JPS63294261A - Switching regulator - Google Patents

Abstract

PURPOSE:To reduce abnormal voltage (ripple voltage), by controlling voltage to lower output voltage, when the capacity of the electrolytic capacitor of a smoothing circuit is extremely reduced and capacity parting is generated. CONSTITUTION:A switching regulator is composed of an input voltage source 1, a controlling circuit 2 for controlling a transistor(Tr) 4 as a switching element and its pulse width, an insulating transformer 3, a rectifier diode 5, and a smoothing circuit with smoothing capacitors 6, 8 and a choke coil 7. In this case, both the ends of the choke coil 7 set in said smoothing circuit are provided with a loop circuit consisting of a resistor 15, a light emitting diode 12 of a photo-coupler 10, and a diode 16 which are connected in series. As a result, by excessive ripple voltage generated on the choke coil 7, the light emitting diode is lightened, and by the controlling circuit 2 via the photo-coupler 10, a device is worked to lower output voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a flyback switching regulator in which a smoothing circuit using a π-type filter is provided on the secondary side.

(Prior Art) Conventionally, as this type of flyback switching regulator, there is one shown in FIG. 2, for example.

In FIG. 2, reference numeral 1 denotes an input DC power supply, which inputs DC voltage to the primary winding 3a of the isolation transformer 3. A control circuit 2 controls the output voltage to a constant voltage, and controls the pulse width of a transistor 4 as a switching element connected in series with the primary winding 3a of the isolation transformer 3. A rectifying diode 5 is connected in series to the secondary winding 3b of the isolation transformer 3, and a smoothing circuit consisting of a π-type filter equipped with a capacitor 6.8 and a choke coil 7 is provided to reduce the ripple contained in the output voltage 9. The voltage is reduced.

On the other hand, an error amplifier 13 is provided for stabilizing control of the output voltage by the control circuit 2, and the output voltage 9 is applied to the inverting input terminal of the error amplifier 13, and the reference voltage of the reference voltage source 14 is applied to the non-inverting input terminal. Voltage is applied. The output of the error amplifier 13 is connected to the cathode side of the light emitting diode 12 provided in the photocoupler 10.
The anode side of is connected to the output stage of the smoothing circuit via a resistor 15, and receives power supply from the output voltage 9.

Further, the output of the transistor 11 provided in the photocoupler 10 is given to the control circuit 2.

The operation of the flyback type switching regulator shown in FIG. 2 is such that when the output voltage 9 becomes higher than the reference voltage of the reference voltage source 14, the output of the error amplifier 13 decreases, causing the light emitting diode 12 of the photoplastic 10 to emit light, which causes the phototransistor to emit light. 11 is turned on, and the control circuit 2, which receives a signal caused by the turning on of the phototransistor 11, controls the transistor 4 to lower the output voltage, thereby making the output voltage constant.

(Problems to be Solved by the Invention) However, in such conventional switching regulators, an electrolytic capacitor is generally used as the capacitor 6.8 of the smoothing circuit provided on the secondary side. Since the lifespan is relatively short compared to other circuit elements, the lifespan of the capacitor 6 on the input side, which receives a large ripple voltage, expires during use, resulting in a state of so-called capacity loss.

When the capacity of the capacitor 6 is damaged in this way, the ripple voltage smoothing function is lost and an excessive ripple voltage is generated across the capacitor 6, resulting in a state in which all the windings of the isolation transformer 3 receive excessive ripple voltage. Since the transformer continues to operate as it is, there is a problem in that the circuit components connected to each winding of the insulating transformer 3 are destroyed.

(Means for Solving the Problems) The present invention has been made in view of the above-mentioned problems of the conventional art. An object of the present invention is to provide a switching transducer that does not destroy circuit components connected to each winding of an insulating transformer.

In order to achieve this object, the present invention includes: an isolation transformer (3); a switching element (4) connected in series with the second winding of the isolation transformer (3); A smoothing circuit that is connected to the secondary winding via a rectifying diode (5) and constitutes a π-type filter with two capacitors (6, 8>) and a choke coil (7); an error amplifier (13) that produces an inverted output according to a difference from a reference voltage;
), the cathode side is connected to the output terminal of the error amplifier (1), and the anode side is connected to the output side of the smoothing circuit.
a photocoupler (10) comprising a light emitting element (12) that emits light by the inverted output of the light emitting element (12) and a light receiving element (1) that receives the output light of the light emitting element (12);
a control circuit (2) that controls the output voltage to a constant voltage by controlling the switching element (4) to lower the output voltage when the received light output of 0) is obtained; A circuit is connected to the light emitting element (12) of the photocoupler (10) to cause a light emitting current to flow through the alternating current pressure generated at both ends of the choke coil (7).

(Function) In the switching regulator of the present invention having such a configuration, the capacitor provided in the smoothing circuit constituting the π-type filter, particularly the capacitor provided on the input side that receives the rectified output by the diode. When the choke coil reaches the end of its life and the capacitance tl decreases, the smoothing function of the capacitor is lost and an excessive ripple voltage (
AC voltage) is generated. The excessive ripple voltage generated in this choke coil is rectified by a diode, for example, and causes a forward current to flow through the photocoupler's light emitting element (light emitting diode), causing it to emit light. Therefore, it is controlled by receiving the light reception output from the photocoupler. The circuit operates to lower the output voltage.

Therefore, even if the capacitor in the smoothing circuit exceeds its capacity, the output voltage is automatically lowered, which prevents excessive voltage from being applied to the circuit components connected to each winding of the isolation transformer and damaging them. It can definitely be prevented.

(Embodiment) FIG. 1 is a circuit block diagram showing an embodiment of the present invention.

In FIG. 1, 1 is an input voltage source, 2 is a control circuit that controls the pulse width of a transistor 4 as a switching element in order to make the output voltage constant, 3 is an isolation transformer,
A diode 5 is connected to the secondary winding of the insulating transformer 3 and performs half-wave rectification of the AC output; 6 and 8 are smoothing capacitors; together with the choke coil 7, they form a smoothing circuit using a π-type filter.

On the other hand, 13 is an error amplifier, which connects the output voltage 9 obtained from the smoothing circuit to an inverting input terminal, and connects a reference voltage source 14 to a non-inverting input terminal, and outputs an error signal according to the difference between the output voltage and the reference voltage. Produces an inverted output. A photocoupler 10 including a light emitting diode 12 and a phototransistor 11 is connected to the output of the error amplifier 13. Photo coupler 10
The light emitting diode 12 has its cathode connected to the output of the error amplifier 13, and its anode connected via a resistor 15 to the output of the smoothing circuit, that is, the connection point between the choke coil 7 and the capacitor 8. The output of the phototransistor 11 provided in the photocoupler 10 is given to the control circuit 2.

Such a circuit configuration is the same as that of a conventional flyback switching regulator, but in addition, in the present invention, the input side of the choke coil 7 provided in the smoothing circuit, that is, the side of the rectifying diode 5, Light emitting diode 1 in photocoupler 10 whose output is connected to error amplifier 13
A signal line is connected to the cathode side of 2, and the alternating current voltage generated across the choke coil 70 is rectified on this signal line, and a forward current is applied to the light emitting diode 12 as shown by the current path 17 of one dotted line at 9. A current diode 16 is provided.

That is, in the present invention, a resistor 15,
A loop circuit is provided in which the light emitting diode 12 of the photocoupler 10 and the diode 16 are connected in series.

Next, the operation of the embodiment shown in FIG. 1 will be explained.

Since the capacitors 6 and 8 in the smoothing circuit provided on the right side of the isolation transformer 3 are electrolytic capacitors, their lifespan is short compared to other circuit elements, especially the half-wave rectification of the diode 5. Since the capacitor 6 that smoothes the output receives a large ripple voltage, it reaches the end of its life first and loses its capacity during use.

When the capacitor 6 becomes overcapacitated in this way, the smoothing function of the capacitor 6 is lost and an excessive ripple voltage is generated across the capacitor. At this time, the smoothing function of the capacitor 6 is lost at both ends of the choke coil 7, and an excessive AC voltage is generated.

The excessive AC voltage generated across the choke coil 7 in this way is removed by the newly added diode 1 according to the present invention.
6, and the rectified current flows through a current path 17 shown by a dotted line. Since the light emitting diode 12 of the photocoupler 10 is provided on this current path 17, the light emitting diode 12 of the photocoupler 10 emits light, turns on the phototransistor 11, and receives a signal caused by the turning on of the phototransistor 11. The control circuit 2 controls the transistors 1 to 4 to lower the output voltage 9. Therefore, it is possible to automatically suppress the excessive abnormal voltage generated due to the capacitance of the capacitor to a low level, and each winding of the isolation transformer 3 It is possible to reliably prevent circuit components connected to the circuit from being destroyed due to heat generation due to large power loss.

On the other hand, during normal operation when the capacitors 6 and 8 function normally, the AC voltage generated across the choke coil 7 is more than the sum of the threshold voltages of the diode 16 and the light emitting diode 12 due to the smoothing function of the capacitor 6. Therefore, the rectified current shown in the current path 17 does not flow, and even if a circuit is added according to the present invention, normal operation is not affected.

In the embodiment shown in FIG. 1, a current limiting resistor 15 is provided in the loop circuit providing the current path 17, but the resistor 15 is not provided and the diode 16 and the light emitting diode 12 are
A loop circuit may be configured by

In addition, in the embodiment shown in FIG. 1, the light emitting element 12 of the photocoupler 10 that transmits the output of the error amplifier 13 is used to detect that the capacitor 6 has caused capacitance, and the control circuit 2 Although a circuit is configured to lower the output voltage, it is also possible to provide a circuit that connects the diode 16 and other photocoupler light emitting elements in series to both ends of the choke coil 7, independent of the transmission system using the error amplifier 3. good.

Furthermore, in the embodiment shown in FIG. 1, a diode 16 is provided which rectifies the alternating current voltage generated in the choke coil and causes a forward current to flow through the light emitting diode 12.
A resistor may be used instead of 6. In this case, the resistor allows the light emitting current to flow through the light emitting diode 12 (AC drive), and
The output bias of the error amplifier 13 is performed.

(Effects of the Invention) As described above, according to the present invention, the capacitance of the electrolytic capacitor provided in the smoothing circuit composed of the π-type filter provided on the secondary side of the isolation transformer is extremely reduced. When so-called capacitance handling occurs, voltage control is performed to lower the output voltage, so the abnormal voltage (ripple voltage) caused by capacitance handling is kept low, and the circuit components connected to each winding of the isolation transformer are Destruction can be reliably prevented.

Additionally, since the output voltage decreases due to the capacitance of the electrolytic capacitor, failures can be detected early.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram showing an embodiment of the present invention, and FIG. 2 is a circuit block diagram showing a conventional example. 1: Input voltage source 2: Control circuit 3: Isolation transformer 4: Transistor 5: Rectifier diode 6.8: Capacitor (electrolytic capacitor) 7; Choke coil 10: Photocoupler 11: Phototransistor 12: Light emitting diode (LED) 13 Two error amplifiers 14: Reference voltage source 15: Resistor 16: Diode 17: Current path

Claims (1)

[Claims] An isolation transformer; a switching element connected in series to the primary winding of the isolation transformer; two capacitors and a choke coil connected to the secondary winding of the isolation transformer via a rectifying diode. a smoothing circuit that constitutes a π-type filter; an error amplifier that generates an inverted output according to the difference between the output voltage from the smoothing circuit and a reference voltage; a cathode side connected to the output terminal of the error amplifier, and a photocoupler, the anode side of which is connected to the output side of the circuit, and includes a light emitting element that emits light by the inverted output of the error amplifier, and a light receiving element that receives the output light of the light emitting element; a control circuit that controls the output voltage to a constant voltage by controlling the switching element to lower the output voltage when the output voltage is obtained; A switching regulator characterized in that a circuit for causing a light emitting current to flow is connected to a light emitting element of the photocoupler.