JPH05184142A - Switching power supply and composite element therefor - Google Patents

Abstract

PURPOSE:To prevent occurrence of overvoltage by detecting abnormal heating of a constant voltage diode for detecting control voltage and then interrupting the output. CONSTITUTION:A ringing choke converter(RCC) circuit comprises an input capacitor C1, a transformer T, a switching transistor Q1 connected with the primary winding NP of the transformer to turn the voltage induced in the base winding NB ON/OFF, and a circuit 10 for rectifying/smoothing the output of a secondary winding NS. Furthermore, a constant voltage control section 12 is built in the base circuit of the switching transistor Q1. A temperature fuse F is inserted into the base section of the switching transistor Q1 and mounted closely to a constant voltage diode ZD1 for detecting the control voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an RCC (ringing choke converter) type switching power supply having an overvoltage protection function for detecting abnormal heat generation and shutting off the output. More specifically, the temperature fuse is inserted in the base portion of the switching transistor and is brought close to the constant voltage diode for the control voltage, and the temperature fuse is blown by the abnormal heat generation of the constant voltage diode to cause the oscillation operation of the switching transistor. The present invention relates to a switching power supply device that is stopped and a composite element used for the same.

[0002]

2. Description of the Related Art An RCC type switching power supply is a self-excited single switching power supply that uses blocking oscillation, has a small number of circuit components, is inexpensive, and is widely used for small electric power.

FIG. 3 shows an example of a typical conventional switching power supply device. This power supply is an RCC circuit incorporating an overvoltage protection circuit. The RCC circuit includes an input capacitor C ₁ , a transformer T, a switching transistor Q ₁ connected to a primary winding N _P of the transformer T, which is turned on / off by an induced voltage of a base winding N _B , and a secondary winding N _S. A rectifying / smoothing circuit 10 for converting the output from the above into a direct current is provided.
Further, it has a constant voltage control unit 12 incorporated in the base circuit of the switching transistor Q ₁ and a reset circuit 14 for setting the exciting current of the primary winding N _P to the initial state.

A starting resistor R _S , a base resistor R _B and a speed-up capacitor C ₁ are connected to the base of the switching transistor Q ₁ . Constant voltage controller 12
Is composed of a constant voltage diode ZD ₁ for detecting an overvoltage, a smoothing capacitor C ₃ , a resistor R _1, and a diode D.

Although the operation of the RCC circuit is well known, the outline thereof is as follows. The induced voltage of the base winding N _B of the transformer T is used to turn on / off the switching transistor Q ₁ and the resulting voltage. Is rectified and smoothed on the secondary side to obtain a desired DC voltage. Then, the constant voltage controller 12 controls the RC
Stabilizes the output of the C circuit. When the output voltage rises,
The induced voltage of the base winding N _B also rises, and the DC control voltage by the diode D and the smoothing capacitor C ₃ also rises. Therefore, by conducting a constant voltage diode ZD ₁ for voltage detection, to reduce the base current of the switching transistors Q _1, increase the time to turn off the switching transistor Q _1. In this way, the output voltage is controlled to be constant.

However, if an excessive output voltage exceeding the control capability of the constant voltage control unit 12 is generated due to some abnormality, the load may be damaged and a large loss may occur in an instant. In particular, when an integrated circuit is used for the load, the damage is large because the degree of integration of the integrated circuit is improved and the power consumption is reduced. Therefore, an overvoltage protection circuit is required to cut off the output voltage immediately when such an overvoltage occurs.

The overvoltage protection circuit 16 is configured to detect an overvoltage on the secondary side of the transformer T and stop the switching operation on the primary side by the signal. The circuit built in the primary side is a series connection of a current limiting resistor R ₃ , a photo thyristor PTh (photo coupler of photo coupler) and a base bias resistor R ₄ between the input terminals, and a base emitter of a switching transistor Q _1. Between transistor switch Q
₂ is provided and its base is connected to the base bias resistor R ₄
And a parallel connection of a resistor R ₂ and a capacitor C ₄ is provided between the gate and cathode of the photo thyristor PTh. The circuit incorporated in the secondary side includes a current limiting resistor R ₅ , a series connection of a constant voltage diode ZD ₂ for overvoltage detection, and a base bias resistor R ₆ , and a collector resistor R ₇
And light emitting diode LED (light emitting element of photo coupler)
And a series connection of transistor switch Q _3, provided in parallel between the output terminal, in which the base of the transistor switch Q ₃ is connected to the base bias resistor R _6.

The operation of the overvoltage protection circuit 16 is such that when an overvoltage occurs, a constant voltage diode Z for detecting an overvoltage on the secondary side.
D ₂ is turned on, a current flows to the base of transistor switch Q _3, transistor switch Q ₃ is turned on,
A collector current flows and the light emitting diode LED emits light. This light is received by the photo thyristor PTh on the primary side to generate a current, the current flows through the gate of the photo thyristor PTh, and the photo thyristor PTh is turned on.
Current flows to the base of transistor switch Q _2, transistor switch Q ₂ is turned on, the base current of the switching transistor Q ₁ is rapidly pulled out. This keeps the switching transistor Q ₁ in the off state and shuts off the output of the power supply.

[0009]

An electrolytic capacitor is used as the smoothing capacitor C ₃ of the constant voltage controller 12 of the RCC circuit. The electrolytic capacitor has a property that a chemical change is internally generated due to aging, and the electrolytic solution is reduced to reduce the capacity. When the capacity of the electrolytic capacitor decreases due to secular change, the terminal voltage of the smoothing capacitor C ₃ rises, and at the same time, the voltage applied to the constant voltage diode ZD ₁ increases, and the constant voltage diode ZD ₁ generates heat. Due to this heat generation, the temperature gradually rises to about 150 to 200 ° C., and the constant voltage diode ZD ₁ may be destroyed by heat. At this time, if it is destroyed in the open mode, it becomes uncontrolled and the output voltage rises sharply. Further, even if the constant voltage diode ZD ₁ itself is not thermally destroyed, the abnormal heat generation burns out the pattern of the printed circuit board or causes ignition or smoke. If the pattern of the printed circuit board is burnt out, it will be an open mode breakdown, and as described above, the control voltage will be uncontrolled and the output voltage will rise sharply.

However, the conventional overvoltage protection circuit as described above cannot detect the occurrence of an abnormality until the output voltage rises because the constant voltage diode ZD ₁ is destroyed. In addition, since the photo coupler is used to transmit the overvoltage signal, there is a large operation delay, and the output cannot be immediately interrupted in response to a sudden increase in output, and there is a risk that the load will be destroyed. Further, this overcurrent protection circuit is complicated, has a large number of parts, and is expensive.

It is an object of the present invention to detect an abnormal heat generation of a constant voltage diode for detecting a control voltage and shut off the output to prevent an overvoltage from occurring, and a switching power supply device and a composite element used therefor. Is to provide.

[0012]

SUMMARY OF THE INVENTION The present invention is a switching power supply device having an RCC circuit and a constant voltage control section incorporated in the base section of a switching transistor of the RCC circuit. Here, the constant voltage control unit includes an electrolytic capacitor for smoothing the control voltage and a constant voltage diode for detecting the control voltage. The present invention has been made by focusing on the above-mentioned overvoltage generation mechanism in such a power supply device, that is, the capacitance decrease of the capacitor due to aging, and the phenomenon of abnormal heat generation of the constant voltage diode based on it.
It has a temperature fuse inserted in the base of the switching transistor and mounted close to the constant voltage diode, and when the abnormal voltage of the constant voltage diode is overheated, the temperature fuse is blown to stop the oscillation of the switching transistor. It is a feature.

In this power supply device, it is desirable to use a composite element in which a constant voltage diode and a thermal fuse are mounted in close proximity and housed in a heat-resistant case. The thermal fuse has a fusing temperature set to a temperature equal to or higher than the temperature at which the constant voltage diode abnormally generates heat and lower than a temperature at which the constant voltage diode is destroyed.

[0014]

The function of the smoothing electrolytic capacitor of the constant voltage control unit decreases with the lapse of time, and its terminal voltage rises. At the same time, the terminal voltage of the constant voltage diode also rises. Therefore, the constant voltage diode gradually generates heat. Since the thermal fuse is mounted close to the constant voltage diode,
Fusing due to abnormal heat generation of the constant voltage diode. Since the thermal fuse is inserted in the base portion of the switching transistor, the base current is cut off and the oscillation is stopped. As a result, an uncontrolled state and overvoltage are prevented from occurring.

[0015]

1 is a circuit diagram showing a preferred embodiment of the present invention. Since the basic circuit configuration of this switching power supply device is almost the same as that shown in FIG. 3, corresponding parts are designated by the same reference numerals, and description thereof will be omitted.

The feature of the present invention resides in that the temperature fuse F is inserted in the base portion of the switching transistor Q ₁ and mounted in the vicinity of the constant voltage diode ZD ₁ for detecting the control voltage, which is a complicated conventional overvoltage. No protection circuit is required.
Although the temperature fuse F is inserted between the starting resistor R _S and the cathode end of the constant voltage diode ZD ₁ , it may be inserted between the switching transistor Q ₁ and the cathode end of the constant voltage diode ZD _1. Good.

The operation of this switching power supply device will be described. When current is applied to the base of the switching transistor Q ₁ through the starting resistor R _S when the power is turned on, the switching transistor Q ₁ becomes conductive. As a result, a voltage is applied to the primary winding N _P and a voltage is also generated on the base winding N _B. Voltage of the base winding N _B becomes a voltage of positive feedback to the base of the switching transistor Q _1, a switching transistor Q ₁ is once turned on, linearly increasing the exciting current. At this time, since the induced voltage in the secondary winding N _S is applied in the opposite direction to the diode of the rectifying and smoothing circuit 10, no current flows in the secondary winding N _S , but only the exciting current flows in the primary winding N _P. This exciting current increases with time, the current of the switching transistor Q ₁ increases, it becomes impossible for the base current to keep the saturation of the switching transistor Q ₁ , and the voltage of the primary winding N _P decreases. The voltage of the base winding N _B also drops, and this change is positively fed back to the base. As a result, switching
The transistor Q ₁ is turned off at once. At this time, the induced voltage of the secondary winding N _S is applied in the forward direction to the diode of the rectifying and smoothing circuit 10, and a current flows to the load side. When the discharge of the current is completed, the current starts to flow to the base of the switching transistor Q ₁ through the base resistor R _B , and the switching transistor Q ₁ is turned on again. In this way, the same operation is repeated to continue the oscillation, and the rectifying and smoothing circuit 10
To obtain the desired DC output.

However, since the output voltage of the RCC circuit is unstable only with this, the constant voltage control unit 12 for stabilization is used.
Is provided. When the output voltage rises, the base winding N
The voltage of _B also rises. Capacitor C that smooths this
The terminal voltage of ₃ rises in proportion to this, and the constant voltage diode ZD ₁ conducts to decrease the base current of the switching transistor Q ₁ to reduce the switching transistor Q 1.
Speed up ₁ off. That is, when the output voltage rises,
In order to prevent this, the base current is controlled to stabilize the output voltage.

The smoothing capacitor C of the constant voltage controller 12
_{No. 3} uses an electrolytic capacitor as described above, so the capacity decreases over time. Therefore, at the same time as the terminal voltage of the capacitor C ₃ rises, the terminal voltage of the constant voltage diode ZD ₁ also rises. Constant voltage diode ZD
_{If 1} heats up and breaks in open mode, the output voltage may become uncontrollable. Therefore, the temperature fuse F is mounted close to the constant voltage diode ZD ₁ , and the temperature fuse F detects abnormal heat generation of the constant voltage diode ZD ₁ . When the temperature fuse F is blown due to abnormal heat generation, the base current is cut off and the oscillation is stopped. As a matter of course, the fusing temperature of the thermal fuse F is determined by the constant voltage diode ZD ₁
Set lower than the destruction temperature of.

By mounting the temperature fuse and the constant voltage diode in close proximity to each other to form a composite element, the detection sensitivity can be improved and the detection accuracy can be improved (the characteristic variation among the elements can be reduced). This embodiment is shown in FIG. A constant voltage diode 2 is placed inside a rectangular parallelepiped case 20.
2 and the thermal fuse 24 are installed as close as possible. The case 20 is made of a heat-resistant material such as ceramics, and has lead insertion holes formed on opposite side surfaces. A constant voltage diode 22 and a thermal fuse 24 are housed in the case 20, a lead 26 is exposed outside from the hole, and a material 28 having good thermal conductivity and heat resistance is filled.

[0021]

According to the present invention, the temperature fuse is mounted close to the constant voltage diode for detecting the control voltage and is incorporated in the base portion of the switching transistor. Therefore, when abnormal heat is generated in the constant voltage diode, Before the output voltage becomes overvoltage, the thermal fuse is blown and the base current of the switching transistor can be cut off to stop the oscillation. Therefore, the power supply device itself can be protected, and the load can be prevented from being destroyed due to the output voltage being out of control, and at the same time, smoke and ignition can be prevented. Furthermore, RCC
Since only a temperature fuse is added to the constant voltage control section of the circuit, the circuit is greatly simplified, the number of parts is small, and the cost is greatly reduced.

Further, since the temperature fuse and the constant voltage diode are combined to form a composite element, a thermal extremely close state is established, anomaly detection capability is improved, and variations in characteristics among the elements can be suppressed.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing an example of a composite element according to the present invention.

FIG. 3 is a circuit diagram showing an example of a conventional switching power supply device.

[Explanation of symbols]

12 constant voltage control unit 20 case 22 constant voltage diode 24 temperature fuse C ₃ capacitor ZD ₁ constant voltage diode Q ₁ switching transistor F temperature fuse

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H02M 3/338 A 8726-5H

Claims (2)

[Claims] 1. A ringing choke converter circuit comprising a ringing choke converter circuit, an electrolytic capacitor for smoothing a control voltage, and a constant voltage diode for detecting a control voltage.
A switching power supply device having a constant voltage control unit incorporated in the base portion of a switching transistor of a converter circuit, comprising a temperature fuse inserted in the base portion of the switching transistor and mounted in proximity to the constant voltage diode, A switching power supply device, characterized in that, when the constant voltage diode heats up abnormally, a temperature fuse is blown to stop the oscillation of the switching transistor. 2. A composite element used in a switching power supply device according to claim 1, wherein a constant voltage diode and a thermal fuse are mounted in close proximity and housed in a heat resistant case.