JP2013013299A - Multi-output switching power-supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-output switching power-supply device that can meet the requirement for downsizing and low cost.SOLUTION: A multi-output switching power-supply device 1 includes a main output circuit 2 that outputs a main output voltage Vby causing a switching element Qto perform a switching operation under the control by a control circuit 4, and a sub-output circuit 3 that outputs a sub-output voltage Vobtained by reducing the main output voltage V. The main output circuit 2 has a voltage detection circuit 5 for detecting an overvoltage state of the main output voltage Vand a reduced-voltage state of the sub-output voltage V. The voltage detection circuit 5 includes a transistor Qswitching from an off-state to an on-state when the main output voltage Vbecomes in the overvoltage state or when the sub-output voltage Vbecomes in the reduced-voltage state. When the transistor Qbecomes in the on-state, the control circuit 4 causes the switching operation of the switching element Qto stop and causes the outputs from the main output circuit 2 and the sub-output circuit 3 to stop.

Description

  The present invention relates to a multi-output switching power supply apparatus that outputs a main output voltage and at least one sub output voltage obtained by stepping down the main output voltage.

  The multi-output type switching power supply device has a main output circuit and at least one sub output circuit, and supplies power to a plurality of load circuits simultaneously. In this type of multi-output switching power supply, for safety reasons, an abnormality such as a short circuit has occurred in one of the load circuits, and the slave output voltage that supplies power to the load circuit is in a reduced voltage state. In this case or when the main output voltage becomes an overvoltage state, it is important to quickly detect this and stop the supply of power.

  FIG. 2 shows a conventional multi-output switching power supply device 1 ′ (see, for example, Patent Document 1). The multi-output switching power supply 1 ′ includes a main output circuit 2 ′ that outputs, for example, +24 [V] as a main output voltage, and a slave output circuit 3 that outputs, for example, +5 [V] as a slave output voltage. Yes.

Of these, the main output circuit 2 'includes a switching element Q ₁ which is connected to the primary winding T ₁ of the transformer T, and a control circuit 4 for controlling the switching element Q _1, the control circuit 4 and the switching element Q ₁ AC voltage when the switching operation the secondary winding T ₂ is adapted to be induce. This AC voltage is rectified and smoothed by the diode _{D 1} and a smoothing capacitor _{C 1,} it is outputted as a direct current of the main output voltage _{V bb (+24 [V])} . Also, amount of the main output voltage V _bb is fed back to the control circuit 4 by a feedback circuit (not shown), thereby the main output voltage V _bb is kept substantially constant.

The slave output circuit 3 is mainly composed of a DC-DC converter circuit, and outputs a DC slave output voltage V _cc (+5 [V]) generated by stepping down the master output voltage V _bb to a load circuit (not shown). .

The main output circuit 2 ', the voltage reduction detection circuit 5 for detecting a voltage reduction state of the secondary output voltage V _cc' and detects the overvoltage state of the main output voltage V _bb, overvoltage protection circuit for protecting a device against overvoltage 6. The photocoupler PC included in the overvoltage protection circuit 6 also serves as a transmission unit that transmits not only the overvoltage but also that the reduced voltage detection circuit 5 ′ detects the reduced voltage state to the primary side.

'In, the steady state that is not any abnormality occurs, the voltage reduction detection circuit 5' This conventional multi-output switching power source device 1 but no current flows through the photo-coupler PC because the transistor Q ₃ is turned on, secondary output voltage When V _cc is reduced voltage condition, the transistor Q ₃ is turned off so that, so that the current flows through the photocoupler PC through the diode D ₃ and resistor R _4. Thus, it has become reduced voltage state is transmitted from the secondary side to the control circuit 4 of the primary side, the control circuit 4 stops the switching operation of the switching element Q _1. Then, the power supply by the main output circuit 2 ′ and the sub output circuit 3 is stopped.

On the other hand, in the conventional multi-output switching power source device 1 ', the main output voltage V _bb is an overvoltage state, the constant voltage diode ZD ₂ overvoltage protection circuit 6 is from the nonconductive state to the conductive state, a constant voltage diode A current flows through the photocoupler PC through ZD ₂ and the resistor R ₄ . As a result, the fact that the overvoltage state has been established is transmitted from the secondary side to the control circuit 4 on the primary side, and the main output circuit 2 ′ and the subordinate output circuit are the same as when the subordinate output voltage _Vcc is in the reduced voltage state. The power supply by 3 stops.

JP 2002-17084 A

However, the conventional multi-output switching power supply device 1 ', the voltage reduction detection circuit 5 for detecting a voltage reduction state of the secondary output voltage V _cc' and overvoltage for detecting an overvoltage state of the main output voltage V _bb Since the protection circuit 6 is provided separately, the number of parts increases, which may increase the mounting space and cost. For this reason, it is difficult for the conventional multi-output type switching power supply device 1 ′ to meet the demands for miniaturization and cost reduction.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a multi-output switching power supply apparatus that can meet the demands for miniaturization and cost reduction.

In order to solve the above-described problems, a multi-output switching power supply device according to the present invention switches a switching element connected to a primary winding of a transformer under the control of a control circuit, thereby alternating current to a secondary winding of the transformer. Multi-output comprising a main output circuit for inducing a voltage and outputting a main output voltage obtained by converting the AC voltage into a direct current, and a sub output circuit for outputting a sub output voltage obtained by stepping down the main output voltage Type switching power supply,
The main output circuit includes a voltage detection circuit that detects an overvoltage state of the main output voltage and a reduced voltage state of the sub output voltage, and a signal that indicates an overvoltage state or a reduced voltage state when the voltage detection circuit detects an overvoltage state or a reduced voltage state. A transmission means for transmitting to the control circuit,
The voltage detection circuit includes switching means that switches from an off state to an on state when the main output voltage is in an overvoltage state or the sub output voltage is in a reduced voltage state,
The control circuit is characterized in that when the switching means is turned on, the control circuit receives the signal from the transmission means and stops the switching operation of the switching element, and stops the output from the main output circuit and the sub output circuit.

  According to this configuration, the overvoltage state of the main output voltage and the reduced voltage state of the subordinate output voltage, which are conventionally detected by separate circuits, are detected by one voltage detection circuit, so that the number of parts can be reduced. It can meet the demands for miniaturization and cost reduction.

  In the multi-output type switching power supply device, the voltage detection circuit is interposed between the main output circuit and the sub output circuit, detects the voltage difference between the main output voltage and the sub output voltage, and according to the voltage difference It further includes a voltage difference detection element that can be switched between a conduction state and a non-conduction state, and detects an overvoltage state of the main output voltage or a reduced voltage state of the sub output voltage when the voltage difference detection element changes from the non-conduction state to the conduction state. The switching unit may be configured to switch from the off state to the on state.

  According to this configuration, the voltage difference detecting element detects the voltage difference between the main output voltage and the sub output voltage, and the non-conducting state is turned on in accordance with the voltage difference, so that the overvoltage of the main output voltage is reliably ensured. The state and the reduced voltage state of the slave output voltage can be detected. In addition, since the switching means is switched from the off state to the on state when the voltage difference detecting element changes from the non-conducting state to the conducting state, a signal indicating an overvoltage state or a reduced voltage state is transmitted via the transmission unit with a simple configuration. Can be transmitted to the control circuit.

  A constant voltage diode is preferably used as such a voltage difference detecting element, and the cathode side of the constant voltage diode may be connected to the main output circuit, and the anode side may be connected to the sub output circuit.

  From the viewpoint of reducing the number of parts of the voltage detection circuit, it is preferable to configure the circuit as follows using a PNP transistor as the switching means. That is, the base of the transistor is connected to the high potential side of the output of the main output circuit via the first resistor, and is connected to the cathode side of the constant voltage diode via the second resistor, and the emitter of the transistor is the main output circuit. It is preferable that the transistor is connected to the high potential side of the output and the collector of the transistor is connected to the transmission means.

  Further, the transmission means in the multi-output type switching power supply device is a photocoupler, and a signal is transmitted to the control circuit by detecting the current supplied from the switching means in which the photocoupler is turned on. Also good.

  ADVANTAGE OF THE INVENTION According to this invention, the multiple output type switching power supply device which can respond to the request | requirement of size reduction and cost reduction can be provided.

1 is a circuit diagram of a multi-output type switching power supply device according to the present invention. It is a circuit diagram of a conventional multi-output type switching power supply device.

  Hereinafter, preferred embodiments of a multi-output type switching power supply according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a circuit diagram of a multi-output switching power supply device 1 according to an embodiment of the present invention. As shown in the figure, the multi-output switching power supply device 1 according to this embodiment outputs a main output circuit 2 that outputs, for example, +24 [V] as a main output voltage, and outputs, for example, +5 [V] as a sub output voltage. The slave output circuit 3 is provided.

The main output circuit 2 includes a switching element (using an FET in this embodiment) Q ₁ connected to the primary winding T ₁ of the transformer T, and a control circuit 4 that controls the switching element Q _1. 4 is adapted to the AC voltage is induced to the switching element Q ₁ in the secondary winding T ₂ when the switching operation.

This AC voltage is rectified and smoothed by the diode _{D 1} and a smoothing capacitor _{C 1,} it is outputted as a direct current of the main output voltage _{V bb (+24 [V])} . Amount of the main output voltage V _bb is fed back to the control circuit 4 by a feedback circuit (not shown), thereby the main output voltage V _bb is kept substantially constant.

The slave output circuit 3 is mainly composed of a DC-DC converter circuit, and outputs a DC slave output voltage V _cc (+5 [V]) generated by stepping down the master output voltage V _bb to a load circuit (not shown). .

Further, the primary output circuit 2, the voltage detection circuit 5 for detecting an overvoltage state of the reduced voltage state and the main output voltage V _bb of secondary output voltage V _cc is provided.

Voltage detecting circuit 5 has an emitter main output circuit 2 outputs (hereinafter, "main output" hereinafter) transistor Q ₂ of PNP type connected to the high potential side of the base of the transistor Q ₂ - is connected between the emitter A resistor R ₁ (corresponding to the “first resistor” in the present invention) and a constant voltage diode ZD ₁ (on the present invention) whose anode side is connected to the high potential side of the output of the slave output circuit 3 (hereinafter referred to as “slave output”). “Corresponding to“ voltage difference detecting means ”) and a resistor R ₂ (corresponding to“ second resistor ”of the present invention) connected between the base of the transistor Q ₂ and the cathode side of the constant voltage diode ZD _1. I have.

As described above, the constant voltage diode ZD ₁ has the cathode side connected to the main output via the resistor R ₁ and the resistor R ₂ , and the anode side connected to the sub output, and the main output voltage V _bb and the sub output detecting the voltage difference between the voltage V _cc, the conductive and non-conductive states are switched in accordance with the voltage difference.

The photocoupler PC (corresponding to the “transmission means” of the present invention) is connected to the light emitting element PC ₁ connected between the collector of the transistor Q ₂ and the low potential side of the main output and the sub output and the control circuit 4. and a light receiving element PC ₂ has. Photocoupler PC is transmitted to the primary side that reduced voltage state of overvoltage or secondary output voltage V _cc of the main output voltage V _bb were detected.

As described above, examples of the main output voltage V _bb and the sub output voltage V _cc in this embodiment are +24 [V] and +5 [V], respectively, and the difference is 19 [V]. Therefore, if the set voltage (breakdown voltage) of the constant voltage diode ZD ₁ is set to about 20 [V], which is slightly higher than 19 [V], a current flows through the resistor R ₁ at the normal time when no abnormality occurs. because does not flow through the transistor Q ₂ is kept off.

Abnormality such as a short circuit in the load circuit being powered is generated by the secondary output circuit 3, the secondary output is reduced voltage condition, the constant voltage diode ZD ₁ is a breakdown condition, the secondary output from the high potential side of the main output toward the high potential side, that a current flows in the reverse direction of the zener diode ZD _1. Then, the voltage drop across the resistor R ₁ by this current, the base of the transistor Q ₂ - emitter voltage rises, the transistor Q ₂ is switched from off to on. Specifically, when the ON voltage of the transistor _{Q 2} and 1.2 [V], secondary output voltage _{V cc} is 2.8 (= 24- (20 + 1.2 )) [V] becomes below, the transistor _{Q 2} Switches from off to on. Thus, in this embodiment, the transistor Q ₂ functions as a "switching means" of the present invention.

Current through transistor Q ₂ to which is in the ON state flowing from the high potential side of the main output, i.e. the collector current of the transistor Q ₂ to which is turned on is flowing through the light emitting element PC ₁ of the photocoupler PC. Thus, a signal indicating a reduced voltage state is transmitted from the secondary side to the control circuit 4 of the primary side, the control circuit 4 stops the switching operation of the switching element Q _1. Then, the outputs from the main output circuit 2 and the sub output circuit 3 (power supply by the main output circuit 2 and the sub output circuit 3) are stopped.

On the other hand, when the main output is overvoltage condition, as if the secondary output becomes reduced voltage condition, the constant voltage diode ZD ₁ is a breakdown state, current flows in the reverse direction of the zener diode ZD _1. As a result, the transistor Q ₂ is switched from the off state to the on state. Specifically, when the main output voltage _{V bb} is 26.2 (= 5 + 20 + 1.2 ) [V] or more, the transistor _{Q 2} is switched from off to on. As a result, the collector current of the transistor Q ₂ is flowing through the light emitting element PC ₁ of the photocoupler PC, is transmitted from a signal indicating the overvoltage condition secondary side to the control circuit 4 of the primary side, the control circuit 4 is a switching element Q ₁ The switching operation is stopped. Then, the outputs from the main output circuit 2 and the sub output circuit 3 are stopped.

  Eventually, according to the multi-output switching power supply device 1 according to the present embodiment, the voltage detection circuit 5 can detect the overvoltage state of the main output and the reduced voltage state of the sub output, thereby reducing the number of components. Can meet the demands for miniaturization and cost reduction.

  The preferred embodiment of the multi-output switching power supply device according to the present invention has been described above, but the present invention is not limited to the configuration of the above embodiment.

For example, in the above embodiment, the PNP transistor Q ₂ is used as the switching means of the voltage detection circuit 5, but another transistor may be used or a switching means other than the transistor may be used. .

Further, the switching element Q _1, and the control circuit 4 for controlling the switching element Q _1, or may be constituted by a single of the IC.

DESCRIPTION OF SYMBOLS 1 Multi-output type switching power supply 2 Main output circuit 3 Sub output circuit 4 Control circuit 5 Voltage detection circuit PC Photocoupler (transmission means)
Q ₁ FET (switching element)
Q ₂ transistor (switching means)
R ₁ first resistor R ₂ second resistor ZD ₁ constant voltage diode (voltage difference detection element)

Claims (5)

The switching element connected to the primary winding of the transformer is switched under the control of the control circuit to induce an alternating voltage in the secondary winding of the transformer, and the main output voltage obtained by converting the alternating voltage into a direct current is output. A main output circuit that
A slave output circuit that outputs a slave output voltage obtained by stepping down the master output voltage;
A multi-output type switching power supply device comprising:
The main output circuit is:
A voltage detection circuit for detecting an overvoltage state of the main output voltage and a reduced voltage state of the sub output voltage;
A transmission means for transmitting a signal indicating an overvoltage state or a reduced voltage state to the control circuit when the voltage detection circuit detects an overvoltage state or a reduced voltage state;
Have
The voltage detection circuit includes switching means for switching from an off state to an on state when the main output voltage is in an overvoltage state or the sub output voltage is in a reduced voltage state,
When the switching unit is turned on, the control circuit receives the signal from the transmission unit, stops the switching operation of the switching element, and stops output from the main output circuit and the sub output circuit A multi-output type switching power supply device characterized in that The voltage detection circuit includes:
It is interposed between the main output circuit and the slave output circuit, detects a voltage difference between the master output voltage and the slave output voltage, and switches between a conducting state and a non-conducting state according to the voltage difference. A voltage difference detecting element;
The voltage difference detecting element is switched from a non-conductive state to a conductive state to detect an overvoltage state of the main output voltage or a reduced voltage state of the sub output voltage, and switches the switching unit from an off state to an on state. The multi-output type switching power supply device according to claim 1. The voltage difference detecting element is a constant voltage diode,
3. The multi-output switching power supply device according to claim 2, wherein a cathode side of the constant voltage diode is connected to the main output circuit, and an anode side is connected to the sub output circuit. The switching means is a PNP type transistor,
A base of the transistor is connected to a high potential side of the output of the main output circuit via a first resistor, and is connected to a cathode side of the constant voltage diode via a second resistor;
The emitter of the transistor is connected to the high potential side of the output of the main output circuit;
4. The multi-output switching power supply device according to claim 3, wherein a collector of the transistor is connected to the transmission means. The transmission means is a photocoupler;
5. The multi-output type according to claim 1, wherein the photocoupler transmits the signal to the control circuit by detecting a current supplied from the switching unit that is turned on. 6. Switching power supply.

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