JP2002101649A - Switching regulator power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely operate a secondary side of a protection circuit in an overloaded or a short-circuited condition of its load. SOLUTION: This switching regulator power supply device is provided with a protection circuit which includes a thermal switch 16 which outputs a protective operation signal to its control circuit by detecting the overloaded or the short-circuited condition of the load and a choke sub-winding 15 which operates the protection circuit by generating a voltage proportional to its winding ratio to a constant voltage which is putted to a choke coil 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rectifying diode, a choke coil and a smoothing capacitor for rectifying and smoothing a voltage induced in a secondary winding of a transformer by on / off control of a switching element and stabilizing the voltage to a constant voltage at a load. The present invention relates to a switching regulator power supply for supplying a DC output.

[0002]

2. Description of the Related Art Conventionally, there is a circuit shown in FIG. 3, for example, as a circuit in a switching regulator power supply device that performs an operation of protecting against heat generation in an overload or short circuit state by using an output voltage on a secondary side.

In FIG. 3, an AC input applied to input terminals 1a and 1b is rectified by a rectifier circuit 2, then smoothed by a smoothing circuit 3 having a capacitor, and converted into a direct current. Subsequent to the smoothing circuit 3, a forward converter is provided. The forward converter includes a transformer 4 having a primary winding 4a and a secondary winding 4b, a switching element 5 using a MOS-FET, rectifier diodes 6, 7, a choke coil 8, and a smoothing capacitor 9, and an output terminal. 10
The DC output is supplied from a and 10b to the load.

The switching element 5 is turned on and off by the control circuit 11 and the main control circuit 13 so as to keep the output DC voltage constant. Incidentally, reference numeral 14 denotes an overcurrent detection resistor.

When the current flowing through the primary winding 4a is interrupted by the on / off operation of the switching element 5, the secondary winding 4
b, an in-phase secondary voltage is induced, and a rectangular wave voltage whose width is the ON time of the switching element 5 is applied to an LC low-frequency filter composed of the inductance L of the choke coil 8 and the capacitance C of the smoothing capacitor 9. At this time, a current in the form of a small DC current superimposed on a large DC current flows through the choke coil 8. As for the current flowing through the choke coil 8, its DC current becomes the output current, and the triangular wave AC current flows through the smoothing capacitor 9. However, since the AC current is sufficiently small, the ripple voltage is small.

The control circuit 11 compares the DC output voltage with the reference voltage, outputs a signal corresponding to the error, drives the photocoupler light emitting unit 12a using the LED to emit light, and receives the photocoupler light using the phototransistor. The on-time of the switching element 5 is controlled by the main control circuit 13 so as to keep the output voltage constant by converting it into an electric signal in the unit 12b.

On the secondary side of the switching regulator power supply device, a protection circuit is provided which causes the main control circuit 13 to perform a protection operation by detecting an overload or short circuit condition of the load. The conventional circuit of FIG.
And the photocoupler light-emitting unit 20a constitute a protection circuit.

When the load connected to the output terminal is overloaded or short-circuited and becomes an overcurrent state, the heat operation switch 16 senses the heat generated by the circuit at this time and turns on the contact.
The photocoupler light-emitting unit 20a is driven to emit light, and the photocoupler light-receiving unit 20b returns to an electric signal and inputs the electric signal to the main control circuit 13. For example, by fixing the switching element 5 to an off state, an overcurrent is suppressed.

[0009]

However, in such a conventional switching regulator power supply device, when the protection circuit operates using the output voltage on the secondary side, the output voltage is necessary for operating the protection circuit. Although the protection circuit can be operated in a range where a proper voltage is output, the output voltage drops or becomes zero in the output short-circuit state, and there is a problem that a voltage for operating the protection circuit cannot be secured.

In order to solve this problem, as shown in FIG. 4, a thermal operation switch 16 arranged on the secondary side is connected to the primary side main control circuit 13 by a signal line, and the output voltage is shorted when the output is short-circuited. Is reduced or becomes zero, the primary side main control circuit 1 is directly turned on when the thermal operation switch 16 is turned on.
3 is performed.

However, when the thermal operation switch 16 is directly connected to the main control circuit 13, the thermal operation switch 16 is required to have primary and secondary insulation performance. Due to the requirement of such insulation performance, a structure that satisfies not only the insulation requirement of the thermal operation switch 16 but also the insulation requirement of the entire device is required, and there is a problem that the structure becomes complicated and the cost increases.

The present invention solves such a conventional problem, reliably operates the protection circuit on the secondary side in an overload or short-circuit state, simplifies the insulation configuration of the entire device, and reduces the cost of the device. It is an object of the present invention to provide a switching regulator power supply device that suppresses switching.

[0013]

To achieve this object, a switching regulator power supply according to the present invention is configured as follows.

First, according to the present invention, a switching element is connected to a primary winding of a transformer to which a DC voltage is input, and a rectifier diode, a choke coil and a smoothing capacitor are sequentially connected to a secondary winding of the transformer. A switching regulator power supply that supplies a DC output stabilized at a constant voltage to a load by rectifying and smoothing a voltage induced in a secondary winding of a transformer by a rectifier diode, a choke coil and a smoothing capacitor by controlling on / off of a switching element. set to target.

The present invention relates to such a switching regulator power supply device. The present invention relates to a protection circuit for detecting an overload or short-circuit condition of a load and outputting a protection operation signal to a control circuit, and a winding for a constant voltage input to a choke coil. And a choke sub-winding for generating a voltage proportional to the ratio to operate the protection circuit.

Here, the protection circuit includes a thermal operation switch for outputting a protection operation signal by turning on a contact upon detecting abnormal heat generation of the circuit due to an overload or short circuit of the load. Further, the protection circuit may include a detection circuit that detects an overload or short-circuit state of the load and outputs a protection operation signal.

According to the switching regulator power supply device of the present invention, even if the load is overloaded or short-circuited, an excessive current flows and the output voltage drops or becomes zero, the choke coil has Despite the fluctuation of the output voltage, a constant voltage is input, so a constant voltage proportional to the choke input voltage determined by the winding ratio with the choke coil is generated in the choke sub winding, and the protection circuit Can be reliably operated. In addition, since the protection circuit has an independent circuit configuration on the secondary side, the insulation configuration of the entire device is simplified, and an increase in device cost is suppressed.

[0018]

FIG. 1 is a circuit diagram of an embodiment of the present invention. In FIG. 1, an AC input applied to input terminals 1a and 1b is rectified by a rectifying circuit 2, then smoothed by a smoothing circuit 3 having a capacitor, and converted to a direct current. Subsequent to the smoothing circuit 3, a forward converter is provided.

The forward converter includes a transformer 4 having a primary winding 4a and a secondary winding 4b, a switching element 5 using a MOS-FET, rectifier diodes 6, 7, a choke coil (choke main winding) 8, and Smoothing capacitor 9
And supplies a DC output to the load from the output terminals 10a and 10b.

The switching element 5 is turned on and off by the control circuit 11 and the main control circuit 13 so as to keep the output DC voltage constant. Note that an overcurrent detection resistor 14 is connected in series with the switching element 5, and the main control circuit 13
To perform the overcurrent protection operation.

The main control circuit 13 interrupts the current flowing through the primary winding 4a by turning on and off the switching element 5. Therefore, an in-phase secondary voltage is induced in the secondary winding 4b of the transformer 4 by the on / off operation of the switching element 5, and an LC low-frequency filter composed of the inductance L of the choke coil 8 and the capacitance C of the smoothing capacitor 9 , A rectangular wave voltage having a width corresponding to the ON time of the switching element 5 is applied. At this time, a current in a form in which a small DC current is superimposed on a large DC current flows through the choke coil 8.

As for the current flowing through the choke coil 8, its DC current becomes an output current, and the triangular wave AC current flows through the smoothing capacitor 9. Since the AC current is small and the AC impedance of the smoothing capacitor 9 is sufficiently low, the ripple voltage is low. small.

The control circuit 11 on the secondary side compares the DC output voltage with an internal reference voltage, outputs a signal corresponding to the error, drives the photocoupler light emitting unit 12a using LEDs to emit light, and outputs a phototransistor. Photocoupler light receiving section 12 using
The signal is converted into an electric signal by b, and the ON time of the switching element 5 is controlled by the main control circuit 13 so as to keep the output voltage constant.

On the secondary side of such a switching regulator power supply device, a protection circuit for detecting an overload or short-circuit state of the load and causing the main control circuit 13 to perform a protection operation is provided. This protection circuit includes a thermal operation switch (THSW:
A thermal switch) 16, a resistor 18 for suppressing surges, and a photocoupler light emitting section 20a.

Furthermore, the choke coil 8 (choke main winding) on the secondary side of the switching regulator power supply device is provided with a choke sub winding 15 in the present invention. The choke sub winding 15 has one end connected to the output side of the choke coil 8 and wound in the same phase, and the other end connected to one end of the thermal operation switch 16 of the protection circuit.

A rectangular wave voltage is input to the choke coil 8 via the rectifier diodes 6 and 7 in synchronization with the ON operation of the switching element 5, and the main control circuit 13 stabilizes the output voltage by switching. Since the ON time of the element 5 is adjusted, the input voltage to the choke coil 8 at the timing of the ON time is always constant regardless of the state of the output voltage to the load.

Therefore, the voltage generated in the choke sub-winding 15 is also constant in proportion to the choke input voltage determined by the winding ratio (N2 / N1) based on the number of turns N1 of the choke coil 8 and the number of turns N2 of the sub-winding. Voltage. The constant voltage generated in the choke sub winding 15 provided in the choke coil 8 is applied to an operation circuit in which a thermal operation switch 16, a diode 17, a surge absorbing resistor 18 and a photocoupler light emitting unit 20 are connected in series. .

A photocoupler light receiving section 20b is connected to the primary side main control circuit 13 corresponding to the photocoupler light emitting section 20a of the protection circuit. When a signal is received by the photocoupler light receiving unit 20b and input to the main control circuit 13, the main control circuit 13 suppresses an overcurrent due to an overload or short circuit of the load, for example, by fixing the switching element 5 to an off state. To control.

Next, the operation of the embodiment shown in FIG. 1 will be described. In the normal operation state, the thermal operation switch 1 of the protection circuit
6 is off, the photocoupler light emitting unit 20a is turned off, and the main control circuit 13 sets the ON time of the switching element 5 based on a signal from the control circuit 11 according to an error so as to keep the output voltage constant. Controlling.

When the load is overloaded or short-circuited and an excessive current flows in such a use state, the heat operation switch 16 of the protection circuit detects the heat generation of the secondary circuit element and turns on the contact. . At this time, the output voltage is greatly reduced or becomes zero. Regardless of the fluctuation of the output voltage, the choke sub winding 15 has a choke coil (choke main winding).
8 and a turns ratio proportional to a constant input voltage (N2 / N
A constant voltage determined by 1) is generated.

Therefore, when the thermal operation switch 16 is turned on without being affected by the fluctuation of the output voltage, the diode 1
7, a drive current determined by the resistor 18 is supplied to the photocoupler light-emitting unit 20a to drive light emission, and an operation signal received by the primary-side photocoupler light-receiving unit 20b is input to the main control circuit 13, and the switching element 5 Overcurrent suppression control is performed to minimize the on-time or fix it off (zero on-time).

FIG. 2 shows another embodiment of the present invention. In this embodiment, the protection circuit detects an overcurrent or short-circuit state of a load instead of the thermal operation switch 16 of FIG. It is characterized in that a detection circuit 21 for turning on is provided.

In this case as well, a constant voltage generated in the choke sub-winding 15 provided in the choke coil 8 is supplied to the protection circuit provided with the detection circuit 21 so that the protection circuit is activated. Even if the output voltage drops or becomes zero due to the overload or short-circuit state, a constant voltage can be applied to the protection circuit and the protection operation can be guaranteed without being affected by the output voltage.

As the detection circuit 21 in FIG. 2, an element such as a thermistor or a varistor whose impedance changes when the load is overloaded or heated in a short-circuit state can be used.

In the above embodiment, the case where the protection operation signal from the protection circuit on the secondary side is supplied to the main control circuit on the primary side using a photocoupler is taken as an example. The protection operation signal may be supplied to the control circuit provided on the next side by connecting the signal line.

[0036]

As described above, according to the present invention, even if the output voltage decreases or becomes zero due to the load being overloaded or short-circuited, the sub-choke winding provided in the choke coil has the following features. Despite the fluctuation of the output voltage, a constant voltage is generated in proportion to the choke input voltage,
The protection circuit can be operated reliably.

In addition, since the protection circuit has an independent circuit configuration on the secondary side, the insulation configuration of the entire device can be simplified and facilitated, and an increase in device cost can be suppressed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of another embodiment of the present invention.

FIG. 3 is a circuit diagram of a conventional example.

FIG. 4 is a circuit diagram of another conventional example.

[Explanation of symbols]

 1a, 1b: input terminal 2: rectifier circuit 3: smoothing circuit 4: transformer 4a: primary winding 4b: secondary winding 5: switching element 6, 7: rectifier diode 8: choke coil (choke main winding) 9 : Smoothing capacitor 10a, 10b: output terminal 11: control circuit 12a, 20a: photocoupler light-emitting unit 12b, 20b: photocoupler light-receiving unit 13: main control unit 14: overcurrent detection resistor 15: choke sub winding 16: thermal operation Switch (Thermal switch: THSW) 18: Surge suppression resistor 21: Detection circuit

Claims (3)

[Claims] 1. A switching element is connected to a primary winding of a transformer to which a direct current is input, and a rectifier diode, a choke coil and a smoothing capacitor are sequentially connected to a secondary winding of the transformer, and a control circuit controls the switching element. In a switching regulator power supply device for supplying a DC output stabilized to a constant voltage to a load by rectifying and smoothing a voltage induced in a secondary winding of a transformer by a rectifier diode, a choke coil and a smoothing capacitor by ON / OFF control, A protection circuit that detects an overload or short-circuit state of the load and outputs a protection operation signal to the control circuit; and generates a voltage proportional to a turn ratio to a constant input voltage input to the choke coil. And a choke sub-winding for operating the protection circuit. Apparatus. 2. The switching regulator power supply device according to claim 1, wherein said protection circuit outputs a protection operation signal by detecting an abnormal heating of the circuit due to a load overload or a short circuit state and turning on a contact. A switching regulator power supply device comprising a thermal operation switch for causing the switching regulator to operate. 3. The switching regulator power supply device according to claim 1, wherein the protection circuit includes a detection circuit for detecting an overload or short-circuit state of a load and outputting a protection operation signal. Switching regulator power supply.