JPH06284708A - Power circuit - Google Patents

Abstract

PURPOSE:To obtain specified performance without damaging a switching element by causing the switching element to operate always at normal timing even if an input alternating current has noise. CONSTITUTION:When an FET 3 is off, a current generated in a choke coil L flows into an electrolytic capacitor C through a flywheel diode D, and charges this capacitor C. On this occasion, a current flowing into the load 4 side becomes smaller, and a voltage drop by a resistor R4 becomes smaller. A control circuit 5 detects the magnitude of the current supplied to the load 4 side from the flywheel diode D by the voltage drop of the resistor R4. And the control circuit 5 turns the FET 3 on through the medium of R1 when the above- mentioned current becomes less than a specified level, and turns the FET 3 off when the above-mentioned current becomes more than a specified level. Consequently, the control circuit 5 performs the switching control of the FET 3 always at normal timing, even if an alternating current supplied from a commercial power source 1 has noise, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit in which a direct current obtained by rectifying an alternating current is boosted by a boost chopper circuit and then supplied to a load.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing an example of a conventional power supply circuit of this type. The alternating current supplied from the commercial power source 1 is rectified by the rectifier circuit 2 to be a direct current (pulsating current). When the FET 3 for the chopper is turned on / off by the control circuit 5 and the FET 3 is turned on, a current flows to the FET 3 side through the primary side coil of the choke coil L. FET3 is O
When FF is performed, the voltage generated by adding the voltage generated in the choke coil and the power supply voltage is rectified by the flywheel diode D, and then the electric field capacitor C is charged, and the charging current of the electric field capacitor C is supplied to the load 4. Control circuit 5
Inputs the voltage V _DET generated in the secondary coil of the choke coil L as shown in FIG. 6, and this voltage is the reference level a.
The FET 3 is turned on at the following timing.

When noise N is added to the AC voltage input from the commercial power supply 1 to the rectifier circuit 2 as shown in FIG. 5A, the voltage generated across the secondary coil of the choke coil L is As shown in B of FIG. 5B, the level may be lower than the original level. As described above, the fact that the voltage difference between the both ends of the primary side coil becomes small means that di / dt approaches 0, and as shown in FIG. 6 generated in the secondary winding of the choke coil L. Voltage V
Where _DET should originally be equal to or higher than the reference level a, it falls below the level a as shown in (b), and the control circuit 5 turns on the FET 3 via the resistor R1. At this time, the choke coil L is an electric field capacitor C.
Is a period in which the flywheel diode D is in the ON state while being charged. In such a period,
When the control for turning on the FET 3 is performed as described above, a reverse current flows from the side of the electric field capacitor C through the diode D as a surge current to the side of the FET 3 and damages the FET 3 and the diode D. In addition, there is a risk that the switching performance of the FET 3 is not normal and the predetermined performance cannot be obtained. 5 (C) shows an example of a current waveform flowing through the choke coil L, FIG. 5 (D) shows an example of a current waveform flowing through the FET 3, and FIG. 5 (E) shows an example of a current waveform flowing through the flywheel diode D. ing.

[0004]

The direct current output from the rectifier circuit as described above is chopped by the switch element through the primary winding of the choke coil L to generate a voltage in the choke coil. In the power supply circuit that charges the capacitor with the sum of this voltage and the power supply voltage via the flywheel diode and supplies this energy to the load, if the AC current input to the rectifier circuit contains noise, the choke coil The voltage generated in the secondary winding of L becomes lower than the original level. Therefore, the control circuit for controlling the on / off of the switch element according to the timing of the voltage generated in the secondary winding of the choke coil L turns it on during the period when the switch element should originally be turned off. Since the erroneous control is performed, there is a possibility that the switch element and the diode may be damaged and there is a drawback that a predetermined performance cannot be obtained as a power supply circuit.

In view of the above, the present invention eliminates the above-mentioned drawbacks, and even when the input AC current is noisy, the switching element is always switched at a normal timing, so that the switching element is not damaged and the switching element is not damaged. It is an object of the present invention to provide a power supply circuit capable of obtaining the above performance.

[0006]

According to the present invention, a pulsating current voltage obtained by rectifying an AC power supply is chopped by a switch element via a choke coil to generate a voltage in the choke coil. In the power supply circuit that charges the capacitor with the sum of the voltages through the flywheel diode and supplies the energy of this capacitor to the load, detect the resistor inserted in the current path that charges the capacitor and the voltage drop of this resistor. And a control circuit for controlling ON / OFF of the switch element by the voltage drop voltage of the resistor detected by the detection circuit.

[0007]

In the power supply circuit of the present invention, the detection circuit detects the voltage drop of the resistor inserted in the current path for charging the capacitor. The control circuit determines the ON timing of the switch element based on the voltage drop voltage of the resistor detected by the detection circuit.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit showing an embodiment of the power supply circuit of the present invention. Reference numeral 1 is a commercial power supply for supplying alternating current, 2 is a rectifier circuit for converting alternating current into direct current, 3 is a chopper FET, 4 is a load, 5 is a control circuit for controlling on / off of FET 3, and C is an electric field. Capacitors, R1, R2, R3,
R4 is a resistance.

FIG. 2 is a circuit diagram showing a detailed example of the control circuit shown in FIG. 51, 52 and 56 are voltage comparison circuits,
53 is a flip-flop, 54 is a buffer amplifier, 55
Is a reference voltage generating circuit for generating a reference voltage of 2.5 V, 5
7 is a multiplier, 58 is an AND circuit, 59 is an inverter, R
5, R6, R8, and R9 are voltage dividing resistors, C1 and C2 are capacitors that form an integrating circuit, C2 and R7 are resistors that form an integrating circuit, and the control circuit 5 is composed of these components.

Next, the operation of this embodiment will be described. The alternating current supplied from the commercial power supply 1 of FIG. 1 is rectified by the rectifier circuit 2 to become a direct current (pulsating current). FET3 for chopper
Is turned on and off by the control circuit 5, and when the FET 3 is turned on, F is passed through the primary side coil of the choke coil L.
A current flows on the ET3 side. When the FET 3 is turned off, the voltage generated by adding the power supply voltage to the voltage generated in the choke coil is rectified by the flywheel diode D and then the electric field capacitor C is charged, and the charging current of the electric field capacitor C is supplied to the load 4.

Next, the operation of the control circuit 5 of this example will be described in detail with reference to FIG. When the current charged in the choke coil L is being supplied to the load 4 through the flywheel diode D, the FET 3 is controlled so as not to be turned on carelessly due to noise of the alternating current, so that the capacitor charging current is changed in this example. Whether or not it is discharged from L is detected by the voltage drop of the resistor R4, and this detected voltage is input to the inverting input terminal of the voltage comparison circuit 52. At this point, the current that charges the capacitor becomes smaller and the resistance R4
Consider the time when the voltage drop due to becomes small. At this time,
Since the inverting input terminal of the voltage comparing circuit 52 becomes equal to or lower than the reference voltage applied to the non-inverting input terminal, the voltage comparing circuit 5
The output side of 2 becomes high level, and this high level signal is input to the input terminal (1) of the flip-flop 53 and the inverter in front of the AND circuit 58. Also, at this time, since the FET 3 is still off, the voltage comparison circuit 5
The non-inverting input terminal of 1 is at a low level compared to the voltage from the multiplier applied to the inverting input terminal, and the output of the voltage comparison circuit 51 is at a high level.

Therefore, the AND circuit 58 receives the low level voltage obtained by inverting the high level output voltage of the voltage comparison circuit 52 and the high level voltage output from the voltage comparison circuit 51. The output becomes low level and is input to the input terminal (2) of the flip-flop 53.
As a result, the output side of the flip-flop 53 becomes low level, but this low level voltage becomes high level by the inverter 59, and this high level voltage becomes the resistance R.
1 is input to the gate of the FET3. This turns on the FET3. When the FET 3 is turned on, a direct current flows into the FET 3 side through the choke coil L, so that the current flowing through the resistor R3 increases and the voltage drop due to the resistor R3 gradually increases. The voltage resulting from this voltage drop is applied to the non-inverting input terminal of the voltage comparison circuit 51 through the integration circuit composed of the resistor R7 and the capacitor C2. Therefore, the potential of the non-inverting input terminal of the voltage comparison circuit 51 gradually rises, becomes higher than the voltage applied from the multiplier 57 to the inverting input terminal of the voltage comparison circuit 51, and the potential of the voltage comparison circuit 51 increases. The output voltage is inverted to the low level, and one input terminal of the AND circuit 58 is set to the low level.

When the FET3 is turned on, the current for charging the capacitor becomes zero, so that the voltage generated at R4 is also zero. Therefore, the output of the voltage comparison circuit 52 remains at the high level. As a result, a high-level voltage is applied to the (1) input terminal of the flip-flop 53, and an inverted voltage of the high-level voltage, that is, a low-level voltage is input to the other input of the AND circuit 58. The output of the circuit 58 becomes low level. As a result, the low-level voltage is input to the input terminal (2) of the flip-flop 53, and the output terminal (3) of the flip-flop 53 is inverted to the high level. This high level voltage is inverted by the inverter 59 and input to the gate of the FET3 via the resistor R1 to turn off the FET3.

By the way, the DC voltage applied to the load 4 divided by the resistors R5 and R6 is input to the non-inverting input terminal of the voltage comparison circuit 56. Further, the 2.5V reference voltage generated from the reference voltage generation circuit 55 is input to the inverting input terminal of the voltage comparison circuit 56, and the voltage comparison circuit 56 multiplies the divided voltage by the difference voltage between the reference voltage. Output to the container 57. On the other hand, the other input terminal of the multiplier 57 is shown in FIG.
The voltage output from the rectifier circuit 2 shown in FIG.
Since the divided voltage obtained by dividing by is input, the multiplier 57 multiplies the divided voltage of the voltage input to the choke coil L by the differential voltage output from the voltage comparison circuit 56, The multiplication result voltage is output to the inverting input terminal of the voltage comparison circuit 51. Therefore, for example, when the voltage applied to the load becomes low due to load fluctuation, the differential voltage output from the voltage comparison circuit 56 becomes large, and therefore the multiplier 5
The multiplication result voltage output from 7 also increases accordingly. Therefore, the FET 3 is turned on and the voltage input to the non-inverting input terminal of the voltage comparison circuit 51 gradually increases, and the time until the output of the voltage comparison circuit 51 is inverted to the low level is lengthened. Therefore, the ON time of the FET 3 is lengthened to control the output voltage to a predetermined value. Therefore, the multiplication result voltage output from the multiplier 57 is FET3.
It is used for controlling the ON time of the output voltage to maintain the output voltage at a predetermined voltage.

According to this embodiment, the control circuit 5 detects the time when the current for charging the capacitor becomes small by the voltage drop of the resistor R4, and at this time controls the FET 3 to be turned on. The voltage difference between both ends of the choke coil L is reduced by the influence of noise superimposed on the alternating current supplied from the diode, and the voltage induced in the secondary winding of the choke coil L is reduced. It is possible to prevent erroneous control such as turning on the FET 3 while the current is flowing through D, and to always perform normal switching operation of the FET 3. This makes it possible to always obtain a predetermined performance without damaging the FET 3 and the diode D.

FIG. 3 is a circuit diagram showing another embodiment of the present invention. In the control circuit 5 of this example, the voltage drop voltage of the resistor R4 that detects the magnitude of the current that charges the capacitor is input to the inverting input terminal of the voltage comparison circuit 52 via the buffer amplifier 60 and the diode 61. In addition to it,
In this example, the voltage generated in the secondary winding of the choke coil L is introduced to the inverting input terminal of the voltage comparison circuit 52 via the resistor R2 and the diode 62. Also, the diode 6
Zener diode 63 and resistor R1 on the anode side of 2
0 is connected. Therefore, since the capacitor charging current detection voltage and the voltage generated in the secondary winding of the choke coil L are input to the inverting input terminal of the voltage comparison circuit 52 via the diodes 61 and 62, both ends up being The logical sum of the detected voltages is input to the inverting input terminal of the voltage comparison circuit 52, and the other configurations are the same as in the previous embodiment. Therefore, due to the AC noise supplied from the commercial power source 1, the detection voltage of the secondary winding of the choke coil L becomes low at a point where it should not originally be low, and the voltage of the voltage comparing circuit 52 of the voltage comparing circuit 52 passes through the diode 62. Even if a low level voltage is input to the inverting input terminal, if a current is flowing through the flywheel diode D at this time, the detection voltage obtained by detecting this current with the resistor R4 is the voltage via the diode 61. Since it is input to the inverting input terminal of the comparator circuit 52, this inverting input terminal maintains a high level, which makes it possible to maintain the FET 3 in the off state, which has the same effect as the previous embodiment.

[0017]

As described above, according to the power supply circuit of the present invention, the switching element and the diode are switched by always switching the switching element at the normal timing even if the input AC current is noisy. The desired performance can be obtained without damage.

[Brief description of drawings]

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

2 is a circuit diagram showing a detailed example of a control circuit shown in FIG.

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

FIG. 4 is a circuit diagram showing an example of a conventional power supply circuit.

5 is a diagram showing an example of voltage waveforms at various parts of the circuit shown in FIG.

6 is a diagram showing an example of a voltage generated in a secondary winding of the choke coil shown in FIG.

[Explanation of symbols]

1 ... Commercial power supply 2 ... Rectifier circuit 3 ... FET 4 ... Load 5 ... Control circuit 51, 52, 5
6 ... Voltage comparison circuit 53 ... Flip-flop 54 ... Buffer amplifier 55 ... Reference voltage generation circuit 57 ... Multiplier 58 ... AND circuit 59 ... Inverter C, C1, C2 ... Capacitor D ... Diode L ... Choke coils R1-R9 ... Resistance

Claims (2)

[Claims] 1. A voltage is generated in the choke coil by chopping a rectified current obtained by rectifying an alternating current through a choke coil with a switch element,
In the power supply circuit for charging the capacitor with the voltage of the sum of this voltage and the power supply voltage through the flywheel diode and supplying the energy of this capacitor to the load, a resistor inserted in the current path for charging the capacitor,
A power supply circuit comprising: a detection circuit for detecting the voltage drop of the resistor; and a control circuit for performing on / off control of the switch element by the voltage drop voltage of the resistor detected by the detection circuit. . 2. A voltage is generated in the choke coil by chopping a pulsating voltage obtained by rectifying an AC power source through a choke coil with a switch element,
In the power supply circuit for charging the capacitor with the voltage of the sum of this voltage and the power supply voltage through the flywheel diode and supplying the energy of this capacitor to the load, a resistor inserted in the current path for charging the capacitor,
A first detection circuit that detects the voltage drop of the resistor, a second detection circuit that detects the voltage generated in the secondary winding of the choke coil, and a detection circuit that detects the voltage generated by the first and second detection circuits. A power supply circuit comprising: a logic circuit that takes a logical sum of both voltages; and a control circuit that performs on / off control of the switch element by the voltage output from the logic circuit.