JPH0779568A - Power transistor drive circuit in inverter - Google Patents

Abstract

PURPOSE:To drive a large-power transistor by a small-capacity driver. CONSTITUTION:When the first transistor Q1 of a predriver 10 is turned on, a base current flows to a power transistor 5 from a base power source E2 as shown by the solid line. Since the transistor 5u1 has a high amplification factor, the transistor 5u1 can be driven with a small base current. When the second transistor Q2 of the predriver 10 is turned on, a current flows to the transistor 5u1 from a reverse bias power source E1 as shown by the broken line. When the terminal voltage of a resistor R1 becomes higher than a set value V0 when the current flows, a third transistor Q0 is turned on and the base B of the transistor 5u1 is short-circuited with the emitter E of the transistor 5u1. As a result, the transistor 5u1 is quickly turned off, since a large reverse bias current IB2 flows to the transistor 5u1. The value of the current flows to the second transistor Q2 of the driver 10 is decided by V0/R1 and the value is set to a small value. Therefore, the capacity of the predriver 10 can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a power transistor drive circuit for an inverter, and more particularly to a drive circuit which can be driven by a small capacity driver.

[0002]

2. Description of the Related Art Generally, an inverter has a DC-AC conversion unit for converting DC into a three-phase AC having a frequency different from a power supply frequency, and in the conversion unit, two powers connected vertically are provided. A transistor is provided as a set, and six power transistors in which three sets are connected in parallel are provided, and six drivers for individually ON-OFF controlling each power transistor corresponding to each power transistor are provided. Have.

[0003]

However, in the prior art, as a power transistor, for example, 20 to 100 A is used.
When using a large-capacity driver, each driver also needed to use a large-capacity driver.

That is, each driver has a function of turning ON the corresponding power transistor in the forward bias state and a function of forcibly maintaining the OFF state in the reverse bias state. For the former function of setting the forward bias state, a power transistor with a high amplification factor HFE can be used to drive with a small base current, so a small capacity driver is sufficient. Regarding the latter function of setting the reverse bias state, as shown in FIG. 4, even if the base current is stopped in the ON state of the power transistor, the OF is turned off.
Since it takes a relatively long time to shift to the F state, a predetermined dead time is provided for ON-OFF switching of the power transistor in order to prevent arm short circuit. In this case, as the dead time is shorter, an output waveform closer to the theoretical value can be obtained. Therefore, in order to minimize the transition time from the ON state of the power transistor to the OFF state, a reverse bias voltage is applied to the power transistor to reverse the reverse bias current. Is generally used to saturate the minority carriers of the power transistor and shorten the OFF time of the power transistor. However, since the OFF time of the power transistor is proportional to the magnitude of the reverse bias current, if the device is designed to pass the necessary reverse bias current, it exceeds the driver's rating, so it is necessary to use a large capacity driver. As a result, in the past,
The size of the driver is increased, and when a total of 6 drivers are combined, the area occupied by the printed circuit board on which the drivers are arranged is large, and the size of the inverter as a whole is large and the cost is high.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a power transistor drive circuit of an inverter which can use a small capacity driver even when a large capacity power transistor is used. To provide.

[0006]

In order to achieve the above object, the present invention limits the reverse bias current flowing through the driver to a small value and secures the reverse bias current flowing through the power transistor at a large value. , A small capacity driver can be used.

That is, a concrete solution of the invention according to claim 1 is to provide six power transistors (5) having a high amplification factor.
u1) to (5w2) are provided corresponding to each, and a pre-driver (10) having first and second power transistors (Q1) and (Q2) for ON-OFF controlling the corresponding power transistors is provided, The first power transistor (Q1) is turned on in response to a control signal to form a forward bias circuit (15) for flowing a base current to the corresponding power transistor, and the second power transistor (Q2) is , The first transistor (Q1) is O
The present invention is intended for a power transistor drive circuit of an inverter, which forms a reverse bias circuit (16) which is turned on in response to a control signal when FF operates and supplies a reverse bias current to the base of the corresponding power transistor. And a resistor (R1) arranged in the reverse bias circuit (16),
A terminal voltage of the resistor (R1) is used as a base voltage, and when the base voltage exceeds a set value, the resistor is turned on and the resistor (R1) is turned on.
1) and a third transistor (Q0) forming a shunt circuit (17) bypassing the reverse bias circuit (16) so as to reduce the current flowing through the second transistor (Q2).

Further, in the invention described in claim 2, in addition to the configuration of the invention described in claim 1, a reverse bias is applied to a part of the shunt circuit (17) except a part shared with the forward bias circuit (15). The diode (D) is inserted in the same direction as the current flow direction.

In addition, in the invention described in claim 1, in addition to the configuration of the invention described in claim 2, the predriver (1
0) Between the power supply terminal and the ground terminal, a capacitor (C0)
Are connected.

[0010]

With the above construction, in the invention according to claim 1,
In the forward biased state of the power transistor in which the first transistor (Q1) is turned on and the second transistor (Q2) is turned off, the power transistor has a high amplification factor, so the first transistor (Q1) flows. Even if the base current has a small value, the power transistor can be driven well.

On the other hand, the second transistor (Q2) is turned on.
In the reverse bias state of the power transistor which is activated and the first transistor (Q1) is turned off, the reverse bias circuit (16) is formed and the reverse bias current is applied to the resistor (R
Since it flows to the second transistor (Q1) via 1),
The reverse bias current flowing through the first transistor (Q2) is limited to a small value by the resistor (R1) and the circuit impedance, so that a small capacity pre-driver can be used.

When the terminal voltage exceeds the set value due to the flow of the reverse bias current to the resistor (R1), the third transistor (Q0) is turned on, and the shunt circuit (17) is formed. The bias current is directly the third
Of the resistor (R1) and the second transistor (Q1).
By bypassing 2), a large reverse bias current is secured and the dead time of ON / OFF switching of the power transistor is shortened.

According to the second aspect of the invention, the shunt circuit (17) is provided by turning on the third transistor (Q0).
Due to the formation of this shunt circuit (17) and the L component of the circuit impedance, the current in the direction opposite to the reverse bias current immediately after the power transistor is turned off,
That is, it is assumed that the base current flows carelessly through the anti-parallel flywheel diode in the shunt circuit (17) and the first transistor (Q2). In this case, it is possible to repeatedly change the magnitude of the reverse bias current and the base current. Therefore, even if it is easy to cause oscillation of the power transistor, the shunt circuit (17)
The presence of the diode (D) inserted in the circuit block the flow of the base current, so that the oscillation of the power transistor is surely prevented.

Further, in the invention according to claim 3, although the impedance of the pre-driver (10) becomes high due to the presence of the diode (D), the pre-driver (10) is apt to malfunction, especially against negative noise. By the capacitor (C0) connected to 10), harmonics of noise flow into the capacitor (C0), and the pre-driver (1
0), the malfunction due to noise is effectively prevented.

[0015]

As described above, according to the power transistor drive circuit of the inverter of the invention described in claim 1, even in the drive circuit for a large capacity power transistor, the reverse bias current of the power transistor is reduced. The reverse bias current flowing through the driver is limited to a small value while securing a large value to effectively reduce the dead time of ON / OFF switching of the power transistor, so a small, low-priced small-capacity driver can be used. By limiting the area occupied by the printed circuit board to a small size, the size and cost of the entire inverter can be reduced.

Further, according to the second aspect of the invention, since the diode is used to surely prevent the oscillation of the power transistor, the damage of the power transistor due to the short circuit of the upper and lower arms of the inverter and the protection device. System down due to operation can be prevented, and the inverter's normal operation can be secured.

Further, according to the third aspect of the invention, since the harmonic component for noise is flown to the capacitor by using the capacitor, the malfunction of the pre-driver due to the noise can be effectively suppressed or prevented, and the inverter of the inverter can be effectively prevented. Normal operation can be secured.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an overall schematic configuration of an inverter. (1) is a three-phase power supply, (2) is a three-phase power supply (1) as an input power supply, for example, a pulse width modulation control type inverter,
(3) is a three-phase induction motor driven by the inverter (2).

The inverter (2) is a three-phase power source (1).
AC-DC converter (4) comprising a diode rectifier circuit (4a) and a capacitor smoothing circuit (4b) for converting the three-phase AC voltage of the above into a DC voltage, and the AC-DC converter (4)
And a DC-AC converter (5) for converting the DC voltage from the DC voltage into a three-phase AC voltage having an appropriate frequency different from the power supply frequency. The DC-AC conversion unit (5) has a total of six power transistors (5u1), (5u2), each of which has three sets of two power transistors vertically connected in series.
(5v1), (5v2), (5w1), (5w2).

Further, the inverter (2) has
A control circuit (6) comprising a microcomputer or the like which receives a start / stop signal or a frequency instruction signal from the outside and generates a PWM signal as a control signal corresponding to the frequency instruction signal (6)
And receiving the PWM signal from the control circuit (6),
According to the M signal, the above six power transistors (5u
1) to (5w2) are individually driven.

The details of the drive circuit (7) are shown in FIG.
In the drive circuit (7) of FIG. 2, since the circuit parts of the power transistors (5u1) to (5w2) are common to each other, only the circuit part for the power transistor (5u1) is shown.

In the figure, a power transistor (5u
1) is composed of transistors (Tr) having a high amplification factor HFE, and shows a case of three-stage Darlington connection as an example. (E1) is a reverse bias power supply that applies a reverse bias voltage between the emitter E-base B of the power transistor (5u1), and (E2) is a base power supply that applies a forward bias voltage between the emitter E-base B of the power transistor (5u1). Is.

(7a) is a microcomputer provided in the drive circuit (7), and (10) is a pre-driver, which receives the PWM signal output from the microcomputer (7a) and emits light. ), The first transistor (Q1), and the second transistor (Q1)
2) and the light emitted by the optical semiconductor (11),
When the PWM signal is ON (Low output), the first transistor (Q1) is turned ON and at the same time the second transistor (Q2) is turned OFF, while when the PWM signal is OFF (High output), the first transistor (Q1) is turned OFF. An interface circuit (1) for turning off the transistor (Q1) and simultaneously turning on the second transistor (Q2)
2) and have. Also, (R0) is the base power supply (E2)
And a first transistor (Q1).

Therefore, the O of the first transistor (Q1)
At the time of N, the base current IB1 flows from the base power source (E2) to the base B of the power transistor (5u1) via the resistor (R0) and the first transistor (Q1) as shown by the solid line in FIG. A forward bias circuit (15) that returns from the emitter E to the base power supply (E2) is formed.

On the other hand, the second transistor (Q2) is turned on.
At times, the reverse bias current I from the reverse bias power source (E1)
B2 is a power transistor (5
A reverse bias circuit (16) is formed which flows from the emitter E of u1) to the base B and then returns to the reverse bias power supply (E1) via the resistor (R1) and the second transistor (Q2).

In FIG. 2, the reverse bias circuit (16) has a circuit connecting the base B of the power transistor (5u1) between the first transistor (Q1) and the second transistor (Q2). Part of the resistance (R1)
Is installed. A third transistor (Q) provided separately is provided on the power transistor (5u1) side of the resistor (R1).
0) is connected to the emitter and the other side is connected to the base of the third transistor (Q0), and the terminal voltage of the resistor (R1) becomes the base voltage of the third transistor (Q0). The collector of the third transistor (Q0) is connected to the ground line (13). Therefore, when the third transistor (Q0) is turned on, the reverse bias power source (E
The reverse bias current due to the voltage of 1) passes through the emitter E and the base B of the power transistor (5u1) and then flows into the resistor (R1) and the second transistor (Q2). When a sufficient bias necessary for the ON operation is applied between the base and the emitter of the third transistor (Q0) by this current, the third transistor (Q0) is turned on.
Then, as indicated by the alternate long and short dash line in the figure, the current immediately flows through the third transistor (Q0) and again the reverse bias power source (E1).
A shunt circuit (17) returning to is formed.

Further, a part of the shunt circuit (17) excluding a part shared with the forward bias circuit (15), that is, a third part.
From the collector of the transistor (Q0) to the ground circuit (1
3) and the reverse bias power supply (E1), then the base power supply (E
2) Between the circuit connection point a and the diode (D)
However, the allowable direction of the current flow is set to be the same as the flow direction of the reverse bias current IB2.

In addition, in the pre-driver (10), the power source terminal (10) to which the base power source (E2) is applied.
The capacitor (C) is connected in parallel with the series circuit of the base power supply (E2) and the reverse bias power supply (E1) between a) and the ground terminal (10b) to which the ground circuit (13) is connected.
0) is connected. Incidentally, in FIG. 2, (Z) is the impedance of the line composed of the resistance and the inductance.

Therefore, in the above embodiment, the PWM signal from the microcomputer 6a is turned on (Low).
Signal), the first transistor (Q1) of the pre-driver (10) is turned on and the second transistor (Q2) is turned off. As a result, the forward bias circuit (15) is formed, and the base current IB1 flows from the base power source (E2) as shown by the solid line in FIG. 2, so that the power transistor (5u1) is turned on in the forward bias state.

Since the power transistor (5u1) having a high amplification factor is used here, the base current IB
1 can drive the power transistor (5u1) satisfactorily even with a small current limited by the resistor (R0) and the resistor (R1), and therefore, the first transistor (Q1) as the pre-driver (10). ) Can use a small capacity.

Further, P from the microcomputer 6a
When the WM signal is OFF (High signal), the first transistor (Q1) of the pre-driver (10) is OF
The F operation is performed, and the second transistor (Q2) is turned on. As a result, the reverse bias circuit (16) is formed, and the reverse bias current flows from the reverse bias power source (E1) as indicated by the broken line in FIG.
In 1), the reverse bias state is set, and the malfunction to the ON operation is effectively prevented.

At this time, in the reverse bias circuit (16), a current that is determined by the combined resistance of the resistance (R1) and the impedance (Z) and the internal impedance of each semiconductor flows, and this current causes the resistance (R1) of the resistance (R1) to flow. A voltage is generated at both ends, and this terminal voltage is the set value V0 (for example, 0.7v)
Then, the third transistor (Q0) is turned on, and the shunt circuit (17) excluding the resistor (R1) and the second transistor (Q2) is formed. Therefore, the emitter of the power transistor (5u1) is A large value of reverse bias current IB2 is determined between the E-base B and the combined resistance of the impedance (Z) and the internal impedance of each semiconductor.
Flows. As a result, the large reverse bias current IB2
As a result, minority carriers of the power transistor (5u1) are saturated in a short time.
The transition time from the ON state to the OFF state in 1) is extremely short and shortened.

Since the current flowing through the second transistor (Q2) of the pre-driver (10) is limited by the resistor (R1) and has a small value, the second transistor (Q2) has a small value.
It is possible to use a small-capacity pre-driver (10) having a small capacity of 2), and it is possible to reduce the size. In this case, the value of the current flowing through the second transistor (Q2) is approximately (V0 / R1
If the current value is set to a large value within the allowable range of the second transistor (Q2),
Since the current value flowing in the third transistor (Q0) (that is, the current value obtained by subtracting the current value flowing in the second transistor (Q2) from the reverse bias current IB2) can be limited to the minimum value, the third transistor (Q0 The capacity of 1) can be set to the minimum, and therefore, further miniaturization becomes possible.

Further, the power transistor (5u1) O
At the time of FF, the collector C-emitter E voltage rises sharply from a very small voltage value to the terminal voltage of the capacitor smoothing circuit (4b) of the AC-DC converter (4). Therefore, the collector C-base of the power transistor (5u1) Due to the capacitance between B (capacitor C1 shown in FIG. 3), a current I having a value (C1 · dV / dt) corresponding to the sudden change in the voltage is generated,
This current I flows as shown by the solid line in FIG.
Since energy is stored in the inductance component of the impedance (Z) of the circuit, after the disappearance of the current I, the shunt circuit (17) and the second transistor (Q2) are reversed as shown by the broken line in the figure. Direction opposite to bias current,
That is, there is a concern that the power transistor (5u1) may turn on due to the current flowing in the forward bias direction. In this case, when the power transistor (5u1) turns off due to the disappearance of the forward bias current, the power transistor (5u1) is turned off. Accordingly, the current I shown by the solid line is generated again, and
Since the above operation is repeated as shown in (b), the oscillation of the power transistor (5u1) is caused. However, in the present embodiment,
The diode (D) arranged in front of the reverse bias power source (E1) blocks the flow of current in the forward bias direction indicated by the broken line in the figure accompanying the above energy storage, and the base current of the power transistor (5u1) in the figure ( As shown in a), since the reverse bias current IB2 disappears and converges to a zero value, the malfunction in which the power transistor (5u1) is turned on is eliminated, and as a result, the pair of power transistors (5u1) forming the upper and lower arms, It is possible to prevent the damages caused by the short circuit of (5u2) and the system down caused by the operation of the protection device, and ensure the normal operation of the inverter (2).

Further, in the circuit of FIG. 2, the series circuit of the base power source (E2) and the reverse bias power source (E1) serves as the operating power source in the pre-driver (10), and the diode (D) is interposed in this series circuit. Due to the installation, the impedance of the pre-driver (10) becomes high and it is easy for the pre-driver (10) to malfunction due to noise. However, a capacitor (C) is connected in parallel between the power supply terminal (10a) and the ground terminal (10b).
0) is connected, and harmonics of noise flow to the capacitor (C0), so that malfunctions due to noise are effectively prevented.

Along with the arrangement of the capacitor (C0), a circulation path as shown by the alternate long and short dash line in FIG. 3 is newly formed and a current flows, so that the power transistor (5u1) oscillates similarly to the above. Although there is a concern, the current value depends on the capacitance value of the capacitor (C0), so that there is no problem if the capacitance value of the capacitor (C0) is appropriately selected so as not to oscillate.

In the above embodiment, the circuit of the power transistor (5u1) forming the upper arm has been described. However, in the power transistor drive circuit, each of the power transistors (5u2), (5v2) forming the lower arm,
Since the circuit of (5w2) is integrated with the three circuits, the present invention can be applied to the drive circuit shown in FIG.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram when an induction motor is driven by an inverter.

FIG. 2 is an electric circuit diagram showing a power transistor drive circuit forming an upper arm.

FIG. 3 is an operation explanatory diagram.

FIG. 4 is an explanatory diagram showing details of a transition from ON operation to OFF operation of a power transistor.

FIG. 5 is a diagram showing a base current when a power transistor oscillates and when it does not oscillate.

FIG. 6 is an electric circuit diagram showing a drive circuit for three power transistors forming a lower arm.

[Explanation of symbols]

 (7) Drive circuit (5u1) to (5w2) Power transistor (10) Pre-driver (Q1) First transistor (Q2) Second transistor (15) Forward bias circuit (16) Reverse bias circuit (R1) Resistance ( E1) Reverse bias power supply (E2) Base power supply (Q0) Third transistor (17) Shunt circuit (D) Diode (C0) Capacitor

Claims (3)

[Claims] 1. A first amplifier provided corresponding to each of the six high-amplification power transistors (5u1) to (5w2), and controlling the corresponding power transistors to be turned on and off.
And a pre-driver (10) having second power transistors (Q1) and (Q2), the first power transistor (Q1) being turned on in response to a control signal and being based on the corresponding power transistor. A forward bias circuit (15) for flowing a current is formed, and the second power transistor (Q2) is the first transistor (Q1).
A power transistor drive circuit of an inverter, which forms a reverse bias circuit (16) which is turned on in response to a control signal and flows a reverse bias current to the base of the corresponding power transistor when the off bias circuit operates. A resistor (R1) arranged in (16) and a terminal voltage of the resistor (R1) are used as base voltages, and when the base voltage exceeds a set value, the resistor (R1) and the second transistor are turned on. The shunt circuit (1) bypassing the reverse bias circuit (16) so as to reduce the current flowing in (Q2).
And a third transistor (Q0) which forms 7), the power transistor drive circuit of the inverter. 2. A diode (D) is inserted in the same direction as the flow direction of the reverse bias current in a part of the shunt circuit (17) excluding the part shared with the forward bias circuit (15). The power transistor drive circuit for an inverter according to claim 1. 3. A power transistor drive circuit for an inverter according to claim 2, wherein a capacitor (C0) is connected between the power supply terminal and the ground terminal of the pre-driver (10).