JPH10229673A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effect constant current voltage drooping type overcurrent control through a simple circuit by an arrangement wherein an overcurrent protection circuit detects a current flowing through the secondary winding of a transformer and actuates overcurrent protective operation for a switching element based on a detection signal. SOLUTION: An overcurrent protection circuit 5 detects a current flowing through the secondary winding 32 of a transformer 3 and actuates overcurrent protective operation for switching elements 11, 12 based on a detection signal. The overcurrent protection circuit 5 comprises a current transformer 51 serving as a current detection means. The current transformer 51 has a primary winding 511 inserted a diode 422 and a second winding 322 constituting the secondary winding 32 of the transformer 3. The primary winding 511 of the current transformer 51 may be inserted a diode 421 and the primary winding 321 of the transformer 3. Consequently, constant current voltage drooping type overcurrent control can be effected through a simple circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a resonance type switching power supply.

[0002]

2. Description of the Related Art Resonant type switching power supplies have attracted attention as switching power supplies that can achieve high efficiency and low noise. Switching power supplies are roughly classified into two types, a hard switching type and a soft switching type. The resonance type switching power supply according to the present invention belongs to the category of the soft switching type. The resonance type switching power supply switches a DC power supply by a switching circuit, causes a switching output to resonate in the resonance circuit, converts the resonance output to DC using an output rectifying and smoothing circuit, and outputs the DC. As the resonance circuit system, various circuit systems such as series resonance, parallel resonance, series-parallel resonance, and multiple resonance are known. Examples of prior art documents relating to the resonance type switching power supply include JP-A-7-298614 and JP-A-7-274.
No. 499, and the like.

In a resonance type switching power supply, output stabilization is performed by controlling a switching frequency. For example, in the case of a resonance type switching power supply that operates in a frequency region higher than the resonance frequency fo of the resonance circuit,
When the output voltage is going to be higher than the reference value, the switching frequency is controlled to be higher, and when the output voltage is going to be lower, the switching frequency is controlled to be lower.

[0004]

Various technical problems to be improved remain unresolved in the resonance type switching power supply. One of them is a problem related to overcurrent control. A preferable control operation of the overcurrent control is to control the switching operation of the switching element such that a constant current voltage drooping characteristic of reducing the output voltage to substantially zero at a constant overcurrent value is obtained. However, it is not easy to obtain a constant current voltage drop characteristic in a resonance type switching power supply. This difficulty in overcurrent control stems from the essential operating characteristics of the resonant switching power supply.

Conventionally, as the overcurrent control means, a current flowing through a switching element or a primary side current flowing through a resonance circuit is detected as described in the above-mentioned prior art document, and the detection signal is used to perform overcurrent control. It was used as a signal for performing.

However, the current flowing through the switching element or the primary current flowing through the resonance circuit is a part of the pseudo sine wave, and the smaller the conduction angle (electrical angle) of the pseudo sine wave, the smaller the current peak value. . For this reason, when the operation frequency is increased and the output voltage is decreased in response to the overcurrent detection, the current peak value decreases. For this reason, in a conventional resonance type switching power supply that performs overcurrent control by detecting a current flowing through a switching element or a primary current flowing through a resonance circuit, it is difficult to perform overcurrent control with a constant current voltage drooping characteristic. is there.
In general, the output characteristic becomes a constant power drooping characteristic, so that the output current becomes too large and the circuit cannot be protected.

In the above conventional overcurrent detection method,
In order to obtain the constant current voltage drooping characteristic, the operation must be stopped at the same time as the overcurrent detection, or a circuit configuration that changes the overcurrent detection level following the change in the peak current value must be adopted. Instead, the circuit becomes complicated. With a simple circuit,
It is extremely difficult to obtain good constant current voltage drop characteristics.

An object of the present invention is to provide a resonance type switching power supply capable of performing a constant current voltage droop type overcurrent control with a simple circuit.

[0009]

In order to solve the above-mentioned problems, a switching power supply according to the present invention comprises two switching elements, a resonance circuit, a transformer, an output rectifying / smoothing circuit, and an overcurrent protection circuit. Including.

[0010] The two switching elements are connected in series, and both ends of the series circuit are led to a DC power supply and driven alternately. The transformer has at least a primary winding,
And a secondary winding. The resonance circuit has a resonance capacitor and a resonance inductor.

The resonance capacitor, the resonance inductor, and the primary winding of the transformer are connected in series, and both ends of a series circuit are connected to the connection point of the two switching elements, and the series connection is formed by the two switching elements. It is connected between one end of the circuit. The output rectifying / smoothing circuit is connected to the secondary winding of the transformer. The overcurrent protection circuit detects a current flowing on the secondary winding side of the transformer, and based on a detection signal,
An overcurrent protection operation is given to the switching element.

In the switching power supply according to the present invention,
The input DC power supply is switched by alternately operating two switching elements connected in series, and the switching output is supplied to the resonance circuit and the primary winding of the transformer.

A resonance capacitor and a resonance inductor forming a resonance circuit and a primary winding of a transformer are connected in series between a connection point of the two switching elements and one end of a series circuit formed by the two switching elements. Since both ends of the connected series circuit are connected, a pseudo sine wave current corresponding to the resonance frequency of the resonance circuit flows through the resonance circuit and the primary winding of the transformer due to the alternate operation of the two switching elements. At this time, an induced voltage is generated in the secondary winding coupled to the primary winding. This induced voltage is converted to direct current by an output rectifying and smoothing circuit connected to the secondary winding of the transformer, and is output.

The overcurrent protection circuit detects a current flowing on the secondary winding side of the transformer, and gives an overcurrent protection operation to the switching element based on the detection signal.

The current flowing on the secondary winding side of the transformer differs depending on the circuit system of the output rectifying / smoothing circuit. When the output rectifying and smoothing circuit is of a choke input type including an output choke coil, a trapezoidal current flows through the secondary winding of the transformer. The trapezoidal current becomes a triangular wave when the output voltage drops to zero volts. Further, the peak value becomes substantially equal to the output current. Therefore, by detecting this current,
By converting the voltage into a voltage signal or the like, overcurrent control of the constant current voltage drooping characteristic can be performed.

When the output rectifying / smoothing circuit is a capacitor input type that does not include an output choke coil,
A sinusoidal current flows through the secondary winding of the transformer. Therefore, by detecting this current and converting the average value into a voltage signal or the like, overcurrent control of the constant current voltage drooping characteristic can be performed.

Other objects, configurations and advantages of the present invention will be described in more detail with reference to the accompanying drawings which are embodiments.

[0018]

FIG. 1 is an electric circuit diagram of a switching power supply according to the present invention. As shown, the switching power supply according to the present invention includes a switching circuit 1, a resonance circuit 2, a transformer 3, an output rectifying and smoothing circuit 4, an overcurrent protection circuit 5, and a control circuit 6.

The switching circuit 1 switches the input DC power source Vin. The switching circuit 1 has a first switching element 11 and a second switching element 12. The first switching element 11 and the second switching element 12 are composed of FETs and the like, and their main circuits are connected in series with each other, and both ends thereof are connected to the DC power supply 7. The DC power supply 7 is usually configured as a rectifying and smoothing circuit that converts AC power into DC. The DC power supply 7 may be provided as a part of the switching power supply, or may be an external element.

The transformer 3 includes at least a primary winding 31
And a secondary winding 32. The embodiment shows a secondary winding structure suitable for a case where the output rectifying / smoothing circuit 4 is a dual-wave rectifying circuit type. The secondary winding 32 is composed of a first winding 321.
And two windings of a second winding 322, and the first winding 321 and the second winding 322 have one ends connected to each other.

The resonance circuit 2 has a resonance capacitor 21 and a resonance inductor 22. The resonance capacitor 21 and the resonance inductor 22 are connected in a circuit loop including the switching circuit 1 and the primary winding 31 of the transformer 3. In the embodiment, the resonance capacitor 21 is connected between one end of the primary winding 31 of the transformer 3 and a connection point of the first switching element 11 and the second switching element 12, and the resonance inductor 22 is connected to the transformer 3 Primary winding 31
And the main electrode of the second switching element 12. Therefore, the resonance circuit 2 forms a series resonance circuit including the resonance capacitor 21 and the resonance inductor 22.

The output rectifying / smoothing circuit 4 is connected to the secondary winding 32 of the transformer 3 and converts an induced voltage generated in the secondary winding 32 into DC and outputs the DC. The output rectifying / smoothing circuit 4 has a smoothing circuit 41 composed of a choke input circuit. The smoothing circuit 41 has an output choke coil 411 and an output smoothing capacitor 412. The rectifier circuit 42 has a first diode 421 and a second diode 422.
The anode of the first diode 421 is connected to the first winding 321.
And the anode of the second diode 422 is connected to the other end of the second winding. The cathodes of the first diode 421 and the second diode 422 are connected to each other, and are connected to one end of an output choke coil 411 constituting the smoothing circuit 41.

The overcurrent protection circuit 5 detects a current flowing on the secondary winding 32 side of the transformer 3 and, based on the detection signal,
The switching elements 11 and 12 are provided with an overcurrent protection operation. The illustrated overcurrent protection circuit 5 includes a current transformer 51 serving as current detection means. The primary winding 511 of the current transformer 51 is connected to the secondary winding 3 of the transformer 3.
2 and a diode 422. The primary winding 511 of the current transformer 51 can be inserted between the first winding 321 of the transformer 3 and the diode 421.

In the case of the embodiment, since the output rectifying / smoothing circuit 4 includes the output choke coil 411, the current IF1 flowing through the primary winding 511 of the current transformer 51 has a trapezoidal waveform. The peak value of the current IF1 is the output current I
It corresponds to the increase or decrease of o. Therefore, the overcurrent protection circuit 5 detects the voltage V1 appearing on the secondary winding 512 of the current transformer 51.
It is reasonable to include a circuit for peak-holding.
In the embodiment, the voltage appearing on the secondary winding 512 is peak-held by the diode 52 and the capacitor 53,
The detection signal S1 is output.

The control circuit 6 controls the switching circuit 1 so that the output voltage Vo output from the output rectifying / smoothing circuit 4 becomes constant. The control circuit 6 controls the switching circuit 1 in a frequency range higher than the resonance frequency fo of the resonance circuit 2.
To work.

The control circuit 6 further increases the operating frequency of the switching circuit 1 based on the detection signal S1 supplied from the overcurrent protection circuit 5, and outputs the output voltage Vo.
Protection action that lowers the

In the embodiment, the overcurrent protection circuit 5 and the control circuit 6 are represented as different blocks, but the overcurrent protection circuit 5 may be regarded as a part of the control circuit 6.

A switching power supply according to the present invention switches a DC power supply inputted by a switching circuit 1 and outputs the switching output to a resonance circuit 2 and a transformer 3.
To the primary winding 31. The resonance capacitor 21 and the resonance inductor 22 constituting the resonance circuit 2 are connected in a circuit loop including the switching circuit 1 and the primary winding 31 of the transformer 3. Therefore, a pseudo sine wave current corresponding to the resonance frequency of the resonance circuit 2 flows through the resonance circuit 2 and the primary winding 31 of the transformer 3 by the switching operation of the switching circuit 1. At this time, an induced voltage is generated in the secondary winding 32. This induced voltage is applied to the secondary winding 32 of the transformer 3.
Is converted into a direct current by the output rectifying / smoothing circuit 4 connected to and output.

The control circuit 6 increases the operating frequency when the output voltage is high, and decreases the operating frequency when the output voltage is low so that the output voltage Vo output from the output rectifying / smoothing circuit 4 becomes constant. Next, the switching circuit 1 is controlled. Thereby, a constant voltage output is obtained.

Next, the overcurrent protection operation will be described. When the output current Io increases, the peak value of the trapezoidal current IF1 flowing through the primary winding 511 of the current transformer 51 increases, so that the peak value of the voltage appearing on the secondary winding 512 of the current transformer 51 also increases. The peak value of this voltage is held by a peak hold circuit including a diode 52 and a capacitor 53, and is supplied to the control circuit 6 as a detection signal S1 for performing overcurrent protection.

When the detection signal S1 supplied from the overcurrent protection circuit 5 corresponds to a preset overcurrent value, the control circuit 6 increases the operating frequency of the switching circuit 1 and outputs the output voltage Vo. And an overcurrent protection operation for reducing the constant current voltage drop characteristic can be performed.

FIG. 2 is a diagram showing another embodiment of the switching power supply according to the present invention. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.
In this embodiment, the output rectifying and smoothing circuit 4 is of a capacitor input type that does not include an output choke coil. More specifically, the smoothing circuit 41 only has the output smoothing capacitor 412. The rectifier circuit 42 has a first diode 421 and a second diode 422. The anode of the first diode 421 is connected to the first winding 3
The other end of the second diode 422 is connected to the other end of the second diode 422. The cathodes of the first diode 421 and the second diode 422 are connected to each other, and are connected to one end of an output smoothing capacitor 412 constituting the smoothing circuit 41.

When the output rectifying / smoothing circuit 4 is of the capacitor input type, the current IF2 flowing through the first winding 321 and the diode 421 constituting the secondary winding 32 of the transformer 3, and the second winding 322 and diode 4
Each of the currents IF1 flowing through 22 is a half-sine wave. The current IF0 flowing through the common line connecting the connection point between the first winding 321 and the second winding 322 and the output terminal is:
A full sine wave is obtained by superimposing the two half sine waves.

The primary winding 511 of the current transformer 51 constituting the overcurrent protection circuit 5 is inserted into a common line connecting the connection between the first winding 321 and the second winding 322 and the output terminal. Accordingly, the sine full-wave current IF0 flows through the primary winding 511 of the current transformer 51. This sinusoidal full-wave current IF0 is supplied to the voltage signal V
1 and is output from the secondary winding 521 as a voltage signal V1.

The voltage signal V 1 appearing on the secondary winding 521 of the current transformer 5 passes through the capacitor 54, is rectified by the diodes 521 and 522, and is averaged by the inductor 55 and the capacitor 53.

Since the average value of the sinusoidal full-wave current IF0 flowing through the primary winding 511 of the current transformer 51 is proportional to the output current Io, the secondary winding 521 of the current transformer 51
Is also proportional to the output current Io. Therefore, based on the averaged detection signal S1,
Overcurrent protection can be performed.

FIG. 3 is a diagram showing another embodiment of the switching power supply according to the present invention. In the figure, the same components as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted.
In this embodiment, the secondary winding 51 of the current transformer 51 is used.
2 is rectified by diodes 521 and 522, and then the inductor 55 and the capacitor 53
Average.

FIG. 4 is a diagram showing another embodiment of the switching power supply according to the present invention. In the drawings, the same components as those in FIGS. 2 and 3 are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, after the voltage signal V1 appearing in the secondary winding 512 of the current transformer 51 is rectified by the diode 52, the voltage signal V1 is averaged by the resistor 56 and the capacitor 53.

While the contents of the present invention have been described with reference to the preferred embodiments, those skilled in the art will be able to make various changes and modifications based on the basic technical concept of the present invention, the disclosed technical contents, and the like. It's obvious what you can do.

[0040]

As described above, according to the present invention, it is possible to provide a resonance type switching power supply capable of performing a constant current voltage droop type overcurrent control with a simple circuit.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram of a switching power supply according to the present invention.

FIG. 2 is an electric circuit diagram showing another embodiment of the switching power supply according to the present invention.

FIG. 3 is an electric circuit diagram showing still another embodiment of the switching power supply according to the present invention.

FIG. 4 is an electric circuit diagram showing still another embodiment of the switching power supply according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Switching circuit 2 Resonant circuit 21 Resonant capacitor 22 Resonant inductor 3 Transformer 31 Primary winding 32 Secondary winding 4 Output rectification smoothing circuit 5 Overcurrent protection circuit 6 Control circuit

Claims (5)

[Claims] 1. A switching power supply including two switching elements, a resonance circuit, a transformer, an output rectifying / smoothing circuit, and an overcurrent protection circuit, wherein the two switching elements are connected in series, and Both ends of the circuit are guided to a DC power supply and are alternately driven. The transformer includes at least a primary winding and a secondary winding. The resonance circuit includes a resonance capacitor and a resonance capacitor. An inductor, wherein the resonance capacitor, the resonance inductor, and the primary winding of the transformer are connected in series, and both ends of a series circuit are connected by a connection point of the two switching elements and the two switching elements. The output rectifying / smoothing circuit is connected to the secondary winding of the transformer. The overcurrent protection circuit is a switching power supply that detects a current flowing on the secondary winding side of the transformer and provides an overcurrent protection operation to the switching element based on a detection signal. 2. The switching power supply according to claim 1, wherein the overcurrent protection operation increases the operating frequency of the switching element and decreases the output voltage. 3. The switching power supply according to claim 1, wherein said overcurrent protection circuit includes a current transformer for current detection. 4. The switching power supply according to claim 3, wherein the output rectifying and smoothing circuit includes an output choke coil, and the overcurrent protection circuit peak-holds an output voltage of the current transformer. Switching power supply including circuits. 5. The switching power supply according to claim 3, wherein the output rectifying and smoothing circuit is a capacitor input type, and the overcurrent protection circuit averages and outputs an output voltage of the current transformer. Switching power supply including circuits.