JPH05199747A - Switching power-supply device - Google Patents

Abstract

PURPOSE:To light an output voltage displaying light-emitting element only when a switching power-supply device is normally worked with set output voltage, and enable it to be identified whether the cause depends on an excess load or depends on the extinction of power-supply voltage when the output voltage displaying light-emitting element is not lit. CONSTITUTION:Resistors 7, 8 connected respectively in series between DC output terminals OP, ON, an output voltage detecting circuit 10 consisting of a resistor 9 connected to the resistors 7, 8 in parallel with each other and respectively in series, an output voltage displaying light-emitting element 12, and a shunt type stabilized-power-supply circuit 6 with the photo-diode 5A of a photocoupler 5 with the photo-transistor 5B connected to the control circuit 2 of a switching element 1, and with the reference voltage terminal R connected to a connected point between the resistor 7 and the resistor 8, and an input voltage displaying light-emitting element 16 connected between DC input terminals IP, IN, via a resistor 15 are provided.

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 widely used as a constant voltage DC power supply for electronic devices.

[0002]

2. Description of the Related Art FIG. 5 is a circuit diagram showing an example of a conventional switching device. A primary coil P of a transformer 3 and a switching element, for example, a collector and an emitter of a transistor 1 are connected in series to DC input terminals IP and IN. The secondary coil S of the transformer 3 is connected to a rectifying / smoothing circuit 4 including a diode full-wave rectifying bridge (not shown) and a smoothing capacitor, and the DC output terminals OP and ON are connected to the output side of the rectifying / smoothing circuit 4. Each is withdrawn. A resistor 7 and a resistor 8 connected in series between the DC output terminals OP and ON, a resistor 9 connected in series with the resistor 7 and a resistor 8 in series, a photodiode 5A of the photocoupler 5 and a shunt type stabilizer. An output voltage detection circuit 10 including the main terminals C and A of the digitalized power supply circuit 6 is provided. The phototransistor 5B of the photocoupler of the output voltage detection circuit 10 is connected to the control circuit 2 of the transistor 1, and the reference voltage terminal R of the shunt type stabilized power supply circuit 6 is connected to the connection point of the resistors 7 and 8. DC output terminal O
A light emitting element 12 for displaying an output voltage is connected via a resistor 11 between P and ON.

Now, the shunt type stabilized power supply circuit 6 of the output voltage detection circuit 10 will be described. The shunt-type stabilized power supply circuit 6 is, for example, a NEC-made μPC1093 high-precision variable shunt-type stabilized power supply circuit, and has a main terminal C
(CATHODE), A (ANODE), and a reference voltage terminal R (REFFFRENCE) have three terminals. When the voltage applied to the reference voltage terminal R is higher than a predetermined reference voltage by a Zener diode (not shown) provided inside. The circuit operates between the main terminals C and A on the conducting side, and between the main terminals C and A on the non-conducting side when the voltage applied to the reference voltage terminal R is equal to or lower than the set reference voltage.

The operation of this switching power supply will be described below. The DC input terminals IP and IN are connected to the DC power source, and the load is connected to the DC output terminals OP and ON. The transistor 1 is controlled by its control circuit 2 to, for example, 100
It is repeatedly turned on and off at a frequency of KHz, and the primary coil P of the transformer 11 is opened and closed by this on and off, and an AC voltage is induced in the secondary coil S thereof. This AC voltage is converted into a DC voltage by the rectifying / smoothing circuit 4, and the DC output terminal O
The output voltage Vo is output from P, ON. The output voltage Vo is extracted from the connection point between the resistors 7 and 8 of the output voltage detection circuit 10 and input to the reference voltage terminal R of the shunt-type stabilized power supply circuit 6. Now, when the voltage exceeds the predetermined reference voltage by this amount, the current (hereinafter referred to as the detection current) flowing through the main terminals C and A of the shunt-type stabilized power supply circuit 6 increases, and the detection current causes the photodiode of the photocoupler 5 to operate. A detection signal is output from 5A to the phototransistor 5B, and the phototransistor 5B outputs the detection signal to the control circuit 2. Based on this detection signal, the control circuit 2 controls the switching width of the transistor 1 to be small and lowers the output voltage Vo. When the output voltage Vo drops and the voltage is reduced to a predetermined reference voltage or less, the detection current flowing through the main terminals C and A of the shunt-type stabilized power supply circuit 6 decreases, and conversely the switching width of the transistor 1 increases. The output voltage Vo rises. In this way, the output voltage Vo is maintained at the set constant voltage.

A resistor 1 is placed between the DC output terminals OP and ON.
The output voltage display light emitting element 12 is connected via 1 and is turned on when the output voltage Vo is output. Incidentally, the transformer 3 is usually provided with an auxiliary coil (not shown), and a control load is connected to the auxiliary coil to prevent the demagnetization due to the direct current component of the transformer 3.

FIG. 6 is a circuit diagram showing a different example of a conventional switching power supply device. The difference from FIG. 5 is that the transformer 3 has an auxiliary coil A in addition to a primary coil P and a secondary coil S. Rectifying element 13 connected to auxiliary coil A
An auxiliary power supply circuit 13 including A and a smoothing capacitor 13B connected to the output side of the rectifying element 13A is provided,
The phototransistor 5B of the photocoupler 5 has a collector connected to the auxiliary power supply circuit 13 and an emitter connected to the control circuit 2 of the switching element 1.

The operation of this switching power supply device is shown in FIG. 5 except that the collector current of the phototransistor 5B of the photocoupler 5 is supplied from the auxiliary power supply circuit 13 instead of the power supply (not shown) of the control circuit 2 in FIG. It is similar to the switching power supply device.

[0008]

In the above switching power supply device, the output voltage display light emitting element is connected between the DC output terminals and is turned on by the output voltage. The output voltage Vo of the switching power supply device is maintained at the set constant voltage up to the rated value of the load current Io as in the output characteristic shown in FIG.
If exceeds the rated value, the capacity will be insufficient and the capacity will decrease. Since the output voltage display light emitting element also lights up at this lowered output voltage, it cannot be determined from this output voltage display light emitting element whether or not the switching power supply device is operating normally at the set output voltage. There's a problem.

The object of the present invention is to solve the above-mentioned problems,
It is an object of the present invention to provide a switching power supply device in which a light emitting element for output voltage is turned on only when normally operating at a set output voltage. Further, the object of the present invention is to
When the output voltage display light emitting element does not light up, it is possible to determine whether the cause is an overload or a power supply voltage loss.

[0010]

In order to achieve the above-mentioned object, the present invention provides a transformer having a primary coil connected to a DC power source, and a transformer connected in series between the DC power source and the primary coil of the transformer. A switching element connected to the transformer, a rectifying / smoothing circuit connected to the secondary coil of the transformer, a DC output terminal drawn from the output side of the rectifying / smoothing circuit, and a photocoupler between the DC output terminals. Connected to the control circuit of the switching element via
When the output voltage output from the DC output terminal exceeds a set value, a detection signal is output to the control circuit of the switching element, and the output voltage display light emission is turned on only when the output voltage is controlled to the set value. And an output voltage detection circuit provided with an element. The output detection circuit includes, for example, a first resistor and a second resistor connected in series between DC output terminals, and the first resistor and the second resistor. Of the photo-coupler and the reference voltage terminal of the photo-coupler having the photo-transistor connected to the control circuit of the output voltage display light-emitting element and the switching element, respectively. And a shunt-type stabilized power supply circuit connected to the connection point of the second resistance and the second resistance. Further, an input voltage display light emitting element connected in parallel with the primary coil and the switching element of the transformer connected in series is provided. Or a primary coil, a transformer having a secondary coil and an auxiliary coil, the primary coil of which is connected to a DC power supply, and a switching element connected in series with these between the DC power supply and the primary coil of the transformer, A rectifying / smoothing circuit connected to the secondary coil of the transformer,
An auxiliary power supply circuit comprising a DC output terminal drawn from the output side of the rectifying / smoothing circuit, a rectifying element connected to the auxiliary coil of the transformer, and a smoothing capacitor connected to the output side of the rectifying element; A photocoupler whose phototransistor is connected between the auxiliary power supply circuit and the control circuit of the switching element via an output voltage display light emitting element, and is connected between the DC output terminal and the photodiode of the photocoupler. An output voltage detection circuit that outputs a detection signal to the control circuit of the switching element via the photocoupler and the output voltage display light-emitting element when the output voltage output from the DC output terminal exceeds a set value. The voltage detection circuit includes a first resistor and a second resistor that are connected in series between the DC output terminals, and these first and second resistors. Of a photocoupler in which the phototransistor is connected to the control circuit of the switching element via the output voltage display light emitting element and the third resistance connected in series to the second resistance and the second resistance, respectively, and its reference The voltage terminal is composed of a shunt-type stabilized power supply circuit connected to the connection point of the first resistor and the second resistor. Further, an input voltage display light emitting element connected to the output side of the auxiliary power supply circuit is provided.

[0011]

In the switching power supply device of the present invention, the output voltage display light emission is connected in series with the photodiode of the photocoupler of the output voltage detection circuit connected between the DC output terminals and the control circuit of the switching element via the photocoupler. The elements were connected. When the output voltage exceeds the set value, the output voltage detection circuit outputs a detection current to the photodiode of the photocoupler and outputs a detection signal to the control circuit of the switching element via the phototransistor of the photocoupler. Then, the switching element controls the output voltage to the set constant voltage. Therefore, when the detection signal is output to the control circuit of the switching element, it means that the output voltage is controlled to the set constant voltage, and the output voltage display light emitting element is connected in series with the photodiode of the photocoupler. Since it is connected and is turned on by the detection current flowing in this photodiode, it is turned on only when the output voltage is controlled to the set constant voltage.

Further, since the input voltage display light emitting element connected in parallel with the primary coil and the switching element of the transformer connected in series, that is, between the DC input terminals, is provided, the output voltage display light emitting element lights up. When not
If the light emitting element for input voltage display is lit, an overload is indicated, and if the light emitting element for input voltage display is not lit, the power supply voltage disappears.

Alternatively, the phototransistor of the photocoupler whose photodiode is connected to the output voltage detection circuit via the output voltage display light emitting element is connected between the auxiliary power supply circuit and the switching element control circuit. .. The output voltage detection circuit outputs a detection signal to the control circuit of the switching element via the phototransistor of the photocoupler when the output voltage exceeds the set value, and the detection current flows through the photodiode. Then, the switching element controls the output voltage to the set constant voltage. Therefore, when the detection signal is output to the control circuit of the switching element, the output voltage is controlled to the set constant voltage, and the output voltage display light emitting element is connected in series to the phototransistor of the photocoupler. Since it is connected and turned on by the detection current flowing in this phototransistor, it is turned on only when the output voltage is controlled to the set constant voltage. Further, since the input voltage display light emitting element connected to the output side of the auxiliary power supply circuit is provided, when the output voltage display light emitting element is not lit, the input voltage display light emitting element is lit as in the above case. If the light emitting element for displaying the input voltage is not lit, the overload is indicated and the power supply voltage disappears.

[0014]

1 is a circuit diagram showing an embodiment of the switching power supply device of the present invention. The difference between the switching power supply device of the present invention shown in FIG. 1 and the conventional switching power supply device shown in FIG. 5, DC output terminals OP, O
Instead of the output voltage display light emitting element 12 connected between N via the resistor 11, the output voltage display light emitting element 12 is connected in series with the photodiode 5A of the photocoupler 5 of the output voltage detection circuit 10. is there.

In the output voltage detection circuit 10, when the output voltage Vo exceeds the set value, a detection current flows into the photodiode 5A of the photocoupler 5, and the detection signal is sent via the phototransistor 5B of the photocoupler 5 to the switching element 1.
Output to the control circuit 2. The switching element 1 controls the output voltage Vo to a set constant voltage. When the detection signal is output to the control circuit 2 of the switching element 1, the output voltage Vo is controlled to the set constant voltage. It is when The output voltage display light emitting element 12 connected in series to the photodiode 5A of the photocoupler 5 is turned on by the detection current flowing in the photodiode 5A, so only when the output voltage Vo is controlled to the set constant voltage. Light. Generally, in order to detect whether or not the output voltage Vo is controlled to a set constant voltage, it is necessary to connect an output voltage detection device to the DC output terminals OP and ON, but in the switching power supply device of the present invention, Such an output voltage detecting device becomes unnecessary.

Further, in the case of a switching power supply device in which the output voltage is a variable voltage, in order to detect the output voltage, an output voltage detection device corresponding to the set output voltage is normally required. However, in the switching power supply device of the present invention, since the output voltage display light emitting element is turned on by the detection current for controlling the output voltage to the set value, regardless of the set value of the output voltage, this kind of No output voltage detector is required.

FIG. 2 is a circuit diagram showing another embodiment of the switching power supply device of the present invention. In the circuit of FIG.
In parallel with the primary coil P and the switching element 1 of the transformer 3 connected in series, that is, the DC input terminal IP,
An input voltage display light emitting element 16 connected between IN and a resistor 15 is provided. The resistor 15 is for current limiting and is used as necessary.

Therefore, when the output voltage display light emitting element 12 does not light up, an overload occurs if the input voltage display light emitting element 16 lights up, and the power supply voltage disappears if the input voltage display light emitting element 16 does not light up. Respectively.
3 is a circuit diagram showing a further different embodiment of the switching power supply device of the present invention. The difference from the conventional switching power supply shown in FIG. 6 is that the DC output terminal O in FIG.
Instead of the output voltage display light emitting element 12 connected via the resistor 11 between P and ON, the output voltage display light emitting element 12 was connected between the auxiliary power supply circuit 13 and the phototransistor 5P of the photocoupler 5. There is a point.

In the output voltage detection circuit 10, when the output voltage Vo exceeds the set value, a detection current flows into the photodiode 5A of the photocoupler 5, and the detection signal is controlled by the phototransistor 5B of the photocoupler to control the switching element 1. Output to circuit 2. The switching element 1 controls the output voltage Vo to a set constant voltage. When the detection signal is output to the control circuit 2 of the switching element 1, the output voltage Vo is controlled to the set constant voltage. It is when Output voltage display light emitting element 1 connected in series to phototransistor 5B of photocoupler 5.
2 is turned on by the detection current flowing through the phototransistor 5B, and is turned on only when the output voltage Vo is controlled to the set constant voltage. As with the switching power supply device, the output voltage detection device for detecting whether or not the output voltage Vo is controlled to the set constant voltage is not required regardless of the set value of the output voltage, as described above.

FIG. 4 is a circuit diagram showing a further different embodiment of the switching power supply device of the present invention. In the circuit of FIG. 3, an input voltage display light emitting element connected to the output side of the auxiliary power supply circuit 13 via a resistor 15. 16 is provided. The resistor 15 is for current limiting and is used as necessary. Similarly to the above, when the output voltage display light emitting element 12 does not light up, an overload occurs if the input voltage display light emitting element 16 lights up, and the power supply voltage disappears if the input voltage display light emitting element 16 does not light up. It becomes as shown respectively. Since the voltage of the auxiliary power supply circuit 13 for control is generally lower than the power supply voltage, the transformers 3 connected in series shown in FIG.
Connected in parallel to the primary coil P and the switching element 1, that is, from the input voltage display light emitting element 12 connected via the resistor 15 between the DC input terminals IP and IN, to the output side of the auxiliary power supply circuit 13 via the resistor 15. The input voltage display light emitting element 12 thus produced is characterized in that the resistance value of the current limiting resistor 15 is low and its circuit loss is low.

The resistors 7, 8 and 9 are respectively connected to the first,
Referred to as the second and third resistors.

[0022]

In the switching power supply device of the present invention, the light emitting element for displaying the output voltage is turned on only when normally operating at the set output voltage, so that the output voltage is kept constant due to overload or the like. When it is no longer maintained, it can be immediately recognized, and the reliability of the electronic circuit device is significantly improved. Further, for this reason, no special device such as an output voltage detecting device is required, so that the cost is reduced.

Further, since the light emitting element for displaying the input voltage is provided, when the light emitting element for displaying the output voltage does not light up, if the light emitting element for displaying the input voltage is on, an overload is generated and the light emitting element for input voltage displaying lights up. If not, the power supply voltage disappearance is indicated and the corresponding action can be taken promptly.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing another embodiment of the switching power supply device of the present invention.

FIG. 3 is a circuit diagram showing still another embodiment of the switching power supply device of the present invention.

FIG. 4 is a circuit diagram showing still another embodiment of the switching power supply device of the present invention.

FIG. 5 is a circuit diagram showing an example of a conventional switching power supply device.

FIG. 6 is a circuit diagram showing a different example of a conventional switching power supply device.

FIG. 7 is a normal output characteristic diagram of the switching power supply device.

[Explanation of symbols]

 1 Switching Element 2 Control Circuit (of Switching Element 1) 3 Transformer 4 Rectifying / Smoothing Circuit 5 Photocoupler 5A Photodiode (of Photocoupler 5) 5B Phototransistor (of Photocoupler 5) 6 Shunt-type Stabilized Power Supply Circuit 7 1st Resistance 8 Second resistance 9 Third resistance 10 Output voltage detection circuit 12 Output voltage display light emitting element 16 Input voltage display light emitting element IP DC input terminal IN DC input terminal OP DC output terminal ON DC output terminal P Primary coil (For transformer 3) S secondary coil (for transformer 3) A auxiliary coil (for transformer 3) Vo output voltage R reference voltage terminal (for shunt-type stabilized power supply circuit 6)

Claims (7)

[Claims] 1. A transformer having a primary coil connected to a DC power source, and a switching element connected in series with the DC power source and the primary coil of the transformer.
A rectifying / smoothing circuit connected to the secondary coil of the transformer, a DC output terminal drawn from the output side of the rectifying / smoothing circuit, and a control circuit for the switching element between the DC output terminals and a photocoupler. When the output voltage output from the DC output terminal exceeds a set value, a detection signal is output to the control circuit of the switching element, and it is turned on only when the output voltage is controlled to the set value. A switching power supply device comprising: an output voltage detection circuit provided with an output voltage display light emitting element. 2. The switching power supply device according to claim 1, wherein the output voltage detection circuit includes a first resistor and a second resistor connected in series between the DC output terminals, and the first resistor and the first resistor. The third resistor connected in parallel to each of the two resistors in parallel with each other, the light emitting element for output voltage display, the photodiode of the photocoupler having the phototransistor connected to the control circuit of the switching element, and the reference voltage terminal thereof are A switching power supply device comprising a shunt-type stabilized power supply circuit connected to a connection point of a first resistance and a second resistance. 3. The switching power supply device according to claim 1, further comprising a primary coil of a transformer connected in series and a light emitting element for input voltage display connected in parallel to the switching element. Power supply. 4. A transformer having a primary coil, a secondary coil and an auxiliary coil, the primary coil of which is connected to a DC power source, and a transformer connected in series between the DC power source and the primary coil of the transformer. A switching element, a rectifying / smoothing circuit connected to the secondary coil of the transformer, a DC output terminal drawn from the output side of the rectifying / smoothing circuit, and a rectifying element connected to the auxiliary coil of the transformer. A phototransistor in which a phototransistor is connected between the auxiliary power supply circuit composed of a smoothing capacitor connected to the output side of the rectifying element and a control circuit for the switching element via the output voltage display light emitting element. A coupler is connected between the DC output terminal and the photodiode of the photocoupler, and an output voltage output from the DC output terminal is set. Switching power supply apparatus characterized by comprising a a detection signal exceeds the value from the output voltage detection circuit for outputting a control circuit of the switching element via the photocoupler and the output voltage display light-emitting device. 5. The switching power supply device according to claim 4, wherein the output voltage detection circuit includes a first resistor and a second resistor connected in series between the DC output terminals, and the first resistor and the first resistor. The third resistor, which is connected in parallel to each of the two resistors in series, the photodiode of the photocoupler whose phototransistor is connected to the control circuit of the switching element via the light emitting element for displaying the output voltage, and its reference voltage terminal are A switching power supply device comprising a shunt-type stabilized power supply circuit connected to a connection point of a first resistor and a second resistor. 6. The switching power supply device according to claim 4 or 5, further comprising an input voltage display light emitting element connected to the output side of the auxiliary power supply circuit. 7. The switching power supply device according to claim 1, wherein the output voltage is a variable voltage.