JPS6264261A - Switching power source circuit - Google Patents

Abstract

PURPOSE:To control output voltage at high precision with little consumption power till light-weight loading, by controlling frequency interrupting the input voltage of a switching power circuit, according to the condition of a detected load. CONSTITUTION:The voltage of a load current detection resistance 8 is divided with resistances 18, 19, and the input to the + terminal of a comparation 15 is provided. The input of grand voltage for reference voltage to - terminal is provided via a resistance 20. By comparing the degree of the voltage of the + terminal with the degree of hysteresis voltage determined by the output voltage of resistances 19, 21 and an auxiliary power source 22, the output of low degree or high degree is generated from a comparator 15, and a transistor TR14 is turned OFF or ON. A relay 13 is made or broken, and a resistance 12 and a resistance 11 are connected in series or short-circuited, and the switching frequency of a control circuit 9 is heightened or lowered. As a result, when a load is lowered, then it is switched with high frequency, and the output voltage of high precision is generated, and consumption power is reduced.

Description

[Detailed description of the invention] Technical field The present invention relates to a switching power supply circuit.

Conventional technology Conventionally, as a measure to suppress the upper limit of the output voltage at light loads in switching power supplies, a bleeder resistor 7 is connected in parallel to the output terminal as shown in Fig. 2, so that the load current is maintained at the bleeder resistance even at light loads. 7 to lower the current discontinuity critical point of the energy storage choke coil 5, or
A method has been adopted to increase the inductance.

Generally, in a switching power supply, the output voltage at light load increases due to discontinuous current flowing through the energy storage choke coil. Particularly in a gastric pressure-down type switching power supply, an abnormal increase in the output voltage in the current discontinuous mode of the energy storage choke coil becomes a problem.

However, among the conventional techniques for lowering the current discontinuity critical point of the energy Mfta choke coil mentioned above, in the former case, the smaller the bleeder resistance 7, the lower the current discontinuity critical point of the energy storage choke coil 5; The loss in the bleeder resistor 7 increases, and the efficiency of the switching power supply decreases.

In addition, in the case of the rear right, in order to increase the inductance, the number of windings of the coil must be increased, which has disadvantages such as an increase in size and shape and an increase in cost.

OBJECT OF THE INVENTION The present invention has been made to eliminate the drawbacks of the conventional ones described above, and aims to provide a switching power supply circuit that can obtain output voltage accuracy up to light loads by adding a simple circuit. purpose.

The switching power supply circuit according to the present invention is configured to detect the load condition and control the oscillation frequency of an oscillation circuit for controlling the input DC voltage intermittently based on the detected output.

1 亙 1 Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention. This is applied to the positive output voltage circuit of a single-wheel switching power supply. In the figure, among the capacitors and resistors connected to the control circuit 9 that determine the switching frequency, the resistor is the resistor 11.
and a resistor 12. Here, in a certain load fluctuation range, the capacitance of the capacitor 10 of the control circuit 9 and the resistor 11
The transistor 1 performs a switching operation at an oscillation frequency determined by the resistance value of the resistor 12 and the resistance value of the resistor 12. However, when the load condition is light, the resistor 12 is used as an open circuit of a relay, FET, etc.
By upper-limiting the oscillation frequency of the control circuit 9, that is, the switching frequency of the transistor 1 by strapping with the Jl element 13, the point at which the current discontinuous mode of the energy storage choke coil 5 occurs is lowered.

This will be explained in detail below. An output current detection resistor 8 is inserted in series in the output stage of the switching power supply, and the voltage drop there is divided by resistors 18 and 19, and the voltage is input to the ten terminals of the comparator 15, and one terminal is connected to the reference voltage. The ground voltage is inputted through the resistor 20 as the ground voltage. The voltage obtained by dividing the voltage drop caused by the output current detection paper resistor by the resistor 18 and the resistor 19 is larger than the hysteresis voltage determined by the output voltage of the resistor 19, the resistor 21, and the auxiliary power supply 22 compared to the ground potential. In other words, if the output current is large, comparator 1
The output level of transistor 5 becomes a low level, and the output level of transistor 14 becomes low.
is in a blocking state, so the switching element 13 does not operate, and the transistor 1 connects Wfa of the capacitor 10, resistor 11, and resistor 1
It operates at a switching frequency determined by the resistance value of 2.

Next, the output current decreases, the voltage drop across the output current detection resistor 8 decreases, and the difference between the two inputs of the comparator becomes smaller (the input potential of the ten terminal approaches the ground potential), and the comparator 15 is smaller than the hysteresis voltage of transistor 1, the output level of comparator 15 is high level, and transistor 1
4 becomes active, so it drives the fl'tltl element 13 and straps the resistor 12. For this reason, among the components that determine the oscillation frequency of the control circuit, the resistance value becomes smaller, so the oscillation frequency changes higher.

As a result, transistors 1 to 1 perform a switching operation at a high frequency when the load current becomes less than a certain value. Since the critical point at which the current in the energy storage choke coil 5 becomes discontinuous is inversely proportional to the switching frequency, the critical point at which the current in the energy storage choke coil 5 becomes discontinuous can be lowered by increasing the switching frequency. can.

As explained above, 1. By adding a simple circuit, the present invention has good output voltage accuracy even during light loads, and the bleeder resistor only needs to have a large resistance value, resulting in low power consumption and high efficiency. It is effective in improving the

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional example. Explanation of symbols of main parts 1...Switching transistor 2...
・Power transformer 5...Choke coil 9...Control circuit 13...Switching element 15...Differential amplifier 22...Auxiliary power supply

Claims (1)

[Claims] A switching power supply circuit comprising an oscillation circuit that generates an output at a predetermined frequency and intermittently controlling an input DC voltage at the oscillation frequency of the oscillation circuit, the switching power supply circuit comprising a detection means for detecting a load state and a detection output of the detection means. A switching power supply circuit comprising: means for controlling the oscillation frequency of the oscillation circuit based on the oscillation frequency of the oscillation circuit.