JPS596086B2 - Power loss reduction circuit for semiconductor switching elements - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a power loss reduction circuit when a switching element is turned off in a power control circuit using semiconductor switching elements.

FIG. 1 is an example of a loss reduction circuit in a conventional power control circuit for a semiconductor switching element. In Figure 1,
1 is a DC power supply, 2 is a switching element, 3 is a free-wheeling diode, 4 is a smoothing reactor 5 as a load, and 6 is a switching loss reduction circuit, which is composed of a capacitor T, a diode 8, and a resistor 9. Figure 2 shows the element current IC and element voltage VC when the switching element is turned off.
Indicates E.

If the loss reduction circuit 6 were not provided, the element voltage VCE would be as shown in FIG. 2a with respect to the element current IC, and the power loss during off-state would be large. In order to improve this problem, a loss reduction circuit 6 as shown in FIG. 1 has conventionally been used. The operation when this circuit is connected will be explained. First, as soon as the switching element 2 begins to recover its voltage, the element current IC transfers to the series circuit of the capacitor 7 and the diode 8. Since the capacitor 7 has previously been charged to the power supply voltage via the resistor 9, the element current IC transfers to the capacitor T, discharging it, and the difference between its terminal voltage and the power supply voltage becomes the element voltage VCE, and the second The result is as shown in b of the figure. Therefore, if the capacitance of the capacitor 7 becomes larger, the element voltage VCE shown in FIG. 2c will have a lower power loss than the element voltage VCE shown in FIG. 2a,
The effect is even greater in the case of FIG. 2c. but,
In this circuit, the charging current of the capacitor T causes a loss in the resistor 9. When the switching frequency is high, this loss increases, resulting in an increase in heat generation from the resistor and a decrease in the efficiency of the control circuit. Furthermore, if the capacitance of the capacitor T is increased in order to enhance the switching loss resistance effect, the above-mentioned drawback becomes more significant. It is an object of the present invention to eliminate the resistance loss, which is the drawback of the conventional method, and to improve the efficiency of the control circuit.

Furthermore, when charging the capacitor in the loss reduction circuit, the capacitor capacity is equivalently halved, reducing the peak value of the charging current and at the same time shortening the charging time, and when discharging the capacitor, the capacitor capacity is equivalently doubled. The purpose of this is to increase the loss reduction effect.

FIG. 3 shows an embodiment of the present invention, and numerals 1 to 5 have the same configuration as in FIG. 1.

6 is a loss reduction circuit, 10, 13 are capacitors, 12,
14 and 15 are diodes, and 11 is a reactor.

When the switching element 2 is turned on, the power supply 1, the load 5, and the reactor 4 constitute a main circuit, and at the same time, in the loss reduction circuit 6, the first capacitor 10, the reactor
, a third diode 12, and a second capacitor 13, a series resonant circuit is formed, and the capacitors 10 and 13 are each charged to the power supply voltage. One of the features of the present invention is that in the series resonant circuit, the capacitor is divided into two parts and each part is charged up to the power supply voltage. The capacitance of capacitors 10 and 13 is CCF],
If the inductance of the reactor 11 is L[H],
In a series resonant circuit, the capacitor capacity becomes 1/2,
The peak value 1p of the resonant power supply is IP when the power supply voltage is V.
=V/P[A], and the resonance time t is t=π/QI'S
ec], the resonance current is suppressed, and the resonance time is also shortened.

This resonant current is a current that flows after the switching element 2 becomes conductive, and the loss of the element hardly increases. What is more desirable is that the resonant current waveform of the present invention is a sine wave compared to the charging current waveform of the capacitor 7 in the conventional example, so that the current when the switching element is on is small, and therefore the switching loss when the switching element is on is reduced. It is to be. Furthermore, the resonant circuit does not have resistance loss unlike the conventional example. Next, when off (the first capacitor 10 and first diode 14 and the second capacitor 13 and second diode 15 operate in the same way as the conventional example, the capacitance of the capacitor is equivalently doubled, and the loss reduction effect is is enhanced.

As described above, according to the present invention, it is possible to reduce the switching loss when the switching element is turned off without causing loss due to resistance, compared to the conventional method, and there is an advantage that the efficiency of the control circuit can be improved. .

Further, since the equivalent capacitance of the capacitor is different during charging and discharging, there is an advantage that the peak value of the charging current is suppressed and the resonance time is shortened during charging, and the loss reduction effect is large during discharging.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional power loss reduction circuit for a semiconductor switching element, FIG. 2 is a diagram illustrating the operation of the conventional example, and FIG. 3 is a circuit diagram showing an embodiment of the present invention. 2... Switching element, 3... Freewheeling diode, 6... Switching loss reduction circuit, 10... First capacitor, 11...・・・
Reactor, 12...Third diode, 13.
...Second capacitor, 14...First diode 15...Second diode.

Claims (1)

[Claims] 1. In a power control circuit composed of a semiconductor element whose switching is controlled and a free-wheeling diode, a first capacitor is connected to the cathode of the free-wheeling diode through a first capacitor.
The cathodes of the diodes are connected, the anode of the first diode is connected to the anode of the freewheeling diode, the cathode of the second diode is connected to the cathode of the freewheeling diode, and the anode of the second diode is connected to the anode of the second diode through a second capacitor. The anode of the third diode is connected to the anode of the free-wheeling diode, the anode of the third diode is connected to the connection point of the first capacitor and the first diode via a reactor, and the cathode of the third diode is connected to the connection point of the first capacitor and the first diode. A power loss reduction circuit consisting of a semiconductor switching element connected to a connection point.