JPH036741B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current-voltage feedback converter circuit that improves the rise characteristics when a switching element starts conducting.

In a DC-AC converter circuit that converts a DC voltage to an AC voltage, a sawtooth wave current flows through the collector of a switching transistor in response to an output current (load current).

In a self-excited DC-AC converter that performs current feedback using such an output current to alternately drive a pair of switching transistors,
Since the base drive current also has a sawtooth waveform, the drive current is insufficient at the start of conduction, making the transistor start-up unstable. As a result, the operating frequency fluctuates significantly as the load fluctuates, and depending on the type of load, the switching waveform may be disturbed and the operation may become unstable.

FIG. 1 is a circuit diagram showing the configuration of a conventional current-voltage feedback converter circuit, and illustrates the case of a half-bridge converter. In the same figure
Q ₁ and Q ₂ are a pair of switching transistors,
T ₁ is a main transformer, T ₂ is a drive transformer, C and C' are capacitors, R ₁ is a current limiting resistor, V _io is a DC input power supply, and V _p is an AC output voltage.

Transistors Q ₁ and Q ₂ are alternately conductive, and when transistor Q ₁ is conductive, the DC power source V _io is connected to transistor Q ₁ , primary winding N ₁ of main transformer T ₁ , and current feedback winding N of drive transformer T ₂ . ₂ and capacitor C′, and when transistor Q ₂ is conductive, current flows from DC power supply V _io to capacitor C, current feedback winding N ₂ of drive transformer T ₂ , primary winding N ₁ of main transformer T ₁ and Current flows through transistor _Q2 . In this way, a sawtooth wave current with alternating directions flows through the primary winding N ₁ of the main transformer T ₁ , which causes an alternating current consisting of a square wave to flow through the secondary winding N ₂ of the main transformer T ₁ . Outputs voltage V _p .

The drive transformer T ₂ is connected to the first drive winding N ₃ , by the voltage generated by the current in the current feedback winding N ₂ .
The second drive winding N ₄ has a winding ratio N ₃ /N ₂ , respectively.
A voltage multiplied by N ₄ /N ₂ is generated, thereby supplying drive current to the bases of transistors Q ₁ and Q ₂ , respectively. The number of turns of the first drive winding N ₃ and the second drive winding N ₄ are usually equal, so that the transistor
Q ₁ and Q ₂ are driven equally. A saturation transformer is used as the drive transformer T ₂ , and saturation of the drive transformer T ₂ causes a sudden drop in drive current, causing commutation in the transistors Q ₁ and Q ₂ . A self-excited DC-AC converter performs a switching operation by repeating such commutation.

If the base is driven only by current feedback in this way, for example, when the load current is no load or extremely light, the feedback current is extremely small, and the rise when the transistor starts conducting becomes unstable, resulting in a significant increase in frequency. Depending on the type of load, especially in the case of an inductive load, the switching waveform may be disturbed and the operation may become unstable. For this reason, a voltage feedback winding N ₁ is provided from the primary winding N ₁ of the main transformer T ₁ to the drive transformer via the current limiting resistor R ₁ and voltage feedback is also _used . Although the increase in the base drive current at the time of rise due to the current is measured to prevent the above-mentioned unstable operation at the start of conduction of the transistor, the effect is not necessarily sufficient.

The present invention aims to eliminate such drawbacks of the prior art, and its purpose is to increase the current at the time when the feedback voltage rises in the voltage feedback circuit, thereby increasing the current at the time when the switching element starts conducting. An object of the present invention is to provide a drive circuit with improved rise characteristics.

In order to achieve this purpose, in the current-voltage feedback converter circuit of the present invention, a series circuit of a resistor and a capacitor or a series circuit of a resistor and a switch element is connected in parallel to a current-limiting resistor connected in series to the voltage feedback winding. The present invention is characterized in that the current is increased when the feedback voltage of the voltage feedback winding rises.

Examples will be described below.

FIG. 2 is a circuit diagram showing the configuration of one embodiment of the current-voltage feedback converter circuit of the present invention. In this figure, the same parts as in FIG. 1 are indicated by the same symbols, _C1 is a capacitor, and _R2 is a resistor.

FIG. 3 is a time chart showing operation waveforms of each part in FIG. 2. In the figure, a is the collector-emitter voltage V _CE of the transistor Q ₂ , b is the collector-emitter voltage V _CE of the transistor Q ₁ , c is the collector current I _c of the transistor Q ₁ , and d is the base-emitter voltage V of the transistor Q ₁ . _BE , e is the base current I _B of the transistor Q ₁ , and f is the base current I _B of the transistor Q ₂ .

The transistors Q ₁ and Q ₂ are alternately made conductive by being supplied with base current by the first drive winding N ₃ and the second drive winding N ₄ of the drive transformer T ₂ , respectively. Figure 3 a, b). In Figure 3b,
V _CE (sat) indicates the collector-emitter voltage of the transistor in its saturated state. The collector current I _c of the transistor flows in a sawtooth waveform corresponding to the base current, and the base-emitter voltage V _BE changes in a square waveform correspondingly (Fig. 3c,
d). In FIG. 3d, V _BE (sat) indicates the base-emitter voltage of the transistor in its saturated state.

In Figure 3, e and f are transistors, respectively.
The base current I _B of Q ₁ and Q ₂ is shown. The waveform of the base current I _B can be considered to be determined by the combination of a differential current component due to voltage feedback and a component proportional to the load current due to current feedback. In FIG. 3f, a period t ₁ indicates a period in which a differential current component due to voltage feedback becomes dominant, and a period t ₂ indicates a period in which a component proportional to the load current due to current feedback becomes dominant. Furthermore, during period t ₃ , the capacitor during commutation
This shows the period during which a reverse bias current flows due to the discharge of the charge stored in _C1 .

In this way, when the collector current rises, by driving with the current generated by differentiating the voltage of the voltage feedback line by the capacitor C ₁ and the resistor R ₂ ,
The transistor is overdriven and rises faster. During the second half of the conduction period, the base current is maintained by current feedback. When the transistor is off, a reverse bias current flows, which serves to erase the accumulated carriers in the transistor, thereby increasing the fall rate.

In other words, if the circuit in Figure 2 had only current feedback, only the excitation current would flow when there is no load, so the drive current at the time the transistor starts conducting would be small and the rise would be slow. Both the rise and fall can be made faster by using a circuit to provide drive currents with waveforms as shown in FIGS. 3e and 3f.

FIG. 4 is a circuit diagram showing a second embodiment of the current-voltage feedback converter circuit of the present invention, showing only the drive transformer and its peripheral circuits, and other parts are the same as FIG. 2. . In Figure 4
SR indicates a saturation reactor, and the other parts are the same as in Fig. 2. However, in the case of FIG. 4, an unsaturated transformer is used as the drive transformer _T2 .

In Fig. 4, the saturation reactor SR is connected in parallel to the voltage feedback winding _N1 of the drive transformer _T2 , and when the voltage of the winding _N1 exceeds a certain value, it saturates and switches off the winding _N1 . Short circuit. This allows the winding
The drive current supplied to the transistor via N ₃ and N ₄ suddenly decreases, causing commutation. In this way, in the case of Fig. 4, DC-
The operating frequency of the AC converter is determined. By making the saturation reactor SR variable, the operating frequency can also be made variable. Other operations are the same as those in FIG. 2.

FIG. 5 is a circuit diagram showing a third embodiment of the current-voltage feedback converter circuit of the present invention, showing only the feedback transformer and its peripheral circuits, and other parts are the same as FIG. 2. . In Figure 5
SW indicates a switch, and the other parts are the same as in Fig. 2.

In FIG. 5, the switch SW is composed of a semiconductor high-speed switch element, etc., and is controlled by a control circuit (not shown) to operate in synchronization with the operating frequency of the converter circuit and repeat opening and closing at twice the frequency. . Therefore the main transformer
The current supplied from the primary winding N ₁ of T ₁ to the voltage feedback winding N ₁ of the drive transformer T ₂ is large in the first half of the conduction period of the transistor and small in the second half. Therefore, the fifth
In the case of the circuit shown in the figure, the rise characteristics of the output current can be improved by compensating for the shortage of drive current at the time of rise due to current feedback in the same manner as described for the circuit of FIG.

As explained above, according to the current-voltage feedback converter circuit of the present invention, voltage feedback is applied sufficiently during the first half of the conduction period of the switching transistor, and voltage feedback is reduced in the second half of the conduction period, and the current feedback is mainly used to drive the switching transistor. This stabilizes the operating frequency against load fluctuations, ensures stable operation even when the type of load changes, and further reduces the rise time and turn-on time during commutation of the switching transistor. It is extremely effective because it can shorten the time.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of a conventional current-voltage feedback converter circuit, FIG. 2 is a circuit diagram showing the configuration of an embodiment of the current-voltage feedback converter circuit of the present invention, and FIG. FIGS. 4 and 5 are circuit diagrams showing second and third embodiments of the current-voltage feedback converter circuit of the present invention, respectively. Q ₁ , Q ₂ ...transistor, T ₁ ...main transformer,
T ₂ ... Drive transformer, C, C' ... Capacitor,
_R1 ...Resistor, _C1 ...Capacitor, SR...Saturation reactor, SW...Switch, _Vio ...DC input power supply, _Vp ...AC output voltage.

Claims (1)

[Scope of Claims] 1. A current feedback winding that feeds back an output current caused by the switching operation of the switching element to a drive transformer for driving a pair of switching elements that are alternately turned on and off, and a switching operation of the switching element. In a self-excited DC-AC converter that has a voltage feedback winding that feeds back the output voltage of 1. A current-voltage feedback converter circuit comprising a series circuit of elements connected in series, and increasing a current when a feedback voltage of the voltage feedback winding rises.