JP3010605B2 - Switching power supply - Google Patents

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 which is 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. A rectifying / smoothing circuit 4 composed of a diode full-wave rectifying bridge and a smoothing capacitor (not shown) is connected to the secondary coil S of the transformer 3, and the DC output terminals OP and ON are output from the output side of the rectifying / smoothing circuit 4. Each is pulled out. 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 resistors 7 and 8, respectively, a photodiode 5A of the photocoupler 5, and a shunt-type stable An output voltage detection circuit 10 including main terminals C and A of the 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 between the resistors 7 and 8. DC output terminal O
An output voltage display light emitting element 12 is connected between P and ON via a resistor 11.

Here, 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, an NEC 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 (REFFFRANCE). When a voltage applied to the reference voltage terminal R is equal to or higher than a predetermined reference voltage by a Zener diode (not shown) provided therein. This circuit operates between the main terminals C and A on the conducting side, and operates between the main terminals C and A on the non-conducting side when the voltage applied to the reference voltage terminal R is lower than the set reference voltage.

The operation of the switching power supply will be described below. The DC input terminals IP, IN are connected to a DC power supply, and the load is connected to the DC output terminals OP, ON. The transistor 1 is controlled by the control circuit 2 to, for example, 100
ON and OFF are repeated at a cycle of KHz, and the primary coil P of the transformer 11 is opened and closed by the ON and OFF, and an AC voltage is induced in the secondary coil S. This AC voltage is converted into a DC voltage by the rectification / smoothing circuit 4 and the DC output terminal O
The output voltage Vo is output from P and ON. The output voltage Vo is extracted from the connection point between the resistor 7 and the resistor 8 of the output voltage detection circuit 10 and is input to the reference voltage terminal R of the shunt-type stabilized power supply circuit 6. Now, if this divided voltage exceeds a predetermined reference voltage, the current flowing through the main terminals C and A of the shunt-type stabilized power supply circuit 6 (hereinafter referred to as detection current) increases, and the detection current causes the photodiode of the photocoupler 5 to operate. A detection signal is output from 5A to phototransistor 5B, and this phototransistor 5B outputs a detection signal to control circuit 2. The control circuit 2 controls the switching width of the transistor 1 based on this detection signal so as to reduce the switching width, and lowers the output voltage Vo. When the output voltage Vo decreases and the voltage falls below a predetermined reference voltage, 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. Output voltage Vo rises. In this way, the output voltage Vo is maintained at the set constant voltage.

A resistor 1 is connected between the DC output terminals OP and ON.
The light-emitting element 12 for displaying an output voltage is connected to the light-emitting element 1 via the reference numeral 1 and is lit when the output voltage Vo is being output. 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 transformer 3 from being demagnetized by a DC component.

FIG. 6 is a circuit diagram showing a different example of the 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. Rectifier 13 connected to auxiliary coil A
A and an auxiliary power supply circuit 13 including a smoothing capacitor 13B connected to the output side of the rectifier 13A.
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 in place of the power supply (not shown) of the control circuit 2 in FIG. It is the same as the switching power supply device.

[0008]

In the above-mentioned switching power supply, the light emitting element for displaying the output voltage is connected between the DC output terminals so as to be turned on by the output voltage. The output voltage Vo of the switching power supply is maintained at a set constant voltage until the load current Io reaches the rated value, as shown in the output characteristics shown in FIG.
If the value exceeds the rated value, the capacity becomes insufficient and decreases. Since the output voltage display light-emitting element is similarly lit at the reduced output voltage, it cannot be determined from the output voltage display light-emitting element whether the switching power supply device is operating normally at the set output voltage. There's a problem.

An object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a switching power supply device in which a light emitting element for output voltage is turned on only when the device is operating normally at a set output voltage. Further, the object of the present invention is
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 loss of power supply voltage.

[0010]

According to the present invention, there is provided a transformer having a primary coil connected to a DC power supply, and a series connected between the DC power supply 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 photocoupler between the DC output terminals. Connected to the control circuit of the switching element through
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 is lit only when the output voltage is controlled to the set value. 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. A third resistor connected in series to the resistor in parallel, a light emitting element for displaying an output voltage, a photodiode of a photocoupler having a phototransistor connected to a control circuit of a switching element, and a reference voltage terminal connected to the first resistor. And a shunt-type stabilized power supply circuit connected to a connection point of the second resistor and the second resistor. Further, an input voltage display light emitting element connected in parallel to 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 being connected to a DC power supply, and a switching element connected in series between the DC power supply 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 an output side of the rectifying / smoothing circuit, an auxiliary power supply circuit including a rectifying element connected to an auxiliary coil of the transformer and a smoothing capacitor connected to an output side of the rectifying element; A photocoupler whose phototransistor is connected between an auxiliary power supply circuit and a control circuit of the switching element via an output voltage display light emitting element, and a photocoupler connected between the DC output terminals and a photodiode of the photocoupler. An output voltage detection circuit that outputs a detection signal to a control circuit of the switching element via the photocoupler and the output voltage display light emitting element when an output voltage output from the DC output terminal exceeds a set value; The voltage detection circuit includes a first resistor and a second resistor connected in series between the DC output terminals, and And a third resistor connected in series to the second resistor in parallel with the second resistor, a photodiode of a photocoupler having a phototransistor connected to a control circuit of a switching element via a light emitting element for displaying an output voltage, and a reference thereof. The voltage terminal comprises a shunt-type stabilized power supply circuit connected to a connection point between the first resistor and the second resistor. Further, a light emitting element for input voltage display connected to the output side of the auxiliary power supply circuit is provided.

[0011]

In the switching power supply according to 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. In the output voltage detection circuit, when the output voltage exceeds a set value, a detection current flows through 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, 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 lit by the detection current flowing through the photodiode, it is lit only when the output voltage is controlled to a 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 is turned on. When not
If the input voltage display light emitting element is turned on, the overload is indicated, and if the input voltage display light emitting element is not turned on, the power supply voltage disappears.

Alternatively, a phototransistor of a photocoupler whose photodiode is connected to the output voltage detecting circuit is connected between the auxiliary power supply circuit and the control circuit of the switching element via a light emitting element for displaying an output voltage. . In the output voltage detection circuit, when the output voltage exceeds a set value, a detection current flows through the photodiode, 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, the output voltage is controlled to the set constant voltage, and the output voltage display light emitting element is connected in series with the phototransistor of the photocoupler. Since it is connected and illuminated with the detection current flowing through the phototransistor, it is illuminated only when the output voltage is controlled to a 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, as described above, when the output voltage display light-emitting element is not lit, the input voltage display light-emitting element is lit. If the light emitting element for displaying the input voltage is not lit, the overload indicates the disappearance of the power supply voltage.

[0014]

FIG. 1 is a circuit diagram showing one embodiment of the switching power supply of the present invention. FIG. 1 is a circuit diagram showing the switching power supply of the present invention shown in FIG. 1 which is different from the conventional switching power supply shown in FIG. 5, DC output terminals OP, O
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 in place of the output voltage display light emitting element 12 connected via the resistor 11 between N. is there.

When the output voltage Vo exceeds a set value, a detection current flows to the photodiode 5A of the photocoupler 5, and the output voltage detection circuit 10 outputs a detection signal to the switching element 1 via the phototransistor 5B of the photocoupler 5.
Is output to the control circuit 2. The switching element 1 controls the output voltage Vo to a set constant voltage. When a 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 you are. 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 through the photodiode 5A, so that 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 of the present invention, Such an output voltage detection device becomes unnecessary.

Further, when the output voltage is a variable voltage switching power supply, in order to detect the output voltage, an output voltage detector corresponding to the set output voltage is normally required for each set output voltage. However, in the switching power supply of the present invention, the output voltage display light emitting element is turned on with the detection current for controlling the output voltage to the set value. No output voltage detector is required.

FIG. 2 is a circuit diagram showing another embodiment of the switching power supply 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 terminals IP,
An input voltage display light emitting element 16 connected between the IN via a resistor 15 is provided. Note that the resistor 15 is used for current limiting and is used as needed.

Therefore, when the output voltage display light emitting element 12 is not lit, the input voltage display light emitting element 16 is lit, causing an overload, and when the input voltage display light emitting element 16 is not lit, the power supply voltage disappears. Respectively.
FIG. 3 is a circuit diagram showing still another embodiment of the switching power supply device of the present invention. The difference from the conventional switching power supply shown 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 is connected between the auxiliary power supply circuit 13 and the phototransistor 5P of the photocoupler 5. On the point.

When the output voltage Vo exceeds a set value, a detection current flows to the photodiode 5A of the photocoupler 5, and the output voltage detection circuit 10 transmits a detection signal to the switching element 1 via the phototransistor 5B of the photocoupler. Output to the circuit 2. The switching element 1 controls the output voltage Vo to a set constant voltage. When a 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 you are. Output voltage display light emitting element 1 connected in series to phototransistor 5B of photocoupler 5
2 is lit by the detection current flowing through the phototransistor 5B, and therefore lit only when the output voltage Vo is controlled to the set constant voltage. In this switching power supply device, similarly to the above, an output voltage detection device for detecting whether or not the output voltage Vo is controlled to the set constant voltage is unnecessary regardless of the set value of the output voltage.

FIG. 4 is a circuit diagram showing still another embodiment of the switching power supply device of the present invention. In the circuit of FIG. 3, a light emitting element for input voltage display connected to the output side of an auxiliary power supply circuit 13 via a resistor 15 16 is provided. Note that the resistor 15 is used for current limiting and is used as needed. As described above, when the output voltage display light-emitting element 12 does not light, the input voltage display light-emitting element 16 is lit, causing an overload, and when the input voltage display light-emitting element 16 is not lit, the power supply voltage disappears. As shown below. Since the voltage of the auxiliary power supply circuit 13 for control is generally lower than the power supply voltage, the transformer 3 connected in series shown in FIG.
Is connected in parallel with the primary coil P and the switching element 1, that is, from the input voltage display light emitting element 12 connected between the DC input terminals IP and IN via the resistor 15 to the output side of the auxiliary power supply circuit 13 via the resistor 15. The input voltage display light emitting element 12 is characterized in that the resistance value of the current limiting resistor 15 is low and the circuit loss thereof is low.

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

[0022]

According to the switching power supply device of the present invention, the light emitting element for displaying the output voltage is turned on only when the light emitting element is operating normally at the set output voltage. When it is no longer maintained, it can be immediately recognized, and the reliability of the electronic circuit device is significantly improved. In addition, since a special device such as an output voltage detecting device is not required, 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 is not lit, if the light emitting element for displaying the input voltage is lit, an overload occurs if the light emitting element for displaying the input voltage is lit. If not, the respective power supply voltage disappearances are indicated, and the corresponding measures can be taken promptly.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one 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 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 another 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]

 Reference Signs List 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 first 8 Second resistor 9 Third resistor 10 Output voltage detection circuit 12 Light emitting element for output voltage display 16 Light emitting element for input voltage display 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)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 3/28 H02M 3/155

Claims (7)

(57) [Claims] A transformer having a primary coil connected to a DC power supply; a switching element connected in series with the DC power supply and a 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 the light 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 according to claim 1, wherein the output voltage detecting circuit includes a first resistor and a second resistor connected in series between the DC output terminals, and the first resistor and the second resistor. A third resistor connected in series with the second resistor, a light emitting element for displaying an output voltage, a photodiode of a photocoupler having a phototransistor connected to a control circuit of a switching element, and a reference voltage terminal of the photocoupler. A switching power supply device comprising: a shunt-type stabilized power supply circuit connected to a connection point between a first resistor and a second resistor. 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 being connected to a DC power supply, and a series connection between the DC power supply and the primary coil of the transformer. A switching element, a rectifying / smoothing circuit connected to a secondary coil of the transformer, a DC output terminal drawn from an output side of the rectifying / smoothing circuit, and a rectifying element connected to an auxiliary coil of the transformer. An auxiliary power supply circuit comprising a smoothing capacitor connected to the output side of the rectifier element, and a photo transistor whose phototransistor is connected between the auxiliary power supply circuit and the control circuit of the switching element via a light emitting element for displaying an output voltage. An output voltage connected between the DC output terminal and the photodiode of the photocoupler and 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 second resistor. A third resistor connected in series with the second resistor in parallel, a photodiode of a photocoupler having a phototransistor connected to a control circuit of a switching element via a light emitting element for displaying an output voltage, and a reference voltage terminal of the photocoupler. A switching power supply device comprising a shunt-type stabilized power supply circuit connected to a connection point between a first resistor and a second resistor. 6. The switching power supply according to claim 4, further comprising an input voltage display light emitting element connected to an output side of the auxiliary power supply circuit. 7. The switching power supply according to claim 1, wherein the output voltage is a variable voltage.