JPH07194106A - Switching power supply apparatus - Google Patents

Abstract

PURPOSE:To supply a stable output to a load regardless of an input fluctuation, a load fluctuation and an input short break in a switching DC power supply apparatus. CONSTITUTION:An AC input is rectified by a rectifier stack DM1 and the ripple component of the rectified output is applied to the primary winding N1 of a transformer T1. The application of the ripple component is switched by a switching transistor Q1. A power induced on the secondary winding N2 of the transformer T1 is rectified by a diode D1 and smoothed by a capacitor C2 and then supplied to a load. Further, a power storing capacitor 1 is connected to the primary side of the transformer T1 and a switching transistor Q2 having a polarity different from the polarity of the switching transistor Q1 is connected to the capacitor C1. The transistors Q1 and Q2 are controlled by the synchronous pulses of a PWM circuit 6 and the charge stored in the capacitor C1 is supplied to the transformer T1 at the time of a momentary interruption.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching type DC power supply device, and more particularly to a power supply device capable of stable output even when the input voltage fluctuates or the input is instantaneously cut off.

[0002]

2. Description of the Related Art Conventionally, a switching type power supply device has been used as a power supply device for various electronic devices.
Especially for the DC power supply, the switching method is small,
It is widely used because it is lightweight and highly efficient.

In such a switching type power supply device, an input commercial power supply voltage is converted into a DC voltage by a capacitor input type rectifier circuit, but this capacitor input type rectifier circuit is small and inexpensive. On the other hand, a large-capacity electrolytic capacitor is required to secure the output holding time. Therefore, there are many harmonics of the input current, the effective value of the input current also increases, and this harmonic may adversely affect peripheral devices.

Therefore, in order to solve the above problem, as one method, the retention time of the output is obtained by another method.
There is a method of deleting the input smoothing circuit and directly switching the pulsating flow. FIG. 3 shows the circuit configuration.

In FIG. 3, reference numerals 1 and 2 denote input terminals of a commercial AC power source, which are connected to an AC input terminal of a rectifier stack DM1 for rectification. Also, the rectifier stack DM1
Is connected to the primary winding N1 of the transformer T1, one terminal of the primary winding N1 is connected to the collector of the switching transistor Q1, and the emitter of the switching transistor Q1 is rectifier stack DM1.
Is connected to the-terminal.

The output of the secondary winding N2 of the transformer T1 is guided to the smoothing capacitor C2 via the rectifying diode D1 and supplied to a predetermined load via the output terminals 4 and 5. ing. Also, the third of the transformer T1
One terminal of the winding N3 is connected to the other terminal of the primary winding N1, and the other terminal is connected to the cathode of the capacitor C1 via the diode D3. Further, the anode of the capacitor C1 is connected to the + terminal of the rectifier stack DM1, and the cathode is connected to the emitter of the switching transistor Q1 via the diode D2 for backflow prevention.

Reference numeral 5 denotes a voltage detection circuit for detecting an output voltage for the load, which is connected in parallel to a load (not shown) connected to the output terminals 3 and 4. The detection value of the voltage detection circuit 5 is transmitted to the PW via the photo coupler Q3.
It is fed back to the M circuit 6.

The PWM circuit 6 controls the switching duty ratio or frequency of the drive pulse given to the base of the switching transistor Q1 according to the input detection value. Then, the output of the PWM circuit 6 drives the switching transistor Q1.

Next, the operation of the circuit shown in FIG. 3 will be described. When a commercial power supply is connected to the input terminals 1 and 2, the input alternating current is rectified by the rectifier stack DM1 and a pulsating flow waveform is obtained. The obtained pulsating current is interrupted by the switching transistor Q1, and the primary winding N1 of the transformer T1.
Applied to.

The switching transistor Q
Energy is stored in the transformer T1 when 1 is turned on, and is discharged from the secondary winding N2 through the diode D1 when turned off. This operation is repeated to transfer power. that time,
The output of the diode D1 is smoothed by the smoothing capacitor C2 and converted into direct current. The converted direct current is supplied to the load from the output terminals 3 and 4.

Similarly, the output of the winding N3 charges the capacitor C1 via the diode D3,
The voltage between both ends of is kept constant in proportion to the output voltage.

A voltage detection circuit 5 is connected in parallel with the load in order to detect the voltage of the load. The detection circuit 5 is composed of an operational amplifier (operational amplifier), a transistor, and the like, compares the voltage of the load connected to the output terminals 3 and 4 with the reference voltage, and outputs the error voltage via the photocoupler Q3 to the PWM circuit. Give to 6. The PWM circuit 6 controls the drive pulse of the switching transistor Q1 according to the error voltage.

In this way, the load voltage is stabilized by controlling the drive pulse of the switching transistor Q1. In addition, when the input voltage is cut off during operation and the output of the rectifier stack DM1 disappears, the charge of the capacitor C1 is discharged through the diode D2, thereby stabilizing the output voltage for a certain period of time.

[0014]

However, in the conventional power supply device having the circuit configuration as shown in FIG. 3, when the input voltage value becomes smaller than the voltage of the third winding, the diode for preventing the reverse current is generated. Does not work, commercial AC input 1
There is a problem that a current flows from the secondary side rectifier circuit, control becomes impossible, and a stable output cannot be supplied to the load.

The present invention has been made by paying attention to the above problems, and provides a switching type power supply device capable of supplying a stable output to a load even when there is an input fluctuation or an input interruption. The purpose is to get.

[0016]

A switching type power supply device of the present invention comprises a rectifying circuit for rectifying an input alternating current, a transformer to which a rectified pulsating current is applied to a primary side, and a switching device for switching the pulsating current. 1 switching element, a power storage capacitor connected to the primary side of the transformer, a rectifying element for rectifying a pulse output generated in the transformer to charge the capacitor, and a capacitor connected to the capacitor. A second switching element, and is configured to supply the electric charge stored in the capacitor by the second switching element to the transformer when the input is cut off.

The second switching element is controlled by the synchronizing pulse of the first switching element.

[0018]

In the switching type power supply device of the present invention,
A second switching element is provided instead of the diode for preventing the backflow current, and the second switching element is driven by, for example, the synchronization pulse of the first switching element, so that the primary side of the commercial AC input is turned on when the switching is on. It is possible to cut off the current from the rectifier circuit and supply power to the high frequency switching circuit (transformer) when it is off.

[0019]

1 is a circuit diagram showing a configuration of a switching power supply device according to an embodiment of the present invention, and the same reference numerals as those in FIG. 3 denote the same components.

In FIG. 1, 1 and 2 are input terminals,
Rectifier stack (current circuit) DM1 that rectifies input AC
It is connected to the AC input terminal of. The + terminal on the output side of the rectifier stack DM1 is connected to the primary winding N1 of the transformer T1 to which the rectified pulsating flow is applied on the primary side, and one terminal of the primary winding N1 is The collector of the switching transistor (first switching element) Q1 that switches (intermittently) the pulsating flow is connected, and the emitter of the switching transistor Q1 is a rectifier stack DM.
1 is connected to the-terminal.

The output of the secondary winding N2 of the transformer T1 is guided to the smoothing capacitor C2 via the rectifying diode D1 and supplied to a predetermined load via the output terminals 4 and 5. ing. Also, the third of the transformer T1
Of the winding N3 has one terminal connected to the other terminal of the primary winding N1 and the other terminal of the winding N3 has a diode D3.
Is connected to the cathode of the capacitor C1 for power storage. Further, the anode of the capacitor C1 is connected to the + terminal of the rectifier stack DM1, and the cathode is connected to the collector of the switching transistor (second switching element) Q2 and the rectifying diode D3. The emitter of the switching transistor Q2 is connected to the emitter of the switching transistor Q1 and the-terminal of the rectifier stack DM1.

Reference numeral 5 denotes a voltage detection circuit for detecting an output voltage for the load, which is connected in parallel to a load (not shown) connected to the output terminals 3 and 4. The detection value of the voltage detection circuit 5 is transmitted to the PW via the photo coupler Q3.
It is fed back to the M circuit 6.

The PWM circuit 6 controls the switching duty ratio or frequency of the drive pulse given to the bases of the switching transistors Q1 and Q2 according to the input detection value. The switching transistors Q1 and Q2 are synchronously driven by the output of the PWM circuit 6.

The above circuit has a configuration in which the smoothing electrolytic capacitor after rectification of the power supply voltage is removed, and the switching transistor Q1 whose conduction angle is controlled by the PWM circuit 6 is the transformer T1 which constitutes this high frequency switching circuit. The pulsating current flowing through the primary winding N1 is switched.

Further, a charging means for charging the power storage capacitor C1 connected to the input side of the high frequency switching circuit is constituted, and in a steady state, the power from the input terminals 1 and 2 is converted. Is supplied to a predetermined load and the pulse output obtained from the high frequency switching circuit is rectified to charge the power storage capacitor C1,
When the input is cut off, the power from the capacitor C1 is interrupted by the switching transistor Q1, and the alternating current power generated thereby is converted into direct current by the diode D1 to supply the power to the load.

Further, the second switching transistor Q
2 has a polarity different from that of the first switching transistor Q1, and the second switching transistor Q2
Is connected between the capacitor C1 for storing power and the charging means, and the emitter is connected between the-terminal of the primary side rectifier stack DM1 and the emitter of the first switching transistor Q1. . The charge from the primary side rectifier circuit is prevented in the steady state, and the charge accumulated in the power storage capacitor C1 is supplied to the high frequency switching circuit when the input is cut off.

Next, the operation of the circuit shown in FIG. 1 will be described. When a commercial power supply is connected to the input terminals 1 and 2, the input alternating current is rectified by the rectifier stack DM1 and a pulsating flow waveform is obtained. The obtained pulsating current is interrupted by the switching transistor Q1, and the primary winding N1 of the transformer T1.
Applied to.

Then, the switching transistor Q
When 1 is on, the switching transistor Q2 is also on, energy is stored in the transformer T1, and when it is off, 2
It is emitted from the next winding N2 through the diode D1. This operation is repeated to transfer power. At that time, the output of the diode D1 is smoothed by the smoothing capacitor C2 and converted into direct current. The converted direct current is supplied to the load from the output terminals 3 and 4.

Similarly, the switching transistor Q
When 1 is off, the output of the winding N3 charges the capacitor C1 via the diode D3, and maintains the voltage across the capacitor C1 at a constant voltage proportional to the output voltage. At the same time, the switching transistor Q2 is turned off by the drive pulse synchronized with the switching transistor Q1, and the charging from the commercial AC input rectifier circuit is prevented.

A voltage detection circuit 5 is connected in parallel with the load in order to detect the voltage of the load. The detection circuit 5 is composed of an operational amplifier, a transistor, etc., compares the voltage of the load connected to the output terminals 3 and 4 with the reference voltage, and supplies the error voltage to the PWM circuit 6 via the photocoupler Q3. The PWM circuit 6 controls the drive pulse of the switching transistor Q1 according to the error voltage.

By controlling the drive pulse of the switching transistor Q1 in this way, the load voltage is stabilized even when there is an input fluctuation or load fluctuation.
In addition, the input voltage is cut off during operation and the rectifier stack DM
When the output of 1 disappears, the electric charge of the capacitor C1 is discharged when the second switching element Q2 is turned off, and the output voltage is stabilized for a certain period of time.

FIG. 2 is a circuit diagram showing the configuration of another embodiment of the present invention. This embodiment is an application example to a forward converter, and the difference from the embodiment of FIG. 1 is that a choke coil L1 for smoothing and a commutation diode D4 are added to the output,
This is the point that the capacitor C1 is charged from the auxiliary winding of the choke coil L1. That is, the third winding N3 of the transformer T1 of the circuit of FIG. 1 corresponds to the sub winding N3 of the choke coil L1 of FIG.

Next, the operation of the circuit of FIG. 2 will be described. When a commercial power source is connected to the input terminals 1 and 2 as in the above, the alternating current is rectified by the rectifier stack DM1.
A pulsating flow waveform is obtained. The obtained pulsating current is interrupted by the switching transistor Q1, and the generated AC output is applied to the primary winding N1 of the transformer T1.

The output corresponding to the applied alternating current is transmitted to the secondary winding N2 of the transformer T1. This output is rectified by the diode D1, smoothed by the choke coil L1, the capacitor C2, and the commutation diode D4, and converted into direct current. This converted direct current is output to the output terminals 3, 4
Supplied to the load from.

A voltage detection circuit 5 is connected in parallel with the load in order to detect the voltage of the load. Then, an AC output having a peak value corresponding to the output voltage is obtained in the sub winding N3 of the choke coil L1, and this output charges the capacitor C1 via the diode D3.
The voltage across the capacitor C1 is maintained at a constant voltage proportional to the output voltage. Subsequent operations are the same as those in the above-mentioned embodiment, and therefore will be omitted.

[0036]

As described above, according to the present invention,
By providing the second switching element controlled by the synchronization pulse of the first switching element or the like to control the charge / discharge of the capacitor for power storage, even in the region where the voltage of the third winding is larger than the input voltage. It is said that the capacitor for power storage is reliably charged, stable output can be supplied in the event of an input interruption, and input fluctuations and load fluctuations can be widely supported, and stable output can be supplied to the load. effective.

[Brief description of drawings]

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

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

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

[Explanation of symbols]

1 Input Terminal (H) 2 Input Terminal (N) 3 Output Terminal (+) 4 Output Terminal (-) 5 PWM Circuit 6 Voltage Detection Circuit DM1 Rectifier Stack (Rectifier Circuit) C1 Capacitor C2 Smoothing Capacitor Q1 Switching Transistor (1st) Switching element) Q2 switching transistor (second switching element) Q3 photocoupler T1 transformer L1 smoothing choke coil N1 primary winding N2 secondary winding N3 third winding N4 fourth winding D1 rectifying diode D3 Rectifying diode (rectifying element) D4 Commutating diode

Claims (2)

[Claims] 1. A rectifier circuit for rectifying an input alternating current, a transformer to which a rectified pulsating flow is applied to a primary side, a first switching element for switching the pulsating flow, and a primary side of the transformer. Connected capacitor for power storage,
A rectifying element for rectifying the pulse output generated in the transformer to charge the capacitor, and a second switching element connected to the capacitor are provided, and the second switching element causes the second switching element to connect the capacitor to the capacitor. A switching type power supply device, characterized in that the stored electric charge is supplied to the transformer. 2. The switching power supply device according to claim 1, wherein the second switching element is controlled by the synchronizing pulse of the first switching element.