JPS6271474A - Switching circuit - Google Patents

Abstract

PURPOSE:To increase power capacity as the whole switching circuit by shortening ON time of a first switching transistor having small power capacity and alternately bringing a first and a second switching transistors to an ON state. CONSTITUTION:First and second switching transistors 3a, 3b are connected in parallel between first and second terminals 1, 2 as both terminals of a switching circuit. Current feedback circuits 4a, 4b are each mounted in response to the switching transistors 3a, 3b. A control winding 9 is supplied with pulses through control terminals 10a, 10b, and the switching transistors 3a, 3b are brought alternately to an ON state. In this case, ON time period of the first switching transistor 3a having small power capacity is shortened, and ON time period of the second switching transistor 3b having large power capacity is lengthened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a switching circuit, and particularly to a power switching circuit used in a switching power supply or the like.

[Technical background of the invention and its problems]

In power switching circuits such as switching power supplies (switching regulators), transistors, thyristors, GTOs, etc. are used as switching elements. However, in conventional power switching circuits, the drive circuit for turning on/off and controlling the switching elements is composed of electronic circuits.
As the power capacity of switching elements increases, a drive circuit with a large power capacity is also required. Therefore, there are problems in that the device becomes expensive and large in size.

[Purpose of the invention]

The present invention was made to solve these conventional problems, and it is possible to turn on and off switching transistors with low power.
The purpose of the present invention is to provide a switching circuit that can be turned off.

[Summary of the invention]

In order to achieve this object, the present invention connects a first switching transistor with a relatively small power capacity and a second switching transistor with a relatively large power capacity in parallel between a first terminal and a second terminal. The on/off control of the first and second switching transistors is controlled by a first current feedback circuit having a saturable core with a relatively small size and a second current feedback circuit having a first resaturable core with a relatively large size. Basically, this is done using a current feedback circuit.

That is, the output windings of each of the first and second current feedback circuits are connected between the base and emitter of each of the first and second switching transistors, and the input windings of each are connected as a whole to form a closed loop. and each feedback winding is connected between the first terminal and the collectors of the first and second switching transistors, respectively.

Further, a control winding is coupled to the input winding of the first current feedback circuit whose saturable core has a smaller dimension, and the on-state switching of the first and second switching transistors is performed via the control winding.
Performs off control. Then, the first and second switching transistors alternately switch between Ts and T2 (however,
It is configured to be in the on state for a time period such that TI<72).

In the switching circuit according to the present invention configured as described above, by applying a pulse to the control winding, the first and second switching transistors and the first and second switching transistors are connected to each other by applying a pulse to the control winding.
A circuit consisting of a current feedback circuit and a current feedback circuit performs an oscillation operation, and both switching transistors are alternately turned on. In this case, the on-time of the first switching transistor with a small power capacity is short, and the on-time of the second switching transistor with a large power capacity is long, so that the power capacity of the entire switching circuit is increased without putting a burden on the switching transistor. can be made larger. To turn the switching circuit off, the control winding is again connected to the first
The oscillation operation may be stopped by passing a current sufficient to saturate the current feedback circuit of the oscillator, or by short-circuiting the control winding.

〔Effect of the invention〕

According to the present invention, with the low power required to saturate the small-sized saturable core in the first current feedback circuit, not only the first switching transistor with small power capacity but also the switching transistor with large power capacity can be used. Since on/off control is possible, the drive circuit can be simplified and the cost and size can be reduced.

[Embodiments of the invention]

FIG. 1 is a circuit diagram of a switching circuit according to an embodiment of the present invention. First and second switching transistors 3a are provided between a first terminal 1 and a second terminal 2, which are both ends of the switching circuit.

3b are connected in parallel. Power capacity P1. of these switch transistors 3a, 3b. P2 is P! It is assumed that the relationship is <P2.

First and second switching transistors 3a, 3b
The first and second current feedback circuits 4a correspond to each of the
, 4b are provided. Current feedback circuits 4a, 4b have output windings lea,
6b, input winding 7a.

7b and feedback windings 8a and 8b, respectively. Here, it is assumed that the first saturable core 5a has a relatively small size, and the second saturable core 5b has a relatively large size. In other words, the average magnetic path length of the core 5a is
It is shorter than the average magnetic path length of b.

The output windings 6a, 6b of the first and second current feedback circuits 4a, 4b are the switching transistors 3a, 3b.
The input windings 7a and 7b are connected at both ends to form a closed loop as a whole.

Further, feedback windings 8a and 8b are connected between the first terminal 1 and the collectors of switching transistors 3a and 3b, respectively.

Then, the input person 978 in the first current feedback circuit 4a
A control winding 9 is coupled to the control winding 9. The other end of the control winding 9 is connected to a drive circuit (not shown) via ilJ a 18 children 10a, 10b.

Next, the operation of this switching circuit will be explained.

First, a pulse is supplied to the control winding 9 via the control terminals 10a, 10b, and the saturable core 5a of the first 'IFIt feedback circuit 4a becomes saturated.

Next, with the fall of the pulse supplied to the control winding 9, the magnetic flux of the saturable core 5a decreases, and this change in magnetic flux causes the output winding 7a to have a uniform voltage between the base and emitter of the first switching transistor 3a. A potential in the direction is generated, and a base current flows through the switching transistor 3a. As a result, the switching transistor 3a is turned on, and the collector current lea begins to flow as shown in FIG. 2(a). With this collector current 1ca, the feedback winding 8a
Positive feedback is applied to the current feedback circuit 4a via the current feedback circuit 4a, and the saturable core 5a is further excited, so that the switching transistor 3a maintains an on state.

And TI = (4Nt Bmt St)
/Vt - (1) (However, N1 is the number of turns of the output winding 6a, 8m1 is the maximum magnetic flux density of the core 5a, and Si is the core 5
(1) is the saturation voltage between the base and emitter of the transistor 3a).

After the time T1 has elapsed, the core 5a becomes saturated, and the connection between the output winding 116a and the feedback winding 7a is broken, and the base current no longer flows through the switching transistor 3a, so the switching transistor 3a is turned off. .

When the first switching transistor 3a is turned off, the magnetic flux of the saturable core 5a decreases in the opposite direction. At this time, the potential generated in the output winding 6a is in the opposite direction with respect to the base-emitter of the switching transistor 3a, and therefore does not turn on the switching transistor 3a. 2
The current is transmitted to the input winding 7b in the current feedback circuit 4b, and changes the magnetic flux of the saturable core 5b. This saturable core 5b
A forward potential is generated in the output winding 6b between the base and emitter of the second switching transistor 3b due to the change in the magnetic flux, so that a base current of the switching transistor 3b flows. Therefore, the second switching transistor 3b is now turned on, and collector current 1cb begins to flow as shown in FIG. 2(b). Thereafter, as before, positive feedback is applied to the current feedback circuit 4b via the feedback winding 8b by the collector current 1cb, and the core 5b is roughly excited, so that the switching transistor 3
b remains on. And T2-<4N2Bm
2S2>/V2-('2 (where, N2 is the number of turns of the output winding 6b, 3m2 is the maximum magnetic flux density of the core 5b, St is the cross-sectional area of the core, and v2 is the saturation voltage between the base and emitter of the transistor 3b) After the time T2 has elapsed, the core 5b becomes saturated, and the coupling between the output winding 6b and the feedback winding 7b is broken.
Since the base current of the switching transistor 3b stops flowing, the switching transistor 3b is turned off.

Thereafter, the first and second switching transistors 3a and 3b are alternately turned on in the same manner. That is, the first
and second switching transistors 3a, 3b and current feedback circuits 4a, 4b-.
Shooting is performed at a frequency of 1/(T1 +72), and the switching circuit is maintained in the on state. In addition, the control terminal 10
a, 10b to control 1 winding 9 again with sufficient current to saturate the saturable core 5a of the first current feedback circuit 4a, or between terminals 108, 10b, i.e. control m'
By shorting both ends of the a-line 9, the switching circuit can be returned to the OFF state.

Here, the first and second switching transistors 3
The relationship between on-time Tl and T2 of a and 3b is TI < 72
is set to Specifically, in equations (1) and (2), St < 82, Bmt -8mz (m1
(assuming that the materials of 75a and 5b are the same), Vr - T2, so N1 - N2 or Nt < N2 may be selected. Further, the ratio TI/T2 is the ratio PI/P of the power capacities of the first and second switching transistors 3a and 3b.
It is desirable to make it approximately equal to 2.

With the above configuration, the first switching transistor 3a, which has a small power capacity, is not kept in an on state for a long time, so that an excessive load is not imposed on the transistor 3a. Also, the small size of this power capacity (′・1st
By saturating the small first saturable core 5a combined with the switching transistor 3a of the first and second switching transistors 3a through the control winding l19.

In order to perform on/off control of 3b, although the second switching transistor 3b has a large power capacity,
The advantage of the on-off system is that the power required to saturate the small saturable core 5a is low enough.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a switching circuit according to an embodiment of the present invention, and FIG. 2 is a waveform diagram for explaining the operation of the switching circuit of the embodiment. 1.2...first and second terminals, 3a, 3b...
first and second switching transistors, 4a, 4
b...first and second current feedback circuits, 5a, 5b.
...first and second saturable cores, 6a. -6b...Output winding, 7a, 7b...Input winding, B
a. 8b... Feedback winding, 9... Control winding, 10a, 10
b...Control terminal.

Claims (1)

[Claims] A first switching transistor with a relatively small power capacity and a second switching transistor with a relatively large power capacity connected in parallel between a first terminal and a second terminal; a first saturable core of relatively small size and a second saturable core of relatively large size, each output winding being connected between the base and emitter of each of the first and second switching transistors. and each input winding is coupled to form a closed loop as a whole, and each feedback winding is connected to the first terminal and the first and second terminals.
a control winding coupled to an input winding in the first current feedback circuit; and a control winding coupled to an input winding in the first current feedback circuit; A switching circuit characterized in that the second switching transistor is configured to be in an on state alternately for times T_1 and T_2 (where T_1<T_2).