KR100366787B1 - A zero voltage switching converter with low output ripple - Google Patents

Abstract

The present invention relates to a low ripple zero voltage switching converter, comprising: first and second transformers TRNS1 and TRNS2 connected in series with a primary side in parallel; A leakage inductor L3 connected to primary input terminals of the first and second transformers TRNS1 and TRNS2; A first switch element (Q1) for switching so that power is applied to the primary sides of the first and second transformers TRNS1 and TRNS2 connected in series; A capacitor C1 connected in parallel to the first switch element Q1; A second switch element Q2 connected in parallel with the first switch element Q1 and connected in series with the capacitor C2; A condenser (C2) connected in series with the second switch element (Q2) and connected in parallel with the first switch element (Q1); And a third switch element Q3 / fourth switch element which transfers the induced voltage to the output filter on the secondary side of the first transformer TRNS1 / second transformer TRNS2 when the first switch element Q1 is shorted / opened. (Q4); consists of two transformers, one of which can act as an inductor to reduce output ripple, with the primary switch capable of zero voltage switching and the secondary switch capable of soft switching. In this way, power loss can be minimized and power conversion efficiency can be maximized because switch devices are implemented with MOSFETs.

Description

A zero voltage switching converter with low output ripple}

The present invention relates to a low-ripple zero voltage switching converter. More specifically, two transformers are connected in series with the primary side and the secondary side in parallel, and one of the two transformers is connected to the inductor when the main switch is shorted or opened. The present invention relates to a low ripple zero voltage switching converter which minimizes power loss by reducing the output ripple and enabling switching in the zero voltage state.

Recently, it is possible to switch in zero voltage state by adopting active clamp circuit, and as a result, it is possible to operate at high frequency to reduce the size of transformer and output filter inductor, and zero voltage switching converter which can improve the overall power conversion efficiency. This zero-voltage switching converter delivers energy to the secondary side of the transformer when the main switch is shorted or opened, respectively, which reduces internal losses, resulting in high power conversion efficiency. Therefore, this zero voltage switching converter is suitable for DC / DC power conversion requiring low output voltage and high output current.

In the above zero voltage switching converter, when the secondary circuit is a double current type, the transformer primary side current stress increases to increase the transformer loss and core loss, and the conduction loss of the auxiliary switch used in the main switch and the active clamp circuit increases. There was a disadvantage. In addition, when the secondary circuit has a center tap, it is difficult to wind the primary side and the secondary side together on a small core due to the high current on the secondary side.

In addition, the secondary rectifier circuit applied to the conventional zero-voltage switching converter has a problem that the power conversion efficiency is reduced because of the large power loss due to the high forward voltage drop of the Schottky diode itself constituting the rectifier circuit.

Accordingly, it is an object of the present invention to provide a low ripple zero voltage switching converter capable of reducing output ripple by allowing one of the two transformers to act as an inductor when the main switch is shorted or opened.

It is another object of the present invention to provide a low ripple zero voltage switching converter having the advantages of a converter having a center tap on the secondary side.

It is still another object of the present invention to provide a low ripple zero voltage switching converter in which the primary side switch elements perform zero voltage switching and the secondary side switch elements perform soft switching to minimize switching losses.

1 is a low ripple zero voltage converter according to the present invention,

2 (a) to 2 (f) are waveforms output from the elements constituting the low ripple zero voltage converter according to the present invention.

* Explanation of symbols for the main parts of the drawings

Q1: first switch element Q2: second switch element

Q3: third switch element Q4: fourth switch element

TRNS1, TRNS2: first and second transformer L3: leakage inductor

D1, D2, D3, D4: Diode

The converter according to the present invention for achieving the above object, the first and second transformers (TRNS1, TRNS2) connected in series on the primary side in parallel; A leakage inductor L3 connected to primary input terminals of the first and second transformers TRNS1 and TRNS2; A first switch element (Q1) for switching so that power is applied to the primary sides of the first and second transformers TRNS1 and TRNS2 connected in series; A capacitor C1 connected in parallel to the first switch element Q1; A second switch element Q2 connected in parallel with the first switch element Q1 and connected in series with the capacitor C2; A capacitor C2 connected in series with the second switch element Q2 and connected in parallel with the first switch element Q1; When the first switch element Q1 is shorted / opened, the third switch element Q3 / four which transfers the induced voltage to the output filter on the secondary side of the first transformer TRNS1 / second transformer TRNS2 Switch element Q4.

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

1 is a circuit diagram of a low ripple zero voltage switching converter according to the present invention.

As shown in the figure, the first and second transformers TRNS1 and TRNS2 have the same magnetizing inductance L1 and the primary side is connected in series. The leakage inductor L3 is connected to the first and the second. 2 is connected to the primary input terminals of the transformers TRNS1 and TRNS2. The first switch element Q1 is zero-voltage-switched by a control voltage input to the gate to the secondary side of the first and second transformers TRNS1 and TRNS2. Energy is transferred. The capacitor C2 maintains the voltage applied to the first switch element Q1 at a constant level when the first switch element Q1 is opened. The second switch element Q2 is the first switch. The primary magnetization inductor L1 and the capacitor C2 of the first and second transformer TRNS2 resonate when the device Q1 is opened. The capacitor C1 discharges when the second switch device Q2 is opened. The first switch element Q1 is short-circuited in the zero voltage state. The third switch element Q3 is connected to the first switch element ( When the short circuit of Q1) occurs, the voltage induced on the secondary side of the first transformer TRNS1 is transmitted to the output filter. The fourth switch element Q4 opens the second switch TRNS2 when the first switch element Q1 is opened. The induced voltage is transferred to the output filter on the secondary side of the.

2 (a)-(f) are waveforms outputted from the elements constituting the low ripple zero voltage converter according to the present invention.

When the control voltage VGS1 for driving the first switch element Q1 is input (see FIG. 2A), the first switch element Q1 is short-circuited by the control voltage VGS1 in the time period T0-T1. The current iQ1 flowing through the first switch element Q1 increases linearly. In this case, the second transformer TRNS2 serves as an inductor to reduce output ripple.

When the first switch element Q1 is opened at time T1, as shown in Figs. 2C and 2D, the capacitor C1 is charged to the input voltage VS by a substantially constant current iQ1.

When the voltage VC1 of the capacitor C1 is equal to the input voltage VS, the primary leakage inductor L3 is a capacitor converted from the secondary side of the capacitors C1 and C2 and the transformers TRNS1 and TRNS2 to the primary side. An equivalent capacitor and an LC resonant circuit are configured to resonate. As shown in FIG. 2 (d), the voltage VC1 applied between the drain and the source of the first switch element Q1 increases in a resonant form. In this section, the current iQ3 flowing in the third switch element Q3 on the secondary side starts to decrease, and the current iQ4 of the fourth switch element Q4 starts to increase. At time T3, the two currents iQ3 and iQ4 become equal.

At time T3-T4, current iQ3 flowing in third switch element Q3 is smaller than current iQ4 of fourth switch element Q4, and diode D2 is formed inside second switch element Q2. ) Becomes conductive, and the current flowing through the capacitor C2 decreases.

At time T4, the secondary side fourth switch element Q4 is completely shorted, and the current iC2 flowing through the capacitor C2 of the primary side clamp circuit gradually decreases, and the direction flowing at T5 is changed. In order for the second switch element Q2 to switch in the zero voltage state, the control signal VGS2 should be applied to the gate of the second switch element Q2 within a short time after T4. In this section, the first transformer TRNS1 operates as an inductor to reduce output ripple, and the second transformer TRNS2 transfers energy to the secondary side.

At time T6, the second switch element Q2 is opened, and the drain-source voltage VC1 of the first switch element Q1 decreases linearly. At time T6-T7, the current iQ4 flowing in the secondary side fourth switch element Q4 is maintained.

At time T7 the current iQ3 of the third switch element Q3 begins to increase, the primary leakage inductor L3 starts to resonate with the equivalent capacitor, and the drain-source voltage of the first switch element Q1. VC1 decreases to zero voltage at time T8.

At time T8, the drain-source voltage VC1 of the first switch element Q1 becomes a zero voltage, and since the diode D1 is conducted, the current due to resonance gradually increases as shown in Fig. 2 (c). Done. In order for the first switch element Q1 to switch in the zero voltage state, the control voltage VGS1 must be applied to the gate of the first switch element Q1 within a short time after T8.

At time T9, the first switch element Q1 is short-circuited, the flowing current iQ1 gradually increases, and the fourth switch element Q4 on the secondary side is fully opened to start a new cycle.

As described above, the DC / DC power conversion of the present invention is normally implemented while the switching of the switch elements Q1 to Q4 is repeated. In addition, since the first switch element Q1 and the second switch element Q2 can be switched in the zero voltage state, the switching loss can be minimized. As a result, the energy conversion efficiency can be maximized, and the high frequency operation can be performed. Therefore, the size of the transformers TRNS1 and TRNS2 and the output filter inductor L4 can be reduced.

Since the first switch element Q1 and the second switch element Q2 on the primary side can switch in a zero voltage state, the third switch element Q3 and the fourth switch element Q4 on the secondary side are also soft switched. This is possible and consequently can contribute to improved efficiency.

In order to drive the first switch element Q1 and the second switch element Q2 on the primary side, a separate control circuit is required, and the third switch element Q3 and the fourth switch element Q4 on the secondary side are transformers. It is driven by the voltage induced on the secondary side of (TRNS1, TRNS2).

Therefore, the converter according to the present invention can reduce the output ripple by acting as an inductor of one of the two transformers when the main switch short-circuit or open using two transformers, the primary side switch is capable of zero voltage switching and 2 The secondary switch can be soft-switched to minimize power loss, and the switching elements are implemented in MOSFETs to maximize power conversion efficiency. Also, no separate control circuit is required to drive the secondary switch elements. The simple configuration and high frequency operation allow the transformer and output filter inductors to be reduced in size, reducing the overall size of the converter.

Claims (6)

First and second transformers TRNS1 and TRNS2 connected in series with a primary side and in parallel with a secondary side; A leakage inductor (L3) connected to primary input terminals of the first and second transformers TRNS1 and TRNS2; A first switch element (Q1) for switching so that power is applied to primary sides of the first and second transformers TRNS1 and TRNS2 connected in series; A capacitor C1 connected in parallel with the first switch element Q1; A second switch element Q2 connected in parallel with the first switch element Q1 and connected in series with a capacitor C2; A condenser (C2) connected in series with the second switch element (Q2) and connected in parallel with the first switch element (Q1); And When the first switch element Q1 is shorted / opened, the third switch element Q3 / four which transfers the induced voltage to the output filter on the secondary side of the first transformer TRNS1 / second transformer TRNS2 Switch element (Q4); low ripple zero voltage switching converter, characterized in that consisting of. The method of claim 1, When the second switch element Q2 is opened in the first switch element Q1, A low ripple zero voltage switching converter, characterized in that the primary magnetization inductor (L1) and the capacitor (C2) of the first and second transformer (TRNS2) to form an LC resonant circuit to resonate. The method of claim 1, And the second transformer TRNS2 acts as an inductor when the first switch element Q1 is shorted and the second switch element Q2 is opened. The method of claim 1, And the first transformer TRNS1 acts as an inductor when the first switch element Q1 is opened and the second switch element Q2 is shorted. The method of claim 1, When the first switch element Q1 is shorted and the second switch element Q2 is opened, the third switch element Q3 is turned on by the control voltage induced on the secondary side of the second transformer TRNS2. Low ripple zero voltage switching converter, characterized in that. The method of claim 1, When the second switch element Q2 is shorted and the first switch element Q1 is opened, the fourth switch element Q4 is turned on by the control voltage induced on the secondary side of the first transformer TRNS1. Low ripple zero voltage switching converter, characterized in that.