JPH11206117A - Multi-type switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably control an output voltage of a sub output circuit and thereby increase the regulation, by installing a second switching element in the sub output circuit formed at the secondary side of a transformer and controlling the second switching element based on the magnitude of the output voltage of the sub output circuit. SOLUTION: In a power circuit having, at the secondary side of a transformer T1, a main output circuit and a sub output circuit P2 outputting the voltage different from that of the main output circuit, a first switching element connected to the primary side of the transformer T1 is controlled based on the output voltage of the main output circuit to stabilize the output voltage of the main output voltage. Here, a transistor TR1 is connected as a second switching element to the sub output circuit P2 and is controlled by means of a base voltage control circuit BC based on the output voltages of output terminals OUT1, OUT2 of the sub output circuit P2. By this method, the output voltage of the sub output circuit P2 can also be controlled stably.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transformer having a main output circuit and a sub output circuit for individually outputting output voltages to a secondary side of a transformer, and a primary winding of the transformer being connected to a primary side input circuit. The present invention relates to a multi-type switching power supply that has a switching element in series, controls the on-time of the switching element based on the output voltage of the main output circuit, and stably controls the output voltage of the main output circuit.

[0002]

2. Description of the Related Art A conventional example of the above-mentioned multi-type switching power supply will be described with reference to FIG. IN is an input terminal, and OUT1, OUT2, and OUT3 are output terminals to which respective loads are individually connected. Vi is the input voltage, V
o1, Vo2, and Vo3 are output voltages supplied to the respective loads, C1 to C4 are smoothing capacitors, and T1 is a transformer (input winding L1 and a plurality of output windings L21 and L2).
2, L23 and a feedback winding (not shown). ), SW is a switching element, D1 to D3 are rectifier diodes, CC is an output voltage V at an output terminal OUT1.
This is a control circuit that detects o1 (illustration of a detection system and the like is omitted) and controls the ON time of the switching element SW based on this detection. The circuit on the primary side of the transformer T1 is called an input circuit, and the circuit on the secondary side is called an output circuit. The output circuits P1 to P3 are a main output circuit P1 and two sub output circuits P2 and P2, respectively.
P3.

In the multi-type switching power supply having the above configuration, when the DC input voltage Vi smoothed by the smoothing capacitor C1 is high, in order to make the output voltage Vo1 of the main output circuit P1 a constant and stable voltage, The on-time of the switching element SW is controlled so as to decrease the output voltage Vo1. When the input voltage Vi is low, the on-time of the switching element SW is increased to increase the output voltage Vo1.
o1 is controlled to be higher, whereby the output voltage Vo1 of the main output circuit P1 is controlled so as to be stably kept constant on average.

The output voltages Vo2 and Vo3 of the sub output circuits P2 and P3 are controlled stably in accordance with the control of the output voltage Vo1.

[0005]

In this type of switching power supply configuration, when it is necessary to increase the output voltage Vo1 from the state of the load at the output terminal OUT1, control is performed so as to lengthen the ON time of the switching element SW. Is done. In this case, from the viewpoint of the state of the load connected to the output terminals OUT2 and OUT3, even if it is not necessary to increase the output voltages Vo2 and Vo3, the output voltages Vo2 and Vo3 are controlled to be high, and the output voltages do not always fluctuate. It becomes large and cross regulation deteriorates. As a general means for improving the cross regulation, as a load system having a large output power capacity in the main output circuit P1, the output voltage Vo1 is controlled by on-time control by the switching element SW, and the sub output circuits P2 and P3 are controlled. As a load system having a small output power capacity, in this system, when the output voltage rises at a light load, means for decreasing the output voltage by a series regulator system to stabilize the output voltage is adopted. In this case, since the dummy circuit is consumed at light load to increase the stability of the output voltage, the overall efficiency is reduced and the internal heat generation is increased, and the life of the switching power supply and the reliability thereof are reduced. Become. This is remarkable at the time of the high input voltage Vi.

Therefore, in the present invention, at least the main output circuit can perform stable output voltage control by controlling the ON time of the switching element on the primary side of the transformer, while the sub output circuit can perform stable output voltage control. The main solution is to improve regulation by doing so.

More specifically, the present invention makes it possible to control not only the main output circuit but also the sub-output circuit with high accuracy in the output voltage, and at the same time, to improve the overall efficiency and reduce the power loss. It is an object of the present invention to improve the life of a switching power supply and its reliability.

An AC / DC converter is also provided in the sub-output circuit to stabilize the output voltage of the sub-output circuit. However, the switching frequency of the switching element in this converter and the switching frequency of the switching element with respect to the main output circuit can be improved. The switching frequency is generated as a fundamental frequency of noise for the switching power supply.

Therefore, another object of the present invention is to prevent such noise from being generated.

[0010]

A switching power supply according to the present invention has a main and sub output circuits for individually outputting output voltages on the secondary side of a transformer, respectively. In a multi-type switching power supply that stably controls the main output voltage by controlling the ON time of a first switching element on the primary side of the transformer based on the voltage), the sub output circuit is connected to the secondary side. A multi-type switching power supply having a second switching element and performing switching control of the second switching element based on the magnitude of its own output voltage (sub output voltage). Has been resolved.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a circuit diagram of a main part of a switching power supply according to the present embodiment. FIG. 1 shows the auxiliary output circuit P of FIG.
This corresponds to 2. The switching power supply of the present embodiment is obtained by changing the circuits of the sub output circuits P2 and P3 in the circuit of FIG. 3 as shown in FIG. Here, the sub output circuit P
2 and P3 are the same circuit, and therefore, in this embodiment, the sub output circuit P2 will be described as a representative.

First, at the time of the high input voltage Vi, in the conventional switching power supply shown in FIG. 3, since the rectifier diode D2 of the sub-output circuit P2 is continuously conducting, the output terminal O
Regardless of the load state of UT2, a high voltage appears on the output terminal OUT2 side. When the load connected to the main output circuit P1 is large, the cross regulation deteriorates as described above.

Therefore, in the present embodiment, a collector / emitter of the transistor TR1 is inserted and connected as a switching element instead of the rectifier diode D2 of FIG. 3, and the base voltage of the transistor TR1 is controlled by a base voltage control circuit BC which will be described later. Therefore, when the output voltage Vo2 on the output terminal OUT2 side does not need to be increased at the time of the high input voltage Vi and at that time, the ON time of the transistor TR1 is set to a shorter time to substantially reduce the switching element SW2. The output voltage Vo2 is obtained so as to obtain the same effect as shortening the ON time of. At this time, it is considered that if the on / off frequency of the transistor TR1 as the switching element is the same frequency synchronized with the surrounding frequency, it is advantageous for noise and the like. by this,
The cross regulation can be improved.

Next, the base voltage control circuit BC will be described. This control circuit BC has a comparison circuit CP composed of an operational amplifier and the like. The output of this comparison circuit CP is connected to the base of the transistor TR1 via a resistor R3. Have been. One input section of the comparison circuit CP is a secondary winding L2.
2 is connected via a resistor R0 and a diode D4 to enable monitoring of the appearance of a positive voltage in the secondary winding L22 and to control the output voltage Vo2 only when it is possible to control the output voltage Vo2. Output is enabled. The other input portion + of the comparison circuit CP is connected to a common connection portion of the resistors R4 and R5 in parallel with the output terminal OUT2, so that a voltage corresponding to the output voltage Vo2 can be input.

In order to stabilize the operation, the comparison circuit CP is supplied with power from a rectifying / smoothing circuit including a diode D5 and a capacitor C5 only when a positive voltage appears on the secondary winding L22. ing.

The operation will be described with reference to FIG. FIG.
FIG. 2 shows a waveform of a voltage Va generated in the secondary winding L22.
b is the waveform of the voltage Vb at the input of the comparison circuit CP, FIG.
Is a waveform of the voltage Vc of the input portion + of the comparison circuit CP, FIG. 2D is a waveform of the output voltage Vd of the comparison circuit CP, FIG. 2E is a waveform of the collector-emitter voltage Vce of the transistor TR1, and FIG. 2F is an output voltage of the output terminal OUT2. The waveform of Vo2 is shown.

The voltage Va generated in the secondary winding L22 is rectified by the diode D4 and is converted into a voltage Vb by the comparison circuit CP.
Is input to one of the input sections. A voltage Vc corresponding to the output voltage Vo2 is applied to the other input section + of the comparison circuit CP. The comparison circuit CP compares the two voltages Vb and Vc, and outputs a voltage Vd corresponding to the magnitude from an output portion thereof. The collector-emitter voltage Vce of the transistor TR1 is determined by the output voltage Vd of the comparison circuit CP in FIG.
It becomes like the waveform of e. In this case, when the collector-emitter voltage Vce is high, the transistor TR1 is off, and when the collector-emitter voltage Vce is low, the transistor TR1 is on. Therefore, the output terminal OUT
2 will change as shown in FIG. 2f. Note that the broken line in FIG. 2F indicates the direction of change of the output voltage Vo2 in the conventional switching power supply having the circuit configuration in FIG. 3, and is compared with the present embodiment.

As apparent from a comparison between the voltage waveform Va of FIG. 2A and the waveform of the output voltage Vo2 of FIG. 2F, the ON time of the switching element SW is lengthened by the high input voltage Vi. So that the secondary winding L
Even if the output voltage Vo2 is increased by increasing the time during which the voltage Va of 22 is generated and the output voltage Vo2 does not need to be increased, the transistor T
By turning off R1, the output voltage Vo2 is prevented from increasing following the on-time. In this manner, in the present embodiment, the output voltage Vo2 of the sub output circuit P2 is stably controlled, so that the regulation voltage accuracy is improved and the efficiency is also improved.

Since the switching frequency of the transistor TR1 is synchronized with that of the switching element SW, even if the transistor TR1 is provided, the switching power supply does not generate noise due to the operation of the transistor TR1.

[0021]

Therefore, according to the present invention, as described above, the sub output circuit is connected to the secondary side connected to the transformer secondary side.
And the switching control of the second switching element based on the magnitude of its own output voltage, so that the main output circuit has a stable output voltage by controlling the ON time of the switching element on the primary side of the transformer. While the control can be performed, the output voltage control can be stably performed also for the sub-output circuit, thereby improving the regulation. Further, according to the present invention, the operation of the switching element for controlling the output voltage stability of the main output circuit and the operation of the switching element for controlling the output voltage stability of the sub output circuit are synchronized, so that noise is generated. There is no.

As described above, according to the present invention, specifically, it is possible to control not only the main output circuit but also the sub-output circuit with high accuracy in the output voltage, and at the same time, to improve the overall efficiency and reduce the power loss. , The life of the switching power supply and the reliability thereof can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a sub output circuit of a switching power supply according to an embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation of FIG. 1;

FIG. 3 is an overall circuit diagram of a conventional switching power supply.

[Explanation of symbols]

 T1 Transformer L22 Secondary winding P1 Main output circuit P2, P3 Secondary output circuit TR1 Transistor BC Base voltage control circuit CP Comparison circuit OUT2 Output terminal Vo2 Output voltage

Claims (4)

[Claims] 1. A primary and a secondary output circuit for individually outputting an output voltage to a secondary side of a transformer, respectively, and a primary and secondary output circuits based on an output voltage (main output voltage) of the main output circuit. A multi-type switching power supply that controls the on-time of the first switching element to stably control the main output voltage, wherein the sub output circuit has a second switching element connected to the secondary side, and has its own output. A multi-type switching power supply, wherein switching control of the second switching element is performed based on a magnitude of a voltage (sub output voltage). 2. The multi-type switching power supply according to claim 1, wherein the sub-output circuit controls the switching of the second switching element in synchronization with the first switching element. 3. The sub-output circuit controls the switching of the second switching element when a voltage having the same sign as the sub-output voltage appears on a secondary side of the transformer. 2. The multi-type switching power supply according to 1. 4. The multi-function device according to claim 1, wherein the sub-output circuit controls the on-time of the second switching element based on the sub-output voltage even at a high input voltage. Type switching power supply.