JPS6096024A - Large current switching circuit - Google Patents

Abstract

PURPOSE:To decrease stably a delay time at switching off by connecting a choke coil in parallel with a base and an emitter of a main transistor (TR) and making a current of the said coil continuous to a comparatively larger value to neutralize stored electric charge between the base and emitter at high speed. CONSTITUTION:A current i1 of the choke coil L2 is increased at a time constant of L2/R2 during on-period of a TRQ2 and decreased by the time constant of L2/ R1 in a closed loop comprising a choke coil L1, a resistor R1, a diode D2. At the off-period of the TRQ2, the coil L2 acts like a current source to neutralize the stored electric charge between the base and emitter of the TRQ1, and when the neutralization is finished and the base and emitter of the TRQ1 is nonconductive, the diode D2 is by-passed and a current i2 is decreased slowly. Thus, the TRQ1 is turned off rapidly by the energy of the coil L2 at trailing time and turned on rapidly at leading time because the current of the coil L2 is increased gradually while being overdriven slightly.

Description

TECHNICAL FIELD The present invention relates to a switching circuit using transistors, and more particularly to a large current switching circuit for operating a DC-DC converter at high frequency.

Prior Art Conventionally, as shown in FIG. 1, this type of switching circuit has two resistors R1 and R2 between the base of the main transistor Q1 and the collector of the active transistor Q2. Connected in series, the main transistor Q
A capacitor C2 is connected across the first resistor R1 connected to the base side of the transistor Q1, and a capacitor C2 is connected between the emitter of the transistor Q1 and the connection point of the first and second resistors. It was constructed by connecting three resistors R3. In the circuit of FIG. 1, while transistor Q2 is on, and thus transistor Q1 is on, charge is accumulated in capacitor C2 with the polarity shown. Next, when transistor Q2 turns off, transistor Q1 stops driving, and a portion of the charge stored in capacitor C2 is released by the circuit formed by the base and emitter of transistor Q1 and resistor R3, and the transistor Neutralizes the accumulated charge between Q1's base and emitter, completely turning off transistor Q1.

In this way, the circuit shown in Figure 1 can turn off the transistor Q1 relatively quickly, but what about the capacitor? Since the discharge circuit of C2 is based on the base, emitter, and resistor of Ql (3), and the other is based on the resistor R1,
If the stored charge in capacitor c2 cannot be fully utilized and the value of resistor R3 is reduced, the value of resistor R3 must also be reduced in order to increase the voltage across capacitor C2, and therefore the collector current of transistor Q2 As a result, the value of the resistor R3 cannot be made very small, and as a result, high-speed switching during large current switching cannot be performed sufficiently.

DISCLOSURE OF THE INVENTION (Objective) An object of the present invention is to connect a choke coil in parallel with the base and emitter of the main transistor, and to make the iu current flowing through the choke coil continuous to a relatively large value. - It is an object of the present invention to provide a large current switching circuit that can quickly neutralize accumulated charges between emitters.

(Structure) The large current switching circuit according to the present invention includes a first transistor whose emitter is connected to the input DC power supply side and whose collector is connected to the load side; 1 transistor pace f: a second transistor to be driven; a first diode connected in parallel between the base and emitter of the first transistor in one direction with the emitter side serving as a cathode; first and second resistors connected in series with each other between the base of the transistor and the collector of the second transistor, and in parallel with the first resistor trap-connected to the base of the first transistor. and a second diode connected in such a direction that the base side of the first transistor becomes a cathode, and a choke coil connected in parallel with the series circuit of the first and second diodes. Ru.

(Effect) Storage between the base and emitter of the switching transistor,
tl#1 [If the inductance energy of the choke coil is used to neutralize the load, a constant current can flow into the base and emitter regardless of the series resistance of the circuit at the time of neutralization, thereby reducing the delay at switching off. The time can be stably reduced.

Next, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a diagram showing a large current switching circuit according to one embodiment of the present invention. This circuit includes an input terminal v1, an output terminal Vo, a first transistor c-1 whose emitter is connected to the input terminal V1, and the first transistor Q.
A diode D1 is connected between the collector of the output terminal VO and the common retrace line G, a capacitor c1 is connected between the output terminal VO and the common retrace line G, and an error voltage input terminal 1 is connected to the output terminal VO. In addition, a power supply terminal 2 is connected to the input terminal 1, a ground terminal 4 is connected to the common return line G, and a pulse current having a pulse width proportional to the error voltage is output. a switching regulator control circuit MZl, and a second transistor Q2 whose base is connected to the terminal 3 of the switching regulator control circuit Z1 and whose emitter is connected to the common return line G.
and the first transistor. 1 base and the second glue transistor. A series circuit of first and second resistors R1 and R2 connected between the collectors of the first transistor Q1 and the base 1411 of the first transistor Q1 so that the base 1411 of the first transistor Q1 (D x emitter 1
ifj K JM connected die d-de D2 and said diode D2. It is composed of a choke coil L2 connected in parallel with DI.

In addition, to give a specific example of the @ elements of the circuit in Fig. 2, R1 is 300Ω, R2 is 500Ω, R3 is IKΩ, and R2 is 5
m H+ Vt is 24 V, Q2 on time is Sμ
S.

The off time of Q2 is 15 μs.

Next, regarding the case where the constants in Figure 2 are changed as follows,
The detailed operation of the circuit shown in FIG. 2 will be described with reference to FIG. 3 showing circuit operation simulation waveforms based on 5PICE.

In FIGS. 2 and 3, the first transistor Q1
is conductive during 12 positive periods and non-conductive during negative periods.

As shown in Figure 3, the tJE current i+ of choke coil L2 is
The on period of the second transistor Q2 K L 2 /
The off period of the second transistor Q2 decreases with a time constant of R2/R1 in a closed loop consisting of choke coil L1, resistor R1 and diode D2.

During the off period of the second transistor Q2, the choke coil L2 operates as a current source, and the tenth transistor Q1
When neutralization is completed and the base and emitter of the first transistor Q1 become non-conductive, the diode D2 is bypassed and the current 1
2 decreases gradually as shown in Figure 3.

In this way, the first transistor Q1 is rapidly turned off by the energy of the choke coil L2 at the falling edge, and is slightly overdriven at the rising edge because the current in the choke coil L2 gradually increases. It operates in such a way that it turns on rapidly.

As explained above, when neutralizing the accumulated charge between the base and emitter of a switching transistor, the present invention allows a constant current to flow through the base and emitter regardless of the series resistance of the circuit at the time of neutralization. This allows the delay time at switching off to be stably reduced.

[Brief explanation of the drawing]

Figure 1 shows a circuit ratio showing an example of a conventional switching circuit;
3 is a circuit diagram showing a switching circuit according to an embodiment of the present invention, and FIG. 3 is a diagram showing pressure and current waveforms of i+ of the switching circuit of FIG. 2. (No.1...>211 transistor, Q2...aE
2 transistor, Di, D2...Diode, Zl...Switching regulator control circuit, Ll, R2...Choke coil, CI, C2...Capacitor, Kl, R2...Resistor. Agent Patent Attorney Rikichi Somekawa 81 pictures! 2V! J

Claims (1)

[Claims] It has a first transistor and a second transistor, and the emitter of the first transistor is connected to an input DC power source 8II.
I, the collector is connected to the load side, the emitter of the second transistor is connected to the return line side of the input DC power supply,
A switching circuit in which the base of the first transistor is driven by the second transistor,
A first diode is connected in parallel between the base and emitter of the first transistor, with the emitter side serving as the cathode.1-1 A first diode is connected between the base of the first transistor and the collector of the second transistor. 1st and 2nd
resistors are connected in series, and a second diode is connected in parallel with the first resistor connected to the base of the first transistor marked # and in a direction where the base side of the first transistor becomes the cathode. A large current switching circuit further comprising a choke coil connected in parallel with the series circuit of the first and second diodes.