KR200266522Y1 - Energy regenerative snubber circuit for 2-switch forward converter - Google Patents

Abstract

A snubber circuit for a two-switch forward converter with no power loss, comprising a snubber circuit for protecting a two-switch of a converter using an inductor, a capacitor, and a diode. By reducing the accumulated snubber energy to the power stage, the efficiency of the snubber circuit can be maximized to meet the power electronic system for high frequency switching.

Description

Energy Regeneration Snubber Circuit for Two-Switch Forward Converter

The present invention relates to a two-switch forward converter, and more particularly, a high voltage across the two-switch due to the leakage inductance and parasitic inductance components of the wiring circuit present in the power transfer transformer of the two-switch forward converter. The present invention relates to a snubber circuit for preventing a stress from being applied.

In general, a two-switch forward converter is a DC / DC converter, and the output DC voltage of the DC / DC converter is fed back by a voltage sensor and compared with a reference voltage signal, and an error signal between the fed back output voltage and the reference voltage is an error. After passing through the amplifier, it is converted into a Pulse Width Modulation (PWM) signal to control the switching device to obtain a stable output DC voltage. In addition, the operation of the converter's main switching element typically involves high-speed switching above the audible frequency of 20KHz, which reduces the size and weight of the transformer and output filter, and also reduces noise.

In addition, the high frequency transformer used in the two-switch forward converter has a leakage inductance component and a magnetizing inductance component therein. When the two switches are turned on at the same time, the converter can prevent a short current from flowing through the switching element due to the inductance component of the transformer connected in series between the two switches. In addition, when the two switches are turned off at the same time, the current flowing through the magnetizing inductance of the transformer is continuously flowed to the input DC power by a free-wheeling diode connected to the transformer primary side, and the magnetization energy is regenerated. Since the voltage stress of the switching device is significantly reduced compared to the single switch forward converter, it is widely used as a battery charger, a communication stop, a general switching power supply, a power supply for a welding machine, and the like.

In the two-switch forward converter, basically, as shown in FIG. 1, one end 1 of the first switch SW1 is connected to the positive polarity (+) terminal of the DC voltage source V1 and the second switch SW2. One end 4 of) is connected to the negative (-) terminal of the DC voltage source V1, and one end 2 of the first switch SW1 and one end 3 of the second switch SW2. The primary winding of the transformer TX1 is connected in series. The anode end of the free-wheeling diode D1 is connected to one end 3 of the second switch SW2, and the cathode end is connected to the positive terminal of the DC voltage source V1. The anode end of the circulating diode D2 is connected to the negative (-) terminal of the DC voltage source V1, and the cathode end is connected to one end 2 of the first switch SW1. In addition, the secondary winding of the transformer TX1 is connected to the rectifier REC including the diodes DR1 and DR2 and the output of the low pass filter FIL including the inductor Lf and the capacitor Cf.

In the two-switch forward converter, the first and second switches SW1 and SW2 connected to the DC voltage source V1 are simultaneously turned on or off to apply an AC voltage to the primary winding of the high frequency transformer TX1 for power transmission. Then, the applied primary side AC power is transferred to the secondary side through the transformer (TX1) by using magnetic coupling, rectified by the diode rectifier (REC), and stable output DC voltage through the output low band filter (FIL). Get

That is, during the switching time in which the first and second switches SW1 and SW2 are simultaneously turned on, the equivalent inductances present in the transformer TX1 connected in series between the first switch SW1 and the second switch SW2 are provided. As a result, the increase in current flowing through the first and second switches SW1 and SW2, which are semiconductor devices, is suppressed, thereby reducing the turn-on loss of the first and second switches SW1 and SW2, and the first and second switches SW1 and SW2. ) Prevents hot spots where current is concentrated at some of the contacts. In addition, while the first and second switches SW1 and SW2 are in a conductive state, the magnetizing inductance current and the leakage inductance current of the high frequency transformer TX1 increase, and the current of the output low band filter FIL inductor Lf becomes the rectifier REC. ) Flows through the diode DR1, during which time power transfer occurs between the primary winding of the transformer TX1 and the secondary winding.

However, while the first and second switches SW1 and SW2 are turned off simultaneously, the leakage inductance current and the magnetizing inductance current of the transformer TX1 continue to flow, and after the first and second switches SW1 and SW2 are turned off, the transformer is turned off. The path of leakage inductance current and magnetizing inductance current of (TX1) is immediately converted into circulating diode (D1)-transformer (TX1)-circulating diode (D2) so that the energy stored in the equivalent inductor of transformer (TX1) is DC voltage source (V1). Must be reduced to

However, in the actual implementation circuit, due to the parasitic inductance present in the electrical wiring circuit, the direction change of the leakage inductance current and the magnetizing inductance current of the transformer TX1 does not occur immediately, and some time delay is required, so the direction of the current This continuous flow flows toward the first switch SW1-the second switch SW2, and a large voltage surge is generated at both ends of the first and second switches SW1 and SW2, thereby turning the switches SW1 and SW2. Off-loss is increased and overvoltage causes damage to the first and second switches SW1 and SW2 which are semiconductor devices.

Accordingly, in the two-switch forward converter, the snubber circuit SC as shown in FIG. 2 is applied to the first and second switches SW1 and SW2 in order to alleviate voltage stress occurring across the switching element when the first and second switches SW1 and SW2 are turned off. It is connected to the two switches SW1 and SW2, respectively.

The snubber circuit shown in FIG. 2 is a conventional lossy snubber, in which a resistor (Rps) and a capacitor (Cps) are connected in series, and a diode (Dps) is connected in parallel to the resistor (Rps). The first and second switches SW1 and SW2 of the forward converter were connected in parallel, respectively.

The lossy snubber circuit SC has a first switch and a second switch SW1, caused by a parasitic inductance present in the electrical wiring circuit when the first and second switches SW1 and SW2 of the two-switch forward converter are turned off at the same time. When a high voltage is applied across both ends of the switch SW2), the diode Dps is turned on to charge the capacitor Cps with a high voltage applied to both ends of the first and second switches SW1 and SW2, thereby switching the first and second switches SW1 and SW2. Suppress the voltage rise at both ends. When the first and second switches SW1 and SW2 are turned on, the snubber energy stored in the capacitor Cps is discharged through the path of the capacitor Cps through the resistor Rps to snubber the energy in the resistor Rps. Consumes as heat.

Such a conventional lossy snubber is easy to design and simple to use, but energy loss is increased by consuming snubber energy from the resistance of the snubber circuit. In addition, resistive snubbers increase losses in proportion to the switching frequency, making them unsuitable for power electronic system applications using high frequency switching technology.

Accordingly, the present invention has been devised to solve such a problem, and an object of the present invention is to prevent energy loss and to provide energy regeneration snubber circuits for two-switch forward converters suitable for power electronic system applications using high frequency switching technology. To provide.

1 is a circuit diagram schematically showing a basic two-switch forward converter,

2 is a circuit diagram showing a two-switch forward converter with a conventional lossy snubber circuit,

3 is a circuit diagram illustrating a two-switch forward converter having an energy regeneration snubber circuit according to the present invention;

4 is a signal waveform diagram illustrating voltage and current waveforms of a two-switch during operation of a two-switch forward converter having an energy regeneration snubber circuit according to the present invention.

In order to achieve the above object, an energy regeneration snubber circuit for a two-switch forward converter according to one feature of the present invention includes a DC voltage source for supplying a DC voltage and a high frequency for transmitting energy of the primary side to the secondary side. Parasitic inductance components and transformers in the wiring circuit when the first and second switching elements are turned on and turned off to supply alternating current to the high frequency transformer and the first and second switching elements are simultaneously turned off. First and second circulating diodes for regenerating the energy by flowing high voltage energy generated by the leakage inductance component present to a DC input power source, and a rectifier for rectifying the high frequency power transmitted from the primary side of the high frequency transformer; In the two-switch forward converter composed of a filtering unit for filtering the rectified power by the rectifier ,

A first snubber diode having a cathode end connected to a common end of the first switching element and the transformer;

A capacitor having one end connected to an anode end of the first snubber diode and the other end connected to a common end of the transformer and the second switching element;

An inductor having one end connected to a common end of the first snubber diode and the capacitor; And

A cathode end is connected to the other end of the inductor, the anode end comprises a second snubber diode connected to the other end of the second switching element.

According to the energy regeneration snubber circuit for a two-switch forward converter, a snubber stored in a capacitor is formed by constructing a snubber circuit having a resonant circuit using an inductor, a capacitor, and a diode instead of a resistor used in a lossy snubber circuit. Can regenerate energy

Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment according to the present invention.

3 is a two-switch forward converter having an energy regenerative snubber circuit according to the present invention, wherein the energy regenerative snubber circuit SC1 includes first and second snubber diodes Ds1 and Ds2, a capacitor Cs, and an inductor. Ls, the anode end of the second snubber diode Ds2 is connected to one end 4 of the second switch SW2 of the two-switch forward converter, and the second snubber diode Ds2 The cathode end is connected to one terminal of the inductor Ls, the other terminal of the inductor Ls is connected to the anode end of the first snubber diode Ds1, and the cathode end of the first snubber diode Ds1 is 2 A terminal of one side of the capacitor Cs is connected to one end 2 of the first switch SW1 of the switch forward converter, and one terminal of the capacitor Cs is connected to one end of the second switch SW2 of the two-switch forward converter. The other terminal of) is connected to the anode terminal of the first snubber diode Ds1.

The operation of the two-switch forward converter including the energy regeneration snubber circuit SC1 will be described with reference to FIGS. 3 and 4.

First, as shown in 'a' of FIG. 4, when the first and second switching devices SW1 and SW2 are 'turned off' at the same time, the leakage inductance of the transformer TX1 and the parasitic inductance of the electric wiring circuit are changed. As a result, an overvoltage is applied to the switching element so that a large current flows. At this time, the current flows through the capacitor C _S -the first snubber diode D _S 1 -transformer TX1, and thus, 'b' and ' As can be seen in the T4-T5 section of d ', a sudden increase in the voltage of the switch element can prevent the phenomenon of high voltage being applied.

In the period T5-T6 of FIG. 4, when the charging voltage of the capacitor C _S becomes similar to the input DC voltage V1, the flow of the equivalent inductor current of the transformer TX1 gradually increases from the first diode D1 to the first voltage. By flowing through the two diodes D2 to transformer TX1, the magnetization energy is regenerated as an input, and the voltage rise between both ends of the first and second switching elements SW1 and SW2 is increased at 'b' and 'd' of FIG. As shown, it is limited by the voltage across the capacitor C _S and the first snubber diode D _S1 .

In the T6-T7 section of FIG. 4, when the magnetization current of the transformer becomes '0' and the circulating diodes D1 and D2 are blocked, the energy charged in the parasitic capacitors of the first and second switching elements SW1 and SW2 is The voltage across the two switching elements is gradually reduced to reduce the input power through the transformer TX1 to form a waveform of 'b' and 'd' of FIG. 4. The voltages at both ends of the first and second switching elements SW1 and SW2 appear to be in a stable state. At this time, the voltages at both ends of the first and second switching elements SW1 and SW2 are equal to each other by the peripheral circuit.

Next, when the first and second switching devices SW1 and SW2 are turned on at the same time in T1 of FIG. 4A, the switching device is set by the counter electromotive force of the equivalent inductance of the transformer TX1 in the T1-T2 section. The increase in the current flowing in the flow is suppressed to rise sharply as in the waveforms of 'c' and 'e' of FIG. 4.

Subsequently, in the sections T2 to T3 of 'e' of FIG. 4, the energy charged in the capacitor C _S is transferred to the second switching element SW2 and the second switch as the first and second switching elements SW1 and SW2 are conducted. As the current flows through the nubber diode D _S2 and inductance L _S , the polarity of the capacitor C _S is reversed, and the magnitude of the current in the T2-T3 section of 'e' It is larger than the T2-T3 section of 'c' of FIG.

In the periods T3-T4 of the waveforms 'c' and 'e' of FIG. 4, a constant current flows through the first and second switch elements SW1 and SW2 during two switch conduction periods.

At this time, since the first snubber diode D _S1 is blocked by an input power supply voltage, the charge stored in the capacitor C _S starts to discharge when the first and second switching elements SW1 and SW2 are 'turned off'. By switching the MOS transistor acting as a switch to facilitate the switching of energy by flowing to the input DC power through the magnetizing inductance of the transformer (TX1) and the circulating diodes (D1, D2).

This operation is repeated repeatedly so that when the switching element is 'turned off' or 'turned on', the energy stored in the capacitor is not consumed and regenerated.

As described above, when the switching element of the two-switch forward converter according to the present invention is 'turned off', the capacitor charges energy when an overvoltage is applied to the switching element by the leakage inductance and the parasitic inductance of the electrical wiring circuit. And, by flowing the energy of the DC input voltage source to the circulating diode, the voltage between the both ends of the switching is controlled, and when the switch is 'turned on' with a lapse of time, the energy stored in the capacitor is discharged while the diode, capacitor, The charging polarity of the capacitor is changed by a resonant circuit composed of an inductor, and when the switch is 'turned off' again with a lapse of time, the polarity is changed so that the charge stored in the capacitor flows from the transformer through the circulating diode to the input DC power source. To smoothly operate the switching element. As well as a line is able to play the energy stored in the capacitor.

As described above, according to the present invention, compared to a conventional lossy snubber circuit composed of a resistor, a diode, and a capacitor, a snubber circuit is formed of a resonant circuit through an inductor, a capacitor, and a diode, so that the two-switch forward converter The snubber energy due to the parasitic inductance of the wiring circuit can be effectively reproduced without loss, which is useful for power electronic system applications using high frequency switching.

Claims (1)

A direct current voltage source for supplying a direct current voltage, a high frequency transformer for transmitting energy on the primary side to the secondary side, first and second switching elements for turning on and off at the same time to supply the alternating current to the high frequency transformer; First and second circulating diodes for regenerating the energy by flowing high voltage energy generated by parasitic inductance component of the wiring circuit and leakage inductance component present in the transformer when the 1,2 switching elements are turned off at the same time to the DC input power source; In the two-switch forward converter comprising a rectifying unit for rectifying the high frequency power transmitted from the primary side of the high-frequency transformer, and a filtering unit for filtering the power rectified by the rectifying unit, A first snubber diode having a cathode end connected to a common end of the first switching element and the transformer; A capacitor having one end connected to an anode end of the first snubber diode and the other end connected to a common end of the transformer and the second switching element; An inductor having one end connected to a common end of the first snubber diode and the capacitor; And And a second snubber diode having a cathode terminal connected to the other end of the inductor and an anode terminal connected to the other end of the second switching element.