JPH0353596Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a switching regulator, and particularly to a switching regulator that uses an inrush current generated at startup.

Conventional technology In general, a switching regulator has a capacitor input type rectifying and smoothing circuit consisting of a rectifying circuit and a capacitor on the input side, and connects the primary winding of the output transformer and the DC line of the rectifying and smoothing circuit. A switching transistor is connected in series, and the switching transistor is turned on and off to supply direct current to a load connected to the secondary winding of the output transformer. However, in this switching regulator, if the load is a lamp load or a load including a capacitor, a rush current flows through the switching transistor at startup, which may destroy the switching transistor.

Problem that the invention aims to solve: In order to prevent such destruction of switching transistors, conventional methods apply pulses whose pulse width gradually increases to the base of the switching transistor to gradually increase the energization time of the switching transistor. method has been adopted. Although this method can also prevent destruction of the switching transistor due to inrush current, it takes time until steady current is supplied to the load, and the above method can be used to rapidly widen the pulse width to supply steady current to the load. If the time until the switching transistor is shortened, the switching transistor may exceed its safe operating range and be destroyed.

Summary of the invention This invention provides a parallel circuit consisting of a resistor and a thyristor in the DC line between the capacitor of the rectifying and smoothing circuit on the input side and the switching transistor, and also connects the thyristor with a gate after a predetermined time after the switching transistor is activated. By connecting a delay circuit that provides a signal to both ends of the resistor,
This is a switching regulator that eliminates the above drawbacks and can shorten the time until steady current is supplied to the load without damaging the switching transistor when supplying power to loads including lamp loads and capacitors. It provides a rater.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

Figure 1 shows a separately excited switching regulator, in which an input smoothing capacitor 2 is connected between the DC lines of a full-wave rectifier circuit 1, and the primary winding of an output transformer 6 is connected to both ends of the capacitor 2. 7, a switching transistor 3, a resistor 4, and a triac (bidirectional three-terminal thyristor) 5, which are connected in series, and a delay circuit 19 is connected in parallel with the resistor 4. The output transformer 6 is provided with a secondary winding 8, and a rectifying and smoothing circuit 9 consisting of a diode 10 and a capacitor 11 is connected to the secondary winding 8.
A load 12 is connected to the output terminal of the rectifying and smoothing circuit 9. Further, a drive circuit 34 is provided to drive the transistor 3, and the drive circuit 34 includes a drive transformer 13 and a control circuit 17 connected to both ends of the load 12. The drive transformer 13 has a primary winding 14 connected to a control circuit 17 and a secondary winding 15 connected between the base and emitter of the transistor 3. The control circuit 17 includes a pulse width modulation circuit, and outputs a drive pulse according to the output voltage. The delay circuit 19 includes an integrating circuit consisting of a resistor 22 and a capacitor 23, and a capacitor 2.
A constant voltage diode 24 that becomes conductive when 3 is charged to a predetermined level, a capacitor 25, and a resistor 26.
The both ends of the capacitor 25 and the resistor 26 are the main electrodes of the triac 5.
Connected between _T1 and gate G. Further, the main electrode T ₂ of the triax 5 is connected to the resistor 4 , the emitter of the switching transistor 3 and the secondary winding 15 .

In the above circuit, when an AC power source (not shown) is applied to the full-wave rectifier circuit 1, the AC voltage is rectified by the full-wave rectifier circuit 1 and charges the smoothing capacitor 2. When capacitor 2 is charged, control circuit 1
A drive pulse as shown in FIG. 2A is applied from 7 to the primary winding 14 of the drive transformer 13, and a voltage in the direction shown by the arrow 40 is induced in the secondary winding 15. Therefore, transistor 3 is turned on and 1
A current flows through the secondary winding 7 and the resistor 4, and a voltage corresponding to the number of turns is induced in the secondary winding 8. This voltage is in a reverse bias direction, indicated at 43, with respect to diode 10.

Next, when the drive pulse is no longer applied from the control circuit 17 to the primary winding 14, no voltage is induced in the secondary winding 15, and the transistor 3 is turned off. As a result, a voltage is generated in the secondary winding 8 that turns on the diode 10, and the transistor 3
The energy accumulated in the output transformer 6 during the on period is released to the load via the rectifying and smoothing circuit 9. When the energy stored in the output transformer 6 is released, the drive pulse from the control circuit 17 turns on the transistor 3 again, and the same operation is repeated. By the way, a part of the current flowing through the transistor 3 during the on period of the transistor 3 flows through the resistor 22 of the delay circuit 19 to the capacitor 23, and when the charging voltage of the capacitor 23 reaches a voltage exceeding the level of the constant voltage diode 24, the current flows to the capacitor 23. As shown in FIG. 2B, a gate signal is generated at a time point _t1 and applied to the gate G of the triac 5. That is, the triac 5 is driven with a predetermined time delay after the transistor 3 is activated. This delay time is set to be the shortest time without destroying the transistor 3 when the triac 5 is turned on. Therefore, when the triac 5 is turned on, a limited current is already being supplied to the load 12, so that no excessive current flows through the transistor 3.

As described above, in the circuit of the present invention, current flows through the transistor 3 via the resistor 4 at startup, and a limited current is supplied to the load. In addition, after a predetermined time, the resistor 4 is short-circuited by the triax 5 and a steady current is supplied to the load 12, so that the destruction of the transistor 3 due to rush current can be prevented, and the time until the steady current is supplied to the load 12 is short-circuited. can do.

The present invention is not limited to the above embodiments, but can be further modified. In the above embodiment, a flyback type regulator is shown that supplies the energy stored in the output transformer 6 to the load 12 when the transistor 3 is off, but a forward type regulator that supplies energy to the load when the transistor 3 is on is shown. can also be applied. Further, a circuit consisting of the resistor 4, the triax 5, and the delay circuit 19 may be provided in a line connecting the collector of the transistor 3 and the input capacitor 2. Further, the triax 5 can be composed of one or reverse conduction thyristors connected in antiparallel. Furthermore, the delay circuit 19 can be modified in various ways.

Effects of the invention In this invention, a parallel circuit consisting of a resistor and a thyristor is provided in the connection line between the capacitor of the rectifying and smoothing circuit on the input side and the switching transistor, and a delay circuit is connected to both ends of the resistor. This has the advantage of preventing damage to the switching transistor and shortening the time until steady current is supplied to the load.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a separately excited switching regulator showing an embodiment of the present invention, and FIG. 2 is a time chart showing the relationship between the drive signal of the switching transistor and the operation of the triac. 1...Full wave rectifier circuit, 2...Capacitor, 4...
...Resistor, 3...Switching transistor, 5...
...Thyristor, 6...Output transformer, 7...Primary winding, 8...Secondary winding, 12...Load, 19...Delay circuit.

Claims (1)

[Scope of utility model registration request] The primary winding of an output transformer and a switching transistor are connected in series between the DC lines of a capacitor-input type rectifying and smoothing circuit consisting of a rectifier circuit and a capacitor, and the switching transistor is turned on and off. Accordingly, in the switching regulator that supplies the output converted into DC from the secondary winding of the output transformer to the load, a parallel circuit of a resistor and a thyristor is provided in a line connecting the capacitor and the switching transistor. The switching regulator is further characterized in that a delay circuit is connected to both ends of the resistor for applying a gate signal to the thyristor after a predetermined period of time after the switching transistor is activated.