JP2867069B2 - Switching power supply - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in efficiency of a switching power supply that inputs a commercial AC power supply and outputs a DC voltage.
Conventionally, a circuit as shown in FIG. 1 has been proposed as an example of such a switching power supply.

In FIG. 1, a capacitor 3 is connected to the output of a full-wave rectifier 2 connected to a commercial AC power supply 1, and a switching element 10 for performing on / off operation with a primary winding 5 of a transformer 4 is provided at both ends of the capacitor 3. Are connected in series, a diode 7 and a capacitor 8 are connected in series to both ends of a secondary winding 6 of the transformer 4, and an electric load 9 is connected to both ends of the capacitor 8.
To supply a DC voltage.

The error amplifier 12 amplifies the difference voltage between the DC voltage at both ends of the capacitor 8 as one input and a predetermined reference voltage 13 as the other input, and the output thereof is connected to the pulse generator 11. . The pulse generator 11 is an error amplifier
When the DC signal is higher than the reference voltage 13, the ON time of the switching element 10 is shortened.When the DC voltage is lower than the reference voltage 13, the ON time of the switching element 10 is reduced. It operates so as to stabilize the DC voltage by generating a long pulse.

The drive circuit 11 amplifies the output of the pulse generator 11 and drives the switching element 10.

However, in a switching power supply such as the above-described conventional example, since an input current flows through a circuit in which two diodes constituting an equivalent full-wave rectifier are connected in series, a diode is generated along with rectification on the primary side. As a result of the loss of two pieces, there was a disadvantage that the efficiency was poor.

An object of the present invention is to provide a circuit for improving such a disadvantage.

First Embodiment FIG. 2 shows a first embodiment of the present invention.

The configuration and operation of the circuit of FIG. 2 will be described with reference to the operation waveform diagram of FIG.

In FIG. 2, the same components as those described in FIG. 1 are denoted by the same reference numerals. In FIG. 2, a capacitor 3 is connected to a commercial AC power supply 1, and diodes 16 and 17 and a primary winding 5 of a transformer 4 are connected in series at both ends of the capacitor 3 so as to have opposite polarities. Connected to the switching element 18 in parallel with the diodes 16 and 17, respectively.
19, the diode 7 and the capacitor 8 are connected in series to both ends of the secondary winding 6 of the transformer 4, and the diode 7 and the capacitor 8 are connected in series to both ends of the tertiary winding 14 of the transformer 4. An electric load 9 is connected to both ends of 8 to supply a DC voltage. Here, the windings of the transformer 4 have the same polarity on the sides marked with black circles in FIG. 2, respectively, and the secondary winding 6 and the tertiary winding 14 of the transformer 4 have the same number of turns.

An error amplifier 12 amplifies the difference voltage between the DC voltage at both ends of the capacitor 8 as one input and a predetermined reference voltage 13 as the other input, and an output thereof is connected to the pulse generator 11. ing. The pulse generator 11 receives the output signal of the error amplifier 12 as an input,
When the voltage becomes larger, the on-time of the switching elements 18 and 19 is shortened, and when the DC voltage becomes smaller than the reference voltage 13, a pulse is generated which lengthens the on-time of the switching elements 18 and 19. Thus, the operation is performed to stabilize the DC voltage. Drive circuits 20 and 21 are pulse generators
The output of 11 is amplified and the switching elements 18 and 19 are driven. The capacitor 3 removes a high-frequency component generated by the switching from the input current.

In the above circuit configuration, regarding the operation in the steady state,
The operation will be described with reference to the operation waveform diagram of FIG.

In the half cycle of the commercial frequency, when the polarity of the commercial AC voltage (A in FIG. 3) is in the direction in which the diode 17 is forward biased (B in FIG. 3), the voltage across the diode 17 (C in FIG. 3) ) Is the forward voltage drop, while
At this time, the diode 16 is reversely biased, and the voltage across the diode 16 becomes a switching waveform (D in FIG. 3) generated by turning on / off the switching element.

The current flowing through the primary circuit is switched from the AC power supply 1 to the primary winding 5 of the transformer 4 and the switching element due to switching.
18. Return to the AC power supply 1 through the diode 17. On the other hand, in the next half cycle of the commercial frequency, the switching element 19, the diode 16, and the primary winding 5
And return to AC power supply 1.

As a result, the voltage of the primary winding 5 of the transformer 4 has the waveform shown in FIG. 3E, and the voltage of the same polarity is applied to the tertiary winding 14 of the transformer 4 and the secondary winding of the transformer 4 On line 6, a voltage of the opposite polarity is generated. (FIG. 3F).

The voltage of the secondary winding 6 of the transformer 4 and the voltage of the tertiary winding 14 of the transformer 4 are rectified by a diode 7 and a diode 15, respectively, butted and smoothed by a capacitor 8 to become a DC voltage. Supplied to

As described above, in the switching power supply such as the configuration example shown in FIG. 2, the loss associated with rectification on the primary side can be equivalently equivalent to the loss of one diode, and as a result, the efficiency is higher than that of the conventional example. Can be improved.

Here, when a MOSFET is used for the switching element, a parasitic diode built in the element can be used instead of the diode 16 and the diode 17, so that there is an advantage that the circuit configuration can be simplified.

Second Embodiment FIG. 4 shows a second embodiment of the present invention.

The configuration and operation of the circuit of FIG. 4 will be described with reference to the operation waveform diagram of FIG. In FIG. 4, the same components as those described in FIG. 2 are denoted by the same reference numerals. In FIG. 4, the distribution circuit 24 detects a commercial AC power supply,
As shown in FIG. 3F, a signal that is inverted every half cycle of the commercial AC power supply is output, and the output is connected to one terminal of the OR circuits 22 and 23, respectively. OR circuit 2
The output of the pulse generator 11 is connected to the other terminals of 2 and 23.

The output of the distribution circuit 24 turns on a switching element connected in parallel to the diode having a polarity such that it is forward biased for a half cycle of the commercial frequency every half cycle of the commercial AC power supply. During this period, the other switching element is connected to the pulse generator 11 as in the first embodiment.
Is turned on / off at a frequency higher than the commercial frequency. As a result, if a switching element whose voltage drop when turned on is smaller than the voltage drop in the diode forward direction is used, the loss due to rectification can be reduced more than in the first embodiment, so that the efficiency is further improved. be able to.

Third Embodiment FIG. 5 shows a third embodiment of the present invention.

The configuration and operation of the circuit of FIG. 5 will be described. In FIG. 5, the same components as those described in FIG. 2 are denoted by the same reference numerals. In FIG. 5, a pulse generator 26 has an output of the error amplifier 12 as a first input, and an input current detection circuit.
When the DC voltage is higher than the reference voltage 13, the on-time of the switching elements 18 and 19 is shortened. When the DC voltage is lower than the reference voltage 13, the switching element 18 is connected to the second input. Generates a pulse that increases the on-time of 19, operates to stabilize the DC voltage, and controls the on / off time of the switching element so that the waveform of the input current is similar to the input voltage. .

It is known that the switching power supply that operates in this manner can increase the power factor. Therefore, by using a circuit configuration as shown in FIG. 5, it is possible to reduce the loss associated with rectification on the primary side as described above. As a result, the efficiency can be improved as compared with the conventional high power factor type switching power supply.

[Brief description of the drawings]

FIG. 1 is a basic circuit diagram of a conventional switching power supply, and FIG.
FIGS. 4 and 5 are circuit connection diagrams showing an embodiment of the present invention, and A, B, C, D, E, F and G in FIG. 3 are operations for explaining the operation of the present invention. Waveform diagram. DESCRIPTION OF SYMBOLS 1 ... Commercial AC power supply 2 ... Full wave rectifier 3 ... High frequency component removal capacitor 4 ... Transformer 7, 15 ... Rectifying diode 8 ... Smoothing capacitor 9 ... Electric load 10, 18, 19 ... ... Switching elements 11, 26 ... Pulse generator 12 ... Error amplifier 13 ... Reference voltages 16, 17 ... Diodes 20, 21 ... Driving circuits 22, 23 ... OR circuit 24 ... Distributing circuit 25 ... Current detection circuit

Claims (2)

(57) [Claims] 1. A commercial AC power supply is input, a capacitor is connected in parallel with the commercial AC power supply, and one end of a transformer, a first diode, and a second diode are connected to both ends of the capacitor.
Are connected in series so that they have opposite polarities,
A first switching element is connected in parallel with the first diode, and a second switching element is connected in parallel with the second diode. A third diode and a second switching element are connected to both ends of a secondary winding of the transformer. A capacitor is connected in series, a fourth diode and the second capacitor are connected in series to both ends of a tertiary winding of the transformer, and a DC voltage is output from both ends of the second capacitor and supplied to a load. In the switching power supply configured as described above, the first and second switching elements are controlled to be turned on and off so that the DC voltage is stabilized at a frequency higher than a commercial frequency. 2. The first and second switching elements are controlled to be on and off so that the DC voltage is stabilized at a frequency higher than the commercial frequency, and are alternately turned on every half cycle of the commercial AC power supply. The switching power supply according to claim 1, wherein the switching power supply is operated.