JPS6158479A - Base drive circuit of transistor inverter - Google Patents

Abstract

PURPOSE:To improve the reliability by providing base voltage detectors in two transistors, respectively and controlling other base current supply circuits each other, thereby effectively preventing a shortcircuit mode from occurring. CONSTITUTION:An inverter in which two transistors TR1, TR2 are connected in series with DC power sources E1, E2, controlled to be alternately turned ON and OFF to supply a rectangular power to a load RL connected with the midpoint of the both transistors, base voltage detectors 8, 9 are respecitvely connected with the bases of the transistors TR1, TR2. The detection signals are supplied to AND circuits 10, 11 connected with the base current supply circuits 6, 7 of the opposite transistors to so control that the base current is not supplied to the other transistor when the base voltage of one transistor is detected.

Description

[Detailed Description of the Invention] [Technical Field] Rokumasuke relates to the base beast-face circuit of Tran, System, and Kuta.

BACKGROUND TECHNOLOGY Transistor inverters play an important role in regulating the speed of air conditioner motors and as DC-AC converters. A transistor inverter alternately turns on two transistors connected in series between the positive and negative sides of a DC power source (this is called commutation), and uses the connection point between the two transistors as an output terminal, and injects DC current there. The basic idea is to obtain a square wave whose amplitude is the power supply voltage, and this is called a unit invar. By arranging three unit inverters, three-phase AC output can be obtained.

It is desirable that, during commutation, one of the two transistors constituting the unit inverter changes from on to off and at the same time the other transistor changes from off to on. As a general property of transistors, when a square wave base current is applied, the change from off to on occurs quickly, but the change from off to on is extremely slow due to the carrier accumulation effect, which can reach more than 10 times as fast. There is also. Therefore, if you apply a base current to two transistors that turns one on and the other off at the same time, the momentary transistor will turn on and the power supply will be shorted, so the transistor will receive an excessive amount of current. Current flows and causes the transistor to heat up. This is called short circuit mode.

To prevent this short-circuit mode from occurring, conventional methods have been used to first turn off the base current of one transistor during commutation, and then allow a certain idle time before passing the on base current to the other transistor. There is.

FIG. 8 shows the configuration of a unit inverter using transistors and a conventional signal supply circuit. The unit inverter is composed of transistors TRI and TR2 connected in series to the DC power source, and the load RL is connected between the output terminal TI of the unit inverter and the midpoint T2 of the DC power sources El and E2.

In a polyphase configuration using two or more unit inverters, a midpoint of the DC power supply is not required. Transistor TRl.

Base current to TRQ is supplied as follows.

Here, the waveforms of each part are shown in FIG. An original signal eQ for setting the frequency and duty factor of the output voltage square wave and a signal obtained by inverting this original signal eQ by an inverting amplifier 1 are used to delay the time at which the signal changes from OFF to ON by an idle time setting circuit 2.3.

These signals are separated from the ground by an insulating element 4.5 such as a pulse transformer or photocoupler, and converted into signals based on the emitter potentials of the respective transistors TRI and TR2 to drive the base current supply circuits 6 and 7. Controls on/off of transistors TRI and TR2. As shown in FIG. 9, the base currents of transistors TR1 and TR2 start flowing with a delay of idle time tl from the original signal eQ, so even if the collector current flows for the accumulation time t2 after the base current is turned off, both transistors TRI, TR2
There will be no short circuit. However, both transistors TRI.

A period t3 in which TR2 is simultaneously off always occurs, and as the switching frequency of the inverter increases, this period has a non-negligible effect on the output voltage.

In other words, the storage time of a transistor generally varies from element to element and changes depending on the flowing load current.
It is necessary to design the play time to be larger than the maximum value of the storage time. However, during the idle time, after the accumulation time ends, both transistors are in an off state, so the output voltage of the unit inverter is not determined, which is not preferable. Design engineers of transistor inverters have always struggled with setting idle time.

<Objective of the Invention> The present invention provides a base drive circuit for a transistor inverter, which aims to eliminate the drawbacks of the above-mentioned conventional circuit.

That is, the present invention is a method for preventing short-circuit mode occurrence in a transistor inverter, which is based on an idea different from the conventional method of providing idle time. The base current of the transistor is configured to be supplied only when it is detected that the signal is on and the other transistor is off.

<Embodiments> The present invention will be described below with reference to the embodiments shown in the drawings. First, FIG. 1 shows a basic circuit diagram of a base drive circuit of a transistor inverter according to the present invention.

In FIG. 1, the same parts as those of the conventional circuit shown in FIG. 8 are given the same reference numerals. Here, the idle time setting circuits 2 and 3 in the conventional circuit shown in FIG. 8 are removed, and instead, base voltage detection circuits 8 and 9, an AND circuit 10.11, and an insulating element 12.13 are added. Therefore, while the collector current is flowing, including the operation during the accumulation time of transistors TRI and TR2, even if the base current is flowing in the opposite direction, the transistor TRl.

By applying the fact that a positive voltage is generated between the base and emitter of TR2, this base voltage is detected, and while the positive voltage is being detected, the supply of base current to the other transistor is blocked. That's what I do.

FIG. 2 shows waveform diagrams at various parts of the circuit of FIG. 1.

Regarding the transistor TRI side, the base voltage of the transistor TR2 maintains a positive voltage at the time when the original signal ego is applied, so the AND circuit 10 is closed based on the detection output of the base voltage detection circuit 9 at this time. Supply of base current from base current supply circuit 6 to transistor TRI is blocked. and transistor TR
When the accumulation time t4 of 2 ends, the base voltage of the transistor TR2 changes to a negative value by the base current supply circuit 7, and the signal is no longer blocked by the AND circuit IO, and the base voltage of the transistor TR2 is changed to a negative value by the base current supply circuit 6. A current is supplied and the collector current of the transistor TRI begins to flow. The operation on the transistor TR2 side is also similar. As can be seen from FIG. 2, the collector currents of the two transistors TRI and TR2 never flow at the same time, and a short circuit between the transistors TRI and TR2 due to failure of the base current supply circuits 8 and 9 is also prevented.

FIG. 3 shows a more specific circuit diagram of FIG.

Regarding the signals on the transistor TRI side, when the original signal eQ is positive, the light emitting diode LDI lights up, and when the light emitting diode LD+2 also lights up, the transistor TR
II is turned on, and current is supplied from the base power supply El+ to the base of the transistor TRI through the transistor TRII and the resistor R1+. When either or both of the light emitting diode LDII and the light emitting diode LD+2 are in the blocking state, the transistor TRI2 is turned on;
A reverse current and a reverse voltage are supplied to the base of the transistor TR1.

FIG. 4 shows only the base voltage detection circuit 9 of the transistor TR2 in FIG. 3, and the same elements as in FIG. 3 are given the same reference numerals. This circuit serves as a comparison circuit for the base voltage and emitter voltage of the transistor TR2. That is, the terminal voltage of the resistor R22 on the diode D2 side follows the higher of the base voltage and emitter voltage of the transistor TR2 due to the diode D2 and the light emitting diode LD+2. When the base voltage is higher than the emitter voltage, the voltage of the resistor R22 follows the base voltage by the diode D2K, so that the light emitting diode LD! 2
is off. When the base voltage is low, the voltage across resistor R22 follows the emitter voltage, so diode D2 is turned off and all current flowing through resistor R22 flows through light emitting diode LD+2. Light emitting diode LD! When no current flows through transistor TRI, supply of base current to transistor TRI is blocked.

5 and 6 show other embodiments of the base current supply circuit 6.7 and the base voltage detection circuits 8, 9. In both cases, the power source for the base current is not a positive or negative power source, but a single power source E20.

In FIG. 5, when the transistor TR2 is turned on, the base current flows from the power supply E20 to the resistor R23 and the transistor TR2.
The base-emitter of the transistor TR21 is supplied. Since the base voltage is higher than the emitter voltage and the voltage applied to the resistor R22 is also small, the light emitting diode LD1
No current flows through 2. When transistor TR2 is turned off, transistor TR22 is turned on. The base reverse current is supplied through the transistor TR22, the emitter/base of the transistor TR2, the resistor R24, and the power supply E20. A voltage close to that of the power supply E2 is applied to the resistor R22, and when the base voltage becomes lower than the emitter voltage, the current of the resistor R22 is transferred from the diode D2 to the light emitting diode LD12, making it possible to supply the base current of the transistor TRI. do.

In FIG. 6, when the transistor TR2 is turned on, the base current flows from the power source E2Q to the transistor TR21 and the resistor R2.
3. The voltage is supplied through the base-emitter voltage regulator diode Z2 of the transistor TR2, and at the same time, the capacitor C2 is charged to the voltage of the voltage regulator diode Z2. When the transistor TR2 is off, the base current flows through the capacitor C2 and the transistor TR2 due to the charge stored in the capacitor C2.
emitter-base, resistor R24, transistor TR2
Supplied through 2. The voltage of the constant voltage diode Z2 operates as a negative power supply with equal restrictions, but the applied pressure is small. Resistance R
22 is connected to the positive power supply terminal, and the current flows through the transistor T.
Since it flows to the lower potential of the base and emitter of R2, it flows through the light emitting diode LD12 when the transistor TR2 is turned off, and acts as a base voltage detector.

FIG. 7 shows another embodiment of the output coupling of the photocoupler, which is the isolation element 4.12 in FIG. When the light-receiving elements of the photocoupler are connected in series, the light-receiving current flows only when the light emitting diodes LD and LD+2 both emit light, so an AND circuit is operated, and only one amplifier is required, simplifying the circuit configuration.

In this way, the on/off state of the two transistors is detected by comparing the base voltages of the two transistors TRI and TR2 with their emitter voltages, and when one is in the on state, the base current supply of the other transistor is blocked. , it is possible to prevent the short-circuit mode of the unit inverter from occurring, and to minimize the time during which the output of the unit inverter is open.

Effects> As described above, according to the present invention, in a transistor inverter in which two transistors are connected in series to a DC power source and are turned on alternately to obtain a square wave output at the connection point of both transistors, Since the two transistors are turned on after confirming that the other is off, a short-circuit mode in which both transistors are turned on at the same time, unlike conventional circuits, does not occur. Further, since the ON signal of one transistor and the OFF signal of the other transistor are supplied simultaneously, when the other transistor is detected to be OFF, the transistor turns ON immediately, and the period during which both transistors are OFF is automatically minimized. This configuration eliminates heat generation due to the short circuit mode of the transistors, eliminates control inaccuracies due to the existence of periods when both transistors are off, significantly improves reliability, and allows the inverter to use PWM (pulse width modulation). This makes it easy to apply advanced control technologies such as

[Brief explanation of the drawing]

FIG. 1 is a basic circuit diagram of a base drive circuit of a transistor inverter according to the present invention, FIG. 2 is a waveform diagram of each part of FIG. 1,
FIG. 3 is a circuit diagram of a more specific embodiment of the base drive circuit of the present invention, FIG. 4 is an explanatory diagram of the base voltage detection section in the first embodiment of FIG. 3, and FIGS. 5 and 6 are Both are circuit diagrams of other embodiments of the base voltage detection section, FIG. 7 is a circuit diagram of another embodiment of the output coupling section of a photocoupler, and FIG. 8 is a circuit diagram of a base drive circuit of a conventional general transistor inverter. FIG. 9 is a waveform diagram of each part of FIG. 8. TRI, TR2...Transistor, 6,7...Base current supply circuit, 8.9...Base voltage detection circuit, 1
0°11...AND circuit. Agent Patent Attorney Aihiko Fuku (and 2 others) No. 1 II!
1 Figure 2 Figure 3 E22 Figure 4 Figure 6' @ Figure 7 Figure 5 Figure 8

Claims (1)

[Claims] 1. In a transistor inverter in which two transistors are connected in series to a DC power source and are turned on alternately to obtain a square wave output at the connection point of both transistors, two bases are used to individually detect the base voltage of each transistor. A voltage detection circuit, two base current supply circuits that individually supply base current to each of the transistors, and each controls on/off supply of the base current of the other transistor based on the detection output of the base voltage detection circuit. 1. A base drive circuit for a transistor inverter, characterized in that both transistors are turned on at the same time to prevent short-circuiting of a DC power supply.