JPS59201678A - Switching regulator - Google Patents

Abstract

PURPOSE:To prevent a switching transistor from remaining in ON state when an abrupt variation in a load occurs by outputting a fixed pulse having a pulse width for turning OFF the transistor separately from a control pulse. CONSTITUTION:A switching regulator SR1 has a switching transistor Q1, an output voltage forming circuit V, and a pulse width controller PWC. The controller PWC has a fixed pulse generator WL for generating a fixed pulse having a suitable pulse width. Even if an abrupt variation in a load occurs so that the slide level of a slice circuit W3 rises with the result that a control pulse is not outputted from a control pulse generator W4, the OFF period of the transistor q1 is obtained in the pulse width of the fixed pulse.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching regulator having a switching transistor.

<Prior Art> A conventional switching regulator of this type includes one shown in FIG. 1, for example. This switching regulator SRo includes a switching transistor Q1 that controls the output voltage to the load RL, and a pulse width control circuit PWC that generates a control pulse that controls the on/off period of the switching transistor Q1. This pulse width control circuit PXvC generates a control pulse P with a long pulse width as shown in FIG. 2a when the load RL is light.
When the pulse becomes heavy, a control pulse P with a short pulse width is generated as shown in FIG. This control pulse Pl turns on the transistor Q2 by being at a high level.
to turn off the switching transistor Q1 (OI
= 'F).

However, in such a conventional example, the load RL suddenly increases.
becomes heavier, the control pulse l′l nostar Q becomes heavier as described above.
However, since the output voltage forming circuit V consisting of the transformer L'', the diodes D and the capacitor C is connected between the switching transistor Q1 and the load RL, the output voltage 19 is Therefore, the pulse width of the control pulse P1 from the pulse width control circuits P to VC becomes shorter and shorter until the control pulse P1 is no longer generated as shown in FIG. 2C.As a result, the switching There was a drawback that the transistor Q1 remained in the on state 1 and the switching transistor (h) was destroyed.

Target The present invention can easily handle sudden load changes.

It is an object of the present invention to provide a stable output voltage that corresponds to the load without the risk of damaging the chip/replacement inverter.

<Example> The present invention will be described in detail based on an example shown in FIGS. 3 and 4.

FIG. 3 is an overall circuit diagram of this embodiment. The switching regulator SR of this embodiment is of a step-up type. This switching regulator SR includes a switching transistor Q+ that controls the output voltage to the load, a step-up transformer T connected between the power supply Vcc and the load 11L and preferably having a secondary winding, a rectifier diode D, and a smoothing capacitor C. and a pulse width control circuit PWC.

The pulse width control circuit PWC has a fixed pulse generating circuit section W] which generates a fixed 7N6 pulse I)2 having an appropriate pulse width as shown in FIG. 3a. This fixed node P2 is connected to a resistor RI+R2 or a transistor Q8. Q2
The pulse width is set so that the output voltage is no more than an appropriate output voltage. /' /The response width control circuit pwc also controls the third pulse width in response to the fixed pulse P2.
It has a triangular wave generating circuit section W2 that generates a triangular wave P3 as shown in the figure, and a slicing circuit section W8 that slices the triangular wave P3 by receiving a voltage from a resistor 3 that detects fluctuations in the load RC. This slice level SI- is the third
It is shown in phantom lines in the figure. The pulse width control circuit pwc further includes a control pulse generation circuit section W4 that generates a control pulse p having a pulse width as shown in FIG. 3C in accordance with the slice level SL of the sliced triangular wave P8.

This control pulse P1 passes through resistor 4 to transistor q
It is designed to be given to 2.

Therefore, such a switching regulator SR
, the fixed pulse P2 is applied to the transistor Q2 via the transistor Qa as an emitter follower, and the control pulse P1 is also applied to this transistor Q2. Therefore, the transistor Q2 is turned on periodically by at least the H/L/S width of the fixed pulse I'2, and among the control pulses whose pulse width changes in response to fluctuations in the load RL, the fixed pulse The control pulse P1 having a pulse width that does not overlap with I'2 makes its on period longer than the pulse width of the fixed pulse. As a result, even if a sudden load change occurs and the slice level SL rises, and the control pulse p is no longer output from the control pulse generation circuit W4, the transistor Q2
The period during which the switching transistor Q1 is turned on and the switching transistor Q1 is turned off is guaranteed to be equal to the pulse width of the fixed pulse P2. In this way, according to this embodiment, even if a sudden load change occurs, the switching transistor Q+ will not remain in the on state and be destroyed, and a stable output voltage can be supplied to the load.

<Effects> As described above, the present invention outputs a fixed pulse having a pulse width that turns off the switching transistor in addition to the control pulse that controls the output voltage, and the control pulse is applied when the load is heavy. Even if the switching transistor is turned off by a fixed pulse, the output voltage remains below a predetermined value. By setting the pulse or at least the pulse width so that the output voltage does not exceed a predetermined value, the switching transistor will not remain in the on state and be destroyed, and the output voltage will be stably supplied to the load. I can do it.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a conventional example, Fig. 2 is a signal waveform diagram for explaining the circuit operation of Fig. 1, Fig. 3 is a circuit diagram of an embodiment of the present invention, and Fig. 4 is a diagram of Fig. 3. FIG. 3 is a signal waveform diagram for explaining the circuit operation of FIG. SR, switching regulator, Ql... switching transistor, PWC... pulse width control circuit, Pl
−・Control pulse, P2・・Fixed pulse Applicant: Kazuhide Okada, Patent Attorney, Nyap Co., Ltd.

Claims (1)

[Claims] (1) A pulse that has a switching transistor that controls the output voltage to the load, and generates a control pulse that has a pulse width that shortens the off period of the switching transistor as the load becomes heavier and controls the magnitude of the output voltage. In the switching regulator including a width control circuit, the pulse width control circuit outputs a fixed pulse having a predetermined pulse width that turns off the switching transistor, separately from a control pulse that controls the output voltage, and turns off the switching transistor. 1. A switch-on regulator characterized in that even if a control pulse is not applied under heavy load, the switching transistor is turned off by the fixed pulse to reduce the output voltage to a predetermined value or less.