JPH11168880A - Power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply unit which is capable of improving its safety, wherein abnormal heating and burning of the transistor of its output- voltage controlling element are avoided in the case of its output side short- circuiting. SOLUTION: In this apparatus, making a pulse form its DC input voltage through the switching operation of a switching element Q1, controlled through a switching control circuit 10 with its output side short-circuit protective function, the pulses are fed to a transformer T1 to output its DC output voltage via its rectification-smoothing circuit provided on the secondary side of the transformer T1. Furthermore, an output-current control transistor Q2 is provided on the secondary side of the transformer T1. In this case, providing a diode D3 connected in forward direction, in parallel with the transistor Q2 wherethrough an output current not smaller than the one determined by the rated voltage of the transistor Q2 bypasses the transistor Q2, the overcurrent of the transistor Q2 accompanied by the output side short-circuit of this apparatus is made to share with the diode D3 to avoid the output side current limiting action of the transistor Q2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a power supply device,
More specifically, the present invention relates to a power supply device having an output short-circuit protection function and employing a series regulator system for stabilizing an output voltage.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a conventional series regulator type power supply device.

This power supply device has a transformer (transformer) T1 having a primary winding Ni and two secondary windings N1 and N2.
And a switching element (FET) controlled by a switching control circuit 10 to apply a DC voltage from an input power supply E to a primary winding Ni of the transformer (transformer) T1.
An intermittent pulse voltage is supplied by the switching operation of Q1.

[0004] A current detection resistor R1 is connected to the primary side of the transformer T1. A main output circuit S11 and a sub output circuit S12 are provided on the secondary side of the transformer T1.

The main output circuit S11 includes a rectifier diode D for converting a pulse voltage induced in the secondary winding N1 into a DC voltage.
1 and a smoothing capacitor C1.

The sub-output circuit S12 has a rectifier diode D2 and a smoothing capacitor C2 for converting a pulse voltage induced in the secondary winding N2 into a DC voltage, a collector at the cathode of the rectifier diode D2, and an output terminal O2. And a smoothing capacitor C3
And a control circuit 11 for detecting the output voltage of the sub output circuit S12 and controlling the base potential of the transistor Q2.

Further, the power supply device includes a main output circuit S11
A detection circuit 12 for detecting the output voltage of the
And a photocoupler 13 for sending the detection voltage of No. 2 to the switching control circuit 10 by photoelectric coupling.

In this power supply, upon receiving a control pulse generated from the switching control circuit 10, the switching element Q1 performs a switching operation. Switching element Q
The pulse voltage generated by switching operation 1 is
The power is transmitted to the secondary windings N1 and N2 via the transformer T1.

The pulse voltages transmitted to the secondary windings N1 and N2 are converted to DC voltages by the main output circuit S11 and the sub output circuit S12, respectively.

The output voltage of the main output circuit S11 is
2 and a detection signal from the detection circuit 12 is transmitted via the photocoupler 13 to the primary side switching control circuit 10.
Is transmitted to The switching control circuit 10 varies the pulse width of the control signal supplied to the gate of the switching element Q1 based on the detection signal, and adjusts the output voltage of the main output circuit S11 to be always constant.

On the other hand, the sub-output circuit S12 is adjusted so that the output voltage output to the output terminal O2 by the operation of the control circuit 11 and the voltage control element Q2 is always constant. Further, the smoothing capacitor C2 smoothes the output voltage from the voltage control element Q2 and stabilizes it.

In the power supply device having such a configuration, for example, the output current increases due to the short-circuit of the output of the sub-output circuit S12, and the current flowing through the switching element Q1 also increases. At this time, a similar current flows through the current detection resistor R1 connected in series with the switching element Q1, and the voltage across the both ends increases. The switching control circuit 10 connected to the current detection resistor R1 supplies the current detection resistor R1
When the voltage at both ends of the power supply is input and the voltage reaches a certain value, the switching control circuit 10 stops the control signal and stops the switching element Q1, thereby protecting the output of the power supply device in the event of a short circuit. Is being planned.

[0013]

The above-mentioned sub-output circuit S
The method used for stabilizing the output voltage of 12 is the series regulator method. In the case of this method, when the output of the sub-output circuit S12 is short-circuited depending on the characteristics of the transistor Q2, the output current of the sub-output circuit S12 is limited by the current limiting action due to the resistance of the transistor Q2. The current flowing through the switching element Q1 on the side becomes smaller, and the voltage across the current detection resistor R1 also becomes
The switching control circuit 10 does not reach a voltage for exhibiting the output short-circuit protection function.

In such a state, there is a problem that the switching element Q1 of the power supply device continues to operate, the resistance loss of the transistor Q2 increases, and abnormal heating or burning occurs.

The present invention has been made in view of the above circumstances, and provides a power supply device capable of avoiding abnormal heating or burning of an output voltage control element and improving safety when an output side is short-circuited. It is intended to provide.

[0016]

According to the first aspect of the present invention,
In a power supply device that converts a DC input voltage by a series regulator type DC-DC converter circuit including an output voltage control element and outputs it as a DC output voltage, a rated voltage of the output voltage control element is provided in parallel with the output voltage control element. And a current bypass element for bypassing an output current equal to or larger than the output current determined by the following equation.

According to the present invention, a current bypass element for bypassing an output current equal to or more than an output current determined by the rated voltage of the output voltage control element is connected in parallel with the output voltage control element provided in the series regulator type power supply device. Therefore, even when the output side is short-circuited and the output current abnormally rises, the output current equal to or higher than the output current determined by the rated voltage of the output voltage control element flows through the current bypass element.
An abnormal overcurrent does not flow through the output voltage control element, thereby making it possible to avoid abnormal heating of the output voltage control element and improve safety.

According to a second aspect of the present invention, the DC input voltage is
The switching operation of a switching element controlled by a switching control circuit having an output short-circuit protection function supplies pulses to the transformer in the form of a pulse, and outputs a DC output voltage by a rectifying and smoothing circuit provided on the secondary side of the transformer. A power supply device including a transistor for controlling an output current on a secondary side of a transformer, comprising: a diode connected to the transistor in a forward direction and diverting an output current equal to or more than an output current determined by a rated voltage of the transistor; The overcurrent caused by the above is shared by the diode to avoid the output current limiting action of the transistor.

According to the present invention, the diode is connected to the transistor in the forward direction so as to bypass an output current equal to or larger than the output current determined by the rated voltage of the transistor. Even if the voltage rises abnormally, an output current higher than the output current determined by the rated voltage of the transistor flows to the diode, and an abnormal overcurrent does not flow to the transistor, thereby avoiding abnormal heating of the transistor. It is possible to improve safety.

[0020]

Embodiments of the present invention will be described below in detail.

FIG. 1 shows a power supply according to an embodiment of the present invention. In this power supply, those having the same functions as those of a conventional power supply are denoted by the same reference numerals.

The power supply according to the present embodiment has a primary winding Ni and two secondary windings N1 and N2, like the conventional power supply.
(Transformer) T1 provided with an input power supply E to the primary winding Ni of the transformer (transformer) T1.
The DC voltage is supplied as an intermittent pulse voltage by a switching operation of a switching element (FET) Q1 controlled by a switching control circuit 10.

A current detecting resistor R1 is connected to the primary side of the transformer T1. On the secondary side of the transformer T1, a main output circuit S11 similar to the conventional example and a sub output circuit S2 unique to the present embodiment are provided.

The main output circuit S11 has the same configuration as the conventional example shown in FIG.

The sub-output circuit S2 has substantially the same configuration as the conventional example shown in FIG. That is, the sub output circuit S2
A rectifier diode D2 and a smoothing capacitor C2 for converting a pulse voltage induced in the secondary winding N2 of the transformer T1 into a DC voltage, an output having a collector connected to the cathode of the rectifier diode D2 and an emitter connected to the output terminal O2. A transistor Q2 as a voltage control element, a smoothing capacitor C3, a control circuit 11 for detecting an output voltage of the sub output circuit S2 and controlling a base potential of the transistor Q2;
The transistor Q2 has a diode D3 which is a current bypass element having an anode connected to the collector and a cathode connected to the emitter.

The transistor Q2 and the diode D3 are set so that the voltage between the collector and the emitter of the transistor Q2 is lower than the forward voltage of the diode D3.

Further, this power supply device has a detection circuit 12 for detecting an output voltage of a main output circuit S11 similar to the conventional example shown in FIG. 2, and a detection voltage of the detection circuit 12 by photoelectric coupling. And a photocoupler 13 for sending out the photocoupler.

Next, the operation of the power supply according to the present embodiment will be described.

In this power supply device, the switching operation of the switching element Q1 during normal operation, the operation of the secondary windings N1 and N2 of the transformer T1, the main output circuit S11
The operation of the sub-output circuit S2 is the same as that of the conventional example shown in FIG.

The output voltage of the main output circuit S11 is monitored by a detection circuit 12, and a detection signal from the detection circuit 12 is transmitted to a primary-side switching control circuit 10 via a photocoupler 13, and the switching control circuit FIG. 2 also shows the operation of changing the pulse width of the control signal supplied to the gate of the switching element Q1 based on the detection signal so that the output voltage of the main output circuit S11 is always constant. This is the same as in the case of the conventional example.

Further, the sub output circuit S2 is connected to the control circuit 11
In addition, the operation of the voltage control element Q2 is adjusted so that the output voltage is always constant, and the smoothing capacitor C2 smoothes the output voltage from the voltage control element Q2 to make it more stable. This is the same as in the example.

During such normal operation, the voltage difference between the collector and the emitter of transistor Q2 is
3, the output current flows only to the transistor Q2 side and does not flow to the diode D3 side as shown by the solid line in FIG.

In such a power supply device, for example, when the output of the sub-output circuit S2 is short-circuited for some reason, first,
A current flows through the transistor Q2 so that the voltage difference between its collector and emitter becomes equal to the forward voltage of the diode D3.
The increase in the output current flows to the diode D3 side as indicated by the dotted line in FIG. 1, and the output current no more than the value determined by the voltage difference between the collector and the emitter does not flow to the transistor Q2 side.

As a result, the output current limiting effect of the transistor Q2 is eliminated, and the current detecting resistor R1 has
A sufficient current flows for the short-circuit protection function of the power transistor Q1 on the primary side to operate, and the switching control circuit 1
The voltage at both ends of the current detection resistor R1 is input to 0, and when this voltage reaches a certain value, the switching control circuit 10 stops the control pulse and stops the switching element Q1. As a result, abnormal heating of the transistor Q2 can be prevented.

Further, since an overcurrent is prevented from flowing through the transistor Q2, it is not necessary to use an element having a higher rating than necessary as the transistor Q2.

[0036]

According to the first aspect of the present invention, even when the output side is short-circuited and the output current rises abnormally, an output current that is equal to or greater than the output current determined by the rated voltage of the transistor flows through the current bypass element. Therefore, an abnormal overcurrent does not flow through the output voltage control element,
A power supply device capable of avoiding abnormal heating of the output voltage control element and improving safety can be provided.

According to the second aspect of the present invention, even when the output side is short-circuited and the output current abnormally rises, an output current that is equal to or greater than the output current determined by the rated voltage of the transistor flows through the diode, An abnormal overcurrent does not flow through the transistor, thereby providing a power supply device capable of avoiding abnormal heating of the transistor and improving safety.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of a conventional power supply device.

[Explanation of symbols]

 Reference Signs List 10 switching control circuit 11 control circuit 12 detection circuit 13 photocoupler E input power supply T1 transformer R1 current detection resistor Q1 switching element Q2 transistor D1 rectifier diode D2 rectifier diode D3 diode C1 smoothing capacitor C2 smoothing capacitor C3 smoothing capacitor S11 main output circuit S2 sub Output circuit

Claims (2)

[Claims] 1. A power supply device for converting a DC input voltage by a series-regulator type DC-DC converter circuit including an output voltage control element and outputting the converted voltage as a DC output voltage, wherein the output voltage is controlled in parallel with the output voltage control element. A power supply device, wherein a current bypass element for bypassing an output current equal to or greater than an output current determined by a rated voltage of a control element is connected. 2. A rectifying / smoothing circuit provided on a secondary side of a transformer, wherein a DC input voltage is supplied to a transformer in a pulse form by a switching operation of a switching element controlled by a switching control circuit having an output short-circuit protection function. In the power supply device having a transistor for output current control on the secondary side of the transformer, the output current is not less than the output current determined by the rated voltage of the transistor connected to the transistor in the forward direction. A power supply device, comprising: a diode that bypasses the output current, and sharing an overcurrent caused by an output short-circuit with the diode to avoid an output current limiting action of the transistor.