MXPA96004531A - Power supply of tuned switch mode with control of corrie mode - Google Patents

Abstract

The present invention relates to a tuned switch mode power supply apparatus comprising: a source of an input supply voltage, a tuned resonant circuit including a capacitance and an inductance coupled to the source of the supply voltage of input, a first transistor switch coupled to the inductance and responding to a periodic switch control signal to generate pulses of current in the pulses in the inductance and resonant pulses in the resonant circuit, the pulses of inductance current being coupled to a charging circuit for generating an output of the power supply, the resonant pulses being coupled in a feedback manner to a control terminal of the first transistor switch, when the first transistor switch is turned off, to control when the first transistor switch is turned off. transistor turns on, so that when the current starts to flow in the first transistor switch, a substantially zero voltage is maintained between a pair of main terminals that conduct current from the first transistor switch to provide zero voltage switching; a source of a second signal to control the output of the power supply according to with the second signal, and a modulator that responds to a given current pulse and the second signal to generate the switch control signal, so that the power supply output is controlled in current mode, according to the second Signal on a current-pulse control basis by current-pul

Description

POWER SUPPLY OF TUNED SWITCH MODE WITH CONTROL OF CURRENT MODE The invention relates to a switch mode power supply. A normal tuned switch mode (SPMI) power supply includes a series arrangement of an inductance and a bidirectional controllable switch connected to input supply voltage terminals to receive an input supply voltage. The switch is formed by a parallel arrangement of a transistor and a damping diode. A tuning capacitor is coupled to the inductance to form a resonant circuit. An impeller or control circuit provides switching pulses to drive the switch alternately in the driving and cutting states, the duration of the switch conduction state, being controllable depending on the output voltage by rectifying oscillations produced during periods when the switch is in short circuit. In said tuned SPMI, a substantially sinusoidal oscillation of a resonant pulse voltage of a large amplitude develops in the inductance. The frequency of the oscillation is determined by the resonance frequency of the resonant circuit. After completing half cycle of oscillation, the diode conducts and ends the half-cycle oscillation. The transistor is turned on when the diode is already conducting. Therefore, a voltage of zero is maintained through the transistor, during the transition interval in the transistor. Therefore, switching losses are reduced. In addition, the resonant circuit prevents the voltage that is developed through the transistor from becoming excessive when the transistor is turned off. A modulator in a tuned control circuit of SPMI of the prior art, responds to an error signal produced in an error amplifier to vary a length of a range when the bidirectional switch is conductive. Therefore, the peak of the current in the inductance is controlled. In this form, the amplitude of the resonant pulse voltage that is developed when the bidirectional switch is turned off, is controlled to provide output voltage regulation. Disadvantageously, in some tuned SPMI's of the prior art, the variation of the input supply voltage is compensated relatively slowly. The slow response time of the control circuit of said SPMI is mainly determined by the momentary response of the feedback control loop. It may be desirable to accelerate the response time of the tuned SPMI. A tuned SP I, which modalizes an inventive aspect, operates in a current mode control, on a pulse current basis by pulse current. The current flowing in a switch ends when it reaches a threshold level established by an error signal. The error signal actually controls the peak current in an inductance that is coupled to the switch. In this way, the control circuit is corrected instantaneously in a forward-forward manner for variations in input voltage without using the dynamic scale of the error amplifier. In this way, both advantages of current mode regulation and tuned SPMI are obtained. A tuned switch mode power supply apparatus, which modalizes one aspect of the invention, includes a source of an input supply voltage and a tuned resonant circuit. The resonant circuit includes a capacitance and an inductance coupled to the source of the input supply voltage. A first switch of the transistor is coupled to the inductance and responds to a switch control signal, periodic, to generate pulses of current in the inductance to produce resonant pulses in the resonant circuit. The resonant pulses are coupled to a load circuit to generate an output of the power supply. When a first transistor switch is being turned on, a substantially zero voltage is maintained between a pair of main current carrying terminals. A source of a second signal is used to control the output of the power supply according to the second signal. A modulator responds to a given current pulse, and to the second signal to generate the switch control signal. The output of the power supply is controlled by the current mode, according to the second signal, on a pulse pulse current control basis. In accordance with an inventive aspect, the modulator includes a pair of transistors that form a regenerative switch to produce a portion of the transistor switch control signal that causes the transistor switch to turn off. The regenerative switch forms a latch that is triggered by a signal representative of the current pulse in the transistor switch. Advantageously, the transition of the control signal is accelerated by the positive feedback on the latch. According to another inventive aspect, an error signal indicating a difference between the output voltage of the power supply and a reference level is coupled to a pair of transistors to establish the trigger threshold level of the latch. In this way, advantageously, the torque transistor also operates as a comparator. According to a further inventive aspect, the inductance forms a first winding of a transformer for coupling via the transformer the input supply voltage to a transistor switch control terminal when the transistor switch is conductive in a feedback form positive. The input supply voltage coupled by the transistor, keeps the transistor switch conductive as long as the current in the transistor switch does not exceed the threshold level of the regenerative switch. The resonant pulse is coupled by the transformer to the latch to turn off the regenerative switch. The resonant pulse is also coupled by the transformer to the control terminal of the transistor switch in a positive feedback form, and derives the regenerative switch, to keep the switch of the non-conductive transistor after the regenerative switch is turned off. Figure 1 illustrates an SPMI that modalizes an aspect of the invention; and Figures 2a, 2b and 2c, illustrate waveforms useful for the explanation of the tuned SPMI, of Figure 1. Figure 1 illustrates a tuned SPMI 100, which modalizes one aspect of the invention. In Figure 1, a N-type metal oxide semiconductor (SOM) power transistor Tr, which operates as a transistor switch, has a consumption electrode coupled through a primary winding L1 of a transformer T1 to a terminal 20 of a direct current (DC) voltage B + of the input supply. In a circuit configuration, not shown, the transformer can serve as an isolation transformer. The voltage B + is derived from, for example, a filter capacitor coupled to a bridge rectifier that rectifies a main supply voltage, not shown. A source electrode of the transistor Tr is coupled via a current sensor or a sampling resistor R12. A damper diode D6 which operates as a switch is coupled in parallel with the transistor Tr and is included in the same package with the transistor Tr, to form a bidirectional switch 22. The capacitor C6 is coupled in parallel with the diode D6 and in series with the winding L1 to form with a winding inductance L1, a resonant circuit 21 when the switch 22 is not conductive. A secondary winding L2, of the transformer T1, is coupled to an anode of a peak rectifier diode D8, and ground to generate an output voltage VOUT in a filter capacitor C10, which is coupled to the cathode of the diode D8. The voltage VOUT is coupled to a load circuit, not shown. An error amplifier 23 includes a comparator transistor Q4, which has a base electrode which is coupled to a voltage divider of the voltage VOUT, formed by the resistors R15 and R17, where a VSENSE voltage develops. The voltage VSENSE is equal to a corresponding portion of the voltage VOUT and, therefore, is proportional to the voltage VOUT. An emitting electrode of transistor Q4 is coupled via a gain determining resistor R16 to a Zener diode D9, which develops a reference voltage VREF of error amplifier 23. Diode D9 is energized via resistors coupled in series R13 and R14 , of the voltage VOUT. A photocoupler IC1 includes a light emitting diode that is coupled between the collector of transistor Q4 and a junction terminal between resistors R13 and R14. An emitting electrode of the transistor of the photocoupler IC1 is coupled to a negative DC voltage V3 via a resistor R4. A collector electrode of the transistor of the photocoupler IC1 is coupled to the capacitor C3. In a circuit configuration, not shown, the optocoupler can serve as isolation. A current from the error collector of the optocoupler IC1 indicates an amount by which the voltage VSENSE is greater than the reference voltage VREF and, therefore, the difference between them. A transistor of the comparator Q2, has a base electrode that is coupled via a resistor R11 to a junction terminal between the source electrode of the transistor Tr and a resistor of the current sensor R12. The transistor Q2 compares a base voltage VBQ2 of the transistor Q2 to an error voltage VBQ2, developed in the emitter of the transistor Q2. The voltage VBQ2 includes a first portion that is proportional to a discharge current of source ID in the transistor Tr. A DC voltage V2 is coupled via a resistor R6 to the base of the transistor Q2 to develop a second portion of the voltage VBQ2 through the resistor R11. The DC voltage V2 is also coupled via the resistor R5 to a feedback loop filter formed by the capacitor C3 to form a current source that charges the capacitor C2. The error current le is coupled to capacitor C3 to discharge capacitor C3. A diode D5 is coupled between the emitter of transistor Q2 and ground. The diode D5 limits the voltage VEQ2 to the diode D5 to the voltage, and limits the maximum current in the transistor Tr The collector electrode of the transistor Q2 is coupled to the base electrode of a transistor Q1, and the collector electrode of the transistor Q1 is coupled to the base electrode of a transistor Q2 to form a switch regenerative 31. A control voltage VG, of the transistor Tr, is developed in the emitter of the transistor Q1 which forms an output terminal of the regenerative switch 31, and is coupled to the gate electrode of the transistor Tr via a resistor R10. A secondary winding L3, of the transformer T1, is coupled via a resistor R9 to produce an AC voltage V1. The voltage V1 is coupled via AC via a capacitor C4 and a resistor R8 ,, to the emitter of the transistor Q1 to generate drive voltage VG of the transistor Tr. The AC-coupled voltage V1 is coupled via a collector resistor R7 to the collector electrode of transistor Q2 and to the base electrode of transistor Q1. The voltage V1 is also rectified by a diode D2 to generate the voltage V3 and by a diode D3 to generate the voltage V2. A resistor R3, coupled between the source of the voltage B + and a terminal 30 of the capacitor C4 that is far from the winding L3, charges the capacitor C4 when it is turned on or started. When the voltage VG on the gate electrode of the transistor Tr exceeds a threshold voltage of the transistor Tr of SOM, the passages of the transistor Tr cause the decrease of a discharge voltage VD of the transistor Tr. As a result, the voltage V1 becomes positive and reinforces the voltage VG to keep the transistor Tr, fully on in a positive feedback form.

Figures 2a-2c, illustrate waveforms useful for explaining the operation of the tuned SPMI 100 of Figure 1. Similar symbols and numbers, in Figures 1 and 2a-2c, indicate similar items or functions. During an interval tO-t 1 of a given period T of the Figure 2c, the current ID of the conductive transistor Tr of FIG. 1 jumps upwardly. Consequently, a portion of corresponding non-resonant current pulses of a current IL1 in the winding L1 jumps upwards and stores magnetic energy in the inductance associated with the winding L1 of the transformer T1 At time t1 of Figure 2c, the voltage VBQ2 of Figure 1, which contains a portion derived from the voltage across the resistor R12, exceeds a drive level of the regenerative switch 31 which is determined by the voltage VEQ2 and turn on transistor Q2. The current flows at the base of the transistor Q1 and the regenerative switch 31 applies a low impedance on the gate electrode of the transistor Tr. Consequently, the gate electrode voltage VG of FIG. 2a is reduced to almost zero volts and turns off the transistor Tr of FIG. 1. When the transistor Tr is turned off, the discharge voltage VD of FIG. 2b is increased, and causes the voltage V1 of Figure 1, which is coupled from the winding L3, to decrease. The load stored in the source capacitance of the gate CG, keeps the operation in the bolt mode until time t2 of Figure 2a. an inventive aspect, when the voltage VG becomes smaller than required to maintain sufficient collector current in the transistor Q1 of Figure 1, a forward conduction in the base electrode of the transistor Q2 ceases, and consequently, the bolt operation mode in the regenerative switch 31. Then, the voltage V1, which continues to decrease, causes a negative portion 40 of the voltage VG of Figure 2a to keep the transistor Tr off of Figure 1. When the transistor Tr is turned off, the discharge voltage VD is increased as shown during the interval t1-t2 of Figure 2b. Capacitor C6 of Figure 1 limits the rate of increase in voltage VD such that transistor Tr is completely non-conductive before voltage VD becomes positive and reinforces voltage VG appreciably increases above zero voltage. Therefore, the commutation and radiated switching noise losses are advantageously reduced. The resonant circuit 21 including the capacitor C6 and the winding L1, oscillates, during the interval t1-t3 of Figure 2b, when the transistor Tr of Figure 1 is turned off. Capacitor C6 limits the peak voltage level VD. Therefore, advantageously, the braking diode and the resistor are not required, in such a way that the efficiency is improved and the switching noise is reduced. The decrease in voltage VD before time T3 of Figure 2b. causes the voltage V1 of Figure 1 to be a positive voltage. At time t3 of Figure 2b, the voltage VD is close to zero volts and slightly negative, causing the damping diode D6 of Figure 1 to turn on and maintain the voltage VD of Figure 2b at approximately zero volts. Therefore, the resonant circuit 21 of Figure 1 exhibits a half cycle of oscillation. After the time t3 of Fig. 2b, the voltage VG of Fig. 2a becomes increasingly positive, due to the change mentioned above, in the polarity of the voltage V1 of Fig. 1. Advantageously, the next ignition of the transistor Tr is delayed for a delay time which is determined by the time constant of the resistor R8 and gate capacitance CG until after time t3 of FIG. 2b when the voltage VD is close to zero volts. Therefore, minimal ignition losses are incurred and commutation noise is reduced. Regulation of negative feedback of voltage VOUT, is achieved by varying the voltage VEQ2 in the filter capacitor 03. When the Voltage VSENSE that is proportional to the voltage VOUT is larger than the voltage VREF, the current is discharged by the capacitor C3 and the voltage VEQ2 decreases. Therefore, the threshold level of the compared transistor Q2 decreases. Consequently, the peak value of the current ID in the transistor Tr and the power distributed to the load circuit, not shown, are reduced. On the other hand, when the voltage VSENSE is smaller than the voltage VREF, the current is zero and the current in the resistor R5 increases the voltage VEQ2 Consequently, the peak value of the current ID in the transistor Tr and the power increase distributed to the charging circuit, not shown. According to another inventive aspect, the tuned SPMI 100 operates in a current mode control, in a current pulse by means of the current pulse control base. The current pulse of the current ID during the interval tO-t 1 of Figure 2c, flowing in the transistor Tr of Figure 1, ends at time t1 of Figure 2c when it reaches the threshold level of! transistor Q2 of Figure 1, which is determined by the voltage VEQ2 and is established by the error current forming an error signal. The error signal actually controls the peak current of the current pulse of the current ID flowing in the inductance of the winding L1. Advantageously, the control circuit is corrected instantaneously in a forward feed mode for voltage input variations of the B + voltage without using the dynamic scale of the error amplifier 23. In this way, both advantages of current mode regulation are obtained. and SPMI tuned. As indicated above, the DC voltage V2 is coupled via the resistor R6 to the base of the transistor Q2 to develop the second voltage portion VBQ2 through the resistor R11 During the interval T0-t1 of Figure 2c, the voltage V2 of Figure 1 is equal to voltage B + multiplied by the ratio of turns of windings L3 and L1 of transformer TI According to an additional inventive aspect, the threshold level of transistor Q2 varies according to voltage V2, and therefore, according to voltage B +. Therefore, the peak value of the ID current also varies according to the voltage B +. Advantageously, this aspect tends to maintain a constant power supply capability, of SPMI 100, such that excessive power can not be supplied to the high AC main supply voltage, not shown. According to a further inventive aspect, the initiation at abnormally low B + input voltage is inhibited by a diode D4 having an anode which is coupled to the base of transistor Q1 and a cathode which is coupled to a junction terminal 35 of a voltage divider 36. The voltage divider 36 is coupled between the voltage B + and earth, and includes the series arrangement of a resistor R1, a Zener diode D1 and a resistor R2 such that the terminal 35 is coupled between the Zener diode D1 and the resistor R2. At the input low voltage B +, the Zener diode D1 is turned off and the voltage V4 at the terminal 35 causes the diode D4 to behave in a way that turns on the transistor Q1 and disables the transistor Tr. On the other hand, at normal voltage levels B +, diode D1 is conductive and diode D4 is driven backwards and has no effect on the operation of the circuit.

Claims (19)

1. CLAIMS 1. A tuned switch mode power supply apparatus, comprising: a source of an input supply voltage (RAW B +); a resonant circuit, tuned, including a capacitance (C6) and an inductance (L1) coupled to said source of said input supply voltage; a first switch of the transistor (Q3) coupled with said inductance and responding to a switch control signal, periodic (V6), to generate pulses of current in said inductance to produce resonant pulses (VD) in said resonant circuit that are coupled to a charging circuit for generating an output (VOUT) of said power supply in such a way, that when said first transistor switch is being turned on, a voltage of substantially zero is maintained between a pair of main current carrying terminals (COLLECTOR) -EMISOR) of said first transistor switch; a source of a second signal (VEQ2) for controlling said output of said power supply according to said second signal; and characterized by a modulator (31, R12) that responds to a given current pulse (lL?) and said second signal to generate said switch control signal, such that such power supply output is controlled by current mode, according to said second signal, on a current-pulse control basis by pulse-current. An apparatus according to claim 1, characterized in that in a given switching period of said first switch of the transistor (Q3), said resonant pulse (VD) forms half cycle of oscillation in such resonant circuit (21). 3. An apparatus according to claim 1, further characterized in that a second switch (D6) coupled to said transistor switch (Q3) for applying a low impedance between said current conducting main terminals of said first transistor switch, when said first transistor switch is being turned on. An apparatus according to claim 3, characterized in that said second switch (D6) comprises a damping diode which is coupled in parallel with said first switch of the transistor (Q3). An apparatus according to claim 1, further characterized in that a resistor (R12) coupled in series with said first switch of the transistor for generating a jump voltage (VR12) indicating a portion of said current pulse jumps. Such a switching control signal (V6) causes the state of said first switch of the transistor to change, during said portion of the current pulse given, when said given current pulse exceeds a level. which is determined by said second signal (VEQ2). 6. An apparatus according to claim 1, characterized in that a change in said second signal (VEQ2) substantially more substantially affects a length of a range between adjacent resonant pulses and substantially less a pulse width of said resonant pulse. An apparatus according to claim 1, characterized in that said modulator (31, R 12) comprises a comparator, the second transistor (Q2) having a control terminal (BASE) that responds to said current pulse a first main terminal which conducts current (EMISSORY) that responds to said output (VOUT) of such power supply and a second main terminal that conducts current (COLLECTOR) coupled to a third transistor (Q 1) in a positive feedback form to form with them a regenerative switch (31) that is coupled to a control terminal (BASE) of said first transistor (Q3). 8. An apparatus according to claim 7, characterized in that said current pulse (lL?) Varies in a hopping pattern and produces a switching transition in said regenerative switch (31) when said current pulse exceeds a threshold level. which is determined by said second signal (VEQ2) to operate said regenerative switch in an operation latch mode, and wherein said resonant pulse (VD) is coupled to said regenerative switch to produce an opposite state change in said regenerative switch. 9. An apparatus according to claim 8, characterized in that said resonant pulse (VD) is coupled to said regenerative switch to disable the bolt operation. An apparatus according to claim 1, characterized in that said source of said second signal (VEQ2) comprises a comparator (Q4) that responds to said output (VOUT) of said power supply and to a signal at a reference level ( VREF) to generate an error signal (le) which is coupled to said modulator (31, R12) via a feedback loop filter (C3) to develop said second signal at an output of said filter. An apparatus according to claim 1, characterized in that a capacitance (C6) which is coupled to one of said main current conducting terminals (HF) of said first switch of the transistor (Q3) substantially reduces a rate of change of said (COLLECTOR-EMITTER) between said pair of main terminals of current conductors, when said first switch of the transistor is being turned off. 12. An apparatus according to claim 1, further characterized in that, a regenerative switch (31) responds to said current pulse (l?) And is coupled to a control terminal (BASE) of said first switch of! transistor (Q3) wherein said current pulse is driven, exceeds a threshold level (VEQ2) of said regenerative switch, said regenerative switch, which operates as a latch, and wherein said resonant pulse (VD) is coupled to said switch regenerative (via R9) to disable the lock operation in said regenerative switch and is also coupled to said control terminal (BASE) of said first switch of the transistor in a form that derives said regenerative switch (via R10) to maintain non-conductive the first transistor switch mentioned, after a time when the bolt operation is disabled. An apparatus according to claim 12, characterized in that said resonant pulse (VD) maintains said first switch of the transistor (Q3) nonconductive while a magnitude of said resonant pulse is within a scale of values, and produces a transition of switching when said magnitude of said resonant pulse is outside said scale of values (> RAW B +). 14. An apparatus according to claim 1, further characterized in that a first winding (L3) of a transformer having a second winding (L1) that is coupled to one of said main current conducting terminals (COLLECTOR) of said first transistor switch (Q3) and said input supply voltage source (RAW B +) for coupling by the transformer, said input supply voltage to a control terminal (BASE) of said first transistor switch, via said first winding in a positive feedback form to produce said control signal (VG) to a first state (HIGH), during a first portion of a period, wherein said resonant pulse is coupled to said control terminal of said first transistor switch via said first winding in a positive feedback form to produce such a control signal in a second state (LOW) during a second portion of said period. 15. An apparatus according to claim 14, further characterized in that a regenerative switch (31) responds to said current pulse (lL?) Is coupled to a control terminal (BASE) of said first transistor switch (Q3) wherein, during said first portion of said period, when such a current pulse exceeds a threshold level of said regenerative switch, the regenerative switch operates as a latch that is operated in a first direction (ON) and wherein said resonant pulse ( VD) is coupled to said regenerative switch to disable the bolt operation and is also coupled to said control terminal to maintain said non-conductive switch after a time when the bolt operation is disabled. 16. A switch mode power supply apparatus, comprising: a source of an input supply voltage (RAW B +); a resonant circuit (21) including a capacitance (C6) and an inductance (L1) coupled to said source of such an input supply voltage; a first switch of the transistor (Q3) coupled to said inductance and responding to a switch control signal (VG), periodic, to generate pulses of current in said inductance (lL?) to produce resonant pulses in such a resonant circuit which are coupled to a load circuit to generate an output (VOUT) of such power supply; a second switch (D6) coupled to such a switch of the transistor to maintain a substantially zero voltage between a pair of main current conducting terminals (HOST-EMITTER) of said first switch of the transistor, during a switching transition interval, when the The first mentioned transistor switch is being switched on; a source of a second signal (VEQ2) for controlling a magnitude of said output of said power supply according to said second signal; and characterized in that a regenerative switch (31) responds to a third periodic signal (VBQ2) and said second signal, and is coupled to a control terminal of said first transistor switch (BASE), the aforementioned regenerative switch, operating as a latch which is actuated when a first difference between said third and second signals occurs, such a regenerative switch, responds to said resonant pulse to disable the bolt operation when said resonant pulse is generated, such that after the bolt operation is disabled , the resonant pulse is coupled to said control terminal to maintain a state (WITHOUT DRIVING) of said first switch of the transistor not changed. 17. An apparatus according to claim 16, further characterized in that a first winding (L3) of a transformer for coupling by transformer said input supply voltage to said control terminal (BASE) of the first transistor switch mentioned via said first winding to produce a change of state (ON) in said control signal (V6) after a portion of the aforementioned resonant pulse. 18. A switch mode power supply apparatus, comprising: a source of an input supply voltage (RAW B +); a resonant circuit (21) including a capacitance (C6) and an inductance (L1) coupled to said source of such an input supply voltage; a switch of the transistor (Q3) coupled to said inductance and that responds to a switch control signal (VG), periodic, to generate pulses of current in said inductance (lL?) to produce resonant pulses in such resonant circuit that are coupled to a load circuit to generate an output (VOUT) of such power supply. a damper diode (D6) coupled to such a transistor and responsive to said resonant pulse to maintain a substantially zero voltage between a pair of main current conducting terminals (HOST-EMITTER) of said first switch of the transistor, when said transistor; a source of a second signal (VEQ2) for controlling a magnitude of said mentioned power supply according to variations of said second signal; and characterized in that a second transistor (Q2) comparator, responds to a third periodic signal (VBQ2) and said second signal, and is coupled to a third transistor (Q1) to form therewith a regenerative switch (31) that is coupled to a control terminal (BASE) of said first switch of the transistor, for generating said control signal, said regenerative switch, operating as a latch that is driven in a first direction when a first difference between said third periodic signal and said second occurs signal, such a bolt responding to said resonant pulse to disable the bolt operation when said resonant pulse is generated. 19. An apparatus according to claim 18, further characterized by a first winding (13) of a transformer for coupling said input supply voltage (RAW B +) to said control terminal (BASE) of the transformer via the transformer; transistor switch for maintaining said transistor switch (Q3) in a first state (DRIVER) before the latch is operated and for coupling said resonant pulse (VD) to said control terminal by transformer to keep the transistor switch in a second state (NOT WITH DUCTOR) after that bolt is disabled. R ESU MEN In a tuned switch mode power supply, a voltage of zero is maintained through the transistor switch (Q3), during both switch-on and switch-on transition intervals, at the transistor switch. The power supply of the tuned switch mode operates in a current mode control over a pulse pulse control of current per pulse of current. A modulator (31) of the power supply includes a pair of transistors (Q1, Q2) that form a regenerative switch to produce a portion of a control signal (VG) of the transistor switch that causes the switch of the transistor to turn off. transistor. A voltage (V 1) of the input supply coupled by the transformer, keeps the transistor switch conductive as long as the current in the transistor switch does not exceed the threshold level of a regenerative switch. A resonant pulse (VD) is coupled by transformer of the resonant circuit to the regenerative switch to turn off the regenerative switch and to keep the transistor switch non-conductive after the regenerative switch is turned off.