JP2001309656A - Ringing choke converter and overload detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ringing choke converter which has an overload protection function which makes it possible to avoid making its efficiency worse and occurrence of overheat in a resistor without using a resistor for overcurrent detection. SOLUTION: In the ringing choke converter which outputs a predetermined constant voltage by switching a DC voltage which is produced by rectifying an AC voltage input and smoothed with a smoothing capacitor by a switching element Q1, and has an overcurrent protection circuit which stops the operation of the switching element Q1 when the converter overload, the overcurrent protection circuit 3 is connected in parallel with the smoothing capacitor C1, and constituted of a ripple voltage detection circuit 3a which extracts a ripple voltage and a control means 3b which is connected to the control terminals of the switching element Q1, and stops the operation of the switching element Q1 when the ripple voltage exceeds a threshold voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ringing choke converter and an overload detection method.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram of a conventional general ringing choke converter.

In FIG. 3, a ringing choke converter includes a commercial AC voltage input terminal Vin, a rectifying bridge diode D1 for rectifying an input AC voltage, and a primary smoothing rectified pulsating voltage to a DC voltage. Capacitor C1, primary winding N1, secondary winding N2, control winding N
, A switching element Q1 and a current detection resistor R8 connected in series to both ends of a primary smoothing capacitor C1 via a primary winding N1 of the transformer T1, a control winding N3 and a switching element Q1 of the transformer T1. An oscillation control circuit 1 configured between the control terminals of the switching element Q1, a starting resistor R1 connected between the positive terminal of the primary smoothing capacitor C1 and the control terminal of the switching element Q1, and an anode connected to the negative terminal of the secondary winding N2 of the transformer T1. A rectifying diode D2 connected to rectify the AC output voltage, and a secondary smoothing capacitor C4 connected between the cathode of the rectifying diode D2 and the positive electrode of the secondary winding N2 of the transformer T1 for smoothing the rectified pulsating voltage. A positive output voltage terminal (+) and a negative output voltage terminal (-) respectively connected to both ends of the secondary smoothing capacitor C4; An output voltage detection circuit 2 connected between the voltage terminals (+) and (-); an output voltage detection circuit 2; an output voltage detection circuit 2; It comprises a current protection circuit 4.

The oscillation control circuit 1 has a capacitor C2 and a resistor R2 connected in series between a positive electrode of a control winding N3 and a control terminal of a switching element Q1, and a collector terminal and an emitter terminal connected to the switching element Q1. An NPN transistor Tr1 connected between the control terminal and the control winding N3, and a connection point between the control terminal of the switching element Q1 and the control winding N3 connected in series to a base terminal of the transistor Tr1 And a capacitor C3.

The output voltage detecting circuit 2 includes resistors R4 and R5 connected in series between output voltage terminals (+) and (-).
And a resistor R3 and a photodiode PD1 connected in series between the output voltage terminals (+) and (-), and a shunt regulator Sr whose reference terminal is connected to a connection point between the resistors R4 and R5. I have. The overcurrent protection circuit 4 includes a current detection resistor R8, a capacitor C7 connected to both ends of the current detection resistor R8,
The collector terminal includes a control terminal of the switching element Q1, and the base terminal and the emitter terminal include an NPN transistor Tr3 connected to both ends of the current detection resistor R8.

In such a configuration, the AC input voltage Vin
Are rectified by a rectifying bridge diode D1 and smoothed by a smoothing capacitor C1 to be a DC voltage. The control terminal (gate) of the switching element Q1 is charged by the DC voltage through the starting resistor R1, the potential rises, and the switching element Q1 starts an ON operation. A DC voltage is applied to the primary winding N1 of the transformer with the positive side being positive, and a voltage is induced in the control winding N3 with the positive side being positive. This voltage is positively fed back to the control terminal of the switching element Q1 via the oscillation control circuit 1, and the switching element Q1 is completely turned on.

When the switching element Q1 is turned on, a primary current Id flows through the primary winding N1 of the transformer T1. The ON period of the switching element Q1 is controlled by the oscillation control circuit 1. Specifically, when the output voltage attempts to rise, the output voltage detection circuit 2 detects this, the shunt regulator Sr is turned on, the photodiode PD1 is turned on, the phototransistor PT1 is turned on, and the transistor Tr1 of the oscillation control circuit 1 is turned on. Turns on. The oscillation control circuit 1 discharges the gate charge of the switching element Q1 through the transistor Tr1, and turns off the switching element Q1. Energy is stored in the primary winding N1 of the transformer T1 until the switching element Q1 is turned off. When the switching element Q1 is turned off, the polarity of all the windings N1 to N3 of the transformer T1 is reversed by the back electromotive force. Therefore, the transformer T1
The secondary current If for charging the smoothing capacitor C4 flows from the negative electrode side of the secondary winding N2 through the diode D2, and the stored energy is released. When the energy is completely released, the polarities of all the windings N1 to N3 of the transformer T1 are inverted again, and the gate of the switching element Q1 is started to be charged again via the oscillation control circuit 1, and the switching element Q1 is turned on. . By repeating these series of operations, the ringing choke converter oscillates and outputs a predetermined constant voltage Vo between the output terminals (+) and (-).

[0008] Here, the ringing choke converter is used in an abnormal situation in which the power supply destination connected to the output terminals (+) and (-) is overloaded due to, for example, a failure. There is a possibility that ignition or smoking may occur due to double failure of the main body or the ringing choke converter.

In order to solve this problem, a current detecting resistor R8, a capacitor C7, an NPN transistor Tr
3 constitutes an overcurrent protection circuit 4, which constantly monitors the voltage across the current detection resistor R8, which is proportional to the rise in load power, and immediately stops the oscillating operation of the ringing choke converter when this voltage rises.

That is, when the voltage between both ends of the current detecting resistor R8 becomes higher and the voltage of the capacitor C7 becomes higher than the base-emitter ON voltage of the transistor Tr3, the transistor Tr3 turns on and the switching element Q1
Is lowered to the collector-emitter saturation voltage (to a low level), the switching element Q1 is turned off, and the oscillation operation is stopped. With such a configuration, in an abnormal situation such as an overload on the main body side to which power is supplied, it is possible to avoid ignition, smoking, and the like due to a double failure of the main body or the ringing choke converter.

[0011]

However, in the configuration of the conventional ringing choke converter described above,
Since a current always flows through the current detecting resistor R8 inserted in series with the primary side main loop constituted by the primary smoothing capacitor C1, the primary winding N1, and the switching element Q1, heat loss is generated, and the ringing choke converter is turned off. Efficiency deteriorates, and in some cases, the current detection resistor R
8 could overheat and cause a serious failure such as ignition.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and detects overload without using a current detection resistor, thereby avoiding the risk of deterioration in efficiency and overheating of the resistor. An object of the present invention is to provide a ringing choke converter having a protection circuit and an overload detection method.

[0013]

In order to achieve the above object, a ringing choke converter according to a first aspect of the present invention rectifies an AC voltage input and smoothes a DC voltage generated by a smoothing capacitor to a switching element. In the ringing choke converter provided with an overcurrent protection circuit for switching and outputting a predetermined constant voltage and stopping the operation of the switching element when overloaded,
The overcurrent protection circuit is connected in parallel to the smoothing capacitor, is connected to a ripple voltage detection circuit that extracts a ripple voltage of the smoothing capacitor, and is connected to a control terminal of the switching element, and when the ripple voltage exceeds a threshold value. And control means for stopping the operation of the switching element.

A ringing choke converter according to a second aspect of the present invention is the ringing choke converter according to the first aspect, wherein the ripple voltage detection circuit is a high-pass filter.

According to a third aspect of the present invention, in the ringing choke converter according to the first aspect, the control means includes a rectifying / smoothing circuit for rectifying and smoothing the ripple voltage and a control terminal of the switching element. A second switching element that is connected and stops the operation of the switching element when the output voltage of the rectifying / smoothing circuit exceeds a threshold value.

A ringing choke converter according to a fourth aspect is the ringing choke converter according to the third aspect, wherein the second switching element has a collector connected to a control terminal of the switching element, an emitter connected to the ground, and a base connected to the rectifier. -Each of the transistors is connected to a smoothing circuit, and is turned on when the output voltage of the rectifying / smoothing circuit exceeds a base-emitter ON voltage.

According to a fifth aspect of the present invention, there is provided a method for detecting an overload in a ringing choke converter, wherein a DC input voltage generated by rectifying an AC voltage input and smoothed by a smoothing capacitor is switched by a switching element to output a predetermined constant voltage. A method for detecting an overload of a ringing choke converter including an overcurrent protection circuit for stopping the operation of the switching element when the load is overloaded, wherein an overload is detected by extracting a ripple voltage of the smoothing capacitor. .

According to a sixth aspect of the present invention, in the overload detecting method for a ringing choke converter according to the fifth aspect, the ripple voltage is extracted by a high-pass filter connected in parallel to the smoothing capacitor. It is characterized by doing.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a circuit diagram of a ringing choke converter according to the present invention. The same components as those of the ringing choke converter of the conventional example shown in FIG. 3 are denoted by the same reference numerals, detailed description thereof will be omitted, and only differences from the conventional example will be described.

The circuit of the ringing choke converter shown in FIG. 1 is different from the circuit of the general ringing choke converter shown in FIG. 3 in that a primary current is used as an overcurrent protection circuit instead of the current detection resistor R8 and the overcurrent protection circuit 4. A ripple voltage detection overcurrent protection circuit 3 is provided between both ends of the smoothing capacitor C1 and between the control terminal of the switching element Q1 and the ground. This ripple voltage detection overcurrent protection circuit 3
Are a ripple voltage detection circuit 3a for detecting a ripple voltage of the smoothing capacitor C1, and a control means 3b for stopping the oscillation operation of the oscillation control circuit 1 when the detection voltage of the ripple voltage detection circuit 3a exceeds a threshold value (predetermined value). It is composed of

The ripple voltage detecting circuit 3a includes a capacitor C5, a resistor R6, and a resistor R7 connected in series to both ends of a primary smoothing capacitor C1. The ripple voltage detection circuit 3a having such a configuration is a high-pass filter,
The ripple voltage of the smoothing capacitor C1 can be extracted at the connection point between the resistors R6 and R7.

The control means 3b includes an NPN transistor Tr2 as a second switching element having a collector terminal connected to the control terminal of the switching element Q1, an emitter terminal connected to the negative terminal of the primary smoothing capacitor, and an anode terminal connected to a resistor. Connected to the connection point between R6 and resistor R7,
A diode D3 having a cathode terminal connected to the base terminal of the NPN transistor Tr2, and a capacitor C6 connected in parallel between the base and the emitter of the transistor Tr2.
And a rectifying / smoothing circuit comprising:
For the sake of explanation, the connection point between the resistors R6 and R7 is a, the base terminal of the transistor Tr2 is b, and the switching element Q
One control terminal is represented by c.

The circuit operation will be described below with reference to the circuit diagram of FIG. 1 and the operation waveform diagram of FIG.

FIG. 2 is a diagram showing an example of an operation waveform of the ripple voltage detection overcurrent protection circuit 3 of the ringing choke converter shown in FIG. In FIG. 2, (1) is a voltage waveform between both ends of the primary smoothing capacitor C1, and (2) is
The voltage waveform between point a and GND, (3) shows the voltage waveform between point b and GND, and (4) shows the voltage waveform between point c and GND. Indicates a waveform at the time of normal load, and indicates a waveform at the time of overload.

A ripple voltage appears at both ends of the primary side smoothing capacitor C1 in a form superimposed on the DC voltage. This ripple voltage shows a small ripple voltage Vrip1 as shown in FIG. 2A under a normal load. Then, only the ripple voltage Vrip1 is extracted by the ripple voltage detection circuit (high-pass filter) including the capacitor C5 and the resistors R6 and R7 to obtain a voltage waveform as shown in FIG. The extracted ripple voltage Vrip1 is rectified and smoothed by a rectifying / smoothing circuit including a diode D3 and a capacitor C6, as shown in FIG.
B-GND voltage (DC voltage) as shown in (3)
Get V1.

The b-GND voltage V1 is equal to the base-emitter ON voltage Vb of the transistor Tr2 under normal load.
Since it is smaller than e (on), the transistor Tr2 is in the off state, the high impedance is between the collector and the emitter, and the high impedance is between c and GND. At this time, a normal oscillation waveform (switching frequency) is applied to the control terminal of the switching element Q1 (FIG. 2 (4)). As a result, the ringing choke converter operates normally.

On the other hand, at the time of overload, a large ripple voltage Vr is applied across the smoothing capacitor C1 as shown in FIG.
ip2 appears. This ripple voltage Vrip2 is extracted (Fig. 2
(2)) and rectified and smoothed to obtain a b-GND voltage (DC voltage) V2 as shown in FIG. 2 (3).

The b-GND voltage V2 is equal to the transistor T
When the base-emitter ON voltage of r2 is reached, the transistor Tr2 is turned on, the impedance between c and GND becomes low impedance, and the control terminal voltage of the switching element Q1 is reduced to the collector-emitter saturation voltage Vce (sat) of the transistor Tr2. Lower. As a result, the switching element Q1 is turned off, and the oscillation operation is stopped (see FIG. 2).
(4)).

As described above, the ripple voltage superimposed on both ends of the primary side smoothing capacitor C1 is detected by the ripple voltage detection overcurrent protection circuit 3, and if the ripple voltage is larger than the threshold value, the control terminal voltage of the switching element Q1 is set to Low.
Then, the oscillation operation of the ringing choke converter is stopped. As a result, overload can be detected without using a current detection resistor, and the ringing choke converter can be protected by avoiding deterioration of efficiency, ignition due to overcurrent, and the like.

[0031]

As described above, according to the first and fifth aspects of the present invention, the ripple voltage of the smoothing capacitor for rectifying the AC voltage input and smoothing with the smoothing capacitor to generate the DC voltage is extracted. By stopping the operation of the switching element when the ripple voltage exceeds the threshold, overload can be detected with a simple circuit configuration without using a current detection resistor, and the efficiency is reduced and the resistance due to overcurrent is reduced. Can be avoided.

According to the second and sixth aspects of the present invention, a simple and inexpensive configuration can be achieved by using a high-pass filter as the ripple voltage detection circuit.

According to the third aspect of the present invention, the control means for stopping the operation of the switching element includes a rectifying / smoothing circuit for rectifying and smoothing the ripple voltage, and a controller for controlling the output voltage of the rectifying / smoothing circuit to exceed a threshold value. A simple circuit configuration can be achieved by using the second switching element that stops the operation of the control circuit.

According to the fourth aspect of the present invention, an inexpensive overvoltage protection circuit can be provided by using a transistor as the second switching element.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a ringing choke converter according to the present invention.

FIG. 2 is a diagram showing an example of an operation waveform of a ripple voltage detection overcurrent protection circuit of the ringing choke converter shown in FIG.

FIG. 3 is a circuit diagram of a conventional general ringing choke converter.

[Explanation of symbols]

1 Oscillation control circuit 2 Output voltage detection circuit 3 Ripple voltage detection overcurrent protection circuit (Overcurrent protection circuit) 3a Ripple voltage detection circuit (High pass filter) 3b Control means 4 Overcurrent protection circuit Vin Commercial AC voltage (+) Output voltage terminal Negative pole of output voltage terminal T1 Transformer N1 Primary winding of transformer T1 N2 Secondary winding of transformer T1 N3 Control winding of transformer T1 Switching element D1 Rectifying bridge diode D2, D3 Rectifying diode C1 Primary smoothing capacitor C2 Secondary smoothing capacitor C3 to C7 Capacitor PD1 Photodiode PT1 Phototransistor R1 Start-up resistor R2 to R7 Resistance element Sr Shunt regulator Tr1, Tr2 NPN type transistor a Ripple voltage detection Ripple voltage peak value detection of overcurrent protection circuit 3 The control terminal of the base terminal c the switching element Q1 of the child b NPN transistor Tr2

Claims (6)

[Claims] An AC voltage input is rectified, a DC voltage generated by smoothing with a smoothing capacitor is switched by a switching element to output a predetermined constant voltage, and operation of the switching element is stopped when an overload occurs. In a ringing choke converter including a current protection circuit, the overcurrent protection circuit is connected in parallel to the smoothing capacitor, and connected to a ripple voltage detection circuit that extracts a ripple voltage of the smoothing capacitor; and a control terminal of the switching element. And a control means for stopping the operation of the switching element when the ripple voltage exceeds a threshold value. 2. The ringing choke converter according to claim 1, wherein said ripple voltage detection circuit is a high-pass filter. 3. The rectifying / smoothing circuit for rectifying and smoothing the ripple voltage, wherein the rectifying / smoothing circuit is connected to a control terminal of the switching element, and when the output voltage of the rectifying / smoothing circuit exceeds a threshold value. The ringing choke converter according to claim 1, further comprising a second switching element for stopping the operation of the switching element. 4. The second switching element, wherein a collector is connected to a control terminal of the switching element, an emitter is connected to the ground, and a base is connected to the rectification / smoothing circuit, and an output voltage of the rectification / smoothing circuit is a base. 4. The ringing choke converter according to claim 3, wherein the transistor is turned on when the emitter-to-emitter turn-on voltage is exceeded. 5. A DC input voltage generated by rectifying an AC voltage input and smoothing with a smoothing capacitor is switched by a switching element to output a predetermined constant voltage.
An overload detection method for a ringing choke converter including an overcurrent protection circuit for stopping operation of the switching element when overloaded, wherein a ringing choke is extracted by extracting a ripple voltage of the smoothing capacitor. Converter overload detection method. 6. The method according to claim 5, wherein the ripple voltage is extracted by a high-pass filter connected in parallel to the smoothing capacitor.