TWI837744B - Power supply circuit with sufficient hold time in high-frequency varying load condition - Google Patents

Abstract

A power supply circuit includes a transformer, a power switch, an input voltage detecting circuit, a varying load detecting circuit, a steady-state current circuit, a first control circuit and a second control circuit. The first control circuit provides a first control signal for periodically turning on and off the power switch, thereby allowing the transformer to convert an input voltage into an output voltage. The input voltage detecting circuit monitors the status of the input voltage, and the varying load detecting circuit monitors the frequency and the peak of the output voltage. Based on the status of the input voltage, the frequency of the output voltage and the peak of the output voltage, the second control circuit determines whether a high-frequency varying load condition is satisfied, and activates the state-converting function of the steady-state current circuit for converting the output current associated with the output current from a varying state to a steady state.

Description

A power supply circuit that provides sufficient sustaining time under high-frequency dynamic load conditions

The present invention relates to a power supply circuit, and in particular to a power supply circuit that can provide sufficient sustaining time under high-frequency dynamic load conditions.

Different components in a computer system require different operating voltages, so a power supply is commonly used to convert the alternating current (AC) indoor power supply into direct current (DC) to drive different components by means of transformation, rectification and filtering. The power supply of the prior art usually includes a rectifier, a transformer, a power switch, a pulse width modulation integrated circuit, and energy storage elements (such as input capacitors and excitation inductors). By switching the power switch at a specific frequency, the power supply can repeatedly charge or discharge the energy storage element according to an input voltage of the mains supply, thereby providing an output voltage different from the input voltage. The pulse width modulation integrated circuit can control the switching condition according to a feedback voltage related to the output voltage, and then appropriately adjust the output voltage value to maintain a constant output.

When the mains power is removed, the power of the load-end device will continue to be supplied by the output capacitor of the power supply for a period of time. This period of time is the hold time defined in the specification. More specifically, the hold time refers to the length of time that the output voltage can maintain the output level normally after the power supply is shut down or powered off. Since the hold time is to ensure that the power system will not cause unstable power output due to factors such as momentary short circuit, overload, power outage or voltage drop, the specification will consider the most severe situation, and generally define the minimum hold time under the conditions of low input voltage and full output load.

With the improvement of computer system configuration and firmware, its working mode is often not a stable load condition, but may be a complex high-frequency dynamic load condition. At this time, the dynamic current value of the load is often greater than the maximum output current value of the power supply. Since the dynamic current of the load is in a high-frequency state, its instantaneous cycle is shorter, so the power supply can still operate normally. However, if the mains is removed instantly under this high-frequency dynamic variable load condition, the energy of the output capacitor will be quickly exhausted due to the excessive dynamic current value, making the power supply's maintenance time too short and unable to continue to power the system. Therefore, a power supply circuit that can provide sufficient maintenance time under high-frequency dynamic variable load conditions is needed.

The present invention provides a power supply circuit capable of providing sufficient sustaining time under high-frequency dynamic load variation conditions, which comprises a transformer, a power switch, an input voltage detection circuit, a dynamic load variation detection circuit, a steady current circuit, a first control circuit and a second control circuit. The transformer is used to induce the energy of an input voltage from a primary side to a secondary side to supply an output voltage, and comprises a primary side winding disposed on the primary side and comprising a first striking end and a first non-striking end, and a secondary side winding disposed on the secondary side and comprising a second striking end and a second non-striking end. A first terminal of the power switch is coupled to the first non-striking terminal of the primary winding, a second terminal is coupled to a first ground potential, and a control terminal is used to receive a first control signal. The input voltage detection circuit is coupled between the input voltage and the first ground potential to provide a first detection voltage related to the input voltage. The dynamic load detection circuit is coupled between the output voltage and the second striking terminal of the secondary winding to provide a second detection voltage related to the value of the output voltage and a third detection voltage related to the peak value of the output voltage. The steady-state current circuit is coupled between the second non-pointing end of the secondary winding and the output voltage, and is used to selectively activate a switching function according to a second control signal to change the state of an output current related to the output voltage. The first control circuit is arranged on the primary side, and is used to provide a power supply status signal according to the first detection voltage, and provide the first control signal. The second control circuit is arranged on the secondary side, and is used to judge the state of the input voltage according to the power supply state signal, to obtain an instantaneous frequency of the output voltage according to the second detection voltage, to judge whether the output voltage meets a high-frequency dynamic load condition according to the instantaneous frequency of the output voltage and the third detection voltage, and when it is judged that the output voltage meets the high-frequency dynamic load condition, the second control signal is output to start the transition function of the steady current circuit, so as to convert the output current from a dynamic load state to a steady state.

10: Rectifier

20: Input voltage detection circuit

30: Dynamic load change detection circuit

40: Steady current circuit

50: First control circuit

60: Second control circuit

100: Power supply circuit

TR: Transformer

NP: Primary side winding set and number of turns

NS: Secondary winding and number of turns

NA: Auxiliary winding and number of turns

CP: Comparator

Q1: Power switch

Q2: Switch

D _OUT : Output diode

D1-D4: diodes

DA: auxiliary diode

R1, R2: voltage divider resistors

RX:resistance

RS: Detection resistance

LM: Magnetizing inductance

LX: Inductor

C _IN : Input Capacitor

C _OUT : Output capacitance

CA: auxiliary capacitor

I _IN : Input current

I _OUT : Output current

V _IN : Input voltage

V _OUT : Output voltage

V _AC : Alternating current voltage

V _REF : Reference voltage

VCC: power signal

VS1, VS2, VS3: voltage detection

GD1, GD2: control signal

S1: Power supply status signal

GND1, GND2: ground potential

T1-T3: Time point

P1-P8: Foot position

Figure 1 is a schematic diagram of a power supply circuit that can provide sufficient maintenance time under high-frequency dynamic load conditions in an embodiment of the present invention.

Figure 2 is a schematic diagram of an implementation of a power supply circuit that can provide sufficient sustaining time under high-frequency dynamic load conditions in an embodiment of the present invention.

Figure 3 is a schematic diagram of related signals when the power supply circuit of the prior art is operating.

Figure 4 is a schematic diagram of the relevant signals when the power supply circuit in the embodiment of the present invention is operating.

FIG. 1 is a schematic diagram of a power supply circuit 100 that can provide sufficient holding time under high-frequency dynamic load conditions in an embodiment of the present invention. The power supply circuit 100 includes a power switch Q1, an input capacitor C _IN , an output capacitor C _OUT , an excitation inductor LM, an auxiliary diode DA, an auxiliary capacitor CA, an output diode D _OUT , a transformer TR, a rectifier 10, an input voltage detection circuit 20, a dynamic load detection circuit 30, a regulated current circuit 40, a first control circuit 50, and a second control circuit 60. The power supply circuit 100 can convert the AC voltage V _AC supplied by the mains into an output voltage V _OUT to drive a load (not shown). The input voltage detection circuit 20 can detect the state of the AC voltage V _AC to determine whether the AC voltage V _AC exists. The dynamic load detection circuit 30 can detect the peak value of the output voltage V _OUT , and the second control circuit 60 can detect the instantaneous frequency of the output voltage V _OUT , and determine whether the output voltage V _OUT meets the high-frequency dynamic load condition according to the peak value and instantaneous frequency of the output voltage V _OUT .

FIG. 2 is a schematic diagram of the implementation of the power supply circuit 100 in the embodiment of the present invention. The rectifier 10 may be a bridge rectifier, which includes diodes D1-D4, and is used to convert the AC power V _AC supplied by the mains into an input voltage V _IN , where I _IN represents the input current of the power supply circuit 100, and I _OUT represents the output current of the power supply circuit 100. However, the implementation of the rectifier 10 does not limit the scope of the present invention.

The transformer TR includes a primary winding (represented by the number of turns NP), a secondary winding (represented by the number of turns NS), and an auxiliary winding (represented by the number of turns NA), wherein the primary winding NP and the auxiliary winding NA are arranged on the primary side of the transformer TR, and the secondary winding NS is arranged on the secondary side of the transformer TR. The first end of the magnetizing inductor LM is coupled to the tapped end of the primary winding NP in the transformer TR, and the second end is coupled to the non-tapped end of the primary winding NP in the transformer TR. The first end of the input capacitor C _IN is coupled to the tapped end of the primary winding NP in the transformer TR, and the second end is coupled to a ground potential GND1. The anode of the output diode D _OUT is coupled to the non-striking end of the secondary winding NS in the transformer TR, and the cathode is coupled to the output end (output voltage V _OUT ) of the power supply circuit 100 through the regulated current circuit 40. The first end of the output capacitor C _OUT is coupled to the output end of the power supply circuit 100 through the regulated current circuit 40, and the second end is coupled to the striking end of the secondary winding NS in the transformer TR, wherein the striking end of the secondary winding NS in the transformer TR is coupled to a ground potential GND2. The anode of the auxiliary diode DA is coupled to the non-striking end of the auxiliary winding NA in the transformer TR, and the cathode is coupled to the first control circuit 50. A first terminal of the auxiliary capacitor CA is coupled to the cathode of the auxiliary diode D _OUT , and a second terminal of the auxiliary capacitor CA is coupled to the ground potential GND1.

The first end of the power switch Q1 is coupled to the non-pointing end of the primary winding NP in the transformer TR, the second end is coupled to the ground potential GND1, and the control end is coupled to the first control circuit 50 to receive a control signal GD1. The power switch Q1 will switch between the on and off states at a high frequency according to the control signal GD1, and then periodically induce the primary side energy of the transformer TR to the secondary side winding NS through the primary winding NP.

In the present invention, the first control circuit 50 can be a pulse width modulation (PWM) integrated circuit, which includes pins P1-P4, which are arranged on the primary side of the transformer TR. Pin P1 is a detection pin coupled to the input voltage detection circuit 20, and is used to receive a detection voltage VS1. Pin P2 is a control pin coupled to the power switch Q1, and is used to output a control signal GD1 to the control end of the power switch Q1. Pin P3 is coupled to the second control circuit 60, and is used to output a power supply status signal S1 to communicate with the second control circuit 60. Pin P4 is a power pin coupled to the auxiliary winding NA in the transformer TR through an auxiliary diode DA and an auxiliary capacitor CA, and is used to receive a power signal VCC. However, the implementation method of the first control circuit 50 does not limit the scope of the present invention.

In the present invention, the second control circuit 60 can be a pulse width modulation integrated circuit, which includes pins P5-P8, which are arranged on the secondary side of the transformer TR. Pin P5 is coupled to pin P3 of the first control circuit 50 to receive the power supply status signal S1. Pin P6 is coupled to the detection pin of the dynamic load detection circuit 30, and is used to receive a detection voltage VS2 of the value of the relevant output voltage V _OUT . Pin P7 is coupled to the detection pin of the dynamic load detection circuit 30, and is used to receive a detection voltage VS3 of the peak value of the relevant output voltage V _OUT . Pin P8 is a control pin coupled to the steady-state current circuit 40, and is used to output a control signal GD2 to selectively activate the switching function of the steady-state current circuit 40. However, the implementation of the second control circuit 60 does not limit the scope of the present invention.

In the present invention, the input voltage detection circuit 20 may include two voltage divider resistors R1 and R2, which are connected in series between the tapping end of the primary winding NP in the transformer TR and the ground potential GND1, wherein the pin P1 of the first control circuit 50 is coupled between the voltage divider resistors R1 and R2. The input voltage V _IN converted by the rectifier 10 from the _AC power source V AC will be established on the input voltage detection circuit 20, and after being divided by the voltage divider resistors R1 and R2, a detection voltage VS1 can be established on the voltage divider resistor R2. Therefore, the first control circuit 50 can determine the state of the input voltage V _IN according to the value of the detection voltage VS1 received by its pin P1, and then control the power supply state signal S1 outputted at the pin P3 accordingly. In one embodiment, when the mains supplies the AC power V _AC normally, the corresponding input voltage V _IN and the detection voltage VS1 are both in a non-0V voltage state, and the first control circuit 50 can output a power supply status signal S1 with a first level (e.g., a high level) at the pin P3; when the mains stops supplying the AC power V _AC , the corresponding input voltage V _IN and the detection voltage VS1 are both in a 0V voltage state, and the first control circuit 50 can output a power supply status signal S1 with a second level (e.g., a low level) at the pin P3.

In the present invention, the dynamic load detection circuit 30 includes a detection resistor RS and a comparator CP. The first end of the detection resistor RS is coupled to the tapping end of the secondary winding NS in the transformer TR, and the second end is coupled to the output end (output voltage V _OUT ) of the power supply circuit 100. When the output current I _OUT related to the output voltage V _OUT flows through the detection resistor RS, a detection voltage VS2 is established on the detection resistor RS. As mentioned above, the second control circuit 60 can be a pulse width modulation integrated circuit. When the detection voltage VS2 is received through the pin P6, the built-in frequency detection function can be used to obtain the instantaneous frequency of the detection voltage VS2, and then the instantaneous frequency of the corresponding output voltage V _OUT can be obtained.

On the other hand, the first input terminal of the comparator CP is coupled to the second terminal of the detection resistor RS to receive the detection voltage VS2, the second input terminal is coupled to a reference voltage V _REF , and the output terminal is coupled to the pin P7 of the second control circuit 60, and the corresponding detection voltage VS3 can be output according to the magnitude relationship between the detection voltage VS2 and the reference voltage V _REF . In one embodiment, when the value of the detection voltage VS2 is greater than the value of the reference voltage V _REF , the comparator CP will output a detection voltage VS3 having a third level (e.g., a high level) at the output end; when the value of the detection voltage VS2 is not greater than the value of the reference voltage V _REF , the comparator CP will output a detection voltage VS3 having a fourth level (e.g., a low level) at the output end.

In the present invention, the second control circuit 60 determines the state of the input voltage V _IN according to the power supply state signal S1 received by the pin P5. When the AC power V _AC is normally supplied by the mains, the corresponding input voltage V _IN and the detection voltage VS1 are both in a non-0V voltage state. At this time, the first control circuit 50 can output the power supply state signal S1 with a first level (e.g., a high level) at the pin P3 to the pin P5 of the second control circuit 60. At this time, the second control circuit 60 can determine that the input voltage V _IN is in a normal power supply state. When the AC power stops supplying the AC power V _AC , the corresponding input voltage V _IN and the detection voltage VS1 are both in a 0V voltage state. At this time, the first control circuit 50 can output a power supply status signal S1 with a second level (e.g., a low level) at the pin P3 to the pin P5 of the second control circuit 60. At this time, the second control circuit 60 can determine that the input voltage V _IN is in an abnormal power supply state.

In the present invention, the second control circuit 60 determines whether the output voltage V _OUT meets the high-frequency load change condition according to the detection voltage VS2 received by the pin P6 and the detection voltage VS3 received by the pin P7. When the second control circuit 60 determines that the instantaneous frequency of the detection voltage VS2 is higher than a critical value and the detection voltage VS3 has a third level (e.g., a high level), it means that the output voltage V _OUT has a high peak value and changes dramatically. At this time, the second control circuit 60 determines that the output voltage V _OUT meets the high-frequency load change condition. When the instantaneous frequency of the detection voltage VS2 is not higher than the critical value and/or the detection voltage VS3 has a fourth level (e.g., a low level), it means that the output voltage V _OUT may have a high peak value but not a dramatic change, a dramatic change but not a high peak value, or not a high peak value and not a dramatic change. At this time, the second control circuit 60 will determine that the output voltage V _OUT does not meet the high-frequency load change condition.

In the present invention, the second control circuit 60 determines the level of the control signal GD2 outputted from the pin P8 according to the power supply status signal S1 received by the pin P5, the detection voltage VS2 received by the pin P6, and the detection voltage VS3 received by the pin P7, thereby selectively activating the transition function of the steady-state current circuit 40.

During the AC mains supply period, the input voltage V _IN first charges the input capacitor C _IN and activates the magnetizing inductor LM to start storing energy. At the same time, the first control circuit 50 outputs a control signal GD1 that switches between an enable potential and a disable potential at a specific duty cycle, so that the power switch Q1 can switch between the on and off states at a high frequency. During the on cycle of the power switch Q1, the primary side energy of the transformer TR can be induced to the secondary side winding NS through the primary side winding NP, thereby charging the output capacitor C _OUT to provide the output voltage V _OUT . At the same time, the primary side energy of the transformer TR will also be induced to the auxiliary winding NA through the primary side winding NP, and the auxiliary capacitor CA will be charged through the forward biased auxiliary diode DA, thereby providing the power signal VCC to the pin P4 of the first control circuit 50 to supply the power required for the operation of the first control circuit 50. In this case, when the input voltage V _IN is determined to be in a normal power supply state according to the power supply state signal S1, the second control circuit 60 will output a control signal GD2 with a fifth level (e.g., a low level) at the pin P8 to turn off the transition function of the steady-state current circuit 40.

When the mains stops supplying the AC power source V _AC , the corresponding input voltage V _IN and the detection voltage VS1 are both at 0V voltage state. At this time, the first control circuit 50 can output a power supply status signal S1 with a second level (e.g., a low level) at pin P3 to pin P5 of the second control circuit 60. When the second control circuit 60 determines that the input voltage V _IN is in an abnormal power supply state according to the power supply status signal S1, if the second control circuit 60 determines that the output voltage V _OUT meets the high-frequency load condition according to the signals received by its pins P6 and P7, it will output a control signal GD2 with a sixth level (e.g., a high level) at pin P8 to activate the transition function of the steady-state current circuit 40.

In one embodiment of the present invention, the steady-state current circuit 40 includes a resistor RX, an inductor LX, and a switch Q2. The first end of the resistor RX is coupled to the cathode of the output diode D _OUT , and the second end is coupled to the output end (output voltage V _OUT ) of the power supply circuit 100. The first end of the inductor LX is coupled to the cathode of the output diode D _OUT , and the second end is coupled to the switch Q2. The first end of the switch Q2 is coupled to the second end of the inductor LX, the second end is coupled to the output end (output voltage V _OUT ) of the power supply circuit 100, and the control end is coupled to the pin P8 of the second control circuit 60 to receive the control signal GD2. The switch Q2 switches between the on and off states according to the control signal GD2, thereby selectively turning on and off the signal transmission path between the second end of the inductor LX and the output end (output voltage V _OUT ) of the power supply circuit 100.

FIG. 3 is a schematic diagram of related signals when the power supply circuit of the prior art is in operation. FIG. 4 is a schematic diagram of related signals when the power supply circuit 100 in the embodiment of the present invention is in operation. For the purpose of illustration, it is assumed that the output voltage V _OUT meets the high-frequency dynamic load condition, and the AC power V _AC is normally supplied by the mains before time point T1, and the AC power V _AC is stopped after time point T1.

As shown in Figure 3, when the output voltage V _OUT meets the high-frequency dynamic load condition, when the AC power is removed instantly at time point T1, the power supply circuit of the prior art will cause the energy of the output capacitor C _OUT to be quickly exhausted due to the excessive value of the dynamic output current I _OUT , resulting in the holding time TH1 (T2-T1) being too short, causing the power supply to be unable to continue to supply power to the system.

As shown in FIG. 4 , when the output voltage V _OUT meets the high-frequency dynamic load condition, when the AC power is removed at time T1, the power supply circuit 100 of the present invention will activate the transition function of the steady current circuit 40, thereby converting the output current I _OUT from the dynamic load state to the steady state. In one embodiment, the current value I _STEADY of the output current I _OUT in the steady state is designed to be the maximum rated output current of the power supply circuit 100, and the energy of the output capacitor C _OUT will not be quickly drained, so that the power supply circuit 100 of the present invention can still provide sufficient holding time TH2 (T3-T1) to avoid the high-frequency dynamic load shortening the holding time and causing it to be quickly disconnected.

In the embodiment of the present invention, the power switch Q1 and the switch Q2 may be a metal-oxide-semiconductor field-effect transistor (MOSFET), a bipolar junction transistor (BJT), or other components with similar functions. However, the types of the power switch Q1 and the switch Q2 do not limit the scope of the present invention.

In summary, the power supply circuit of the present invention uses an input voltage detection circuit to monitor the state of the input voltage, and uses a dynamic load change detection circuit to monitor the instantaneous frequency and peak value of the output voltage V _OUT to determine whether it meets the high-frequency load change condition, and when it is determined that the high-frequency load change condition is met, the transition function of the steady-state current circuit is activated to convert the output current from the dynamic load change state to the stable state. Therefore, the power supply circuit of the present invention can provide sufficient maintenance time under high-frequency dynamic load change conditions. The above is only a preferred embodiment of the present invention, and all equal changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

10: Rectifier 20: Input voltage detection circuit 30: Dynamic load detection circuit 40: Steady current circuit 50: First control circuit 60: Second control circuit 100: Power supply circuit TR: Transformer NP: Primary winding and turns NS: Secondary winding and turns NA: Auxiliary winding and turns Q1: Power switch D _OUT : Output diode DA: Auxiliary diode LM: Magnetizing inductor C _IN : Input capacitor C _OUT : Output capacitor CA: Auxiliary capacitor I _IN : Input current I _OUT : Output current V _IN : Input voltage V _OUT : Output voltage V _AC : AC voltage GND1, GND2: Ground potential

Claims (10)

A power supply circuit capable of providing sufficient sustaining time under high-frequency dynamic load conditions, comprising: A transformer for inducing the energy of an input voltage from a primary side to a secondary side to supply an output voltage, comprising: A primary side winding, arranged on the primary side, comprising a first striking end and a first non-striking end; and A secondary side winding, arranged on the secondary side, comprising a second striking end and a second non-striking end; A power switch, comprising: A first end, coupled to the first non-striking end of the primary side winding; A second end, coupled to a first ground potential; and A control end, for receiving a first control signal; An input voltage detection circuit coupled between the input voltage and the first ground potential, used to provide a first detection voltage related to the input voltage; A dynamic load detection circuit coupled between the output voltage and the second tapping terminal of the secondary winding, used to provide a second detection voltage related to the value of the output voltage, and a third detection voltage related to the peak value of the output voltage; A steady-state current circuit coupled between the second non-tapping terminal of the secondary winding and the output voltage, used to selectively activate a transition function according to a second control signal to change the state of an output current related to the output voltage; A first control circuit is arranged on the primary side, and is used to provide a power supply status signal according to the first detection voltage, and to provide the first control signal; and A second control circuit is arranged on the secondary side, and is used to: Determine the state of the input voltage according to the power supply status signal; Determine an instantaneous frequency of the output voltage according to the second detection voltage; Determine whether the output voltage meets a high-frequency dynamic load condition according to the instantaneous frequency of the output voltage and the third detection voltage; and When it is determined that the output voltage meets the high-frequency dynamic load condition, the second control signal is output to activate the transition function of the steady-state current circuit to convert the output current from a dynamic load state to a stable state. A power supply circuit as described in claim 1, wherein the input voltage detection circuit comprises: A first voltage-dividing resistor, comprising: A first end coupled to the first tapping end of the primary winding in the transformer to receive the input voltage; and A second end coupled to the first control circuit; and A second voltage-dividing resistor, comprising: A first end coupled to the second end of the first voltage-dividing resistor; and A second end coupled to the first ground potential. A power supply circuit as described in claim 1, wherein the steady-state current circuit comprises: a resistor comprising: a first end coupled to the second non-striking end of the secondary winding in the transformer; and a second end coupled to the output voltage; and an inductor comprising: a first end coupled to the second non-striking end of the secondary winding in the transformer; and a second end; and a switch comprising: a first end coupled to the second end of the inductor; a second end coupled to the output voltage; and a control end coupled to the second control circuit to receive the second control signal. A power supply circuit as described in claim 1, wherein the dynamic variable load detection circuit comprises: A detection resistor for providing the second detection voltage according to the output current, comprising: A first end coupled to the second tapping end of the secondary winding in the transformer and a second ground potential; and A second end coupled to the output voltage; and A comparator for outputting the corresponding third detection voltage according to the magnitude relationship between the second detection voltage and a reference voltage, comprising: A first input end coupled to the second end of the detection resistor to receive the second detection voltage; A second input end coupled to the reference voltage; and An output terminal, used to output the third detection voltage. A power supply circuit as described in claim 1, wherein the transformer further includes an auxiliary side winding, arranged on the primary side, which includes a third striking terminal and a third non-striking terminal, for sensing the energy of the input voltage to provide a power signal, thereby supplying the power required for the operation of the first control circuit. The power supply circuit as described in claim 5 further comprises: an auxiliary diode comprising: an anode coupled to the third non-striking end of the auxiliary winding in the transformer; and a cathode coupled to the first control circuit; and an auxiliary capacitor comprising: a first end coupled to the cathode of the auxiliary diode; and a second end coupled to the first ground potential. The power supply circuit as described in claim 1 further includes an excitation inductor coupled between the first striking end and the first non-striking end of the primary side winding. The power supply circuit as described in claim 1 further includes an input capacitor coupled between the first pad terminal of the primary side winding and the first ground potential. The power supply circuit as described in claim 1 further comprises: an output diode comprising: an anode coupled to the second non-striking end of the secondary winding; and a cathode coupled to the steady-state current circuit; and an output capacitor comprising: a first end coupled between the cathode of the output diode and the steady-state current circuit; and a second end coupled to the second striking end of the secondary winding. The power supply circuit as described in claim 1 further includes a rectifier coupled to the transformer for converting an AC power from a mains supply into the input voltage.