JP2002165447A - Chopper switching power-supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chopper switching power supply unit, capable of constituting the filter of one stage located on the secondary side of a transformer. SOLUTION: A switching device 9 is turned on synchronously with the switching of voltage generated at a secondary winding 1B of the transformer 1. Therefore, energy can be positively supplied to a load from the secondary winding 1B, without attaching a conventional filter on the input of the chopper circuit 13. When voltage level across the secondary winding 1B is high, a turn- off period for the switching device 9 becomes long, and when the voltage level is low, the turn-off period for the switching device 9 becomes short. It is thus possible to stabilize the output voltage Vo.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chopper type switching power supply device in which a desired output voltage is obtained by a chopper circuit on a secondary side of a transformer.

[0002]

Generally, this type of chopper type switching power supply device is widely applied to a multi-output power supply device capable of taking out a separate output voltage from each output terminal. FIG. 7 is a circuit diagram showing an example of such a chopper type switching power supply device, wherein 1 is a transformer for insulating a primary side from a secondary side, and 2 is a transistor or a MOS type F.
The transformer 1 and the main switching element 2 constitute an inverter circuit 3 which is a main switching element such as an ET. Then, by switching the main switching element 2, the DC input voltage Vin of the inverter circuit 3 is intermittently applied to the primary winding 1A of the transformer 1.

On the other hand, the secondary winding 1B of the transformer 1 has a rectifying and smoothing circuit 8 on the chopper input side comprising a rectifying diode 4, a flywheel diode 5, a choke coil 6 and a smoothing capacitor 7, and a switching comprising a PNP transistor. Element 9, flywheel diode 10,
A chopper circuit 13 including a choke coil 11 and a smoothing capacitor 12 is connected in order. A control circuit 14 controls the conduction width of the drive pulse supplied to the switching element 9 in accordance with the detection level of the DC output voltage Vo generated between both ends of the smoothing capacitor 12, thereby stabilizing the DC output voltage Vo. It is trying to make it. Although not shown here, the secondary windings 1C of the other transformers 1 are provided with the same rectifying / smoothing circuit 8, chopper circuit 13 and control circuit 14 so as to stabilize each output voltage. I have to.

When the main switching element 9 is turned on, the DC input voltage Vin is applied to the primary winding 1A of the transformer 1.
, A positive voltage is induced at the dot side terminal of the secondary winding 1B, and the rectifier diode 4 is turned on.
The flywheel diode 5 turns off. This allows
Rectifying diode 4
Through the choke coil 6 and the smoothing capacitor 7. On the other hand, when the main switching element 2 turns off, the rectifier diode 4 turns off and the flywheel diode 5 turns on. As a result, the choke coil 6 releases the energy stored up to that time, and a current whose linear slope decreases with time flows through the choke coil 6 and the smoothing capacitor 7 via the flywheel diode 5. Thus, the voltage induced in the secondary winding 1 </ b> B is
Is applied to the chopper circuit 13 as a DC voltage.

The chopper circuit 13 widens the pulse conduction width to the switching element 9 when the DC output voltage Vo is high, and narrows the pulse conduction width to the switching element 9 when the DC output voltage Vo is low. The DC voltage from the rectifying / smoothing circuit 8 is converted into a rectangular wave. This rectangular wave is rectified and smoothed by the choke coil 11 and the smoothing capacitor 12 to obtain a desired DC output voltage Vo.

In a chopper type switching power supply device having a chopper circuit on the secondary side of the transformer 1 as described above, the voltage generated in the secondary winding 1B is filtered by a smoothing filter comprising a choke coil 6 and a smoothing capacitor 7. Since it is smoothed to a DC voltage and applied to the chopper circuit 13,
Choke coil 11 and smoothing capacitor at the subsequent stage
In combination with 12, a two-stage smoothing filter had to be provided. Therefore, there has been a problem that the cost is increased and the power supply device cannot be downsized.

Therefore, the present invention solves the above problems,
It is an object of the present invention to provide a chopper type switching power supply device in which a smoothing filter on the secondary side of a transformer can be configured in one stage.

[0008]

In order to achieve the above object, a chopper type switching power supply according to the present invention comprises a secondary winding of a transformer connected to a chopper circuit having a switching element. In a chopper type switching power supply device for stabilizing an output voltage by controlling a pulse signal width, the PWM control circuit turns on the switching element at a timing when a voltage generated between the secondary windings is switched. The switching element is turned off in accordance with a voltage level generated between the secondary windings.

According to the above configuration, since the switching element is turned on at a timing synchronized with the switching of the voltage generated in the secondary winding of the transformer, a smoothing filter is not provided on the input side of the chopper circuit as in the related art. However, it is possible to reliably supply energy from the secondary winding to the load. Therefore, the smoothing filter on the secondary side of the transformer can be configured in one stage, and cost reduction and downsizing of the power supply device can be achieved. Also, depending on the voltage level generated between the secondary windings of the transformer, the turn-off time of the switching element is prolonged when the voltage level is high, and conversely, when the voltage level is low, the turn-off time of the switching element is low. The time is shortened, so that the output voltage can be stabilized.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a chopper type switching power supply according to the present invention will be described with reference to the accompanying drawings. The same parts as in the conventional example are denoted by the same reference numerals,
The description of the common part will be omitted because it is duplicated.

FIG. 1 and FIG. 2 show a first embodiment of the present invention. In FIG. 1 showing the overall configuration of a power supply device, a switching element 9 constituting a chopper circuit 13 is shown in FIG.
Is connected between one end (dot side terminal) of the secondary winding 1B of the transformer 1 and the anode of the rectifier diode 4 to form a series circuit with a resistor 21 as a current detector. A synchronizing circuit 22 outputs a signal synchronized with a positive voltage generated at the dot side terminal of the secondary winding 1B of the transformer 1. The synchronizing signal from the synchronizing circuit 22 is a pulse conduction of the switching element 9. It is sent to a PWM (pulse width) control circuit 23 for controlling the width. In addition, between output voltage lines of the DC output voltage Vo, resistors 26 and 27 as output voltage detection circuits are provided to monitor a voltage level generated in the secondary winding 1B.
And a voltage detection signal obtained by dividing the DC output voltage Vo is sent to the PWM control circuit 23 from the connection point of the resistors 26 and 27. Then, when the dot side terminal of the secondary winding 1B of the transformer 1 rises to the positive polarity, an ON pulse signal is supplied to the switching element 9 in synchronization with the synchronization signal, and then the secondary winding 1B is supplied to the secondary winding 1B. This is to supply an ON trigger signal to the switching element 9 at a timing according to the generated voltage level. Specifically, when the voltage level generated between the secondary windings 1B when the main switching element 2 is turned on is low, the on time of the switching element 9 is extended, and conversely, when the main switching element 2 is turned on, the secondary winding is turned on. When the voltage level generated during 1B is high, the off time of the switching element 9 is extended to stabilize the output voltage Vo between both ends of the load.

Reference numeral 24 denotes an overcurrent protection circuit for preventing an overcurrent from flowing on the secondary side of the transformer 1. The overcurrent protection circuit 24 includes a resistor 21 as a current detector. When the secondary current increases to a predetermined amount or more due to a load short circuit or the like, the PWM control circuit 23 is configured to reduce the pulse conduction width of the drive signal to the switching element 9 to a minimum and perform an intermittent oscillation operation. I have. Then, the cathode of the flywheel diode 5 is connected to the other end of the secondary winding 1B, that is, the non-dot side terminal, and the flywheel diode 5 and the anode of the rectifier diode are connected to each other. A rectifying / smoothing circuit 25 is formed by connecting a smoothing filter composed of a series circuit of a choke coil 11 and a smoothing capacitor 12, thereby eliminating the need for the choke coil 6 and the smoothing capacitor 7 in the conventional example.

In the above configuration, as the switching element 9, it is preferable to use a MOS FET having good response characteristics here. The other secondary windings 1C have the same circuit configuration. The main switching element 2 is
On and off are driven by pulse signals having the same frequency and pulse conduction width. That is, since the ON / OFF timing of the main switching element 2 is fixed, the PWM control circuit 23 can set the OFF timing of the pulse signal to the switching element 9 earlier than the OFF timing of the main switching element.

Next, the operation of the above configuration will be described with reference to the waveform diagram of FIG. In FIG. 2,
The upper part is a voltage waveform VM generated between the secondary windings 1B of the transformer 1, and the lower part is a signal from the PWM control circuit 23 to the switching element 9.
2 shows a voltage waveform Vs of a pulse signal supplied to the power supply.

The main switching element 2 is repeatedly turned on and off at a fixed timing, and the voltage waveform VM shown in FIG.
As shown in (1), during the ON period of the main switching element 2, a positive voltage is induced at the dot side terminal of the secondary winding 1B of the transformer 1. At the same time, the synchronous circuit 22
The zero cross of the voltage generated between B is detected, and a signal synchronized with the zero cross is output to the PWM control circuit 23. In response to the synchronization signal from the synchronization circuit 22, the PWM control circuit 23 determines when a positive voltage is generated at the dot-side terminal of the secondary winding 1B a predetermined time after the synchronization circuit 22 detects the zero cross, As shown by the voltage waveform Vs in FIG. 2, an ON signal is output to the switching element 9. As a result, the switching element 9 is turned on, and energy is supplied from the secondary winding 1B to the choke coil 11, the smoothing capacitor 12, and the load through the switching element 9, the resistor 21, and the rectifier diode 4.

The PWM control circuit 23 uses a voltage detection signal obtained at the connection point between the resistors 26 and 27 at a timing corresponding to the voltage level generated between the secondary windings 1B as shown by the voltage waveform Vs in FIG. An off signal is output to the switching element 9. Thereby, the switching element 9 is turned off,
The supply of energy from the secondary winding 1B to the choke coil 11 and the smoothing capacitor 12 is cut off. In this case, the higher the voltage level generated between the secondary windings 1B when the main switching element 2 is turned on, the shorter the on-time t1 of the switching element 9 becomes, and conversely, the voltage level generated between the secondary windings 1B decreases. The lower the ON time t1 of the switching element 9 is,
Becomes longer, and the output voltage Vo is stabilized.

On the other hand, during the off-period of the main switching element 2, the energy stored so far in the choke coil 11 is discharged to the smoothing capacitor 12 and the load through the flywheel diode 5.

As described above, according to the present embodiment, the chopper circuit 13 having the switching element 9 is connected to the secondary winding 1B of the transformer 1, and the pulse signal width to the switching element 9 is a control circuit. In the chopper-type switching power supply device which stabilizes the output voltage Vo by controlling with the PWM control circuit 23, the secondary winding 1B of the transformer 1
The PWM control circuit 23 turns on the switching element 9 at a timing at which the voltage generated between them switches, and turns off the switching element 9 at a timing according to the voltage level generated between the secondary windings 1B of the transformer 1. Is composed.

In this case, the switching element 9 is turned on at the timing synchronized with the switching of the voltage generated in the secondary winding 1B of the transformer 1, so that a smoothing filter is provided on the input side of the chopper circuit 13 as in the prior art. Energy can be reliably supplied from the secondary winding 1B to the load without the need to provide the energy. Therefore, the smoothing filter (the choke coil 11) on the secondary side of the transformer 1
In addition, the smoothing capacitor 12) can be configured in one stage, so that cost reduction and downsizing of the power supply device can be achieved. Further, according to the voltage level generated between the secondary windings 1B of the transformer 1, the turn-off time of the switching element 9 is prolonged when this voltage level is high, and conversely, when the voltage level is low, the switching element 9 is turned off. Is turned off, thereby stabilizing the output voltage Vo.

In this embodiment, the current flowing through the switching element 9 is detected by a resistor 21 serving as a current detector. When the current level is equal to or higher than a predetermined value, a driving signal to the switching element 9 is transmitted to a PWM control circuit 23. An overcurrent protection circuit 24 for minimizing the pulse conduction width of the pulse width and performing an intermittent oscillation operation is provided. Thus, even if the main switching element 2 operates at a fixed ON / OFF timing having no feedback circuit, overcurrent protection can be easily performed by using the PWM control circuit 23 of the switching element 9.

The above configuration is particularly useful in a multi-output chopper type switching power supply. In other words, by having the same circuit configuration in each of the secondary windings 2B, 2C,...

Next, a second embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. The same portions as those in the first embodiment are denoted by the same reference numerals, and the description of the common portions will be omitted because they are duplicated.

In this embodiment, the switching element 9, the choke coil 11, and the resistor 21 are connected to the secondary winding 1 of the transformer 1.
B is inserted into a negative output voltage line connected to the other end of B. Specifically, the resistor 21 is connected to the secondary winding 1B.
And one end of the switching element 9 are connected between
A series circuit of a smoothing capacitor 12 and a choke coil 11 is connected between both ends of the flywheel diode 5 connected between the other end of the switching element 9 and the cathode of the rectifier diode 4. When the dot side terminal of the secondary winding 1B rises to the positive polarity, the PWM control circuit 23 supplies an ON pulse signal to the switching element 9 in synchronization with the synchronization signal, and thereafter, the PWM control circuit 23 outputs the ON pulse signal. During the period in which a positive polarity voltage is generated at the dot side terminal of the secondary winding 1B at a timing according to the voltage level generated in the above, an OFF pulse signal is supplied to the switching element 9. Also in this case, when the main switching element 2 is turned on, the secondary winding 1
When the voltage level generated between B and B is low, the ON time of the switching element 9 is extended, and conversely, the main switching element 2
When the voltage level generated between the secondary windings 1B at the time of turning on is high, the off time of the switching element 9 is extended, thereby stabilizing the output voltage Vo across the load.

Next, the operation of the above configuration will be described with reference to the waveform diagram of FIG. In FIG. 4,
The upper part is a voltage waveform VM generated between the secondary windings 1B of the transformer 1, and the lower part is a signal from the PWM control circuit 23 to the switching element 9.
2 shows a voltage waveform Vs of a pulse signal supplied to the power supply.

Also in this embodiment, the main switching element 2 is repeatedly turned on and off at a fixed timing, and as shown by the voltage waveform VM in FIG. A positive voltage is induced at the dot side terminal of the next winding 1B. With this,
The synchronization circuit 22 outputs to the PWM control circuit 23 a signal synchronized with the positive voltage generated at the dot side terminal of the secondary winding 1B. By the synchronization signal from the synchronization circuit 22, the PWM
When a positive voltage is generated at the dot-side terminal of the secondary winding 1B a predetermined time after the synchronization circuit 22 detects a zero cross, as shown in the voltage waveform Vs in FIG. An on signal is output to the switching element 9. As a result, the switching element 9 is turned on, and the secondary winding 1 is turned on.
Energy is supplied to the load from B.

The PWM control circuit 23 uses a voltage detection signal obtained at the connection point between the resistors 26 and 27 at a timing corresponding to the voltage level generated between the secondary windings 1B as shown by the voltage waveform Vs in FIG. An off signal is output to the switching element 9. Thereby, the switching element 9 is turned off,
The supply of energy from the secondary winding 1B to the choke coil 11 and the smoothing capacitor 12 is cut off. In this case, as the voltage level generated between the secondary windings 1B when the main switching element 2 is turned on is higher, the on-time t2 of the switching element 9 is shorter, and conversely, the voltage level generated between the secondary windings 1B is smaller. The lower the ON time t2 of the switching element 9 is,
Becomes longer, and the output voltage Vo is stabilized.

As described above, also in this embodiment, the switching element 9 is turned on at the timing when the voltage generated between the secondary windings 1B of the transformer 1 switches, and the voltage is generated between the secondary windings 1B of the transformer 1. The PWM control circuit 23 is configured to turn off the switching element 9 at a timing according to the voltage level. Energy can be reliably supplied from the winding 1B to the load. Therefore, the smoothing filter (the choke coil 11 and the smoothing capacitor 12) on the secondary side of the transformer 1 can be configured in one stage, so that the cost can be reduced and the power supply device can be downsized. Further, according to the voltage level generated between the secondary windings 1B of the transformer 1, the turn-off time of the switching element 9 is prolonged when the voltage level is high, and conversely, when the voltage level is low, the switching element 9, the turn-off time is shortened, and the output voltage Vo can be stabilized.

Next, a third embodiment of the present invention will be described with reference to FIGS. The same portions as those in the first and second embodiments are denoted by the same reference numerals, and the description of the common portions will be omitted because they are duplicated.

In this embodiment, the transformer 1 is composed of one primary winding 1A and two secondary windings 1B and 1D connected in series with two additional polarities, and a resistor is provided at a connection point between the secondary windings 1B and 1D. twenty one,
One end of a series circuit including the switching element 9 and the choke coil 11 is connected. The anode of the rectifier diode 4A is connected to one end of the secondary winding 1B, that is, the dot side terminal, and the anode of the rectifier diode 4B is connected to the other end of the secondary winding 1B, that is, the non-dot side terminal. The cathodes of 4A and 4B are connected. Then, a smooth output voltage line is provided between the connection point between the rectifier diodes 4A and 4B and one end of the load (not shown), and a minus output voltage line extending from one end of the choke coil 11 to the other end of the load. The capacitor 12 is connected, and the rectifier diodes 4A and 4B and the flywheel diode 5 are connected.
And a choke coil 11 and a smoothing capacitor 12 to constitute a rectifying and smoothing circuit 25.

The synchronizing circuit 22 in the present embodiment is configured such that when a positive voltage is induced at the dot-side terminal of one secondary winding 1B, a positive-polarity voltage is applied to the non-dot side terminal of the other secondary winding 1D. When the voltage is induced, each rising signal is represented by P
Output to the WM control circuit 23. When the dot side terminal of the secondary winding 1B rises to a positive polarity, the PWM control circuit 23 supplies an ON pulse signal to the switching element 9 in synchronization with the synchronization signal, and thereafter, the PWM control circuit 23 generates the secondary winding 1B. While a positive polarity voltage is being generated at the dot side terminal of the secondary winding 1B at a timing corresponding to the voltage level, an OFF pulse signal is supplied to the switching element 9 and the secondary winding 1D is turned off. When the non-dot side terminal rises to the positive polarity, an ON pulse signal is supplied to the switching element 9 in synchronization with the synchronizing signal, and then the secondary element is driven at a timing corresponding to the voltage level generated in the secondary winding 1D. While a positive voltage is being generated at the non-dot side terminal of the winding 1D, an OFF pulse signal is supplied to the switching element 9. Also in this case, when the voltage level generated between the secondary windings 1B and 1D when the main switching element 2 is turned on is low,
On the other hand, if the voltage level generated between the secondary windings 1B and 1D is high when the main switching element 2 is turned on, the off time of the switching element 9 is widened. The output voltage Vo during this period is stabilized.

Next, the operation of the above configuration will be described with reference to the waveform diagram of FIG. In FIG. 6,
The upper stage shows the voltage generated between the secondary windings 1B and 1D of the transformer 1, that is, the voltage waveform VM generated between the connection point of the rectifier diodes 4A and 4B and the connection point of the secondary windings 1B and 1D.
The lower part shows the voltage waveform Vs of the pulse signal supplied from the PWM control circuit 23 to the switching element 9.

Also in this embodiment, the main switching element 2 is repeatedly turned on and off at a fixed timing. As shown by the voltage waveform VM in FIG. A positive voltage is induced at the dot side terminal of the secondary winding 1B, and the rectifier diode 4A connected to the secondary winding 1B is turned on, while the rectifier diode 4B connected to the secondary winding 1D is turned off. The synchronization circuit 22 outputs to the PWM control circuit 23 a signal synchronized with the positive voltage generated at the dot side terminal of the secondary winding 1B. In response to the synchronization signal from the synchronization circuit 22, the PWM control circuit 23 applies a positive voltage to the dot-side terminal of the secondary winding 1B a predetermined time after the synchronization circuit 22 detects the rise of the secondary winding 1B. At the time point when an error occurs, an ON signal is output to the switching element 9 as shown by the voltage waveform Vs in FIG. Thereby, the switching element 9 is turned on,
Secondary winding 1B → Rectifier diode 4A → Smoothing capacitor 12
A current flows through a path of → choke coil 11 → switching element 9 → resistor 21 → secondary winding 1B.

The PWM control circuit 23 uses the voltage detection signal obtained at the connection point between the resistors 26 and 27 at a timing according to the voltage level generated between the secondary windings 1B as shown by the voltage waveform Vs in FIG. An off signal is output to the switching element 9. Thereby, the switching element 9 is turned off,
The supply of energy from the secondary winding 1B to the choke coil 11 and the smoothing capacitor 12 is cut off. In this case, the higher the voltage level generated between the secondary windings 1B when the main switching element 2 is turned on, the shorter the on-time t3 of the switching element 9 becomes, and conversely, the voltage level generated between the secondary windings 1B decreases. The lower the ON time t3 of the switching element 9 is, the lower the time is.
Becomes longer, and the output voltage Vo is stabilized.

Thereafter, when the main switching element 2 is turned off, a positive voltage is induced at the non-dot side terminal of the secondary winding 1D of the transformer 1, and the rectifier diode 4A connected to the secondary winding 1B is turned off. On the other hand, the rectifier diode 4B connected to the secondary winding 1D turns on. The synchronization circuit 22 outputs a signal synchronized with a positive voltage generated at the non-dot side terminal of the secondary winding 1D to the PWM control circuit 23. In response to the synchronization signal from the synchronization circuit 22, the PWM control circuit 23 applies a positive polarity signal to the non-dot side terminal of the secondary winding 1D a predetermined time after the synchronization circuit 22 detects the rise of the secondary winding 1D. When the voltage is generated, an ON signal is output to the switching element 9 as shown by a voltage waveform Vs in FIG. As a result, the switching element 9 is turned on again, and a current flows through the secondary winding 1D → rectifier diode 4B → smoothing capacitor 12 → choke coil 11 → switching element 9 → resistor 21 → secondary winding 1D. Energy is supplied to the load through 11 and the smoothing capacitor 12.

The PWM control circuit 23 uses the voltage detection signal obtained at the connection point between the resistors 26 and 27 at a timing corresponding to the voltage level generated between the secondary windings 1D as shown by the voltage waveform Vs in FIG. An off signal is output to the switching element 9. Thereby, the switching element 9 is turned off,
The supply of energy from the secondary winding 1D to the choke coil 11 and the smoothing capacitor 12 is cut off. In this case, the higher the voltage level generated between the secondary windings 1D when the main switching element 2 is turned off, the shorter the on-time t4 of the switching element 9 becomes, and conversely, the voltage level generated between the secondary windings 1D decreases The lower the ON time t4 of the switching element 9 is,
Becomes longer, and the output voltage Vo is stabilized.

As described above, also in the present embodiment, the switching element 9 is turned on at the timing when the voltage generated between the secondary windings 1B and 1D of the transformer 1 switches, and the secondary windings 1B and 1D of the transformer 1 are turned on. Since the PWM control circuit 23 is configured to turn off the switching element 9 at a timing according to the voltage level generated between the two,
Even if a smoothing filter is not provided on the input side of the chopper circuit 13 as in the related art, it is possible to reliably supply energy from the secondary winding 1B to the load. Therefore, the smoothing filter (the choke coil 11 and the smoothing capacitor 12) on the secondary side of the transformer 1 can be configured in one stage, so that the cost can be reduced and the power supply device can be downsized. Also, the secondary windings 1B and 1D of the transformer 1
When the voltage level is high, the turn-off time of the switching element 9 is long, and when the voltage level is low, the turn-off time of the switching element 9 is short. Thus, the output voltage Vo can be stabilized.

In the present embodiment, in particular, the two secondary windings 1
B and 1D, when the main switching element 2 is turned on and off, the switching element 9 is turned on by the synchronizing signal from the synchronizing circuit 22, which is twice as large as the circuit configuration of the first and second embodiments. The switching element 9 can be operated at the frequency of. Therefore, the choke coil 11 and the smoothing capacitor 12 constituting the smoothing filter can be reduced in size with the increase in the frequency of the switching element 9. Also, when the main switching element 2 is turned on and off, the secondary winding 1
When the B and 1D voltages are switched, the voltage waveform V shown in FIG.
As shown in M, noise is likely to occur when both voltages are switched. However, if the PWM control circuit 23 is configured so that the switching element 9 is turned off in the ON region as in the present embodiment, During the time period when the voltages of the secondary windings 1B and 1D are switched, the transmission of energy from the secondary windings 1B and 1D can be cut off by the switching element 9, and the generation of noise due to the influence of leakage can be suppressed.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention.

[0039]

According to the chopper type switching power supply of the present invention, the smoothing filter on the secondary side of the transformer can be formed in one stage, and the output voltage can be stabilized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a power supply device according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram showing a voltage generated in a secondary winding of the transformer and a voltage of a pulse signal to a switching element.

FIG. 3 is a circuit diagram showing a configuration of a chopper type switching power supply according to a second embodiment of the present invention.

FIG. 4 is a waveform diagram showing a voltage generated in a secondary winding of the transformer and a voltage of a pulse signal to a switching element.

FIG. 5 is a circuit diagram showing a configuration of a chopper type switching power supply according to a third embodiment of the present invention.

FIG. 6 is a waveform diagram showing a voltage generated in a secondary winding of the transformer and a voltage of a pulse signal to a switching element.

FIG. 7 is a circuit diagram of a chopper type switching power supply device showing a conventional example.

[Explanation of symbols]

 Reference Signs List 1 transformer 1B, 1D secondary winding 9 switching element 23 PWM control circuit (control circuit)

Claims (1)

[Claims] 1. A chopper type switching power supply device for stabilizing an output voltage by connecting a chopper circuit having a switching element to a secondary winding of a transformer and controlling a pulse signal width to the switching element. ,
The PWM control circuit turns on the switching element at a timing at which a voltage generated between the secondary windings switches, and turns off the switching element according to a voltage level generated between the secondary windings. A chopper-type switching power supply device.