JPH0595672A - Starting circuit for multiple output power supply - Google Patents

Abstract

PURPOSE:To make it possible to use a power supply having the optimum capacity by turning on each switch in a power supply circuit after detecting the rise of voltage at the secondary side of the power supply circuit. CONSTITUTION:A rush current flows to a power supply circuit 10 when turning on the power supply, and thus its output decreases. Output of the power supply circuit 10 gradually rises to the normal voltage after the flow of the rush current. When it rises to the normal voltage, a rise detection circuit 11 sends control signals to each switch SW10 of the power supply circuit, and these switches SW10 are turned on. As a result, a rapid rise of power supply becomes possible. By doing this, the equipment will not be stopped by the rush current, an excess increase in the capacity of power supply is not required, and the power supply having the optimum capacity can be utilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-output power supply starting circuit for a multi-output power supply circuit using a DC / DC converter.

[0002]

2. Description of the Related Art FIG. 4 is a diagram showing a configuration example of a conventional circuit. In the figure, SW is a power-on switch (hereinafter referred to as a power switch), and a DC voltage is applied between terminals A and B. T is a transformer to which a DC voltage is applied, and three secondary windings are provided here. Q is an FET for voltage on / off (for switching). Reference numeral 1 is a control circuit for giving a switching signal to the FETQ. CT is a current transformer that detects the current flowing through the primary side of the transformer T, and its output is in the control circuit 1. The control circuit 1 compares this current transformer CT output with a set value (threshold value),
It operates so as to narrow down the output when it becomes larger than the set value.

Reference numerals 2, 3 and 4 denote power supply circuits provided on the secondary winding side of the transformer T, which are rectifying diodes D1 and D1, respectively.
D2, a smoothing coil L, and a smoothing capacitor C. Reference numeral 5 is a three-terminal regulator provided in the power supply circuit 3, and the three-terminal regulator 5 stabilizes the DC output by a series control method.

6 receives the outputs 1 to 3 of the respective power supply circuits,
The detection circuit detects an output voltage and gives a control signal corresponding to the detected voltage to the control circuit 1. The operation of the circuit thus configured will be described below.

When the power switch SW is turned on, a DC voltage is switched by the FET Q, and an AC voltage is induced on the secondary side of the transformer T. Each of the power supply circuits 2 to 4 rectifies and smoothes the induced AC voltage and outputs a DC voltage having a predetermined value. Of these, the power supply circuit 3 outputs a stabilized DC voltage by the three-terminal regulator 5.

The detection circuit 6 inputs the values of the outputs 1 to 3 and feeds back, for example, a signal related to the added value of these outputs to the control circuit 1. The control circuit 1 changes the duty ratio of the FETQ according to this feedback signal and performs PWM control operation so that each output voltage becomes a constant value.

[0007]

When a capacitor input type (capacitive) load is connected to at least one of the secondary-side outputs, when the power switch SW is turned on, the capacitor is connected to the capacitive load. An inrush current flows to charge the battery. As the load current increases, a current exceeding the rating also flows in the transformer primary winding.

This excessive current is detected by the current transformer CT and enters the control circuit 1. The control circuit 1 controls the FETQ so as to narrow down the output. As a result, transformer 2
The secondary output drops. The detection circuit 6 detects this output voltage and feeds back the control signal to the control circuit 1. Upon receiving this feedback signal, the control circuit 1 determines that an abnormality has occurred in the circuit and stops the output.

This rush current is temporary and has the property of disappearing with time. It is inconvenient that the operation of the power supply circuit is stopped due to such a current. Therefore, the following method can be considered. Increase the secondary side output capacity. The detected current of the primary side current transformer CT is increased.

However, the method described in (1) increases the capacity of the power supply, so that there is a problem that the power supply device becomes large and the cost increases. Further, in the method shown in (3), the current transformer CT may not react even if a power source having a small capacity is short-circuited. Moreover, since the current is regulated by the primary side current, there is a problem that the overcurrent set values of other outputs become large.

The present invention has been made in view of the above problems, and provides a multi-output power supply start-up circuit capable of providing a power supply having an optimum capacity without stopping the device due to a rush current. The purpose is to

[0012]

FIG. 1 is a block diagram showing the principle of the present invention. The same parts as those in FIG. 4 are designated by the same reference numerals. In the system shown in the figure, the primary side of the transformer T is switched by the switching element SW1, and from the AC voltage induced in a plurality of secondary windings provided on the secondary side of the transformer T, a predetermined voltage is generated by the power supply circuit 10. It constitutes a circuit that obtains the output.

Reference numeral 1 is a control circuit for switching the switching element SW1 and is configured to stop the switching operation when the current detected by the current transformer CT provided in the primary winding becomes excessive. Further, the outputs of the plurality of power supply circuits 10 are configured to be connected to the load via the switch SW10. Reference numeral 11 denotes each switch of the power supply circuit 10 after detecting the rising of the secondary side provided on any one of the plurality of power supply circuits 10 and detecting that the secondary side voltage has risen. SW
The rising detection circuit outputs a control signal for turning on 10.

In the figure, the rising detection circuit 11 is provided in the nth power supply circuit 10, but the rising detection circuit 11 may be provided in any power supply circuit 10. The power supply circuit 10 provided with the rising detection circuit 11 does not need the switch SW10.

[0015]

When the power switch SW is turned on, only the power circuit 10 provided with the rising detection circuit 11 supplies current to the load. The other power supply circuit 10 is a switch SW1.
0 is off and is not supplying power to the load. Since the rush current flows in the power supply circuit 10 when the power is turned on, its output becomes low. The current detection transformer CT on the primary side does not react when the rush current flows through one power supply circuit 10, so that the circuit does not stop.

The output of the power supply circuit 10 gradually rises to the normal voltage after the rush current flows. Then, when the voltage rises to the normal voltage, the rise detection circuit 11 sends a control signal to each switch SW10 of the power supply circuit 10 to turn on these switches SW10. As a result, the power supply can be quickly started up. According to the present invention, the device does not stop due to the rush current,
Moreover, it is not necessary to unnecessarily increase the capacity of the power source, and the power source having the optimum capacity can be used.

[0017]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 is a configuration block diagram showing an embodiment of the present invention. The same parts as those in FIGS. 1 and 4 are designated by the same reference numerals. The figure shows a case where three power supply circuits 10 are provided as secondary side outputs. Of these, DC output is stabilized on the output 2 side by a three-terminal regulator 5.

On the primary side of the transformer T, Q is an FET as a switching element SW1. Its drain
A noise removal circuit including a resistor R11 and a capacitor C11 is connected between the sources. R13 is FETQ
Is a bias resistor connected between the gate and source of the.
The noise removing circuit including the resistor R12 and the capacitor C12 is connected to the current transformer CT.

On the secondary side of the transformer T, Q1 is an FET as a switch SW10. A resistor R6 and phototransistors Q11 and Q1 are provided between the outputs of the power supply circuit 10.
Two series circuits are connected, and these phototransistors Q
The emitters of 11 and Q12 are connected to the gate of the FET Q1. The phototransistors Q11 and Q12
A resistor R5 and a Zener diode D13 are connected to the emitter of
Parallel circuit is connected. The Zener diode D13 is a protection diode for clipping the drain-source voltage of the FET Q1 to a constant value. C1 on the output 2 side is a smoothing capacitor provided at the inlet of the three-terminal regulator 5, and C is a smoothing capacitor provided at the outlet.

The rising detection circuit 11 includes resistors R1 to R1.
5, a transistor Q3, a Zener diode D10, and photodiodes D11 and D12.
The voltage dividing circuit of the resistors R1 and R2 is connected across the output 3, and the divided voltage is connected to the cathode of the Zener diode D10. The anode of the Zener diode D10 is connected to the base of the transistor Q3 and also to the resistor R3. The other end of the resistor R3 is connected to the common line.

A series circuit composed of a resistor R4, a photodiode D11 and a resistor R5, and a photodiode D12 is connected to the load of the transistor Q3.
The emitter of the transistor Q3 is connected to the common line. Then, these photodiodes D11 and D1
Reference numeral 2 forms a pair with the above-mentioned phototransistors Q11 and Q12 to form photocouplers PC1 and PC2. The operation of the circuit thus configured will be described below.

When the power switch SW is turned on, the transformer primary side switching circuit starts the switching operation of the input DC voltage. That is, the drive pulse from the control circuit 1 causes the FETQ to start the on / off operation of the DC voltage.
As a result, an AC voltage is induced on the secondary side of the transformer T. Power supply circuit 10 provided on the secondary side of the transformer T
Rectifies and smoothes the induced AC voltage and outputs a DC voltage. On the output 2 side, the 3 terminal regulator 5
Further, the DC voltage is stabilized.

However, since the FET Q1 functioning as a switch is off on the output 1 and output 2 sides, no current flows through the load. Therefore, a current flows only to the output 3 on the load side. If a capacitive load is connected to the output 3 side, a rush current flows through this load. However, even if the rush current flows only in the output 3, the current transformer CT provided on the primary side of the transformer
Since the current detected by is not excessive and is smaller than the threshold value, the control circuit 1 does not narrow down the output.

FIG. 3 is a diagram showing the load characteristics of the power supply circuit 10 for the output 3. The horizontal axis represents the current I and the vertical axis represents the voltage V. Maximum current Imax due to rush current when power is turned on
Flows. As a result of the rush current flowing through the load, its output voltage temporarily drops due to the load characteristics shown in the figure,
It becomes Vmin. Therefore, the Zener diode D10 of the rising edge detection circuit 11 is not turned on. Since no current flows through the Zener diode D10, the transistor Q
3 remains off. Therefore, no current flows through the photodiodes D11 and D12, which are the loads, and the photocouplers PC1 and PC2 do not operate. As a result, output 1,
The FET Q1 on the output 2 side remains off, and no current is supplied to the load.

Here, when the predetermined time has elapsed, the charging of the current to the load capacitance is completed and the rush current stops flowing. As a result, the output 3 rises to the rated voltage Vo shown in FIG. When the output voltage rises to the rated voltage, the resistance R
The voltage voltage exceeds the Zener voltage of the Zener diode D10 by 1 and R2, and the Zener diode D10 is turned on. As a result, a forward voltage is applied to the base of the transistor Q3 and the transistor Q3 turns on.

When the transistor Q3 is turned on, the photodiodes D11 and D1 which are loads of the transistor Q3.
An electric current flows into 2 and light is emitted. These photodiodes D1
Light emission of 1 and D12 is transmitted to the phototransistor side of the photocoupler. Then, these photodiodes D1
Phototransistors Q11, Q paired with 1, D12
12 turns on.

These phototransistors Q11 and Q12
When turned on, a current flows through the loop of the resistor R6 → Q11 → the resistor R5 on the output 1 side, and the resistor R6 → Q on the output 2 side.
12 → Current flows in the loop of the resistor R5. As a result, F
A bias voltage is applied to the gate of ETQ1 and these FETQ1 are turned on. In this way, the power is supplied to the load after a predetermined time has elapsed since the power switch SW was turned on. At this time, the rush current flowing through the load is also small, and the control circuit 1 does not narrow down the output.

As described above, according to the present invention, the device is started up without the rise detection circuit 11 detecting a low voltage due to the rush current (inrush current) and without changing the overcurrent set value on the primary side. can do. Therefore, according to the present invention, by providing a switch in series on the output side,
A rush current load can be handled with a simple circuit without increasing the capacity of the power supply.

In the above description, the case where the FET Q1 is used as the switch SW10 for disconnecting the power supply circuit 10 from the load side is taken as an example, but the present invention is not limited to this.
Other switches, such as relay contacts, can also be used.

[0030]

As described above in detail, according to the present invention, it is possible to provide a multi-output power supply start-up circuit capable of providing a power supply having an optimum capacity without stopping the device due to a rush current. You can

[Brief description of drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a configuration block diagram showing an embodiment of the present invention.

FIG. 3 is a diagram showing load characteristics of a power supply circuit.

FIG. 4 is a diagram showing a configuration example of a conventional circuit.

[Explanation of symbols]

 1 Control Circuit 10 Power Supply Circuit 11 Rise Detection Circuit SW Power Supply Switch SW1 Switching Element SW10 Switch T Transformer CT Current Transformer

Claims (2)

[Claims] 1. A switching element (SW1) is used to switch the primary side of the transformer (T),
In a circuit for obtaining a predetermined voltage output from a power supply circuit (10) from an AC voltage induced in a plurality of secondary windings provided on the secondary side, a control circuit (10) for switching the switching element (SW1) includes: The switching operation is stopped when the current detected by the current transformer (CT) provided in the primary winding becomes excessive, and the outputs of the plurality of power supply circuits (10) are output from the switch (SW1).
0) is connected to the load, and the rising of the secondary side is detected in any one of the plurality of power supply circuits (10) to detect that the secondary side voltage has risen. After detection, each switch (SW) of the power supply circuit (10)
A multi-output power supply start-up circuit comprising a rising edge detection circuit (11) for outputting a control signal for turning on (10). 2. The output section of the rising edge detection circuit (11) and the signal receiving section of the power supply circuit (10) are each composed of a pair of photocouplers, and a switch (SW10) of each power supply circuit (10). 2. The multi-output power supply start-up circuit according to claim 1, wherein is a FET.