JPH02246774A - Synchronous switching frequency multi-output power supply - Google Patents

Abstract

PURPOSE:To reduce the number of parts and the cost by subjecting AC voltage produced through a primary circuit to width control through a secondary circuit without subjecting the AC voltage to rectification. CONSTITUTION:A synchronous switching frequency multi-output power supply comprises a primary circuit 1, a secondary circuit 2, a source transformer 3, a drive circuit 4, a switching transistor 5, a rectifying diode 6, a smoothing circuit 8, and the like. A switch 7 and a control circuit 9 are provided at the side of the secondary circuit, then the output voltage from the smoothing circuit 8 is fed back and the duty of the switch 7 is regulated thus stabilizing DC voltage.

Description

[Detailed Description of the Invention] (Summary) Regarding switching power supplies used in electronic exchanges, etc., the purpose is for the output of a multi-output power supply provided with a large number of secondary circuits to operate in synchronization with the primary circuit frequency. A primary circuit that converts DC input into AC with a constant frequency and duty cycle using a switching transistor, a power transformer that transforms the AC voltage of the primary circuit into multiple outputs, and a multiplex circuit that is connected to the secondary side of the power transformer. In a switching power supply having a secondary output circuit, the multi-output secondary circuit includes a switch connected in series with a rectifier diode that rectifies alternating current, a control circuit that controls on/off of the switch, and a control circuit that controls on/off of the switch. A smoothing circuit for smoothing the output of the circuit is provided, and the multi-output secondary circuit is configured to send out an output voltage having a frequency synchronized with the switching frequency of the primary circuit.

[Industrial application field]

The present invention relates to a switching frequency cycle type multi-output power supply used in electronic exchanges and the like.

The power supplies used in electronic exchanges, etc. include -48V, -24V, +12ν DC power supplies used for subscriber circuits, etc., and -5V, +5V DC power supplies used for control circuits, etc. Generally, a -48V DC power supply is transformed and stabilized using a switching power supply.

In particular, systems that handle analog signals such as electronic exchanges use devices such as operational amplifiers and codecs, so ±5
A power supply with positive and negative polarity like V is required. recent years,
Most power supplies use a switching method, and switching noise is inevitably superimposed on the output. If this noise is superimposed on the positive and negative outputs separately, it will leak to the output of the device. Therefore, it is necessary to synchronize the positive and negative power supplies to prevent noise leakage.

[Conventional technology]

FIG. 4 shows a circuit configuration diagram of a conventional general switching frequency synchronous type multi-output power supply. In the figure, l is the primary circuit, 2 is the secondary circuit, 3 is the power transformer, 4 is the drive circuit, and 5
is a switching transistor, 6 is a rectifier diode, 8
1 is a smoothing circuit, and 10 is a chopper circuit.

The primary circuit 1 includes a drive circuit 4 and a switching transistor 5
It consists of an electrolytic capacitor and inputs DC -48V, turns on and off the switching transistor 5 by the oscillation pulse from the drive circuit 4, converts it to AC with a constant frequency and duty cycle, and connects it to the primary winding of the power transformer 30. Output.

The power transformer 3 transforms the alternating current input to the primary winding and branches it to a multi-output secondary winding. In this circuit, - for 5V, +
It is branched into three windings, one for 5V and one for +12V, and sent to the respective secondary circuits 2.

The secondary circuit 2 consists of a rectifier diode 6, a smoothing circuit 8, and a chopper circuit 10, and rectifies each AC voltage transmitted to the secondary winding of the power transformer 3, smoothing it, and converting it into a stabilized DC voltage. It is sent from the chopper circuit IO. From the secondary circuit 2, for each voltage -5ν5+5v, +1
2ν is sent out, and the earth side terminal E is commonly connected to each power source.

The chopper circuit 10 is a stabilizing circuit that turns on and off a DC input using a switching transistor to send out a constant DC output. That is, the input voltage is compared with a reference voltage and fed back, and the duty of the switching transistor is adjusted to supply a stable DC voltage. In order to make the oscillation frequency for turning on and off this switching transistor constant for each secondary circuit, the oscillation frequency f+, fz,
h is synchronized. This cancels out the noise waveform generated from the sawtooth wave of the DC voltage sent from each chopper circuit IO by synchronizing the oscillation frequency. That is, the positive and negative power supplies are operated synchronously to prevent noise. For this reason, the conventional circuit requires a photocoupler or the like to synchronize each chopper circuit.

[Problem to be solved by the invention]

In conventional switching frequency synchronized multi-output power supplies, alternating current generated in a primary circuit is once rectified, and then the voltage is converted into DC/DC using a chopper circuit or the like. Since there are as many chopper circuits as there are outputs, each circuit is connected with a photocoupler or the like for synchronization. Therefore, this conventional method requires an oscillator and a photocoupler for synchronization, which increases the number of parts and costs.

Conventional circuits have the disadvantage that once the alternating current generated in the primary circuit is rectified, it must be converted to alternating current for the next voltage control.

An object of the present invention is to achieve synchronization by performing width control in a secondary circuit without rectifying the alternating current generated in the primary circuit.

[Means for Solving the Problems] FIG. 1 shows a basic configuration diagram of a switching frequency synchronized multi-output power supply according to the present invention. In the figure, 1 is a primary circuit, 2 is a secondary circuit, 3 is a power transformer, 4 is a drive circuit, 5 is a switching transistor, 6 is a rectifier diode, 7 is a switch, 8 is a smoothing circuit, and 9 is a control circuit.

The primary circuit 1 turns on and off the switching transistor 5 based on the oscillation frequency of the drive circuit 4 to convert the -48V DC power into AC with a constant frequency and duty cycle, and sends it to the primary side of the power transformer 3. The power transformer 3 transforms this AC voltage and branches it into multiple output voltages. In the secondary circuit 2, this branched AC voltage is converted into a positive pulse by a rectifier diode 6, the duty of this pulse is adjusted by turning on and off a switch 7, and the DC voltage is passed through a smoothing circuit 8 to +5V, -5ν, Outputs +12V.

This output voltage is controlled by a switch 7 by a control circuit 9.
The DC voltage is fed back and the duty of the switch 7 is adjusted to stabilize and output the DC voltage.

[Effect]

In the present invention, when the switch 7 is inserted in series with the rectifier diode 6 and the conduction time of this element is adjusted, it is the same as changing the conduction time on the primary side. On the secondary side, the alternating current from the primary side is used as is, so if you add as many secondary circuits as the number of outputs, they will all operate at the same frequency.

The switch 7 in FIG. 1 may be replaced with a transistor or a FET (field effect transistor).

The switching transistor 5 of the primary circuit 1 is set to the maximum duty that can ensure the output of the secondary circuit 2 when the input voltage is the lowest. If the duty is unchanged, the output voltage will rise when the input voltage is normal, so the control circuit 9 adjusts the conduction time of the switch 7 to shorten it so that the output voltage becomes the specified output voltage. By performing this operation in each secondary circuit 2, it appears as if the duty on the primary side is changing. Further, since all secondary circuits are driven by the same primary circuit, the secondary circuits are completely synchronized with each other.

〔Example〕

An embodiment of the switch and control circuit of the secondary circuit is shown in FIG. In the figure, 7 is a switch and FET.

The control circuit 9 includes voltage dividing resistors R1 and R2, a reference voltage VE, a comparator COMP, and a latch circuit RACH.

The comparator COMP compares the voltage V1 obtained by dividing the output voltage sent by rectifying the AC voltage from the primary side with the reference voltage VE, and when the divided voltage ν1 is less than the reference voltage vE, the The output of the comparator CO controls the base of the switch 7 to keep it in the on state, and when the divided voltage Vl exceeds the reference voltage νE, the output from the comparator CO is inverted and the base of the switch 7 is turned on. The voltage is reversed and switch 7
is turned off, the latch circuit holds this state, and the next input voltage is reset to "H". This cuts the input waveform and shortens the output voltage waveform.

That is, the switching waveform having the same frequency as the input circuit adjusts the duty of the output voltage by turning on and off the switch 7 based on the feedback of the output voltage, and sends out a stable output. Therefore, even if the input voltage becomes high, the output voltage is adjusted to the reference value.

A timing chart of input waveforms and output waveforms is shown in FIG. In the figure, ■ is the input voltage waveform, ■ is the reference voltage,
(2) is the divided voltage, and (2) is the source waveform of the switch 7.

When the switch 7 is in the on state, the input voltage (2) sends out a voltage with an on/off waveform of the same frequency and duty cycle as the output voltage of the primary circuit. When the output voltage of the primary circuit increases, the input voltage (■) also increases, and the divided voltage (■) also increases accordingly, reaching the reference voltage (■). When the reference voltage ■ is reached, the comparator inverts and turns off the switch, so the active part of the input voltage ■ is cut off and the waveform ■ is output. The input waveform (2) is adjusted to be shorter like the output waveform (2), so the output voltage decreases and the reference voltage is sent out. Therefore, it is possible to send out a secondary side output whose duty is adjusted in synchronization with the primary side frequency. Since each of the above secondary side outputs is driven from the primary circuit, the frequencies of the secondary circuits are completely synchronized with each other, and the voltage adjustment is adjusted by each secondary circuit, so there is no difference in synchronization. Generation of noise can be prevented.

〔Effect of the invention〕

As described above, according to the present invention, the output of the secondary circuit can be synchronized without using an external circuit for synchronization such as a photocoupler, so that the number of parts and cost can be reduced compared to the conventional method. Further, by providing a large number of secondary circuits, the switching frequency power supply can have multiple outputs.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of the present invention, FIG. 2 is a circuit diagram of an embodiment, FIG. 3 is a timing chart of the embodiment, and FIG. 4 is a circuit diagram of a conventional example.

Claims (1)

[Claims] A primary circuit (1) that converts DC input into AC with a constant frequency and duty cycle using a drive circuit (4) and a switching transistor (5), and a system that converts the AC voltage of the primary circuit (1) into In a switching power supply having a power transformer (3) that transforms into an output, and a multi-output secondary circuit (2) connected to the secondary side of the power transformer (3), the multi-output secondary circuit (2) , a switch (7) connected in series with a rectifier diode (6) that rectifies alternating current, and a control circuit (9) that controls on/off of the switch (7).
) and a smoothing circuit (
8), wherein the multi-output secondary circuit (2) sends out an output voltage having a frequency synchronized with the switching frequency of the primary circuit (1).