JPH01286779A - Semiconductor switch device - Google Patents

Abstract

PURPOSE:To suppress an overvoltage by providing a diode, a second semiconductor switch, and a flywheel diode in a series circuit of the primary winding of a current transformer and a first semiconductor switch. CONSTITUTION:In an inverter bridge circuit using semiconductor switch devices, the semiconductor switch device 1P has main circuit terminals P, Q, and a semiconductor switch device 1N has main circuit terminals Q, N, and they are connected in series. A load 10 is connected between the terminals Q and N of the devices 1P, 1N, and a DC power source 9 is connected between the terminals P and N. Both the devices 1P, 1N have the same structure, which is composed of a bipolar transistor(Tr) 1, a power MOSFET 2, etc. further composed of a series unit of a Zener diode 14, a second MOSFET 15, and a flywheel diode 12. Both the FETs 2, 15 are cooperated to be controlled ON, OFF. Thus, a reverse recovery current between the base and the collector of the Tr 1 is prevented to bypass a circulating load current from a current transformer.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a semiconductor switch device, and more specifically, it proposes a semiconductor switch device using a semiconductor switch in which a bipolar transistor and a MOSFET are connected in series. .

[Conventional technology]

FIG. 5 shows, for example, International Rect
rHEXFET published by ifier in 1982
It is a circuit diagram of the semiconductor switch device shown on page A-113 of DATABOOK J. The emitter E of bipolar transistor (hereinafter referred to as transistor) 1 is
It is connected to the drain D of a power MOSFET (hereinafter referred to as MOSFET) 2 to form a semiconductor switch. The collector C of the transistor 1 is the primary winding 3 of the current transformer 3.
The other end of the primary winding 3a is connected to one main circuit terminal P. The source S of MOSFET 2 is connected to the other main circuit terminal Q. Both ends of the secondary winding 3b of the current transformer 3 are connected to both ends of a series circuit in which a diode 6 and a Zener diode 5 are connected in anti-series,
An intermediate point between the diode 6 and the Zener diode 5 is connected to the base B of the transistor 1. Further, the anode of the Zener diode 5 is connected to the source S of the MOSFET 2. Bases B and M of transistor 1
A capacitor 4 is connected between the source S of the OSFET 2, and a series circuit of a diode 7 and a resistor 8 with the anode on the collector C side is connected between the collector C and base B of the transistor 1. There is. Further, a snubber capacitor 11 is connected between the collector C of the transistor 1 and the source S of the MOSFET 2, and these constitute a semiconductor switch device.

and the main circuit terminal P of the semiconductor switch device.

9, a series circuit of a DC power supply 9 and a load 10 is connected with the negative pole of the DC power supply 9 being connected to the main circuit terminal Q side.

This semiconductor switch device performs a switching operation as shown in FIG. Now, transistor 1 and MOSFE
When both T2 are off, the capacitor 4 is charged via the diode 7 and the resistor 8 by the voltage 1 of the DC power supply 9. The voltage of this capacitor 4 is, for example, about 10V. Now, at time t0, when MOSFET 2 is turned on by inverting the gate voltages of MOSFET 2 from negative to positive, a discharge current flows from capacitor 4 through transistor 1 and MOSFET 2, and transistor 1 is immediately turned on. do. Then, the load current flows from the DC power supply 9 to the transistor 1 through the load IO.
The collector current ■c begins to flow. At this time, the secondary current I CTt of the current transformer 3 is lc/n (n is the turns ratio of the current transformer)
Diode 6 and transistor 1 as shown by the arrow.
, flows through MOSFET2. Then, due to the positive feedback effect of the current transformer 3, the base current of 1 m is applied to the transistor 1.
is supplied to keep transistor 1 in the on state.

Next, at time t2, as soon as the gate voltage VGS of MOSFliT 2 is inverted to negative, MOSFET 2 is turned off. Therefore, the emitter side of transistor 1 becomes open-circuited, and the collector current I, of transistor 1 becomes
The current flows between the collector C and the base 8 to the capacitor 4 and Zener diode 5 side. At this time, capacitor 4
acts to suppress the switching surge voltage between the drain D and source S of MOSFET 2. Then, at time t3 when the current blocking force between the collector C and base B of the transistor 1 is restored, the collector current ■ is cut off, and the voltage V□ across the series circuit of the transistor 1 and the MOSFET 2 becomes The voltage rises to the level of voltage v11. At this time, the snubber capacitor 11 is overcharged to a voltage higher than the voltage 2 of the DC power supply 9 due to an inductance component existing in the circuit between the transistor 1 and the MOSFET 2.

Since this overcharge voltage component Δ■a is discharged to the DC power supply 9 side via the current transformer 3, the secondary winding 3b of the current transformer 3
, a reset voltage ■□SET of n·Δ■7 is induced with opposite polarity.

Next, the operation when this semiconductor switch device is applied to an inverter will be explained with reference to FIG. FIG. 7 shows half of a bridge circuit that constitutes an inverter, and this bridge circuit consists of the same circuit as the semiconductor switch device shown in FIG. It is constructed by connecting parallel-connected semiconductor switch devices IP and IN in series. A DC power supply 9 is connected between the main circuit terminals P and N at both ends of the series circuit of the semiconductor switch devices IP and IN, with the positive terminal on the side of the circuit terminal P.

Further, a load 10 is connected between a main circuit terminal Q and a main circuit terminal N of the semiconductor switch device IN.

If the semiconductor switch device IP is currently on, current flows from the DC power supply 9 to the load 10 via the semiconductor switch device IP. Next, when the semiconductor switch device IP is turned off, the current of the load 10 will circulate through the semiconductor switch device IN.

In this case, MOSFET 2 of the semiconductor switch device IN
When the gate voltage of the capacitor 4 is held negative, the electric charge of the capacitor 4 that has been charged with the polarity of + and - passes through the base B and collector C of the transistor 1,
Discharge occurs through the primary winding 3a of the current transformer 3. The current in the load 10 then passes through the flywheel diode 12,
It circulates through the primary winding 3a of the current transformer 3. At this time, the direction of the current I C70 in the secondary winding 3b of the current transformer 3 is opposite to the arrow mark, and is blocked by the diode 6, causing an overvoltage to occur in the secondary winding 3b. Subsequently, when the semiconductor switch device flP is turned on again, the semiconductor switch device IN
A reverse recovery current flows through the semiconductor switch device IP between the flywheel diode 12 and the collector C and base B of the transistor 1 .

[Problems to be Solved by the Invention] In the conventional semiconductor switch device described above, the current of the load 10 circulates through the primary winding 3a of the current transformer 3, so Overvoltage occurs.

Therefore, it is necessary to add overvoltage suppressing means to the secondary winding 3b. Further, the turn-on current on the side of the semiconductor switch device that turns on is the reverse recovery current of the flywheel diode of the semiconductor switch device through which the load current flows and the collector C of the transistor.

The reverse recovery current between the bases 8 is superimposed on the load current and increases. Therefore, the MOS of the semiconductor switch device turns on.
When the voltage drop between the drain D1 and the source S of FET 2 becomes large and exceeds the Zener voltage of Zener diode 5, the secondary winding current I of current transformer 3, ? 2 flows to the Zener diode 5 and is not supplied to the base B of the transistor 1, causing a problem in that the turn-on loss of the transistor 1 increases.

In view of such problems, it is an object of the present invention to provide a semiconductor switch device that can suppress overvoltage caused by circulation of load current and reduce turn-on loss of the semiconductor switch device.

[Means to solve the problem]

The semiconductor switch device according to the present invention includes a first semiconductor switch in a series circuit of a primary winding of a current transformer and a first semiconductor switch in which a bipolar transistor and a MOSFET are connected in series.
A diode provided in the forward direction of the semiconductor switch,
The bipolar transistor includes a second semiconductor switch provided to supply a base current to the bipolar transistor, and a flywheel diode connected in antiparallel to the series circuit of the primary winding, the diode, and the first semiconductor switch.

[Effect]

The diode blocks reverse recovery current flowing between the base and collector of the bipolar transistor.

A second semiconductor switch provides a base current that turns on the bipolar transistor. The flywheel diode bypasses the circulating load current from the current transformer.

As a result, the circulating load current does not flow through the current transformer.

Further, the base current of the bipolar transistor is supplied by the second semiconductor switch.

〔Example〕

The present invention will be explained in detail below with reference to drawings showing embodiments thereof. FIG. 1 is a circuit diagram showing half of an inverter bridge circuit to which a semiconductor switch device according to the present invention is applied.

The semiconductor switch device IP has main circuit terminals P and Q, and the semiconductor switch device 11N has main circuit terminals Q and N, respectively.

Semiconductor switch devices IP and IN are connected in series by connecting Q.

and the main circuit terminals Q of the semiconductor switch devices IP and IN.
A load 10 is connected between the main circuit terminal N of the semiconductor switch device IN and the main circuit terminal P of the semiconductor switch device IP, and a DC power supply 9 is connected between the main circuit terminal P of the semiconductor switch device IP and the main circuit terminal N of the semiconductor switch device flN. , and are connected with the positive terminal thereof as the main circuit terminal P side.

These semiconductor switch devices IP and IN both have the same structure and are constructed as described below. The emitter E of bipolar transistor (hereinafter referred to as transistor) 1 is a power MO5FET (hereinafter referred to as MOS).
Ft! T) is connected to the drain D of 2 to form a first semiconductor switch. The collector C of the transistor 1 is connected to one end of the primary winding 3a of the current transformer 3 via a diode 13 whose cathode is connected to the collector C, and the other end of the primary winding 3a is connected to one end of the primary winding 3a. It is connected to the main circuit terminal P of. The source S of MOSFET 2 is connected to the main circuit terminal Q.

Both ends of the secondary winding 3b of the current transformer 3 are connected to both ends of a series circuit in which a diode 6 and a Zener diode 5 are connected in reverse series.
The intermediate point between the two terminals is connected to the base B of the transistor 1. Also, the anode of Zener diode 5 is a MOS
Connected to source S of FET 2. A capacitor 4 is connected between the base B of transistor 1 and the source S of MOSFET 2, and the collector C of transistor 1 is
, and the base 8, a series circuit of a diode 7 and a resistor 8 with an anode on the collector C side is connected. Further, a snubber capacitor 11 is connected between the other end of the primary winding 3a of the current transformer 3 and the source S of the FET 2, and a flywheel diode 12 is connected to the snubber capacitor 11, and its anode is connected to the snubber capacitor 11. It is connected in parallel as the source S side of MOSFET 2. Further, the other end of the primary winding 3a of the current transformer 3 is connected to the cathode of a Zener diode 14, and the anode of the Zener diode 14 is connected to the drain D2 of the 5FET 15, which is a second semiconductor switch. The source S2 is connected to the base B of the transistor 1, and these constitute a semiconductor switch device.

Note that the MOS in the semiconductor switch devices IP and IN
FETs 2 and 15 are controlled to be on/off in conjunction.

Next, the operation of the semiconductor switch device configured as described above will be explained with reference to FIG. Semiconductor switch device IP, IN
When turning on MOSFET 2 and M
A positive voltage is applied to the gates G and Gt of the OSFET 15 at the same time. Then, a base current I flows into the transistor 1 from the capacitor 4, which had been charged up to that point, and the MOSFET 15. Then, the voltage between the collector C and emitter E of the transistor 1 is the voltage across the Zener diode 14.
What if the Zener voltage drops below the zener voltage? The supply of base current I from 'l05FET15 is stopped. However, the collector current I of transistor 1.

When begins to flow, the secondary winding current ICTt of the secondary winding 3b of the current transformer 3 becomes the base current {circle around (2)} and flows to the base B.

Therefore, the collector current of MOSFET 15 of transistor 1 is ■. During the short period until the rise of the base current l
, supply.

Now, the semiconductor switch device fIP is turned off, the capacitor 4 of the semiconductor switch device IN is discharged, and the load 1
When the current flows back to zero, the discharge current of the capacitor 4 which attempts to flow from the base B of the transistor 1 through the collector C is blocked by the diode 13. Therefore, the discharge current will be discharged through the MOSFET 15 and the Zener diode 14. Then load 10
The current flows back through the flywheel diode 12, and the current of the load 10 does not flow back through the primary winding 3a of the current transformer 3. As a result, no overvoltage occurs in the secondary winding 3b of the current transformer 3.

After that, when the semiconductor switch device IP is turned on again, the turn-on current is a current in which the reverse recovery current of the flywheel diode 12 of the semiconductor switch device IN is superimposed on the current flowing through the load 10, which is different from the conventional one. The reverse recovery current between the collector C and base B of the transistor 1 disappears, and the turn-on loss of the transistor 1 is reduced.

For example, in the semiconductor switch device IN, the MOSFET 15 operates during a period when the current of the load 10 is circulating.
When the current direction of the load 10 is reversed, if the capacitor 4 is discharged, the base current will not flow to the transistor 1 even if the MOSFET 2 is turned on, so the semiconductor switch device IN will not be turned on and the semiconductor switch device IP side will not turn on. It also has the function of circulating current to.

Also, at this time, transistor 1 of the semiconductor switch device IN
When the voltage between the collector C and emitter E of the MOSFE increases and exceeds the Zener voltage of the Zener diode 14, the MOSFE
T15 and MOSFET 2 are turned on, base current flows through transistor 1, and semiconductor switch device IN is turned on.

In this embodiment, a resistor 8 and a diode 7 for initial charging of the capacitor 4 are provided, but since the base current of the transistor 1 can be supplied by the MOSFET 15, they may be omitted. Further, the capacitor 4 can have a small capacitance, and the capacitance of the capacitor 4 may be selected by considering only the function of the snubber capacitor 11 that suppresses the switching surge voltage.

In addition, as the second semiconductor switch, in FIG.
Although the MOSFET 15 is used, a transistor 20 or an IGBT 21 may be used instead of the MOSFET 15, for example, as shown in FIGS. 2(a) and 2(b). In these cases as well, the diode 16 for blocking reverse recovery current is replaced with the transistor 20 or IGBT 2 as in the case of the MOSFET 15.
They may be connected in series in the same direction as the forward direction of No. 1.

Further, in this embodiment, the snubber capacitor 11 is connected in parallel to the flywheel diode 12, but it may be connected in parallel to the series circuit of the transistor 1 and the MOSFET 2.

It may also be connected between eminters E.

FIGS. 3 and 4 show other embodiments of the present invention. In the semiconductor switch device IP shown in FIG. 3, a current transformer 3 is provided on the source S side of the MOSFET 2, and an anode is placed on the secondary winding 3b side between the MOSFET 15 and the secondary winding 3b. A diode 16 is interposed, and the other configuration is the same as that shown in FIG.

Further, the semiconductor switch device shown in FIG. 4 has a series circuit of a Zener diode 14 and a MOSFET 15 interposed between the connection intermediate point between the diode 13 and the collector C of the transistor 1 and the base of the transistor 1. The rest of the configuration is the same as that shown in FIG. In this case, the semiconductor switch device 1 shown in FIG.
The diode 16 for blocking reverse recovery current shown in P can be omitted, and the diode 13 can also have this function.

Note that these other embodiments can also provide the same effects as the above-described embodiments.

[Effects of the Invention] As described in detail above, according to the present invention, it is possible to prevent overvoltage occurring in the secondary winding of a current transformer when a load current circulates.

Moreover, it is possible to reduce the turn-on loss during switching of the bipolar transistor, and to provide an excellent effect of providing a semiconductor switch device that reliably turns on.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a half part of a bridge circuit of an inverter to which a semiconductor switch device according to the present invention is applied, FIG. 2 is a circuit diagram showing another embodiment of a circuit including a second semiconductor switch, and FIG. 4 and 4 are circuit diagrams of a semiconductor switch device showing another embodiment of the present invention, FIG. 5 is a circuit diagram of a conventional semiconductor switch device, FIG. 6 is a time chart of its on and off operations, and FIG. The figure is a circuit diagram of a half part of an inverter bridge circuit to which a conventional semiconductor switch device is applied. 1... Bipolar transistor 2... Power MO
SFET3... Current transformer 4... Capacitor 6...
・Diode 9...DC power supply 10...Load 11
... Snubber capacitor 12 ... Flywheel diode 15 ... Second semiconductor switch IP, I
N: Semiconductor switch device In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A first semiconductor switch formed by connecting a bipolar transistor and a MOSFET in series, and a current transformer having its primary winding connected in series to the first semiconductor switch, The current in the secondary winding of the current transformer is supplied to the base of the bipolar transistor, and in connection with the on/off operation of the first semiconductor switch, the current in the primary winding of the current transformer is supplied to the base of the bipolar transistor. In a semiconductor switch device configured to supply current to a load connected in parallel in a series circuit with a first semiconductor switch, the primary winding of the current transformer is connected in series with the first semiconductor switch. a diode provided in the circuit in the forward direction of the first semiconductor switch; a second semiconductor switch provided to supply base current to the bipolar transistor; and the primary winding, the diode, and the first semiconductor switch. and a flywheel diode connected in antiparallel to the series circuit.