JPH0539189U - Active power circuit of switching power supply - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] Active damping that reduces the deviation from the set value of the output voltage that occurs when the load balance of each output deviates to one side in a switching power supply having two output circuits. The purpose is to provide a circuit. [Structure] A secondary side control circuit that detects and controls the sum voltage of each set output voltage, a resistor that expresses the midpoint potential of the sum voltage, its intermediate potential, and the voltage of the output common connection part. It is assumed that the transistor to be compared and the resistor for flowing a dummy current by the transistor are provided.

Description

[Detailed description of the device]

[0001]

[Explanation of the field to which the device belongs]

 The present invention relates to an active dummy circuit which operates when the load balance of a switching power supply having two output circuits is biased to one side.

[0002]

[Prior art and its problems]

 A common method for adjusting the voltage of a switching power supply having two outputs is to detect one output and stabilize the other by using a series regulator. In this case, no dummy resistor is required, but there are drawbacks that the price is high and the exchange efficiency is low.

[0003]

[The purpose of the device]

 2 When the load balance of the two output circuits is not even and uneven, the active dummy circuit on the output side where the voltage rises operates and the fluctuation of the output voltage is minimized. It is intended to provide a circuit method that realizes.

[0004]

[Means of the Invention for Solving Problems]

 In the present invention, the secondary side control circuit for detecting and controlling the sum voltage of the respective set output voltages, the resistor for expressing the midpoint potential of the sum voltage, the intermediate potential thereof and the output common connection portion are provided. It is characterized in that a transistor for comparing voltages and a resistor for flowing a dummy current by the transistor are provided.

[0005]

【Example】

 FIG. 1 is a circuit diagram showing an embodiment of the present invention. 1 is a transformer 2 is a switching transistor 3 is a primary circuit control section, 4 is an input power source 5-1 and 5-2 is a rectifying diode 6-1. , 6-2 is a smoothing capacitor 7-1 is a load on the positive output side, 7-2 is a load on the negative output side, 8 is a secondary control unit 9-1, 9-2 is a resistor for generating an intermediate voltage 10-1 is an NPN transistor 10-2 is a PNP transistor 11-1, and 11-2 is a resistor which consumes a current which serves as a dummy load.

The secondary circuit control section 8 is configured as a whole circuit so as to detect the voltage across both output terminals and control it to a constant value. Therefore, even if the load balance is deviated and each output voltage fluctuates, the both-end voltage is always maintained at a constant value. In the case of a circuit configuration in which the respective output voltages have the same voltage, if the resistors 9-1 and 9-2 have the same value, the voltage at point A in FIG. 1 is defined as the intermediate voltage of the two outputs. Transistors 10-1 and 10-2 are provided to compare the voltage at the point A with the actual voltage at the common connection.

A potential difference occurs between the voltage at the point A and the voltage at the common connection portion, and the voltage between the base emitters of either the transistor 10-1 or 10-2 is the on-voltage (about 0 (3) 0.6 V) of each. By the time the temperature reaches 0, the transistor 10-1 or 10-2 operates so that the dummy current flows through the dummy resistor 11-1 or 11-2 and the voltage between the base-emitters is not further increased. That is, the load of the positive side output is reduced and the positive side output is controlled to be twice the set voltage value.・ When the on-voltage (0.6) of the emitter is exceeded, the transistor 10-1 operates so that a dummy current flows through the resistor 11-1 and the positive side output does not deviate from the set value of 0.6V or more. Is. At this time, the output voltage on the negative side is 0.6V lower than the set value. When the load on the negative output side decreases and the negative output voltage rises, the transistor 10 -2 and the resistor 11-2 operate and the reverse operation is performed.

FIG. 2 is an output characteristic diagram of the present invention compared with the conventional example. According to the present invention, the conventional example (characteristics b and b ') having no dummy resistance as shown in characteristics (a) and (a') is shown. It is clear that the positive side output voltage (a) and the negative side output voltage (a ') and their fluctuations are extremely small in comparison with.

[0009]

[Effect of the device]

 According to the present invention, even if the load balance between the two outputs is deviated and the output voltage deviates from the set value, it is possible to keep the output voltage within ± 0.6 V without fail. In addition, this active dummy circuit does not consume power when each output voltage is within ± 0.6V with respect to the set value, so power loss during normal use is very small, and only a constant resistance is used. It can contribute to energy saving and has a high utility value compared to the method that suppresses the output voltage by using reactive power.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is an output characteristic diagram comparing the present embodiment with the conventional example (4).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 transformer 2 switching transistor 3 primary circuit control section 4 input power supply 5-1 and 5-2 rectifying diode 6-1 and 6-2 smoothing capacitor 7-1 positive output side load 7-2 negative output side load 8 Secondary circuit control section 9-1, 9-2 resistance 10-1 NPN transistor 10-2 PNP transistor 11-1, 11-2 dummy resistance

Claims (1)

[Scope of utility model registration request] 1. A switching device having at least two positive and negative output numbers, wherein the absolute values of the rated values of the positive and negative output voltages are equal, and one end of each output end is commonly connected. The power supply has a secondary side control circuit configured to detect a voltage across the output other than the common connection and adjust the voltage to a constant value, and to output an intermediate voltage of the voltage across the secondary side. 1 and a second resistor, a PNP transistor and an NPN transistor having an emitter and a base connected between the common connection terminal and the intermediate voltage terminal, and a collector of the NPN transistor via the third resistor. Is connected to the output terminal of
An active dummy circuit of a switching power supply, wherein a collector of an NP transistor is connected to the negative output terminal via a fourth resistor.