JP2776533B2 - Power control circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply control circuit, and more particularly, to generating a control pulse in synchronization with an input when controlling a pulse width in a switching regulator. The present invention relates to a power supply control circuit that can be limited to a value.

[Conventional technology]

Conventionally, power supply control circuits used for this kind of purpose include:
There were not many things that could be operated synchronously, and only those that could trigger a slave circuit via a resistor or capacitor were used.

The setting of the pulse width at the time of limiting the pulse width is to set the pulse width by using a triangular wave oscillator separately.

FIG. 2 shows an example of a conventional circuit when the pulse generation circuit is operated synchronously with the synchronous input.

In the conventional example shown in FIG. 2, the transistor 2 is turned on and off by an output clock 6 of a master oscillator 1 composed of a free-running multivibrator, and the emitter output is passed through a differentiating circuit composed of a resistor 3 and a capacitor 4. Differentiate to obtain the output pulse. This output pulse is applied to the synchronous input 7
As a slave oscillator 5 composed of a monostable multivibrator.
Can be synchronized with the master oscillator 1 to generate a pulse output.

FIG. 3 shows an example of a conventional circuit for obtaining a limited pulse width output for limiting a pulse width.

The triangular wave output from the triangular wave oscillator 8 in FIG. 3 is applied to the positive input terminal of the comparator 11. An input voltage obtained by dividing a constant voltage by the resistors 9 and 10 is applied to a negative input terminal of the comparator 11. The comparator 11 generates a limited pulse width output 12 whose length changes according to the period during which the triangular wave exceeds the divided voltage input.

The photocoupler 31 detects an output power supply voltage of a switching regulator (not shown), and its impedance changes according to the power supply voltage. Therefore, by comparing a voltage obtained from a constant voltage through a parallel circuit of the photocoupler 31 and the setting resistor 32 with the triangular wave output of the triangular wave oscillator 8 by another comparator 33, a pulse that changes according to the power supply voltage is obtained. Get the width signal. This signal is limited to a pulse width not exceeding the limited pulse width output 12 by taking the logical product of the limited pulse width output 12 in the NAND circuit 34.

The output of the NAND circuit 34 serves as an input control pulse of a pulse width modulation (PWM) unit in a drive circuit that controls the output voltage of a switching regulator (not shown), and the pulse width is limited by the limited pulse width output 12. Therefore, it is possible to prevent saturation of the power transformer in the switching regulator circuit due to an excessive pulse width.

[Problems to be solved by the invention]

As described above, conventionally, a circuit that generates a pulse in synchronization with a synchronization input and a circuit that obtains a limited pulse width output for limiting a pulse width are known.

However, in order to generate a pulse in synchronization with the synchronization input and to obtain a limited pulse width output, these known circuits must be used separately, so that the number of components increases and an efficient circuit configuration is required. There was a problem that it was not possible.

[Object of the invention]

The present invention is to solve such a problem of the prior art, and provides a power supply control circuit capable of generating a pulse in synchronization with a synchronization input and obtaining a limited pulse width output by the same circuit. Its purpose is to do.

[Means for solving the problem]

In the present invention, the power supply control circuit generates a control pulse having a pulse width that varies according to the output power supply voltage using a triangular wave to drive a pulse width modulation unit in the switching regulator, and performs the control using the limited pulse width output. A switching regulator for limiting the pulse width of the pulse to a predetermined value is provided.

Further, a synchronous input is input to a trigger terminal via an AND circuit, and a pulse having a pulse width determined by one of the time constant circuits composed of an externally connected resistor and a capacitor is generated in accordance with the synchronous input. A first mono-multi that generates a triangular wave output at both ends of the capacitor of the time constant circuit, and the output of this mono-multi is connected to the trigger terminal, and the other time constant circuit composed of an externally connected resistor and capacitor A pulse having a determined pulse width is obtained as a limited pulse width output, and an inverted output pulse of the pulse is provided with a second mono-multi connected to one input of an AND circuit. The configuration is such that a limited pulse width output 12 is obtained. This aims to achieve the above-mentioned object.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG. In FIG. 1, an output of a master oscillator (not shown) is provided as a synchronization input 7. The synchronization input 7 is input to a trigger terminal 21a of a monostable multivibrator (M / M; hereinafter abbreviated as "monomulti") 18a via an AND circuit 17.

The mono-multi 18a is operated by the power supply 13, and generates a high-level pulse having a constant pulse width at the Q output, triggered by the rise of the pulse at the trigger terminal 21a. Therefore, this output is synchronized with the synchronization input 7. Here, the resistor 15 and the capacitor 16 form one time constant circuit, and the time constant determines the output pulse width of the mono-multi 18a. At this time, a triangular wave output 14 is generated at both ends of the capacitor 16 as is well known.

The mono-multi 18b is operated by the power supply 13, and generates a high-level pulse having a constant pulse width on the Q output, triggered by the rise of the output pulse of the mono-multi 18a at the trigger terminal 21b. Here, the resistor 20 and the capacitor 19 form the other time constant circuit, and the output pulse width of the mono-multi 18b is arbitrarily determined by the time constant. The Q output of the mono multi 18b is synchronized with the synchronization input,
This is the desired limited pulse width output 12.

On the other hand, the photocoupler 31 detects a power supply output voltage of a switching regulator (not shown), and its impedance changes according to the power supply voltage. Therefore, the voltage obtained through a parallel circuit of the photocoupler 31 and the setting resistor 32 from the constant voltage and the triangular wave output 14 at both ends of the capacitor 16 are compared by another comparator 33, so that the voltage is determined according to the power supply voltage. Obtain a signal of varying pulse width.

This signal is output to the limited pulse width in the NAND circuit 34.
By ANDing with 12, the limited pulse width output 12
Is limited to a pulse width not exceeding. The output of the NAND circuit 34 is a pulse width modulation (PMW) in a drive circuit that controls the output voltage of a switching regulator (not shown).
The pulse width is limited by the limited pulse width output 12. Therefore, it is possible to prevent saturation of the power transformer in the switching regulator circuit due to an excessive pulse width.

Incidentally, the Q output of the monomulti 18 is used as one input of the AND circuit 17 in the synchronous input of the monomulti 18a,
By interrupting the synchronous input during the generation of the limited pulse width output, malfunction of the power supply control circuit is prevented.

〔The invention's effect〕

As described above, according to the present invention, by using a mono-multi connected in two circuits, the limited pulse width output for limiting the input pulse width of the pulse width modulation unit of the switching regulator is synchronized with the synchronization input. It is possible to obtain a triangular wave output for identifying the power supply output of the switching regulator. Further, according to the present invention, it is possible to provide an unprecedented superior power supply control circuit capable of greatly reducing the number of components as compared with a conventional circuit to achieve the same object.

[Brief description of the drawings]

1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing an example of a conventional circuit when a pulse generating circuit is operated synchronously, and FIG. 3 is a conventional circuit for obtaining a limited pulse width output. It is a figure showing an example of. 12: Limited pulse width output, 13: Power supply, 14: Triangular wave output, 15, 20: Resistor, 16, 19: Capacitor, 17: AND circuit, 18a, 18b: Monostable multivibrator (M / M), 21a, 21b: Trigger terminal, 31: Photocoupler, 32: Setting resistor, 33: Comparator, 34: NAND circuit.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-129863 (JP, A) JP-A-58-31427 (JP, A) JP-A-61-251472 (JP, A) JP-A-62 221872 (JP, A) Japanese Utility Model 63-90986 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) H02M 3/00-3/44

Claims (1)

(57) [Claims] 1. A control pulse having a pulse width varying in accordance with an output power supply voltage is generated by using a triangular wave to drive a pulse width modulation unit in a switching regulator, and the control pulse width is output by using a control pulse width output. In a power supply control circuit of a switching regulator, a synchronization input is input to a trigger terminal via an AND circuit, and a pulse having a pulse width determined by a time constant circuit including a resistor and a capacitor connected externally is used for the synchronization. A first monostable multivibrator (hereinafter abbreviated as "monomulti") that generates a triangular wave output at both ends of the capacitor while being generated in accordance with the input; Limits the pulse width determined by the time constant circuit consisting of the selected resistor and capacitor A second mono-multi connected to one input of the AND circuit, the triangular wave output and the limited pulse width output in synchronization with the synchronization input. And a power supply control circuit characterized by: