JP3137765B2 - Power converter using semiconductor element with control pole for rectifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter which uses a semiconductor device with a control electrode such as an FET as a rectifier to reduce the loss of a rectifier circuit.

[0002]

2. Description of the Related Art FIG. 3 shows a circuit configuration of a conventional example of a power converter using a semiconductor element with a control electrode in a rectifier circuit, and FIG. 4 shows operation waveforms thereof.

In FIG. 3, 1 is a DC power supply and 2 is a FET.
, 3 is a transformer, 4 and 5 are F
A semiconductor element with a control electrode such as ET, 4 is a semiconductor element with a control electrode for rectification, 5 is a semiconductor element with a control electrode for flywheel, 6 is a choke coil for smoothing, 7 is a capacitor for smoothing, and 8 is an output terminal. , 9 and 10 are parasitic diodes of the semiconductor elements 4 and 5 with control electrodes, respectively, and n ₁ is _one of the transformers 3.
A secondary winding, n _2, is a secondary winding of the transformer 3.

A series circuit of a DC power supply 1 and a switching element 2 is connected to a primary winding n ₁ of a transformer 3.
On the other hand, 2 on one side of the winding n ₂ of the transformer 3 (filled circle (-
One side of the semiconductor element 5 with the control electrode for flywheel in a circuit in which the semiconductor element 5 with the control electrode for flywheel is connected in parallel to the series circuit of the choke coil 6 for smoothing and the capacitor 7 for smoothing Connected, secondary winding n
The ₂ other side, the other end control commutation of the flywheel control Kiwametsuki semiconductor element 5 in the circuit Kiwametsuki semiconductor element 4
Connected through. Here, the control electrode of the rectifying control Kiwametsuki semiconductor element 4, on one side of the secondary winding n _2, the control electrode of the control flywheel Kiwametsuki semiconductor element 5 is the secondary winding n ₂
On the other side. The output terminal 8 for connecting a load is connected to both ends of the smoothing capacitor 8.

In FIGS. 3 and 4, a, b, and c denote a control pole voltage (gate-drain voltage in the case of FET) and an output terminal current (FET
, The current flowing from the source to the drain) and the output terminal voltage (the source-drain voltage in the case of the FET), and d, e, and f are the control pole voltages (FETs) of the semiconductor element 5 with the control pole for flywheel, respectively. In the case of, a gate-drain voltage), an output terminal current (a current flowing from a source to a drain in the case of an FET), and an output terminal voltage (a source-drain voltage in the case of an FET).

The circuit operation of the conventional example shown in FIG. 3 will be described below with reference to FIG. When a positive voltage is applied to the control pole of switching element 2 at time t ₀ shown in FIG. 4, switching element 2 is turned on, and the voltage of DC power supply 1 is applied to primary winding n ₁ of transformer 3. , black circles in the secondary winding n ₂ (· mark) side is positive polarity voltage occurs. As a result, the exciting inductance (not shown) of the transformer 3 is excited, the control pole voltage a becomes positive polarity, and the rectifying control semiconductor element 4 is turned on (see a and c in FIG. 4).
The current flows from the lower terminal of the output terminal 8 to the semiconductor element 4 having the control electrode for rectification, the secondary winding n ₂ , the choke coil 6, and the output terminal 8.
Flows to a load (not shown) through the upper terminal (see b in FIG. 4).

When the voltage of the control electrode of the switching element 2 is reduced to zero at time t ₁ , the switching element 2 is turned off. Here, by the energy stored in the exciting inductance of the transformer 3, the exciting inductance of the transformer 3 and the output capacity of the switching element 2 (sum of the drain-source capacity and the drain-gate capacity in the case of FET), rectification control The output capacitance of the semiconductor element 4 with a pole (the sum of the capacitance between the drain and the source and the capacitance between the drain and the gate in the case of the FET), and the input capacitance of the semiconductor element 5 with the control pole for the flywheel (the capacitance between the gate and the source in the case of the FET) And drain
(Sum of capacitance between gates). As a result, the voltages of the primary winding n ₁ and the secondary winding n ₂ of the transformer 3 are inverted, and a sine wave voltage (hereinafter referred to as a flyback voltage) having a negative polarity on the black circle (•) side is generated. . With this voltage, the control electrode voltage a becomes negative polarity and the semiconductor element 4 with the control electrode for rectification is turned off (see a and c in FIG. 4), and the control electrode voltage d
Becomes positive polarity, and the flywheel-controlled semiconductor element 5 is turned on (see d and f in FIG. 4). The current of the choke coil 6 flows back through the load connected to the output terminal 8 through the semiconductor element 5 with the control electrode for flywheel (see e in FIG. 4).

When the flyback voltage of the transformer 3 becomes zero at time t ₂ , the semiconductor element 5 with the flywheel control pole is turned off (see d and f in FIG. 4), and the current of the choke coil 6 is controlled by the flywheel. The electric current returns through the parasitic diode 10 of the semiconductor element 5 with a pole and through the load connected to the output terminal 8 (see e in FIG. 4).

When a positive voltage is applied to the control pole of switching element 2 at time t ₃ , switching element 2 turns on,
Trans again filled circle in the secondary winding n ₂ (· mark) side is positive polarity voltage induced control electrode voltage a rectification control Kiwametsuki semiconductor element 4 becomes positive polarity is turned on, Control pole voltage d
Becomes negative polarity, the semiconductor element 5 with the control electrode for flywheel is turned off, and thereafter the same operation is repeated.

[0010] Now, in the circuit of Figure 3, during the period for on-the rectifying control Kiwametsuki semiconductor element 4 (t ₀ ~t _1), but the control electrode voltage a is applied, the control flywheel Kiwametsuki since the control electrode voltage d of the semiconductor element 5 is used flyback voltage of the main transformer 3, the flyback voltage generator to have a period of t ₁ ~t ₂ of the period to be on (t ₁ ~t ₃₎ Only the drive voltage is applied to the control pole (see d in FIG. 4). Thus t ₂ ~t flywheel control Kiwametsuki semiconductor element 5 in the period of ₃ does not turn on, the parasitic diode 10 is turned on, when the output terminal voltage is controlled flywheel Kiwametsuki semiconductor element 5 On this period (The voltage between the source and the drain in the case of FET).
(F in middle).

[0011]

The reason why a semiconductor element with a control electrode such as an FET is used in a rectifier circuit is to reduce the on-voltage to 0.1 to 0.2 V to reduce the loss. However, in the circuit configuration of the above-described conventional power converter, there is a period during which no drive voltage is applied to the control pole of the semiconductor element 5 with the flywheel control pole, so that the effect of reducing the loss of such a rectifier circuit is sufficient. There was a drawback that it could not be demonstrated.

SUMMARY OF THE INVENTION The present invention has been made to eliminate the above-mentioned drawbacks, and an object of the present invention is to provide a semiconductor device with a control electrode for a flywheel which is turned on over the entire period when the semiconductor device with a control electrode for a flywheel is to be turned on. It is an object of the present invention to provide a power converter in which a control pole voltage necessary for turning on is obtained, so that the effect of reducing the loss of the rectifier circuit can be sufficiently exhibited.

[0013]

According to the present invention, in order to achieve the above object, in the present invention, a series circuit of a DC power supply and a switching element is connected to a primary winding of a transformer, and a choke coil and a load are connected in series. In a circuit in which a first semiconductor element with a control pole is connected in parallel to a circuit, one end of both ends of the semiconductor element with a control pole is directly connected to one side of a secondary winding of the transformer, and the other end is connected to a second side. The secondary winding output voltage of the transformer, which is connected to the other side of the secondary winding via a semiconductor element with a control pole and is generated when the switching element is periodically turned on and off, is connected to the first winding. When the semiconductor element with a control electrode is turned on, the second semiconductor element with a control electrode is turned off, and when the former is off, the latter is turned on. Power conversion equipment , A capacitor is connected in parallel with the second control electrode-equipped semiconductor element, and when the switching element is off, the flyback voltage generated in the secondary winding of the transformer until immediately before the switching element is next turned on is It shall be the structure in which to set the capacitance value of the capacitor to be equal to or greater than the threshold value of the control electrode of the first control Kiwametsuki semiconductor device.

[0014]

The semiconductor device with a control electrode according to the present invention is used in a rectifier circuit.
Power converters with flywheel control poles
A capacitor with a predetermined capacity is attached in parallel with the semiconductor element.Addition
Switch on the transformer flyback voltage generation period.
And the flyback
Control voltage for the flywheel
With control pole for flywheel by setting higher than pressure
It is turned on for the entire period when the semiconductor element is to be turned on,
The ON voltage is kept low to realize a low-loss rectifier circuit.
ing.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a circuit diagram for explaining the structure of one embodiment of the present invention, and FIG. 2 is an operation waveform diagram for explaining the operation of the circuit. In FIG. 1, 1 is a DC power supply, 2 is a switching element, 3 is a transformer, 4 is a semiconductor element with a control electrode for rectification, 5 is a semiconductor element with a control electrode for flywheel, 6 is a choke coil for smoothing, and 7 is a smoothing choke coil. A capacitor, 8 is an output terminal, 9 and 10 are parasitic diodes of the semiconductor elements 4 and 5 with control electrodes, 11 is a capacitor,
n ₁ is a primary winding of the transformer 3, and n ₂ is a secondary winding of the transformer 3.

The connection configuration of each of the above members is as follows. A series circuit of a DC power supply 1 and a switching element 2 is connected to the primary winding n ₁ of the transformer 3. On the other hand, in parallel secondary winding n ₂ of one side to the (black circles (-) mark side) control flywheel to the series circuit of the smoothing choke coil 6 and a smoothing capacitor 7 Kiwametsuki semiconductor element 5 of the transformer 3 Semiconductor element 5 with control pole for flywheel in connected circuit
Connected one end of the direct, on the other side of the secondary winding n _2, control of the flywheel in the circuit Kiwametsuki semiconductor element 5
Is connected via a semiconductor element 4 with a control electrode for rectification. Here, the control electrode of the rectifying control Kiwametsuki semiconductor element 4, on one side of the secondary winding n _2, the other side of the control electrode 2 winding n ₂ of the flywheel control Kiwametsuki semiconductor element 5 , Are connected respectively. The output terminal 8 for connecting a load is connected to both ends of the smoothing capacitor 8. Further, in this embodiment, by connecting a capacitor 11 in parallel to the rectification control Kiwametsuki semiconductor element 4, the switching element 2 is the flyback voltage occurring in the secondary winding n ₂ of the transformer 3 during the OFF, the switching element 2 The capacitance value of the capacitor 11 is set so as to be equal to or more than the threshold value of the control electrode of the semiconductor element 5 with the control electrode for flyback until immediately before is turned on.

In FIGS. 1 and 2, a, b, and c denote control electrode voltages (FETs) of the semiconductor element 4 having a rectifying control electrode, respectively.
In the case of, the gate-drain voltage) and the output terminal current (F
In the case of ET, it is a current flowing from the source to the drain), and an output terminal voltage (source-drain voltage in the case of FET), and d, e, and f are control electrode voltages (FETs) of the semiconductor element 5 having a control electrode for flywheel, respectively. In the case of, a gate-drain voltage), an output terminal current (a current flowing from a source to a drain in the case of an FET), and an output terminal voltage (a source-drain voltage in the case of an FET). The times t ₀ , t ₁ , and t ₃ in FIG. 2 correspond to t ₀ , t ₁ , and t ₃ in FIG. 4 showing the operation waveforms of the conventional example for easy comparison.

The operation and operation of the embodiment configured as described above will be described below.

First, the circuit operation of the above embodiment will be described with reference to FIGS. When a positive voltage is applied to the control pole of the switching element 2 at time t ₀ in FIG. 2, the switching element 2 is turned on, and the DC power supply 1 is connected to the primary winding n ₁ of the transformer 3.
The voltage of the applied black dot in the secondary winding n ₂ (· mark) side is positive polarity voltage occurs. As a result, the exciting inductance (not shown) of the transformer 3 is excited, and the control pole voltage a becomes a positive polarity to turn on the semiconductor element 4 with the rectifying control pole (see a and c in FIG. 2). A current flows from the lower terminal of the output terminal 8 to the load (not shown) through the semiconductor device 4 with the control electrode for rectification, the secondary winding n ₂ , the choke coil 6, and the upper terminal of the output terminal 8. (See b in FIG. 2).

When the voltage at the control pole of the switching element 2 is reduced to zero at time t ₁ , the switching element 2 is turned off, and the energy stored in the excitation inductance of the transformer 3 causes the excitation inductance of the transformer 3 and the output capacitance of the switching element 2 ( In the case of an FET, the sum of the drain-source capacity and the drain-gate capacity), the output capacity of the semiconductor element 4 with a rectifying control electrode (in the case of the FET, the sum of the drain-source capacity and the drain-gate capacity), Input capacitance of semiconductor element 5 with control electrode for flywheel (for FET,
Sum of gate-source capacitance and drain-gate capacitance)
And resonance with the capacitor 11. As a result, the voltages of the primary winding n ₁ and the secondary winding n ₂ of the transformer 3 are inverted, and a sine wave flyback voltage having a negative polarity on the black circle (•) side is generated. With this voltage, the control pole voltage a has a negative polarity and the semiconductor element 4 with a control electrode for rectification is turned off (see a and c in FIG. 2), and the control pole voltage d has a positive polarity and is used for a flywheel. The semiconductor element 5 with the control electrode is turned on (see d and f in FIG. 2), and the current of the choke coil 6 passes through the semiconductor element 5 with the control electrode for flywheel and passes through a load (not shown) connected to the output terminal 8. Reflux through (see e in FIG. 2).
When the capacitor 11 is added in this manner, the resonance period of the flyback voltage of the transformer 3 becomes longer. Therefore, the generation period of the flyback voltage such that the period until time t ₃ when turned on next switching element 2 from the time t ₁ (corresponding to a period of about half the resonance period), and the flyback voltage Of the control electrode of the flywheel control electrode-equipped semiconductor element 5 so that the absolute value of
When the capacitance of 1 is selected, the semiconductor element 5 with the control electrode for flywheel continues to be turned on from time t ₁ to time t ₃ , and its ON voltage is kept low (see f in FIG. 2).

When the switching element 2 is turned on at time t ₃ , a positive polarity voltage is again induced on the secondary winding n ₂ of the transformer 3 on the black circle (•) side, so that the control pole voltage a has a positive polarity. As a result, the semiconductor element 4 with a control electrode for rectification is turned on, the control electrode voltage d becomes negative polarity, and the semiconductor element 5 with a control electrode for flywheel is turned off. Thereafter, the same operation is repeated.

Incidentally, the capacitor 11 in the above embodiment is used.
Is connected between the control electrode and the output terminal of the semiconductor element 5 with the control electrode for flywheel, the same effect as described above can be obtained.

The flyback voltage generation period can be extended by connecting a capacitor in parallel with the winding of the transformer 3, but charge and discharge loss of the capacitor occurs when the switching element 2 is switched. On the other hand, when the capacitor 11 is connected in parallel to the semiconductor element 4 having a control electrode for rectification, the charge and discharge of the capacitor 11 are performed by resonance of the flyback voltage, so that there is an advantage that no loss occurs.

[0025] As a reference example, instead of adding the capacitor 11, the transformer 3 so that the next period until time t ₃ when the switching element 2 is turned on flyback voltage generating period of the transformer 3 from time t ₁ The same effect can be obtained if the exciting inductance of (1) can be selected.

The capacitance value of the capacitor 11 can be set using the following equation. The voltage of the DC power supply 1 is E ₁ , the on-time of the switching element 2 is T ₁ , the switching repetition period is T, the number of primary windings of the transformer 3 is N ₁ , the number of secondary windings is N ₂ , and the primary winding is The excitation inductance viewed from line n ₁ is L
m, the output capacitance value of the switching element 2 (for an FET,
The sum of the drain-source capacitance and the drain-gate capacitance is represented by C ₂ , and the output capacitance value of the semiconductor element 4 having a rectifying control electrode (for a FET, the drain-source capacitance and the drain-source capacitance).
The sum of the gate-to-gate capacitance) is C ₃ , the input capacitance value (the sum of the gate-source capacitance and the drain-gate capacitance in the case of an FET) of the semiconductor element 5 with the control electrode for flywheel is C ₄ , and the capacitance of the capacitor 11. a value of the C _11, 2 of the transformer 3
The absolute value υ (t) of the instantaneous flyback voltage value induced in the next winding n ₂ is given by the following equation (1).

[0027]

(Equation 1)

Here,

[0029]

(Equation 2)

T represents the time from time t _{0 in} FIG.

In order for the absolute value of the flyback voltage at time t ₃ in FIG. 2 to become higher than the control pole threshold voltage Vth of the flywheel control pole semiconductor device 5, it is necessary to satisfy the following condition: 満 足 (T) ≧ Vth (2) is there. Substituting equation (1) into equation (2)

[0032]

(Equation 3)

## EQU1 ## (3) selecting the capacitance value C _{1 1} capacitor 11 so as to satisfy the equation. If the absolute value of the flyback voltage at time t ₃ becomes too higher than the control pole threshold voltage Vth of the flywheel control pole semiconductor element 5, the output capacitance of the switching element 2 and the input capacitance of the rectification control pole semiconductor element 4. , The charge / discharge loss such as the output capacity of the semiconductor element 5 with the control electrode for the flywheel increases,
(3) of the left side of the value may be set the capacitance value C _{1 1} capacitor 11 so that the vicinity of the control electrode the threshold voltage Vth of the control Kiwametsuki semiconductor device 5 for the flywheel.

For example, E ₁ = 48 V, T ₁ = 1.14
μs, T = 2.5 μs, N ₁ / N ₂ = 4, Lm = 100
μH, C ₂ = 170 pF, C ₃ = 1.2 nF, C ₄
= 6.9 nF, Vth = 3 V , and when the capacitance value C ₁₁ of the capacitor 11 becomes 23.5NF.

Here, the effect of the present embodiment will be described below in comparison with a conventional example by a specific example. For example, input voltage 48V, output 5V10A, conversion frequency 400kHz
When the power converter of the present embodiment in FIG. 1 is operated at z, the power loss of the entire device without the capacitor 11 according to the conventional example in FIG. 3 is 5.5 W, and the power conversion rate is 89.4%. However, by adding a capacitor having a capacitance value of 25 nF as the capacitor 11, the power loss is reduced by 10% to 4.9 W and the power conversion efficiency is increased by 2% to 91.5%. In addition, the peak value of the flyback voltage is reduced by extending the flyback voltage generation period of the transformer to the entire period of the switching element off period. For example, in the above-described power converter according to the present embodiment, the peak value of the flyback voltage is 24 V on the secondary side of the transformer when there is no capacitor 11 according to the conventional example in FIG.
By adding a capacitor having a capacitance value of 25 nF, the peak value is reduced to 14 V by 40%. For this reason, in the case of the conventional example of FIG. 3 without the capacitor 11, a withstand voltage of about 40 V is required as the semiconductor element with the control electrode.
In this embodiment, the addition of the capacitor 11 improves the breakdown voltage to about 20V. Thus, a semiconductor element with a control electrode having a low withstand voltage and a small on-voltage can be used, so that the loss of the rectifier circuit can be further reduced.

As described above, by selecting the capacitance value of the capacitor 11, the semiconductor elements 4, 5
Is suppressed to a low value throughout the ON period as shown by c and f in FIG. 2, and a low-loss rectifier circuit is realized.

In this embodiment, the control pole of the semiconductor element with the control pole is described as a rectifier circuit which is directly driven by the secondary winding of the transformer. However, another winding is provided in the transformer to drive the control pole. A similar effect can be obtained even with a rectifier circuit that performs this operation.
A similar effect can be obtained in a power conversion circuit in which the flyback voltage of the transformer is clamped by the DC power supply 1, the smoothing capacitor 8, a separately provided DC power supply, or the like so as to suppress the peak value of the flyback voltage. .

[0038]

As described above, according to the present invention, according to the present invention, in the power conversion device, and pressurized with a capacitor in parallel to the flywheel control Kiwametsuki semiconductor element, the switching element flyback voltage generating period of the transformer And the absolute value of the flyback voltage is set to be higher than the threshold voltage of the control electrode for the flywheel control electrode, so that the flywheel control electrode semiconductor element is turned on. A voltage can be applied to the control pole of the flywheel control pole-equipped semiconductor element over the entire period.
As a result, the ON voltage can be kept low throughout the ON period of the semiconductor element with a control electrode for a flywheel, and a low-loss rectifier circuit can be configured.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a waveform chart showing operation waveforms of the circuit of the embodiment shown in FIG.

FIG. 3 is a circuit diagram showing a conventional example of a power conversion circuit in which a semiconductor element with a control electrode is used as a rectifier.

FIG. 4 is a waveform chart showing operation waveforms of the circuit of the conventional example shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... DC power supply 2 ... Switching element 3 ... Transformer 4 ... Rectifier control electrode semiconductor element 5 ... Flywheel control electrode semiconductor element 6 ... Smoothing choke coil 7 ... Smoothing capacitor 8 ... Output terminal 9, 10 ... Control electrode Parasitic diode of attached semiconductor element 11 ... Capacitor a ... Control electrode voltage of rectifying control electrode semiconductor element 4 b ... Output terminal current of rectifying control electrode semiconductor element 4 c ... Output terminal of rectifying control electrode semiconductor element 4 Voltage d: Control pole voltage of semiconductor element 5 with control electrode for flywheel e: Output terminal current of semiconductor element 5 with control pole for flywheel f: Output terminal voltage of semiconductor element 5 with control pole for flywheel

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-175975 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 3/28

Claims (1)

(57) [Claims] 1. A control circuit in a circuit in which a series circuit of a DC power supply and a switching element is connected to a primary winding of a transformer, and a semiconductor element with a first control pole is connected in parallel to a series circuit of a choke coil and a load. One end of both ends of the attached semiconductor element is directly connected to one side of the secondary winding of the transformer, and the other end is connected to the other side of the secondary winding via a second semiconductor element with a control pole. The secondary winding output voltage of the transformer, which is generated when the switching element is periodically turned on and off, and the second control electrode-equipped semiconductor element is turned off when the first control electrode-equipped semiconductor element is turned on; In the power converter, when the former is off, the latter is turned on, and the latter is alternately operated, so that the power is rectified and smoothed to supply power to the load. Connect When the switching element is turned off, the flyback voltage generated in the secondary winding of the transformer until immediately before the switching element is turned on next becomes equal to or higher than the threshold value of the control pole of the first control poled semiconductor element. A power converter using a semiconductor element with a control electrode for a rectifier circuit, wherein a capacitance value of a capacitor is set.