JPH0642785B2 - Driver circuit for transistor inverter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a drive circuit for a transistor inverter.

Generally, 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 the connection point of the two transistors is used as an output terminal. It is based on obtaining a square wave whose amplitude is a DC power supply voltage, which is called a unit inverter. Using a large number of inverters for each unit, set the phase of each output square wave appropriately, or change the pulse width of the output square wave with time (pulse width modulation, hereafter referred to as PWM) to create a multi-phase AC or sine wave. It is applied to obtain close voltage waveforms.

It is desirable that one of the two transistors forming the unit inverter changes from on to off and the other transistor changes from off to on during commutation. As a general characteristic of a transistor, when a base current is made to flow in a square wave, off-to-on is performed quickly, but the change from off-to-on is very slow due to a carrier accumulation effect and reaches 10 times or more. Sometimes. Therefore, when a base current that turns on one of the transistors and turns off the other is applied to the two transistors at the same time, both transistors are momentarily turned on and the power supply is short-circuited. Flow and cause heat generation in the transistor. This is called short circuit mode.

Conventionally, one pulse transformer is used for each transistor to drive the bases of the transistors forming the inverter. In that case, it is necessary to provide a period in which neither transistor is driven during commutation, that is, a play time, so that each unit inverter does not create a short circuit mode.

If two pulse transformers in a unit inverter are combined into one and the secondary winding of the transformer connected between the bases and emitters of the transistors is reversed in polarity with two transistors, the bases of the two transistors are equivalently equivalent.・ The emitters are connected in anti-parallel. When the primary winding of the transformer is driven with a constant current, at the time of commutation, the other transistor is not driven until one transistor is turned off.
Do not create short circuit mode. However, since positive and negative symmetrical voltages are applied to the windings of the transformer, the duty ratio of the unit inverter cannot be changed from 1: 1 in order to increase the exciting current of the transformer, which is not practical.

FIG. 4 shows a base drive circuit including a unit inverter used as a conventional general transistor inverter and one pulse transformer. Here, the unit inverter is composed of a pair of transistors TR ₁ and TR ₂ that are alternately turned on, and the connection point A is the output terminal. The load R _L is the output terminal A and the midpoint B of the currents E ₁ and E ₂ . Connected to
When a large number of unit inverters are included, they are connected between output terminals, so the middle point of the power supply is not necessary. Diode D _F1 , D _F2
Is an anti-parallel diode connected in anti-parallel to TR ₁ and TR ₂ , respectively, and provides a path for the reverse current generated by the inductive load. The transistors TR ₃ and TR ₄ are alternately turned on by the input signal e ₀ , and the current flowing from the power source + Vcc through the resistor R ₁ is supplied to the primary winding of the transformer T with the polarity changed. FIG. 5 shows the voltage / current waveforms of the respective parts of the circuit of FIG. 4, and FIGS. 6 (a) and 6 (b) show the transistor TR ₂
FIG. 3 is a circuit diagram for explaining a commutation operation from the IC to TR ₁ .

First, before time t _11, the transistor TR ₂ is in a steady state of being on, and at this time, the primary current is i ₁₂ and the transistor T 2 is
Flowing through R ₄ . The secondary current is i ₂₂ and the transistor TR
Driving the base of ₂ . Load current is transistor T
It is flowing through R _2. When the input signal e ₀ becomes positive at time t ₁₁ , the transistor TR ₄ is turned off, the transistor TR ₃ is turned on, and the primary current immediately becomes i _{11 and the} polarity is inverted.
The operation circuit in this case is shown in FIG. 6 (a). Secondary current i ₂₂ of the transformer T is also immediately polarity is reversed, the base-emitter voltage of the transistor TR ₂ is for Kyaria cumulative effect, keeping the time t ₁₁ the previous voltage + E _B, the transistor TR ₂ is the load current - Continue to flow i _C. Since -E _B appears in each winding of the transformer T, the base potential of the transistor TR ₁ is opposite and no current flows and it is not driven. The transistor TR ₁ remains off. This state continues until time t ₁₂ when a predetermined charge determined by the storage carrier is extracted from the base of the transistor TR ₂ . The base and emitter of a predetermined charge from the base of the transistor TR ₂ is pulled out transistor TR ₂ is also cut off at the same time the collector current when reverse recovery. After time t _12, transformer T
Secondary current i ₁₁ , the secondary current becomes i ₂₁ and flows to the base of the transistor TR ₁ . The transistor TR ₁ is turned on to allow collector current + ic to flow, and the base
Emitter voltage + E _B is the winding voltage of the transformer T. The diode D ₁₂ is the transistor TR between the times t _{11 and} t _12.
The reverse voltage is prevented from being applied to the collector of No. ₄ . In addition,
The solid line of the load current waveform ic in FIG. 5 is for a resistive load, and the dotted line is for an inductive load. In the inductive load, the value of + ic is negative in the first half of the ON period t _{12 to} t ₂₂ of TR ₁ , and + ic flows through the diode D _F1 and the value of positive + ic flows in the transistor TR ₁ in the second half. How long ic is positive depends on the load condition. For example, if positive ic is over reversal flow period, during + ic a t ₁₂ ~t ₂₂ flows through TR _1, -ic between t ₂₂ ~t ₃₂ is DF ₂
Flowing through. If ic is negative over one commutation period, t
_{From 22 to} t ₃₂ , −ic flows through TR ₂ , and from t _{12 to} t ₂₂ + i
c flows through DF ₁ . While the current flows through the anti-parallel diode, the current is supplied to the base of the transistor,
Since it is driven on, carrier accumulation occurs, a short circuit mode similarly occurs at the time of commutation, and the transformer T prevents the short circuit mode from being generated by the same operation as described above. Thus, in the connection of FIG. 4, the transistors TR ₁ ,
Commutation TR ₂ is not caused orderly conducted short mode, so that the applied always + E _B or -E _B as winding voltage of the transformer T as in the fifth view. As is well known, the voltage-time integral of the transformer winding is equal to the amount of change in the magnetic flux of the transformer, so if the areas of the positive and negative half cycles of the winding voltage waveform are not equal, the magnetic flux will increase significantly and eventually the transformer will saturate. . When the transformer saturates, its exciting current remarkably increases, and it becomes a state close to a short circuit, and a predetermined output cannot be obtained. Therefore, if + E _B and −E _B are equal, the transistors TR ₁ and TR ₂ can operate with a duty ratio of only 1: 1 and cannot be changed to other values.

<Purpose> The present invention is intended to eliminate the above-mentioned drawbacks of the conventional circuit, and in a unit inverter that drives a base by each transformer, a transformer drive circuit that does not create a short circuit mode and can change the duty ratio is provided. It is provided.

<Example> An example of the present invention shown in the drawings will be described below.

FIG. 1 shows a circuit diagram of an embodiment of a drive circuit for a transistor inverter according to the present invention, in which the same circuit elements as those in the conventional circuit shown in FIG. 4 are designated by the same reference numerals. Note that D
F ₁ and DF ₂ are omitted.

Here, in particular, pulse transformers T ₁ and T ₂ are used for driving the _two transistors TR ₁ and TR ₂ , respectively, and a tertiary winding is provided in each of these transformers T ₁ and T ₂ ,
Both tertiary windings are coupled to each other via the diode D ₂ with only one polarity. In the carrier accumulation time, the transformers T ₁ and T ₂ are coupled through the diode D _{2 in the} polarity that should prevent the driving of the other transistor, and the transformers T ₁ and T ₂ are in the polarity that resets the biased magnetic flux during the ON period. The diode D ₂ becomes a reverse voltage and the two transformers are not coupled.

FIG. 2 shows voltage / current waveforms of various portions of the embodiment shown in FIG.
3 (a) and 3 (b) are circuit diagrams for explaining the operation at the time of commutation from the transistor TR ₂ to TR ₁ . Time t ₁₁ previously located transistor TR ₂ is in a steady ON state, the transistor TR ₂ is transistor TR _4, are driven base through transformer _{T 2.} After time t ₁₁ when the polarity of the input signal e ₀ changes, the transistor TR ₄ is turned off, the transistor TR ₃ is turned on, and the power source + Vcc changes to the resistor R ₁
The current flowing through the diode D ₁₁ transistor TR ₃ comes to flow, and the primary current of the transformer T ₁
i becomes ₁₁ . The winding of the transformer T ₁ tries to become a positive voltage, but it does not become positive for the following reasons. Transistor TR ₂
Since the carrier is stored in the base of the positive voltage E
Remains a _B12, 2 winding of the transformer _{T 2,}
The tertiary winding has the same voltage. Diode D ₂ becomes forward voltage when winding of the transformer T ₁ is intends to become positive, eventually the current i ₁₁ is next i _31, the transformer T ₂ becomes current i ₃₁ is i ₃₂
Stream flows through the base and the emitter of the transistor TR ₂ in the opposite direction becomes i ₂₂ (reverse current), the transistor TR ₂
It flows to discharge the electric charge accumulated in the base of the. The operation circuit diagram of FIG. 3 (a) is obtained. Since the voltage drop across the transformer T winding voltage upsilon ₂ of ₂ and diode D ₂ are almost the same, the winding voltage of the transformer T ₁ is not able to substantially higher than 0V, the base of the transistor TR ₁ is not driven. Between time t ₁₁ ~t ₁₂ represents Kyaria storage time of the transistor TR _2. During this period, the transistor TR ₂ remains on. Between the base and the emitter of the transistor TR ₂ with the Kyaria accumulation time is over collector current -i _c is cut off at time t ₁₂ and the reverse recovery, reverse current does not flow. The winding voltage of the transformer T ₁ rises, the voltage i ₁₁ drives the base of the transistor TR ₁ as i ₂₁ , the transistor TR ₁ turns on, and the collector current + i _c flows. Winding voltage upsilon ₁ of the transformer _{T 1} becomes the base voltage _{E B11} of the transistor TR _1. Transformer T
_2, the winding voltage of the transformer T ₂ becomes a large negative voltage because the exciting current causes the current i ₂₂ to continue to flow. However,
Excitation current is much smaller than i ₁₁ . The exciting current of the transformer T ₂ cannot flow because it is in the opposite direction to the diode D ₂ , and flows as a base-emitter reverse breakdown current of the transistor TR ₂ having the lowest breakdown voltage. In this case, the operation circuit diagram is as shown in FIG. 3 (b). Since the base-emitter reverse breakdown voltage E _B22 is more than 10 times larger than the forward voltage E _B12 , a large reverse voltage is applied to the winding of the transformer T ₂ and the exciting current decreases rapidly. At the same time, the bias of the magnetic flux of the transformer T ₂ is reset. After time t ₁₃ , the transistor TR ₁ is on and the transistor TR ₂ is off. Time t ₂₁ subsequent commutation from transistor TR ₁ to the transistor TR ₂ is performed, a detailed description will be exactly the same operation will be omitted. Explaining the exciting current of the transformer, regarding the transformer T ₁ , the time t
What positive winding voltage during the ₁₂ ~t ₂₂ is pressurized, in proportion to the voltage time integral, as shown in FIG. 2 increased with time, reduced by the time t ₂₂ Thereafter reverse voltage, t ₁₂ ~ It disappears at time t ₂₃ reaches a voltage equal time integral and between t _22. Time when the transistor TR ₁ is on, that is, time t
₁₂ ~t ₂₂ is long and the reset time t ₂₂ ~t ₂₃ becomes longer. The reset period is possible until the next transistor TR ₃ is turned on, that is, until the time t ₂₃ reaches t ₃₁ .
Therefore, the duty ratio of the transistors TR ₁ and TR ₂ can be changed to about 1:10 to 10: 1. The diode D ₂ may be a constant voltage diode having a voltage lower than the base-emitter breakdown voltage of the transistor, and the reset current of the transformer may be added to the base current of the counterpart transistor. The operation of the transformer T ₂ is similar to that of the transformer T ₁ described above, and only the time is different.

<Effect> As described above, according to the present invention, two pulse transformers for driving a unit inverter are coupled by a tertiary winding via a diode, so that the magnetic flux reset operation of the transformer is prevented from being impaired. This can be prevented from occurring, and variable duty ratio drive can be effectively performed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of a transistor inverter drive circuit of the present invention, FIG. 2 is a voltage / current waveform diagram of each portion of the embodiment, and FIGS. 3 (a) and 3 (b) are commutations of the embodiment. Circuit diagram for explaining operation, Fig. 4 is a circuit diagram of a conventional transistor inverter drive circuit, Fig. 5 is a voltage / current waveform diagram of each part of the conventional circuit, and Fig. 6 (a) and (b) are commutations of the conventional circuit. It is a circuit diagram for operation explanation. TR ₁ , TR ₂ ... Transistor T ₁ , T ₂ ... Pulse transformer D ₁ ... Diode

Claims (1)

[Claims] 1. In a transistor inverter for supplying a square wave pulse voltage to a load by two transistors which are alternately turned on from a DC power supply, two secondary windings are connected between the base and emitter of each transistor. A tertiary winding is provided in each of the pulse transformers, and the tertiary windings of both transformers are connected in series via a diode to form a closed circuit. When a primary current is applied to the one pulse transformer, A transistor inverter drive circuit that can supply the base reverse current of the transistor from the secondary winding of the other pulse transformer through the tertiary winding and diode.