JPH08205520A - Switching power supply - Google Patents

Abstract

PURPOSE: To suppress a harmonic current over a wide range by a method wherein a capacitor is discharged when an input voltage is lower than a capacitor voltage and the capacitor is charged by an energy from a choke coil when the input voltage is higher than the capacitor voltage. CONSTITUTION: If an input voltage is gradually elevated, a differential voltage between the voltage of capacitors C1 and C2 and the input voltage is applied to a choke coil L1. If the ON-period of a switching device Q1 is constant, a current applied to the choke coil L1 is proportional to the input voltage only when the input voltage is higher than the voltage of the capacitor C1 and C2. This state is continued until the input voltage becomes lower than the voltage of the capacitors C1 and C2 in accordance with the elevation or decline of the input voltage. Therefore, the choke coil L1 functions as a step-up chopper and the input current can be proportional to the input voltage and hence the input current contains only a low harmonic current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to reduction of input current harmonics in a switching power supply.

[0002]

2. Description of the Related Art FIG. 8 is a conventional circuit diagram and FIG. 9 is an operation waveform diagram thereof. This circuit is known as an inexpensive circuit with harmonic countermeasures, but as shown in FIG. 9, a steep input current such as rising or falling of the input current flows,
Higher harmonic currents will increase.

[0003]

It is an object of the present invention to provide an inexpensive switching power supply which has a wide range of reduction of input current harmonics.

[0004]

SUMMARY OF THE INVENTION Rectifying diodes D1, D2, D3, D4 for rectifying an input AC voltage.
And capacitors C1, C2 for smoothing the input voltage, and C
Diodes D6 and D7 for discharging C1 and C2 and a choke L1 that acts as a step-up chopper (3) when the input voltage becomes higher than the voltages C1 and C2 and reduces harmonics of the input current.
And a diode D5 for charging the energy stored in L1 to C1 and C2, and a switching element Q1, a transformer T1, and a secondary side rectifying diode for converting electric power to the secondary side. D8, a capacitor C3, a control circuit CONT for controlling the next output voltage, and a load resistor RL are provided.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 6 is an operation waveform diagram of each part thereof.
2, D3, D4 are rectifying diodes that form a full-wave rectifying circuit.
L, L1 is a boosting choke coil, C1 and C2 store the energy released by the choke coil L1, and when the input voltage is lower than the voltage of the capacitors C1 and C2, when the switching element Q1 is turned on, the energy is Is a capacitor for supplying. D6 and D7 are capacitors C1 and C, respectively
2 is a diode for releasing energy, D5 is a blocking diode for preventing the energy emitted by the choke coil L1 from returning to the input, T1, Q1, D8,
C3 and CONT are transformers, switch elements, rectifying diodes, smoothing capacitors and control circuits that form a normal switching power supply, and RL is a load.

Next, the operation of this will be described. First, when the input AC 100V is explained, the switching element Q is still
It is assumed that 1 is off and the capacitors C1 and C2 store 70 V, which is about half the peak value of the input voltage. Then, the switch element Q1 is turned on. When the input voltage is zero V and is lower than the voltage of the capacitors C1 and C2, energy is supplied from the capacitors C1 and C2, and power is transmitted to the secondary side through the transformer T1. When the input voltage becomes higher than the voltage charged in the capacitors C1 and C2, the current flowing through the switch element Q1 is supplied from the input through the boost choke coil L1. Then Cho - the choke coil L1 is also, since the current flows in the switching element Q1, 1/2 × L1 × IQ 1 2 energy - is stored, the switch element Q1 is in a path off (4) when C1, D5, C2 Discharged and capacitor C
1. Charge C2. When the input voltage gradually rises, the difference between the voltage of the capacitors C1 and C2 and the input voltage is reduced by the choke.
Assuming that the ON time of the switch element Q1 is approximately constant, the current flowing through the choke coil L1 is
Only when the input voltage is higher than the voltage of the capacitors C1 and C2, a current similar to the input voltage flows. This causes the input voltage to rise and fall and the input voltage to rise to the capacitors C1 and C2.
Continue until below voltage. That is, the choke coil L1 works as a step-up chopper only when the input voltage is higher than the voltages of the capacitors C1 and C2, and the input current can be made similar to the input voltage and can be a low harmonic current.

FIG. 6 is an operation waveform diagram of each part during the above operation, where (a) is an input AC waveform, and (b) is a waveform after full-wave rectification and a diagram showing the voltages of capacitors C1 and C2 as one diagram. It is described in. (C) is the voltage waveform of the switch element Q1, and it can be seen that when the input voltage is lower than the voltage of the capacitors C1 and C2, operation is performed with the voltage of the capacitors C1 and C2. The input voltage is capacitors C1 and C
When the voltage is higher than the voltage of 2, it can be seen that L1 starts to operate as a boosting choke coil, and thus the voltage is doubled. (D) is a current waveform of the boost choke coil L1. When the input voltage becomes higher than the voltage of the capacitors C1 and C2, a current similar to the input voltage waveform starts to flow.
(E) is an input current waveform. (F) is capacitor C
1 and C2 are charge and discharge current waveforms, and when the input voltage is lower than the capacitors C1 and C2 voltage, the capacitors C1 and C2
2 and the input voltage is higher than the voltage of the capacitors C1 and C2, it means that the energy is charged from the choke coil L1.

FIG. 7 is a harmonic current characteristic diagram of the present invention in comparison with the conventional example (FIG. 8). The vertical axis shows current (A) and the horizontal axis shows harmonic order. In the figure, (a) is the characteristic of the embodiment of the present invention, and (b) is the conventional characteristic. As is clear from the figure, in the third harmonic current, the conventional example is 0.25A, (5) The embodiment of the present invention has 0.4A, which is a little inferior in the current value but the other fifth one. The current value decreases from the harmonic to the 31st harmonic, which indicates that the harmonic current can be suppressed in a wide range.

2, FIG. 3, FIG. 4 and FIG. 5 are circuit diagrams of other embodiments of the present invention. FIG. 2 shows an example in which a capacitor C4 is connected (added) in parallel with the switch element Q1. FIG. 3 shows an example in which the connecting position of the choke coil L1 is connected to the negative side of the full-wave rectifier, and FIG. 4 shows the choke coil L1 at the positive side (L
An example in which it is inserted into both 1) and the negative electrode side (L3) is shown. The above embodiment shows an example of the power supply to which the flyback system (ON-OFF type) is applied. Next, FIG. 5 shows the forward method (ON-0
(N type), the polarity of the secondary side (n2) of the transformer T1 is reversed, and the smoothing diode D9 is used.
And a choke coil L2 for smoothing are added. In addition, also in the embodiment of FIG. 5, the above embodiment (FIGS. 2 to 4)
Can be changed according to.

[0010]

As is apparent from the above description, according to the present invention, the structure is simple and the harmonic current can be suppressed in a wide range, so that the present invention can be applied to a power source in which harmonics are regulated in general. Is big.

[Brief description of drawings]

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

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

FIG. 3 is a circuit diagram of another embodiment of the present invention.

FIG. 4 is a circuit diagram of another embodiment of the present invention (6)

FIG. 5 is a circuit diagram of another embodiment of the present invention.

FIG. 6 is an operation waveform diagram of each part of the circuit diagram (FIG. 1) of the embodiment of the present invention.

FIG. 7 is a harmonic current characteristic diagram of the present invention compared with a conventional example.

FIG. 8 Conventional circuit diagram

FIG. 9: Input voltage and current waveform diagram of conventional circuit

[Explanation of symbols]

 D1, D2, D3, D4 Input voltage rectifying diode L1, L2, L3 Choke coil C1, C2 Smoothing capacitor D5 Charging diode D6, D7 C1, C2 Discharging diode T1 Power conversion transformer Q1 Power conversion switch element D8 Secondary side rectification diode C2 Secondary side rectification capacitor RL Load CONT Output voltage control circuit C4 Resonance capacitor

Claims (5)

[Claims] 1. A full-wave rectifier circuit that receives an input AC voltage and outputs a rectified voltage, and a first choke connected to the positive electrode side of the full-wave rectifier, and the other end of the first choke. A connected first capacitor, a cathode is connected to the other end of the first capacitor, and an anode is connected to the negative side of the full-wave rectifier. -A second diode having a cathode connected to the other end of the pole, one end connected to the anode of the second diode, and the other end connected to the negative side of the full-wave rectifier. A second capacitor, connected between the cathode of the first diode and the anode of the second diode, and a cathode connected to the anode of the second diode. , The cathode of the primary winding of the first transformer is connected to the cathode of the second diode, and the other end is the first diode on the negative side. Switch diode connected to the anode of the first transformer, and a fourth diode having the anode connected to the negative side of the secondary side of the first transformer, one end of which has the positive side of the first transformer. A switching power supply comprising a third capacitor connected to the other end and connected to the cathode of the fourth diode at the other end. 2. A full-wave rectifier circuit that receives an input AC voltage and outputs a rectified voltage, and a first choke connected to the positive electrode side of the full-wave rectifier, and the other end of the first choke. A connected first capacitor, a cathode is connected to the other end of the first capacitor, and an anode is connected to the negative side of the full-wave rectifier. -A second diode having a cathode connected to the other end of the pole, one end connected to the anode of the second diode, and the other end connected to the negative side of the full-wave rectifier. A second capacitor, a cathode connected between the cathode of the first diode and an anode of the second diode, and a cathode connected to the anode of the second diode. The positive side of the primary winding of the first transformer is connected to the cathodes of the third diode and the second diode, and the other end is the first die on the negative side. A switch element connected to the anode of the mode is connected, and a fourth diode and a fourth diode in which the node is connected to the positive electrode side of the secondary side of the first transformer are connected. The cathode is connected to the cathode and the anode is the first transformer.
The fifth diode connected to the negative electrode side of (2), one end of which is connected to the cathode of the fifth diode, and the other end of which is the second chord connected to one end of the third capacitor. A switching power supply in which the other end of the third capacitor is firstly connected to the negative side of the transformer. 3. The switching power supply according to claim 1, wherein a fourth capacitor is connected in parallel with the switching element. 4. The first choke is connected to the negative side of the full-wave rectifier and the anode side of the first diode.
The switching power supply described in a few items. 5. A third choke is connected to the negative side of the full-wave rectifier and the anode side of the first diode.
The switching power supply described in a few items.