JP2003174771A - Switching power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stop the operation of a switching power supply when abnormal temperature is detected and thereafter keep the power supply from returning without increase in the number of parts. <P>SOLUTION: Main input terminals 10 are connected with a rectifier 16 and an input smoothing capacitor 17 for rectifying and smoothing alternating current with a fuse element 15 in-between. A control circuit 18 has a switching signal generation circuit 31 including an oscillator, an overheat protection circuit 32, and a NOR circuit 33 which outputs the output signals thereof to the gate of a switching element 12. The overheat protection circuit 32 includes an overheat temperature detection circuit 32a, a restarting circuit 32b, and an RS flip flop circuit 32c. The RS flip flop circuit 32c receives output signals from the overheat temperature detection circuit 32a at a set terminal S and output signals from the restarting circuit 32b at a reset terminal R, and outputs the results of these computations to the NOR circuit 33 through an noninverting output terminal Q. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply device, and more particularly to a switching power supply device having a heating protection function.

[0002]

2. Description of the Related Art A conventional switching power supply device having a heat protection function will be described below with reference to the drawings.

(First Conventional Example) FIG. 2 shows a circuit configuration of a switching power supply device according to the first conventional example in which an input side and an output side are electrically insulated by a transformer.

The switching power supply device according to the first conventional example is for power conversion, and has a primary winding 101a and a control winding 101.
b, a transformer 101 including a secondary winding 101c, and a switching element 1 connected to the first primary winding 101a.
02 and a control circuit 103 for controlling the operation of the switching element 102.

A fuse element 105 is provided between the primary winding 101a of the transformer 101 and the main input terminal 104 of the device.
The rectifier 106 and the input smoothing capacitor 107 are connected.

In the secondary winding 101c of the transformer 101,
An output rectifying / smoothing circuit 108 including a diode and a capacitor is provided, and the output rectifying / smoothing circuit 108 is connected to the load 109.

In the control winding 101b of the transformer 101,
Control circuit rectifying / smoothing circuit 110 including a diode and a capacitor for supplying a control current to the control circuit 103.
Is provided.

The control circuit 103 has a switching signal generation circuit 121 including an oscillator and a heating protection circuit 122, which are a NAND circuit 123 and a drive circuit 12.
4 is connected to the gate of the switching element 102.

Here, for example, the switching element 102
When the temperature of the switching element 102 rises abnormally due to the failure of the above, the heating temperature detection circuit 125 included in the heating protection circuit 122 outputs a high level signal to the set terminal of the RS flip-flop circuit 126. .
At this time, a low level signal is output from the inverting output terminal of the RS flip-flop circuit 126 to the NAND circuit 123, so that the switching operation of the switching element 102 is stopped. After that, for example, if the power supply voltage of the control circuit 103 is lowered by temporarily cutting off the voltage of the input power supply or the like, a high level signal from the restart circuit 127 is output to the reset terminal of the RS flip-flop circuit 126. . Therefore, when the input power is turned on again, the switching operation of the switching element 102 is restored.

As described above, in the switching power supply device according to the first conventional example, when the temperature of the switching element 102 rises due to some abnormality, the heating protection circuit 122.
As a result, the operation of the switching element 102 is stopped, so that the abnormality of the switching power supply device can be prevented from spreading, and the stopped state of the device is maintained unless the device is disconnected from the input power supply.

(Second Conventional Example) FIG. 3 shows a circuit configuration of a switching power supply device according to a second conventional example. Figure 3
In the above, the same components as those of the first conventional example are designated by the same reference numerals and the description thereof will be omitted. As shown in FIG. 3, in addition to the fuse element 105 of the entire device, a temperature fuse element 111 is provided between the control winding 101b and the control circuit 103.

The thermal fuse element 111 is attached to, for example, a heat radiating plate of the switching element 102, detects the temperature of the switching element 102 via the heat radiating plate, and blows when the detected temperature exceeds a predetermined temperature. Therefore, the control current is not supplied to the control circuit 103, and the operation of the switching element 102 is stopped.

As described above, in the switching power supply device according to the second conventional example, when the temperature of the switching element 102 rises due to some abnormality of the device, the temperature fuse element 111 is blown, so that the switching element 10
The operation of the device 2 is stopped and the operation of the device is not restored.

(Third conventional example) FIG.
The circuit structure of the switching power supply device which concerns on the 3rd prior art example described in the 153 publication is shown. In this publication,
There is disclosed a protection circuit that blows the fuse element 4 when the temperature of the switching element 2 exceeds a predetermined value.

As shown in FIG. 4, a temperature detector 11 attached to a heat dissipation plate of the switching element 2 for detecting the temperature of the switching element 2 and a conduction state of the switching element 2 upon receiving an output of the temperature detector 11. And a gate means including a thyristor 16 for melting the fuse element 4 by holding.

[0016]

However, in the switching power supply device according to the first conventional example, the switching operation is restored when the input power is turned on again without removing the defective component, so that the normal operation is achieved. There is a problem in that it is impossible to prevent secondary destruction in which even parts are destroyed.

In the switching power supply device according to the second conventional example, the operation of the device itself is not restored once an abnormality occurs due to the melting of the temperature fuse element 111.
Although secondary destruction does not occur, since the thermal fuse element 111 needs to be newly provided, there is a problem that the number of parts increases, which hinders miniaturization and causes a cost increase.

Further, in the switching power supply device according to the third conventional example, since the temperature detector 11 is attached to the heat dissipation plate of the switching element 2, the switching element 2
There is a problem that the temperature of itself cannot be detected. Furthermore, it is necessary to newly provide a gate means for holding the switching element 2 in a conducting state at the time of abnormality, which causes a problem that the number of parts increases or the cost increases.

Further, in the case of a switching power supply device having a relatively small power supply capacity of about 10 W of output power, a heat sink is generally not provided in the switching element, so that it is necessary to provide a heat sink for the temperature detector 11. Occurs.

It is an object of the present invention to solve the above-mentioned conventional problems, and to stop the operation of the switching power supply device and prevent the operation from recovering once the abnormal temperature is detected without increasing the number of parts.

[0021]

To achieve the above object, a first switching power supply device according to the present invention comprises a transformer, an input terminal of which is connected to a primary winding of the transformer. A switching element that receives a first DC voltage via
Output voltage generation that is connected to the secondary winding of the transformer and rectifies and smoothes the output voltage on the secondary side of the transformer to generate and output the second DC voltage from the first DC voltage. A circuit and a control circuit for controlling the operation of the switching element,
A control circuit connected to a control winding of a transformer to generate a primary-side output voltage that is proportional to a secondary-side output voltage, and rectify and smooth the generated primary-side output voltage. And a fuse element provided between the transformer and an input side of the transformer, the control circuit generates and outputs a switching signal to be applied to the switching element. The switching signal generating circuit, the temperature detecting circuit that detects the temperature of the switching element, and the conduction holding unit that holds the conduction of the switching element based on the output signal from the temperature detecting circuit.

According to the first switching power supply device, the control circuit includes a temperature detection circuit for detecting the temperature of the switching element and a continuity holding means for holding the conduction of the switching element based on the output signal from the temperature detection circuit. Therefore, when the temperature detection circuit detects a heating abnormality, the switching element continues to conduct without performing a switching operation, so that the fuse element itself generates heat to melt the fuse element. As a result, it is possible to prevent the operation from being restored when the temperature is abnormal due to a failure without adding a new component to the conventional switching power supply device having the transformer and having the heating protection circuit.

A second switching power supply device according to the present invention comprises a transformer, a switching element whose input terminal is connected to the primary winding of the transformer, and which receives the first DC voltage via the transformer, and a transformer. Is connected to the secondary winding of the transformer and rectifies and smoothes the output voltage on the secondary side of the transformer.
Connected to the output voltage generation circuit that generates and outputs the second DC voltage from the DC voltage, the control circuit that controls the operation of the switching element, and the control winding of the transformer, and is proportional to the output voltage on the secondary side. And a power supply voltage generation circuit that generates a power supply voltage for the control circuit by rectifying and smoothing the generated output voltage on the primary side. A switching signal generation circuit that generates and outputs a switching signal applied to the switching element, a temperature detection circuit that detects the temperature of the switching element, and a conduction that maintains the conduction of the switching element based on the output signal from the temperature detection circuit. Holding means and
The input terminal or the output terminal of the switching element is connected to the external terminal by a wire that melts and cuts in a conductive and held state.

According to the second switching power supply device, the control circuit includes a temperature detection circuit for detecting the temperature of the switching element and a conduction holding means for holding the conduction of the switching element based on the output signal from the temperature detection circuit. In addition, since the input terminal or output terminal of the switching element is connected to the external terminal by a wire that melts and cuts in a conductive holding state, when the temperature detection circuit detects a heating abnormality, the switching element switches Since the wire continues to conduct without performing any operation, the wire is melted by the heat generated by the wire itself. As a result, it is possible to prevent the operation from being restored when the temperature is abnormal due to a failure without adding a new component to the conventional switching power supply device having the transformer and having the heating protection circuit.

In the first or second switching power supply device, it is preferable that the continuity holding means is an RS flip-flop circuit. In this way, the RS flip-flop circuit can hold (latch) the input signal, and therefore, it is necessary to hold the switching element in the conductive state.
A simple structure and reliable operation can be performed without using a special circuit.

In the first or second switching power supply device, the switching element and the control circuit are arranged on one semiconductor substrate such that the input terminal and the output terminal of the switching element and the control terminal of the control circuit are external connection terminals. It is preferable that they are integrated and formed. With this configuration, the switching element and the control circuit can be integrated into one chip, so that the number of parts can be significantly reduced and the size of the device can be reduced.

In the first or second switching power supply device, the switching element and the control circuit are housed in one package such that the input terminal and the output terminal of the switching element and the control terminal of the control circuit are external connection terminals. Are preferably formed. In this way, the switching element and the control circuit can be packaged in one package, so that the number of parts can be reduced and the size of the device can be reduced.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic circuit configuration of a switching power supply device according to an embodiment of the present invention.

As shown in FIG. 1, the switching power supply device according to this embodiment uses a transformer for a first DC voltage applied to the main input terminal 10, which is obtained by rectifying and smoothing an AC current from a commercial power supply, for example. While being applied to the primary side of the (transformer) 11, the output voltage generation circuit 13 provided on the secondary side of the transformer 11 is the second DC voltage by the switching operation by repeating the on / off operation of the switching element 12. The switching power supply device outputs a desired output voltage to the main output terminal 14.

The switching power supply device will be described in detail below.

The transformer 11 is composed of a primary winding 11a, a control winding 11b and a secondary winding 11c.

A rectifier 16 composed of a diode bridge or the like for rectifying an alternating current through a fuse element 15 and an input smoothing capacitor 17 for smoothing a rectified signal to generate a direct current voltage are connected in parallel to the main input terminal 10. It is connected to the. The generated DC voltage is input to the primary winding 11a of the transformer 11 and then, for example, N-type power MOSFE
It is input to the drain terminal T _D of the switching element 12 made of T. Source terminal T _S of switching element 11
Is connected to the cathode terminal of the input smoothing capacitor 17, and the control signal from the control circuit 18 for controlling the operation of the switching element 12 is input to the gate thereof.

The switching power supply device according to the present embodiment may have a structure in which the rectifier 16 is not provided. In that case, the first DC voltage may be rectified in advance and then input to the main input terminal 10. In addition, the fuse element 1
5 is provided between the input smoothing capacitor 17 and the primary winding 11a of the transformer 11.

An output voltage generation circuit 13 is connected to the secondary winding 11c of the transformer 11. The output voltage generation circuit 13 smoothes the rectified signal and a first diode 13a that rectifies a current due to an electromotive force generated by magnetic induction of a first DC voltage that is applied to the primary winding 11a and switched. And a first output capacitor 13b that outputs a second DC voltage.

A load 19 is connected between the high-level side terminal and the low-level side terminal of the main output terminal 14 connected to the output voltage generating circuit 16.

In the control winding 11b of the transformer 11, a power supply voltage generation circuit 20 which generates an output voltage on the primary side proportional to the output voltage on the secondary side and supplies the output voltage to the control circuit 18 as a control current. Is provided.

The power supply voltage generation circuit 20 includes a control winding 11b.
Second diode 20a for rectifying the output voltage on the primary side generated in the second and second for smoothing and outputting the rectified signal
Output capacitor 20b.

In the present embodiment, the area surrounded by the broken line 40, that is, the switching element 12 and the control circuit 18
And a drain terminal T _D and a source terminal T _{S of} the switching element 12 and an input terminal of the control circuit 18, which is externally connected to at least three terminals of a control terminal T _C that receives a control current from the power supply voltage generation circuit 20. Can be input and output. Here, a region including the drain terminal T _D , the source terminal T _S, and the control terminal T _C is referred to as a substrate formation region 40, which means that the substrate formation region 40 can be formed on one semiconductor chip. ing. The on-substrate formation region 40 may be divided into a plurality of semiconductor chips instead of being formed on one semiconductor chip. However, even when the semiconductor chip is divided into a plurality of semiconductor chips, in order to reduce the size, the above-mentioned three terminals T _D , T _S , and T
It is preferable to store them in one package that allows external connection with _C.

The control circuit 18 has an oscillation frequency of, for example, 10
Generates and outputs a switching signal of about 0 kHz
Switching signal generation circuit 31 including a shaker and heating protection
Circuit 32 and NOR circuit 33 that receives these output signals
And receives the output of the NOR circuit 33, amplifies it, and switches it.
The inverter element that outputs to the gate of the switching element 12
Drive circuit 34 for driving. In addition, the drain
Terminal T_D And control terminal T _C Internal circuit current supply between
The circuit 35 is provided, and the internal circuit current supply circuit 3 is provided.
5 is an operation for starting from the primary winding 11a when the apparatus is started
An electric current is supplied to the control circuit 18.

The heating protection circuit 32 is the heating temperature detection circuit 3
2a, restart circuit 32b, and R as continuity holding means
It is composed of an S flip-flop circuit 32c.
The RS flip-flop circuit 32c receives the output signal from the heating temperature detection circuit 32a at the set terminal S, the output signal from the restart circuit 32b at the reset terminal R, and outputs the operation result of the received signal to the non-inversion output terminal Q. To NOR circuit 3
Output to 3.

In the switching power supply device configured as described above, when the temperature of the switching element 12 rises abnormally due to a failure of the switching element 12 or the like, for example, the heating temperature detection circuit 32a outputs a high level signal. , And is input to the set terminal S of the RS flip-flop circuit 32c. As a result, the NOR circuit 33 is transferred from the non-inverting output terminal Q of the RS flip-flop circuit 32c.
A high level signal is output to the switching element 1
Since the gate of 2 is latched at a high level, the switching element 12 stops its switching operation and is held in a conductive state. At this time, if the switching element 12 continues to conduct, the fuse element 15 melts due to its own heat generation, and the operation of the switching power supply device stops.

As described above, when some abnormality occurs in the switching power supply and the temperature of the switching element 12 rises abnormally, the heating temperature detection circuit 32a and the RS flip-flop circuit 32c cause the switching element 12 to conduct. The state is maintained, and the fuse element 15 is blown. As a result, the switching operation of the switching element 12 is completely stopped, so that it is possible to prevent the operation from being restored when the temperature is abnormal due to a failure. As a result, the switching power supply device has almost the same configuration as the switching power supply device according to the first conventional example, and the switching power supply device can be completely stopped by detecting the abnormal temperature once without adding a new component. Therefore, it is possible to prevent the abnormal portion from expanding to the device.

The fuse element 15 is used to detect an abnormal temperature.
Instead of using the wire, a wire used for connection between the drain terminal T _D of the switching element 12 and a drain pad on the semiconductor chip (not shown) or the source terminal T _S of the switching element 12 and the drain terminal on the semiconductor chip (not shown). The wire used for connection with the source pad may be provided by selecting the diameter and the number of wires so that the wire is blown when an abnormal temperature is detected.

[0045]

According to the switching power supply device of the present invention, when the temperature detecting circuit detects a heating abnormality, the switching element maintains the conducting state without performing the switching operation and the fuse element is blown, so that the transformer It is possible to prevent the operation from being restored when a temperature abnormality is caused by a failure without adding a new component to the conventional switching power supply device having the heating protection circuit.

[Brief description of drawings]

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

FIG. 2 is a schematic circuit diagram showing a switching power supply device according to a first conventional example.

FIG. 3 is a schematic circuit diagram showing a switching power supply device according to a second conventional example.

FIG. 4 is a circuit diagram showing a switching power supply device according to a third conventional example.

[Explanation of symbols]

10 Main Input Terminal 11 Transformer (Transformer) 11a Primary Winding 11b Control Winding 11c Secondary Winding 12 Switching Element 13 Output Voltage Generation Circuit 13a First Diode 13b First Output Capacitor 14 Main Output Terminal 15 Fuse Element 16 rectifier 17 input smoothing capacitor 18 control circuit 19 load 20 power supply voltage generation circuit 20a second diode 20b second output capacitor 31 switching signal generation circuit 32 heating protection circuit 32a heating temperature detection circuit 32b restart circuit 32c RS flip-flop circuit (Conduction holding means) 33 NOR circuit 34 Drive circuit 35 Internal circuit Current supply circuit 40 Substrate formation region T _D Drain terminal T _S Source terminal T _C Control terminal

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazuharu Hayashi             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F term (reference) 5H730 AA20 BB43 CC01 DD04 DD22                       EE07 VV06 XX19 XX38 XX43

Claims (5)

[Claims] 1. A transformer, a switching element whose input terminal is connected to the primary winding of the transformer, and which receives a first DC voltage via the transformer, and a secondary winding of the transformer. An output voltage generation circuit that is connected and that rectifies and smoothes the output voltage on the secondary side of the transformer to generate and output a second DC voltage from the first DC voltage; and the switching element. Connected to the control winding of the transformer to generate an output voltage on the primary side that is proportional to the output voltage on the secondary side, and to output the generated output voltage on the primary side. The control circuit includes: a power supply voltage generation circuit that generates a power supply voltage of the control circuit by rectifying and smoothing; and a fuse element provided between the transformer and an input side of the transformer. Is applied to the switching element A switching signal generation circuit that generates and outputs an switching signal, a temperature detection circuit that detects the temperature of the switching element, and a conduction holding unit that holds the conduction of the switching element based on an output signal from the temperature detection circuit. And a switching power supply device. 2. A transformer, a switching element whose input terminal is connected to the primary winding of the transformer, and which receives a first DC voltage via the transformer, and a secondary winding of the transformer. An output voltage generation circuit that is connected and that rectifies and smoothes the output voltage on the secondary side of the transformer to generate and output a second DC voltage from the first DC voltage; and the switching element. Connected to the control winding of the transformer to generate an output voltage on the primary side that is proportional to the output voltage on the secondary side, and to output the generated output voltage on the primary side. A power supply voltage generation circuit that generates a power supply voltage of the control circuit by rectifying and smoothing, and the control circuit generates a switching signal to be applied to the switching element and outputs the switching signal. , The temperature detection circuit for detecting the temperature of the switching element, and, based on the output signal from the temperature detection circuit, has a conduction holding means for holding the conduction of the switching element, the input terminal or the output terminal of the switching element Is connected to an external terminal by a wire that melts and cuts while maintaining electrical continuity. 3. The switching power supply device according to claim 1, wherein the continuity holding means is an RS flip-flop circuit. 4. The switching element and the control circuit are integrated and formed on one semiconductor substrate such that the input terminal and the output terminal of the switching element and the control terminal of the control circuit are external connection terminals. The switching power supply device according to claim 1, wherein the switching power supply device is provided. 5. The switching element and the control circuit are formed by being housed in one package so that an input terminal and an output terminal of the switching element and a control terminal of the control circuit are external connection terminals. 4. The switching power supply device according to claim 1, wherein the switching power supply device is a switching power supply device.