another example, the circuit 1 10 recei ves feedback signals from the other components indicative of the operations of the other components, and provides the control signals to control the operations of the other components based on the feedback signals.

[0022] According to an embodiment of the disclosure, the circuit 110 includes a regulator circuii 120 and a control circuit 130 The regulaior circuii 120 is configured to receive electric energy, store and regulate the received electric energy, and provide the electric energy to other circuit, such as the control circuit 130, to enable the operation of the other circuit. In an example, the regulator circuit 120 recei ves the rectified voltage V< rr, regulate and maintain a voltage QUT having a relatively constant voltage value in a desired range, and provide the voltage Vo OT t other circuits, such as the control circuit 130, to enable the operations of the other circuits. The control circuit 130 is configured to generate control signals to control, for example, the regulator circuit 120 to maintain the voltage V r-

|O023] According to an aspect of the disclosure, the regulator circuit 120 is also a start-up circuit to initially receive power supply and setup the voltage Vour- Specifically, in an embodiment, the circuit 1 10 has an initial power receiving stage and a normal operation stage. In an example, when a power cord of the electronic system Ϊ 00 is plugged in the wail outlet, the regulator circuit 120 starts to receive power supply, and the circuit 1 10 enters the initial power receiving stage. In another example, when a switch is switched on that couples the electronic s stem 100 with the energy source 101 , the regulator circuit 120 starts to receive power supply, and the circuit 1 10 enters the initial power receiving stage. [0024] During the initial power receiving stage, the regulator circuit 120 starts to receive power supply and sets up the voltage VOUT. In an example, the regulator circuit 120 includes a capacitor 123 (CI ), and the voltage V UT is the voltage on the capacitor 123. During the initial power receiving stage, the regulator circuit 120 charges up the capacitor 123. According to an embodiment of the disclosure, the control circuit 130 requires a supply voltage to be larger than a threshold. Thus, in a example, before the voltage V O UT on the capacitor 123 is charged up to a certain level, such as about 15-volt and the like, the control circuit 130 is unable to provide suitable control signals to the regulator circuit 120, and the regulator circuit 320 is in a self- control operation mode that the regulator circuit 120 operates without control from other circuits,

1002 j When the voltage V OUT on the capacitor 123 is charged up to the certain level, th voltage VOUT is large enough to enable the operations of the control circuit 130, and the circuit 1 10 enters the normal operation stage. During the normat operation stage, the control circuit 130 provides suitable control signals to the regulator circuit 120 to control the operations of the regulator circuit .120 in order to maintain the voltage V O UT o the capacitor .123.

[0026] According to another aspect of the disclosure, the circuit 100 includes a separate start-up circuit (not shown) to initially receive power supply and setup the voltage VOUT- Specifically, in an embodiment, the circuit 1 .10 has an initial power receiving stage and a normal operation stage. In an example, when a power cord of the electronic system 100 is plugged in the wall outlet, the separate start-up circuit starts to receive power supply, and the circuit 110 enters the initial power receiving stage. n another example, when a switch is switched on that couples the electronic system 100 with the energy source 101 , the separate start-up circuit starts to receive power supply, and the circuit 1 10 enters the initial power receiving stage.

0027 J During the initial power receiving stage, the separate start-up circuit starts to receive power supply and sets up the voltage V O UT. During the initial power receiving stage, the separate start-up circuit charges up the capacitor 123. In an example, the separate start-up circuit is configured in a self-control operation mode that operates without control from other circuits to charge the capacitor .123. According to an embodiment of the disciosure, the control circuit .130 requires a supply voltage to be larger than a threshold. Thus, in an example, before the voltage V O T on the capacitor 123 is charged up to a certain level, the control circuit 130 is unable to provide suitable control signals to the regulator circuit 120, The regulator circuit 120 may not operate during the initial power recei ving stage. [0028] When the voltage Votrr on the capacitor 123 is charged up to the certain level, the voltage Vom is large enough to enable the operations of the control circuit 130, and the circuit 110 enters the normal operation stage. During the normal operation stage, the separate start-up circuit is disabled. The control circuit 130 provides suitable control signals to the regulator circuit 120 to control the regulator circuit 120 to suitably charge the capacitor 123 to maintain the voltage Vo¾.:r on the capacitor 123.

[0029] According to another aspect of the disclosure, the regulator circuit 120 is configured only as a start-up circuit to initially charge the capacitor 123 from zero V to a certain level, such as 15V, and to enable the control circuit 1 0 to operation. In a example, when the control circuit 130 is enabled, the control circuit. 130 controls a switch (not shown) coupled to a transformer (not shown) to control the transformer to transform the electric energy from the rectified voltage VRKCT to an appropriate form. The control circuit 130 is then powered by the transformed electric energy, and the regulator circuit 120 is suitably disabled

[0030] in the Fig. 1 example, the regulator circuit 120 includes a transistor 121 (Ml ) coupled with a diode 122 (D1 ) to charge the capacitor 123. In an embodiment, the transistor 121 is a depletion mode transistor, such as an N-type depletion mode metal-oxide-semiconductar- field-effeci-transistor (M.OSFET) that has a negative threshold voltage (e.g., negative 3V), configured to he conductive when control voltages are not available. For example, when the regulator circuit 120 serves as a start- up circuit during the ini tial power receiving stage, because the gate-to-source and the gate-to-drain voltages of the N-type depletion mode MOSFET 121 are about zero and are larger than the negative threshold voltage, thus an N-type conductive channel exists between the source and dram of the N-type depletion mode MOSFET 121 even wi thout a gate control voltage. The N-type depletion mode MOSFET 121 allows an inrush current to enter the circuit 1 0 and charge the capacitor 123 at the time when the circuit 100 enters the initial power receiving stage. Further, when the circuit 1 0 enters the normal operation mode, the control circuit 130 provides control signals to control the N-type depletion mode MOSFET 121 to charge the capacitor 123 and maintain the voltage on the capacitor 123

[0031] in another embodiment, the transistor 121 is an enhance mode transistor, such as an N-type enhance mode MOSFET 121 having a positive threshold (e.g., positive 3V). Then, during the initial power receiving stage, a separate start-up circuit charges up the capacitor 123; and during the normal operation stage, the separate start-up circuit is disabled, and the control circuit 130 provides control signals to the reguiator circuit 120, such as a gate control voltage to the N-type enhance mode MOSFET 1 21 , to control the capacitor charging and maintain the voltage on the capacitor 123.

{0032 j In the Fig. 1 example, the control circuit ] 30 includes a gate control circuit 131. In an embodiment, the gate control circuit 131 is coupled to the transistor 121 and the capacitor 123 to form a feedback loop to detect, the voltage on the capacitor, and control the transistor 121 based on the detected voltage to maintain the voltage on the capacitor 123. For example, when the gate control circuit 1 31 detects that the voltage on the capaci tor 123 drops to a lower limit of a desired range, the gate control circuit 1 31 turns on the transistor 1 21 to charge the capacitor 123; when the gate control circuit 131 detects that the voltage on the capacitor 123 increases to an tipper limit of the desired range, the gate control circuit. 131 turns off the transistor 121 to stop charging the capacitor 1 23.

{0033] Further, in the Fig. 1 example, the regulator circuit 120 includes a protection circuit 140 to protect the regulator circuit 120 from negative effects of step voltage changes in the rectified voliage VRECT- According to an aspect of the disclosure, beca use the transistor 121 is coupled to the rectified voltage VRECT as energy entrance to the circuit 1 10, no matter whether the reguiator circuit 120 is enabled or disabled, step voltage changes in the rectified voltage VRE C T affect the transistor 121.

{003 j According to an embodiment of the disclosure, when the dimmer angle of the dimmer 102 is non-zero, the rectified voltage VRECT has a ste voltage change when the phase of the AC voltage AC changes from a non-conductive angle to a conductive angle.

J 0035) Fig. 2 shows a plot 200 of waveforms tor the energy source 101 according to an embodiment of the disclosure. The plot 200 includes a first waveform 210 for the AC supply voltage V ; c, a second waveform 220 for the T iAC voltage VBU AC , and a third waveform 230 for the rectified voltage VRKCT-

10036] As can he seen in Fig. 2, the AC voltage V A c has a sinusoidal waveform, and has a frequency of 50 Hz. The TRIAC voltage VTRI A C is zero when the phase of the AC voltage is in the non-conduction angle and follows the shape of the AC voltage V A when the phase of the AC voltage is in the conductive angle. The rectified voltage RE T is rectified from the TRIAC voltage V' R to have positive polarity. {0037 j Specifically, in the Fig. 2 example, the dimmer 102 lias a dimming angle a. In each cycle [0, 2π], when the phase of the AC voltage V A c is within [0, ) or [π, π-HXj, the TRIAC voltage VtRi A C output from the forward-type TRI AC dimmer 102 is about zero, and the rectified voltage V R J;;CT is about zero; when the phase of the AC voltage V A c is within α, κ], the AC voltage VAC is positive, the TRIAC voltage WRIAC follows the AC voltage VAC, and the rectified voltage VRECT is about the same as the TRIAC voltage Vrkw and when the phase of the AC voltage V¾ is within [j +o, 2π], the the AC voltage VAC is negative, the TRIAC voltage VTBJAC follows the AC voltage V A C, and the rectified voltage VRKCT is about negative of the TRIAC ' voltage VrRiAC

0038 J Thus, in each cycle [0, 2π{, when the phase of the AC voltage V A is at a or at WHi, the rectified voltage VRECT has a step voltage change. The amplitude of the step voltage change depends on the dimming angle (L In an example, when the dimming angle is tt/2, the rectified voltage \¼or has the largest step voltage change. It is noted that the step voltage change happens in a short time, such as in less than 5 ps.

JO039] According to an embodiment of the disclosure, the step voltage change in the rectified voltage VRECT may negatively affect a regulator circuit. For example, without the protection circuit 140, when the rectified voltage VRECT has a step voltage change, the step voltage change is coupled to the gate termi nal of the transistor .121 via gate-drain capacitance Cgd, and th us increases the gate voltage of the transistor 121. When the gate voltage of the transistor 121 is larger than the threshold voltage, the transistor 121 is conductive., and allows electric energy to enter the circuit 1 1 0. In an example, when the step voltage change is relatively- large, a relati vely large amount of current passes through the transistor 121. Because the rectified voltage VRECT is also large, a large amount of electric energy enters the circuit 1 10 in a short time and may damage the circuit 1 10, such as the transistor 121 , and the like.

J0040] According to an embodiment of the disclosure, it may take a relatively long time for the feedback loop formed by the transistor 121 , the capacitor 123 and the gate control circuit 131 to react to the step voltage change.

J 041 ] According to an embodiment of the disclosure, the protection circuit 140 responds to the step voltage change in a relatively short time, such as in the order of 200 ns and the like, to counteract the influence of the step voltage change on the transistor 1 21, such as to reduce the gate voltage of the transistor 21. and thus reduce the amount of electric energy that enters the circuit I 10 during the step voltage change period.

(0042] in the Fig. 1 example, the protection circuit 140 includes a transistor 1 1 (M2), a capacitor 142 (C2), and a resistor 143 (Rl) coupled together as shown in Fig, 1 , in an example, the transistor 141 is an N-type enhanc mode MOSFBT having a positive threshold voltage. The drain terminal of the transistor 141 is coupled to the gate terminal of the transistor 121 , the gate terminal of the transistor 141 is coupled to the source terminal of the transistor 121 via the capaci tor 142, and the source terminal of the transistor 141 is connected to the ground, the resistor 143 is connected between the gate terminal of the tra nsistor 1 and the ground.

(0043] During operation, before the rectified voltage V r has a step voltage change, the gate voltage of the transistor 141 is tied to ground by the resistor 1 3, and thus the transistor 1 1 is turned off, and the gate terminal of the transistor 121 is controlled by the gate control circuit 133 to maintain the voltage on the capacitor 123, in an example. n another example, before a power start-up, the voltage on the capacitor 123 is zero, and the control circuit 130 is unable to operate, the gate voltage and source voltage of the transistor 121 are about zero.

(0044) When the rectified voltage VRECT h&s a step voltage change, the step voltage change causes the gate voltage of the transistor .121 to increase due to the Cgd coupling. When the gate voltage of the transistor 121 is larger than the threshold of the transistor 121 , the transistor 121 is turned on. When the transistor 121 is turned on, the source voltage V-SOUKCE of the transistor 121 is pulled up. The increase of the source voltage VSOURCE is coupled to the gate terminal of the transistor 1 1 via the capacitor 142, and pulls up the gate voltage of the transistor 141 Then, the transistor 141 is turned on to pull down the gate voltage of the transistor 121 to counteract the effect of the Cgd coupling,

(0045] Further, the resistor 143 forms a discharging path to discharge the gate terminal of the transistor 141 and to re-tie the gate terminal of the transistor 141 to ground. The resistance of the resistor 143 can be suitably determined to set a time constant to discharge the gate terminal of the transistor 142 and tie the gate terminal of the transistor 142 to ground.

(0046] According to an aspect of the disclosure, the protection circuit 140 is self-powered, and does not rely on the electric energy stored on the capacitor 123 or an electric energy transformed under the control of the control circuit 1 0. Thus, in an example, when the regulator circuit 120 is disabled, the protection circuit 140 can still operate and protect the circuit 1 10, Further, the protection circuit 140 does not require control from other circuit, and responds to the step voltage change in a self-con (rolled manner. n addition, the protection circuit 140 reacts to the step voltage change, and pulls down the gate voltage of the transistor 121 in a relatively short time, such as in the order of 200 ns,

[0047] Fig. 3 shows a flowchart outlining a process 300 according to an embodiment of the disclosure. The circuit 110 operates according to the process 300 to protect the circuit 110 from damage due to step voltage change in the power supply . The process starts at S301 , and proceeds to S305.

[0048] At S305, the transistor 1 21 in the circuit \ \ 0 is controlled as an energy entrance to control electric energy from the power supply VRE C T to enter the circuit 1 10 and to be stored in the capacitor 1.23.

[004 j At S310, the circuit 110 receives a step voltage change in the power supply. In an example, the dimming angle of the dimmer 102 is non-zero. Thus, the rectified voltage VRE C T is about zero when the phase of the AC power supply corresponds to non-conduction angle., and follows the AC voltage V A c when the phase of the AC power supply corresponds to conduction angle. Thus, when the phase of the AC voltage VAC changes from the non-conduction angle to the conduction angle, the rectified voltage V RECT has a step voltage change.

J O50) At S320, the step vol tage change causes a voltage change of the transistor 121. For example, the step voltage change is coupled to the gate terminal of the transistor 121 by the gate- drain capacitance Cgd. and increases the gate voltage of the transistor 121.

{0051] At $330, the protection circuit 1 0, which is self-powered that does not rely on the electric energy stored on the capacitor 123, counteracts to the voltage change of the transistor 121. For example, the gate voltage increase causes the transistor 121 to be turned on, and pulls up the source voltage V SO UR C E at the source terminal of the transistor 121. The source voltage increase at the source terminal of the transistor 121 is coupled to the gate terminal of the transistor 141 via the capacitor 142. The gate voltage increase of the transistor 141 turns on the transistor 141 to form a discharging path to pull down the voltage at the gate terminal of the transistor 121. After a time duration determined by the resistor 143, the transistor 141 is turned off and the discharging path is disabled. Then, the process proceeds to $399 and terminates [0052] Figs. 4A-4B show waveforms according to an embodiment of the disclosure.

0053 J Fig. 4A shows a plot 400A of waveforms when the circuit 1 10 includes the protection circui t 140 to avoid entrance of a large amount of electric energy during a period of step voltage change in the power supply. The plot 400 A includes a first waveform 41 OA for the rectified voltage YRKOT, a second waveform 420A for the drain current " (-DRAIN of the transistor 121, and a third waveform 430A for the ga te voltage VO A TE of the transistor 121.

[0054] in Fig. 4A example, the dimmer 102 has a dimming angle of jt 2, thus at about time 0.015 seconds, the rectified voltage VREOT has a step voltage change, for example, from zero to 150V in 5 us. The step voltage change causes the gate voltage VQATE of the transistor \ 21 to increase and turns on the transistor 121 temporally and allows drain current I DRA JN to enter the circuit 1 1 . When the transistor 121 is turned on, the source voltage of the transistor i 21 is pulled up. The source voltage increase of the transistor 121 is coupled to the gate terminal of the transistor 1 41 via the capacitor 142, and turns on the transistor 1 1 . The transistor 14.1 serves as a discharging path to discharge the gate terminal of the transistor 121 and pulls down the gate voltage VO A IE of the transistor 121. Because the protection circuit 1 0 works in a self-powered and self-controlled manner, and thus responds to the step voltage change in a relatively fast speed. Then, the gate voltage VQ ATE increase is relatively small, such as about 1.6V and lasts for a relatively short time period, such as less than 0.2 μ$. Thus, a relatively smai! amount of drain current 1DR, » such as less than 0.015 A, enters the circuit 110, during the short time period. Thus, the total electric energy that enters into the circuit 1 1 due to the step voltage change has been reduced,

[0055] Fig. 4B shows a plot 400B of waveforms when the circuit 110 does not include the protection circuit 140. The plot 400B includes a first waveform 410B for the rectified voltage VRECT, a. second waveform 420B for the drain current I O R A IM of the transistor 121, and a third waveform 430B for the gate voltage V A TE of the transistor 121.

[0056] In Fig. 4B example, the dimmer 102 has a dimming angle of ir/2, thus at about time 0.0 ! 5 seconds, the rectified voltage V RKC has a step voltage change, for example, from zero to 150V in 5 μ$. The step voltage change causes the gate voltage V O ATE of the transistor 12.1 to increase and turns on the transistor 121 and allows drain current IO RA I N to enter the circuit i 10. Because the gate control circuit 131 is not fast enough to respond to the step voltage change during the time period (e.g. , 5 ,u.s) when the ste voltage change happens, the gate voltage O A TE is relati ely high, such as at 15V, and the drain current Ι Ο Κ ΛΪ. is also relatively high, such ss over 0.2A during the time period (e.g., 5 μ$). Because the rectified voltage VRE C is also high, a relatively large amount of electric energy enters the circuit 1 10 during time period when the step voltage change happens, and may cause damage to the circuit 110.

[0057] While aspects of the present disclosure have been described in conjunction with the specific embodiments thereof that are proposed as examples, alternatives, modificatioiis, and variations to the examples may be made. Accordingly, embodiments as set forth herein are intended to be illustrative and not limiting. There are changes that may be made without departing from the scope of the claims set forth below.