KR100591034B1 - Half Bridge Power Converter - Google Patents

Abstract

A soft switching power converter circuit is provided. In the power converter circuit according to the present invention, the power converter circuit includes: first and second capacitors connected in series between the first and second input terminals; first and second switches connected in series between the first and second input terminals; And a secondary winding insulated from the primary winding and the primary winding connected between the connection point between the first and second capacitors and the connection point between the first switch and the second switch, wherein a predetermined point of the secondary winding A transformer connected to the first output terminal, a first rectifier connected between one terminal of the secondary winding of the transformer and a second output terminal, and a second rectifier connected between the other terminal of the secondary winding of the transformer and the second output terminal; And an output stage capacitor connected between the first and second output terminals. According to the present invention, in a soft switching power converter circuit, the input stage is implemented in a half-bridge manner, thereby reducing the breakdown voltage of the primary side switch, and switching loss of the primary side switch by zero voltage switching. Can be reduced.

Power Converters, Soft Switching, Converters, Half-Bridges, Converter Circuits

Description

Half Bridge Power Converter

1 is a circuit diagram showing an embodiment of a half-bridge power converter according to the present invention.

Figure 2 is a waveform diagram for explaining the operation of the half-bridge power converter according to the present invention.

3 is a circuit diagram showing another embodiment of a half bridge power converter according to the present invention;

* Explanation of symbols for the main parts of the drawings

101: input terminal

102: first capacitor

103: second capacitor

104: second power switch

105: first power switch

106: first transformer

107: second transformer

108: first rectifying diode

109: second rectifying diode

110: smoothing capacitor

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to power converter circuits, and more particularly, to power converter circuits for converting power of a direct current (DC) input voltage by a pulse width modulation method of a constant frequency. More particularly, the present invention relates to a half-bridge type power converter circuit having an auxiliary circuit.

Various types of power converters have been developed to obtain the desired output voltage from the input voltage. Among these power converters, a power converter by a switching system is used in recent years.

In developing a power converter based on such a switching method, the key elements are miniaturization and high efficiency. As a method for miniaturizing a power converter by a switching method, there is a method of increasing the switching frequency. By increasing the switching frequency, the size of the filter and transformer can be reduced, which in turn can reduce the volume of the power converter. However, as the switching frequency is increased, more switching losses occur and a bulkier heat dissipation mechanism is required.

As a power converter operating at a high switching frequency and relatively low switching loss, there is a soft converter power converter. Also in such a soft switching method, an active clamp circuit is used most widely. An example of an active clamp soft switching power converter is Korean Patent No. 10-19837 entitled "Switching Power Supply."

The active clamp system includes a main switch and an auxiliary switch, and is configured to use the auxiliary switch to reflux the leakage and magnetizing inductance current of the transformer during the extinguishing period of the main switch. In the active clamp system, since the main switch switches zero voltage, the switching loss is reduced and the efficiency is high. However, about twice the voltage of the input voltage is applied as a voltage stress to the main switch and the auxiliary switch. Therefore, a high breakdown voltage main switch and an auxiliary switch should be used. High breakdown voltage switches have a small current capacity and are expensive.

It is an object of the present invention to provide a switching power converter circuit having high efficiency and high power density and having low voltage stress.

In order to achieve this object, the present invention provides a power converter that converts the power of the DC input voltage applied between the first and second input terminals and outputs it through the first and second output terminals. The power converter circuit according to the present invention includes a first charging unit and a second charging unit connected in series between the first and second input terminals, a first switch and a second switch connected in series between the first and second input terminals, and a first switch. A primary winding and a secondary winding insulated from the primary winding, which are connected between the connection point between the live part and the second live part and between the first switch and the second switch, wherein a predetermined point of the secondary winding is the first output. A transformer connected to the terminal, a first rectifier connected between one terminal and a second output terminal of the secondary winding of the transformer, a second rectifier connected between the other terminal and the second output terminal of the secondary winding of the transformer, And an output terminal charging portion connected between the first and second output terminals.

According to the present invention, in a soft switching power converter circuit, the input stage is implemented in a half-bridge manner, thereby reducing the breakdown voltage of the primary side switch and reducing the switching loss of the primary side switch with zero voltage switching. Decrease. In addition, by making the turns ratio of the main transformer and the auxiliary transformer not the same, it is possible to use a small amount of the auxiliary switch, the auxiliary transformer and the auxiliary rectifier together with the main switch, the main transformer and the main rectifier. Therefore, the burden of the auxiliary switch, the transformer and the rectifier can be minimized.

As shown in FIG. 1, in the power converter circuit according to an embodiment of the present invention, a DC input voltage Vs 101 is applied between both input terminals. In addition, a first capacitor 102 and a second capacitor 103 are connected in series between both input terminals 101.

In addition, the first power switch 105 and the second power switch 104 are connected in series between both input terminals 101. The first power switch 105 and the second power switch 104 may be implemented with MOS transistors Qm and Qa, respectively. Between the drain and the source of these power switches Qm and Qa are parasitic capacitors Cm and Ca having inherent capacitance. In addition, the body diodes Dm and Da are present in each of the power switches Qm and Qa. Separate capacitors and diodes may be provided to supplement the functions of the parasitic capacitors and body diodes of transistors Qm and Qa, or for additional functions.

The power converter circuit according to the invention also comprises a first transformer 106 and a second transformer 107 connected in series. That is, the primary winding and secondary winding of the 1st transformer 106 and the 2nd transformer 107 are connected in series, respectively. The dot-side terminal of the primary winding of the first transformer 106 and the non-dot side terminal of the primary winding of the second transformer 107 may be a connection point between the first capacitor 102 and the second capacitor 103 and the first terminal. It is connected to the connection point between the power switch 105 and the 2nd power switch 104, respectively.

On the dot side terminal of the secondary winding of the first transformer 106 and the non-dot side terminal of the secondary winding of the second transformer 107, the cathodes of the first rectifying diode 108 and the second rectifying diode 109 are provided. Each is connected. The anodes of the first rectifying diode 108 and the second rectifying diode 109 are commonly connected to the negative terminal of the output terminal. On the other hand, the connection point of the non-dot side terminal of the secondary winding of the first transformer 106 and the dot side terminal of the secondary winding of the second transformer 107 is connected to the positive terminal of the output terminal. On the other hand, the smoothing capacitor 110 is connected between the positive (+) terminal and the negative (-) terminal of the output terminal. Subsequently, a load 111 is connected between the positive terminal (+) and the negative (-) terminal of the output terminal.

One side of both input terminals 101 may be grounded. Likewise, the negative terminal of the output terminal can be grounded.

Hereinafter, an operation of the power converter circuit as shown in FIG. 1 will be described with reference to the waveform diagram of FIG. 2.

The first power switch and the second power switch are controlled by switching control signals having duty cycles of D and 1-D, respectively. The signal supplied between the gate and the source of the transistor Qm for controlling the first power switch 105 is called Vgs (Qm), and the signal supplied between the gate and the source of the transistor Qa for controlling the second power switch 104. Is defined as Vgs (Qa). As shown in Fig. 2, Vgs (Qm) and Vgs (Qa) are pulse signals that alternate with each other with a predetermined dead time. The turns ratio on the primary and secondary sides of the first transformer 106 is referred to as Nmp / Nms, and the turns ratio on the primary and secondary sides of the second transformer Ta 107 is referred to as Nap / Nas.

The voltage applied to the primary side of the first and second transformers in the steady state must satisfy the voltage time balance condition. That is, the main switch Qm conducts during D to apply the voltage Vs2 to the primary sides of the first and second transformers, and the auxiliary switch Qa conducts during 1-D to apply the voltage Vs1 to the primary sides of the first and second transformers. Therefore, the voltage time balance condition as shown in Equation 1 is satisfied.

Vs2D = Vs1 (1-D)

The voltages Vs1 and Vs2 applied to the input capacitors Cs1 and Cs2 from Equation 1 are determined by the ratio D, as shown in Equation 2, respectively.

Vs1 = Vs (1-D)

Vs2 = VsD

Where D is the rate at which the main switch is operated and the maximum rate is 0.5 in this embodiment. Therefore, in the steady state, Vs1 is larger than Vs2.

First, the section M1 will be described. In the section M1, Vgs (Qm) is on. Correspondingly, the first power switch 105 is in a conductive state, and the second power switch 104 is in a non-conductive state. Vs2, which is part of the input voltage Vs, is applied to the primary windings of the first transformer and the second transformer. At this time, the voltages Vnmp and Vnap applied to the first transformer and the second transformer both have positive values.

Vnmp> 0, Vnap> 0

Due to the inductance of the primary windings of the first and second transformers, the current Iprim flowing in the primary winding increases with time. As a result, a positive voltage is induced at the dot-side terminal of each secondary winding. Therefore, the voltages Vnms and Vnas induced in the secondary windings of the first transformer and the second transformer both have positive values.

Vnms> 0, Vnas> 0

Thus, the first rectifying diode 108 Dm is not conducting while the second rectifying diode 109 Da is conducting. As illustrated in FIG. 2, the current Irm conducting through the first rectifying diode 108 is 0 in the M1 section, while the current Ira conducting through the second rectifying diode 109 has a positive value. The value of the current Ira conducting through the second rectifying diode 109 is the sum of the current induced by the current Iprim conducting in the primary winding of the second transformer and the current due to the predetermined energy already stored in the second transformer. . The predetermined energy stored in the second transformer is accumulated in the section M3 to be described later.

Current due to energy stored in auxiliary transformer Ta at Irm = 0, Ira = Iprim * (Nap / Nas) + M3

At this time, energy is transferred from the secondary winding of the second transformer to the output capacitor 110 and the load 111 through the second rectifying diode 109. At this time, the output voltage Vo is equal to the voltage Vnas at both ends of the secondary winding of the second transformer, and through this, the voltage of the primary winding is obtained as follows.

Vnas = Vo, Vnap = Vo * (Nap / Nas)

At this time, the voltage of the primary winding of the first transformer is as follows.

Vnmp = Vp (= Vs2)-Vnap

In the first transformer, energy based on the above voltage is accumulated due to the current Iprim flowing in the primary winding. This energy is transferred to the secondary winding in step M3, which will be described later.

As Vgs (Qm) applied to the first switch is extinguished to the off state, the M1 section ends.

Next, the M2 section will be described. In the M2 section, both the first switch 105 and the second switch 104 are in a non-conductive state. At this time, the first capacitor 102, the primary winding, and the parasitic capacitor Cm of the first switch 104 are connected in series, and resonance is performed together with the second capacitor 103 and the second switch 104 parasitic capacitor Ca. see. Therefore, as the current Iprim flowing in the primary winding in the M1 stage is charged and discharged through the resonant circuit, electric charges are accumulated in the parasitic capacitor Cm of the first switch 105 which is turned on in the M1 stage, and is not conducted in the M1 stage. In the parasitic capacitor Ca of the second switch 104, the charge accumulated in the M1 stage is discharged. As a result, the voltage Vds (Qm) across the first switch 105 is increased while the voltage Vds (Qa) across the second switch 104 is reduced to zero. After the voltage Vds (Qa) across the second switch 104 is reduced to zero, the reverse internal diode of the second switch is turned on. Since the control signal Vgs (Qa) of the second switch 104 is turned on while the voltage Vds (Qa) of both ends of the second switch 104 is zero, zero-voltage switching is performed to turn-on switching loss. Can be reduced.

As the current Iprim conducting through the primary windings of the first and second switches continues to decrease, the current Ira conducting through the secondary windings of the second switch also decreases proportionally. Subsequently, when the current Ira becomes zero, the M2 phase is terminated.

Next, the M3 step will be described. In the M3 stage, the second switch 104 is turned on because Vgs (Qa) is on. Accordingly, the voltage Vs1 at both ends of the first capacitor 102 is applied in the reverse direction to the primary windings of the first transformer and the second transformer connected in series. Therefore, the voltage applied to the primary winding is negative, and the voltage induced on the secondary winding is also negative.

Vnmp <0, Vnap <0, Vnms <0, Vnas <0

Thus, the second rectifying diode 109 is reverse biased and not conducting, while the first rectifying diode 108 is forward biased and conducting. As shown in FIG. 2, the current Ira conducting through the second rectifying diode 109 is zero, while the current Irm conducting through the first rectifying diode 108 has a positive value. The value of the current Irm conducting through the first rectifying diode 108 is the sum of the current induced by the current Iprim conducting through the primary winding of the first transformer and the current due to the energy stored in the first transformer 106. .

Current based on energy stored in main transformer Ta at Ira = 0, Irm = Iprim * (NMp / NMs) + M1

At this time, energy is transferred from the secondary winding of the first transformer to the output capacitor 110 and the load 111 through the first rectifying diode 108. At this time, the output voltage Vo is equal to the voltage Vnms of both ends of the secondary winding of the first transformer, and the voltage of the primary winding is obtained as follows.

Vnms = Vo, Vnmp = Vo * (NMp / NMs)

At this time, the voltage of the primary winding of the second transformer is as follows.

 Vnap = Vp (= -Vs2)-Vnmp

In the second transformer, energy based on the above voltage is accumulated due to the current Iprim flowing in the primary winding. This energy is transferred to the secondary winding in the M1 stage as described above.

As Vgs (Qa) applied to the second switch is extinguished to the off state, the M3 section ends.

Next, the M4 section will be described. In the M2 section, both the first switch 105 and the second switch 104 are in a non-conductive state. At this time, the parasitic capacitor Ca of the first capacitor 102, the primary winding, and the second switch 105 exhibits resonance with the parasitic capacitor Cm of the second capacitor 103 and the second switch 104. Therefore, as the current Iprim flowing in the primary winding in the M3 stage is charged and discharged through the resonant circuit, electric charges are accumulated in the parasitic capacitor Ca of the second switch 104 which is turned on in the M3 stage, and is not conducting in the M3 stage. In the parasitic capacitor Cm of the first switch 105, the charge accumulated in the step M3 is discharged. As a result, the voltage Vds (Qa) across the second switch 104 is increased while the voltage Vds (Qm) across the first switch 104 is reduced to zero. After the voltage Vds (Qm) of both ends of the first switch 105 is reduced to zero, the reverse internal diode of the first switch is turned on. Since the control signal Vgs (Qm) of the first switch 105 is turned on while the voltage Vds (Qm) of both ends of the first switch 105 is zero, zero-voltage switching is performed to turn-on switching loss. Can be reduced.

As the current Iprim conducting through the primary windings of the first switch and the second switch continues to decrease, the current Irm conducting through the secondary winding of the first switch also decreases in proportion thereto. Subsequently, when the current Irm becomes zero, the M4 step is terminated.

3 is a circuit diagram showing another embodiment of a power converter circuit according to the present invention. The power converter circuit shown in FIG. 3 is very similar to the power converter circuit shown in FIG. 1 and replaces the first and second capacitors with one capacitor 202 connected in series with the first and second transformers. It is characterized by being provided.

Comparing the power converter according to the present invention with the active clamp type switching power converter as described above shows the following advantages. That is, in the active clamp type power converter, the voltage stress applied to the primary side switch is about twice the input voltage, that is, 2 Vs, whereas the voltage stress of the input voltage is applied in the present invention. Accordingly, the present invention enables the use of a switch having a lower voltage capacity than the active clamp method, so that a small switch package can be used, the cost can be reduced, and the on-resistance is smaller than that of the active clamp method. In addition, in an active clamp type power converter, transformers having similar capacities are used, whereas in the present invention, a transformer having a small capacity can be used together with a large capacity transformer, so that the overall circuit can be miniaturized and manufacturing costs can be reduced. . Similarly, in the active clamp circuit, rectifiers having similar capacities are used as rectifiers, while the present invention has the advantage of using a large rectifier and a small rectifier together. This also contributes to achieving the miniaturization and low cost of the circuit. In addition, the active clamp type power converter can obtain high efficiency in applications where the output voltage is generally 5-15V, whereas the power converter according to the present invention is required in applications requiring a low voltage of 5V or less. High efficiency can be obtained. In addition, in the active clamp system, the input current ripple is almost discontinuous, whereas the power converter according to the present invention is almost continuous in the input current ripple, thus enabling the use of a small input filter.

As described above, in the present invention, a soft switching power converter circuit having a low voltage stress may be implemented using a half-bridge type circuit. The power converter circuit according to the present invention can be made highly efficient and miniaturized, and can be implemented at low cost.

In addition, the second switch 104, the second transformer 107, and the second rectifying diode 109 may have less current than the first switch 105, the first transformer 106, and the first rectifying diode 108. Can flow. In the present invention, such a circuit group will be referred to as an auxiliary circuit. In practice, only about 10% or less of the total conduction current is conducted through the auxiliary circuit. Through this auxiliary circuit, the pulsation component of the output current can be reduced, and the energy conversion efficiency can be maximized.

Claims (8)

In the power converter for converting the power of the DC input voltage applied between the first and second input terminal and output through the first and second output terminal, A first charging unit and a second charging unit connected in series between the first and second input terminals; A first switch and a second switch connected in series between the first and second input terminals; A primary winding connected between a connection point between the first charging unit and a second charging unit and a connection point between the first switch and the second switch, and a secondary winding insulated from the primary winding, wherein a predetermined one of the secondary windings is provided. The point of is a transformer connected to the first output terminal, A first rectifier connected between one side terminal of the secondary winding of the transformer and the second output terminal; A second rectifier connected between the other terminal of the secondary winding of the transformer and the second output terminal, The transformer comprises a first transformer and a second transformer each having a primary winding and a secondary winding insulated from the primary winding, The primary winding of the first transformer is connected in series with the primary winding of the second transformer, The secondary winding of the first transformer is connected in series with the secondary winding of the second transformer, The primary winding of the transformer comprises a primary winding of the first transformer and a primary winding of the second transformer connected in series with each other, and the secondary winding of the transformer is a secondary of the first transformer connected in series with each other. A winding and a secondary winding of the second transformer, And a predetermined point of the secondary winding corresponds to a series connection point of the secondary winding of the first transformer and the secondary winding of the second transformer. The method of claim 1, When a predetermined voltage is applied across the primary winding of the transformer, a high voltage is induced at the one terminal of the secondary winding of the transformer, The cathode of the first rectifier is connected to the one terminal, the anode of the first rectifier is connected to the second output terminal, The cathode of the second rectifier is connected to the other terminal, and the anode of the second rectifier is connected to the second output terminal. And a power converter. delete The method of claim 1, Output stage charging unit connected between the first and second output terminal A power converter further comprising. The method according to claim 1 or 2, And the second input terminal and the second output terminal are grounded. The method according to claim 1 or 2, The first switch and the second switch each includes a control terminal, Each control terminal receives an alternate pulse signal, And the first switch and the second switch operate on and off depending on the level of the applied pulse signal. The method according to claim 1 or 2, The first switch and the second switch each include a transistor including a source, a gate and a drain, Sources and drains of the first switch and the second switch are connected to the first and second input terminals, respectively. And a parasitic capacitor and a body diode between the source and gate of the first switch and the second switch. In the power converter for converting the power of the DC input voltage applied between the first and second input terminal and output through the first and second output terminal, An input terminal charger connected at one side to the first input terminal; A first switch and a second switch connected in series between the first and second input terminals; A primary winding connected between the other side of the input terminal charging part and a connection point between the first switch and the second switch and a secondary winding insulated from the primary winding, wherein a predetermined point of the secondary winding is 1 transformer connected to the output terminal, A first rectifier connected between one side terminal of the secondary winding of the transformer and the second output terminal; A second rectifier connected between the other terminal of the secondary winding of the transformer and the second output terminal; An output terminal charging unit connected between the first and second output terminals, The transformer comprises a first transformer and a second transformer each having a primary winding and a secondary winding insulated from the primary winding, The primary winding of the first transformer is connected in series with the primary winding of the second transformer, The secondary winding of the first transformer is connected in series with the secondary winding of the second transformer, The primary winding of the transformer comprises a primary winding of the first transformer and a primary winding of the second transformer connected in series with each other, and the secondary winding of the transformer is a secondary of the first transformer connected in series with each other. A winding and a secondary winding of the second transformer, And a predetermined point of the secondary winding corresponds to a series connection point of the secondary winding of the first transformer and the secondary winding of the second transformer.

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