JPH0998570A - Switching power supply - Google Patents

Abstract

(57) Abstract: Provided is a switching power supply device which improves the efficiency at a low input voltage of a regenerative control type power supply having a wide input voltage range used in various electric devices and improves reliability. A rectifier diode (7) connected to a secondary winding (3c) to turn on / off an input voltage from a DC power supply (1) by a switching element (4) and to energize the primary winding (3a) with energy.
And a smoothing capacitor 9 are rectified and smoothed by a series circuit, and a part of the energy of the smoothing capacitor 9 is regenerated to the primary side. In the switching power supply, a signal from the input voltage detection means 13 turns on the secondary switching element 8. The amount of returning a part of the energy of the smoothing capacitor 9 to the primary side is changed by controlling the.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply device for supplying a regulated DC voltage to industrial and consumer electronic devices.

[0002]

2. Description of the Related Art In recent years, power supply devices have been required to be compact, highly efficient, and have a long life. For this reason, regenerative control has been used (for example, JP-A-2-261053).

The conventional regenerative control will be described below.
FIG. 3 shows a configuration of a conventional regenerative control. In FIG. 3, 1 is a DC power supply for rectifying and smoothing an AC voltage,
Alternatively, the input terminal 2 is composed of a battery or the like.
The input voltage is supplied to a-2b, the positive voltage is connected to the input terminal 2a, and the negative voltage is connected to the input terminal 2b. 3 is a transformer, one end of the primary winding 3a is connected to the input terminal 2a, the other end is connected to the input terminal 2b through the switching element 4, one end of the secondary winding 3c is connected to the output terminal 11b,
Connect the other end to output terminal 11a via diode 7,
One end of the bias winding 3b is connected to the input terminal 2b, and the other end is connected to the synchronous oscillation circuit 6. Reference numeral 4 denotes a switching element, which is turned on / off by an on / off signal of the synchronous oscillation circuit 6 applied to the control terminal to apply or cut off the input voltage to the primary winding 3a. Reference numeral 6 denotes a synchronous oscillating circuit, which turns on the switching element 4 during an on period determined by the control circuit 10, and turns off the switching element 4 so that it continues until the induced voltage of the bias winding 3b is inverted. Oscillation is continued by repeating this on / off. Reference numeral 7 denotes a rectifying diode, the anode side of which is connected to one end of the secondary winding 3c and the cathode side of which is connected to the output terminal 11a. Reference numeral 8 denotes a secondary switching element, and the energy of the transformer 3 stored during the ON period of the switching element 4 is changed to 2 during the OFF period of the switching element 4.
After being discharged from the rectifying diode 7 or the secondary switching element 8 to the smoothing capacitor 9 through the secondary winding 3c, 2
The control circuit 12 controls the backflow period during which the secondary current flows through the secondary winding 3c via the next switching element 8. Reference numeral 9 denotes a smoothing capacitor, which is connected between the output terminals 11a and 11b, rectifies the induced voltage of the secondary winding 3c through the rectifying diode 7, and smoothes it by the smoothing capacitor 9 to obtain an output voltage. A control circuit 10 detects the voltage between the output terminals 11a and 11b and compares it with an internal voltage reference to change the ON period of the primary switching element 4. A control circuit 12 controls the backflow period of the secondary switching element 8 to be constant.

The operation of the regenerative control configured as described above will be described below with reference to FIG. In FIG. 4, (a) shows the voltage waveform V _DS across the switching element 4, (b) shows the primary current I _D flowing through the primary winding 3 a, and (c) shows the synchronous oscillator circuit 6. Shows the drive pulse waveform V _G1 which is the output of the above, and (d) shows the secondary current waveform I _O flowing through the secondary winding 3c.
(E) shows the drive pulse waveform V _G2 of the secondary switching element 8 which is the output of the control circuit 12, and the low input in which the secondary current flows through the secondary winding 3c during the period shown by the diagonal lines in the off period. The reverse current period at voltage is shown. In FIG. 4, the dotted line shows the case where the input voltage is high, and the solid line shows the case where the input voltage is low. In either case, the control circuit 12 controls the backflow period of the secondary switching element 8 to be constant. Synchronous oscillation circuit 6
The pulse of the ON period controlled by is applied to the switching element 4, and the primary current I flowing through the primary winding 3a.
_The transformer 3 is excited by _D. At this time transformer 3
Induced voltage is generated in the secondary winding 3c of the
The secondary switching element 8 is turned off while a voltage is applied in the direction of reverse biasing the gate 7. When the switching element 4 is turned off by the signal from the synchronous oscillation circuit 6, a flyback voltage is generated in the primary winding 3a and a flyback voltage is also generated in the secondary winding 3c, and the rectifying diode 7 is forward biased. Since a voltage is applied in the direction, the excitation energy stored in the transformer 3 is discharged as a secondary current through the secondary winding 3c, smoothed by the smoothing capacitor 9, and supplied as output voltage to the output terminals 11a-11b. It At this time, the secondary switching element 8 is also turned on by the control circuit 12, but there is no change in operation irrespective of which secondary current flows. When all the energy stored in the transformer 3 is released and the secondary current becomes zero, the voltage across the smoothing capacitor 9, that is, the output voltage, is applied to the secondary winding 3c via the secondary switching element 8 which is already turned on. A secondary current flows in the opposite direction from the smoothing capacitor 9, and a magnetic flux in the opposite direction is generated in the transformer 3 to accumulate energy. In this state, the polarity of the induced voltage generated in each winding of the transformer 3 does not change and the flyback voltage of the bias winding 3b does not change, so that the synchronous oscillation circuit 6 maintains the OFF period of the switching element 4. The ON period of the secondary switching element 8 is fixed by the control circuit 12, and when the secondary switching element 8 is turned off, the induced voltage generated in each winding of the transformer 3 is inverted, so that the induced voltage generated in the secondary winding 3c is induced. Since the voltage reverse biases the rectifying diode 7 and the secondary switching element 8 is also off, the secondary winding current disappears, and the polarity of the induced voltage generated in the bias winding 3b is reversed, so that the synchronous oscillation circuit 6 Turns on the switching element 4.
At this time, the induced voltage generated in the primary winding 3a is generated in such a direction that the connection end with the switching element 4 becomes a negative voltage and the connection end with the input terminal 2a becomes a positive voltage. If not shed secondary current in the reverse direction, not a change is below V _C -V _F from the sum (V _C + V _F) of the DC power source 1 of the input voltage (V _C) and the flyback voltage (V _F) On the other hand, when a secondary current is passed in the opposite direction, V _C +
When the DC power supply voltage is high and the voltage across the switching element 4 immediately before turn-on becomes high because the voltage drops from V _F to V _C −V _F or less, the turn-on loss of the switching element 4 decreases. At this time, the energy stored in the transformer 3 during the off period via the switching element 4 is regenerated to the DC power supply 1. When all the energy accumulated in the transformer 3 is released during the off period and the primary current becomes 0, the primary current flows from the DC power supply 1 via the switching element 4 so as to discharge in the opposite direction to the above, and the transformer 3 A magnetic flux is generated in and energy is accumulated. In this state, the polarity of the induced voltage generated in each winding of the transformer 3 does not change, and the synchronous oscillation circuit 6 keeps the switching element 4 on. When the switching element 4 operating in the ON period controlled by the synchronous oscillation circuit 6 is turned off, the energy stored in the transformer 3 is discharged as a secondary current via the secondary winding 3c. By repeating these operations, the output voltage is continuously supplied to the output terminals 11a-11b.

[0005]

However, in the secondary side regenerative switching power supply device having the above configuration, the reverse current period is fixed in accordance with the maximum input voltage even when the input voltage changes, so that the maximum input voltage does not depend on the input voltage. It produces the same regenerative loss as in the case of voltage. Such a switching power supply does not cause a problem when the input voltage is fixed, but a switching power supply having a wide input voltage range such as a wide-wide input has a low efficiency at a low input voltage, resulting in an increase in power consumption. It is necessary to increase the size of the
Since the shape is enlarged and the ripple of the smoothing capacitor 9 is increased, when an electrolytic capacitor is used for the smoothing capacitor 9, there is a problem that the operating life is shortened and the reliability is lowered.

An object of the present invention is to solve the above problems and to provide a small-sized and highly reliable switching power supply device, which prevents the efficiency from being lowered at a low input voltage.

[0007]

In order to achieve this object, a switching power supply device of the present invention comprises a first switch means connected across the input voltage and a series circuit of a primary winding of a transformer, and A series circuit of rectifying means and smoothing means connected to the secondary winding of the transformer, first control means for controlling the ON period of the first switch means by the output voltage of the smoothing means, and the rectifying means. Second switch means connected in parallel, and second control means for controlling the ON period of the second switch means by a signal from the input voltage detection circuit while the first switch means is OFF. And has a configuration for changing the ON period of the second switch means according to the input voltage.

[0008]

With this configuration, the optimum amount of regeneration can be determined by the input voltage, and the amount of unnecessary energy regenerated to the input via the transformer can be reduced while maintaining zero-cross switching, and switching loss and transformer It is possible to reduce loss and prevent a decrease in efficiency at low input voltage.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a switching power supply device according to an embodiment of the present invention. In FIG. 1, the same parts as those in FIG.
Reference numeral 1 is a DC power source, 2a-2b are input terminals, and 3 is a transformer. Primary winding 3a, bias winding 3b, secondary winding 3
c is provided, 4 is a switching element as a first switching means, 6 is a synchronous oscillation circuit, 7 is a rectifying diode, 9 is a smoothing capacitor, and 10 is a smoothing capacitor.
Is a control circuit, and 11a-11b are output terminals.
Reference numeral 8 denotes a secondary switching element as a second switching means, and the energy of the transformer 3 stored during the ON period of the switching element 4 is rectified by the rectifying diode 7 through the secondary winding 3c during the OFF period of the switching element 4. Alternatively, after being discharged from the secondary switching element 8 to the smoothing capacitor 9, the secondary winding 3c is connected to the secondary winding 3c via the secondary switching element 8.
The backflow period during which the next current flows is controlled by the control circuit 12,
The backflow period is changed by the signal of the input voltage detection circuit 13. A control circuit 12 controls the backflow period of the secondary switching element 8 by a signal from the input voltage detection circuit 13. Reference numeral 13 is an input voltage detection circuit, which transmits an input voltage signal to the control circuit 12.

The operation of the switching power supply device configured as described above will be described below. In FIG. 2, (a) shows the voltage waveform V _DS across the switching element 4, (b) shows the primary current I _D flowing through the primary winding 3 a, and (c) shows the synchronous oscillator circuit 6. Of the drive pulse waveform V _G1 which is the output of the above, (d) shows the waveform of the secondary current I _o flowing through the secondary winding 3c, and (e) shows the secondary switching which is the output of the control circuit 12. The drive pulse waveform V _G2 of the element 8 is shown. Further, in FIG. 2, the dotted line shows the case where the input voltage is high, and the control circuit 12 controls the reverse current period of the secondary switching element 8 according to the input voltage so that the voltage across the switching element 4 immediately before turn-on becomes 0 volt. Is controlled to increase more than when it is low.
Further, in FIG. 2, the solid line shows the case where the input voltage is low, and the control circuit 12 controls the reverse current period of the secondary switching element 8 according to the input voltage so that the voltage V _DS at both ends immediately before the switching element 4 is turned on becomes 0 volt. Control so that the input voltage is reduced or eliminated as compared with the case of high input voltage. With such an operation, the backflow period of the secondary switching element 8 at a low input voltage is narrowed or eliminated, and the energy regenerated in the primary winding 3a is reduced or eliminated, so that the ON period of the switching element 4 is also shortened. The current flowing through the primary winding 3a and secondary winding 3c of No. 3 decreases.

It goes without saying that the first switch means and the second switch means also include semiconductor elements such as transistors and FETs.

When an FET is used as the second switch means, the rectifying means connected in parallel can also serve as the internal diode of the FET.

The input voltage detection circuit may detect the input voltage by utilizing the induced voltage generated in the winding of the transformer.

The input voltage detection circuit is a 100 V system, 20
The effect of the present invention can be easily obtained even if the 0V system is judged and the presence or absence of regeneration is switched.

If the input voltage to be used is known in advance, the same effect can be obtained by omitting the input voltage detection circuit and changing the regeneration amount by a switch.

A capacitor may be connected in parallel with the first and second switch means for reducing noise during switching.

[0017]

As described above, according to the present invention, by changing the reverse current period according to the input voltage by the input voltage detection circuit and changing the on period of the secondary switching element, the primary winding of the transformer at a low input voltage. Wire, the current flowing in the secondary winding is reduced, and the magnetic flux change width, that is, the magnetic flux density, generated in the magnetic core is also reduced, and the loss such as copper loss and iron loss generated in the transformer can be greatly reduced, and the transformer loss can be reduced. To do. Furthermore, the switching element connected to the primary winding, the secondary switching element connected to the secondary winding, and the current flowing in the diode can be reduced to reduce the loss, and at the same time, the ripple current flowing in the smoothing capacitor can be reduced. An excellent switching power supply with significantly improved smoothing capacitor life and longer life, resulting in significantly improved efficiency at low input voltage, longer life, and significantly improved reliability. The device can be realized.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a switching power supply device of the present invention.

FIG. 2 is an operation waveform diagram of the embodiment shown in FIG. 1 of the present invention.

FIG. 3 is a circuit configuration diagram of a conventional switching power supply device.

FIG. 4 is an operation waveform diagram of the circuit configuration shown in FIG. 3 of the conventional switching power supply device.

[Explanation of symbols]

 1 DC Power Supply 2a-2b Input Terminal 3 Transformer 4 Switching Element 6 Synchronous Oscillation Circuit 7 Rectification Diode 8 Secondary Switching Element 9 Smoothing Capacitor 10 Control Circuit 11a-11b Output Terminal 12 Control Circuit 13 Input Voltage Detection Circuit

Claims (2)

[Claims] 1. A series circuit of first switching means connected to both ends of an input voltage and a primary winding of a transformer, and a series circuit of rectifying means and smoothing means connected to a secondary winding of the transformer. A first control means for controlling an ON period of the first switch means by an output voltage of the smoothing means, a second switch means connected in parallel with the rectifying means, and a second switch means. And a second control means for controlling an on period by a signal from an input voltage detection circuit that detects an input voltage during a period when the first switch means is off. 2. An input voltage from a DC power supply is turned on / off by a switching element to be applied to the primary side of the transformer, and an output is obtained by rectifying and smoothing from a secondary side of the transformer by a series circuit of a rectifying diode and a smoothing capacitor. In a switching power supply that regenerates a part of the energy of the smoothing capacitor to the primary side of a transformer, a change in the input voltage is detected, and a part of the energy of the smoothing capacitor is transferred to the primary side according to the detection result. A switching power supply device characterized in that it is configured to change the returning amount.