JPH07231650A - Boosting chopper circuit - Google Patents

Abstract

PURPOSE:To prevent an output overvoltage with a simple circuit, by using an overcurrent protective circuit for stopping on-off operation of a switching element when a current in the switching element is over a given level. CONSTITUTION:An overvoltage protective circuit 39 is used for stopping on-off operation of a switching element 6 when a current in the switching element 6 is over a given level. The current carried at the switching element 6 is detected by a resistor 21. A switching control circuit 11 is stopped in operation by turning on a transistor 36, and the switching element 6 is held in an off state when the sum of voltages at a diode 35 and the resistor 21 becomes over a voltage between the base and emitter of the transistor 36. In this way, the current of the switching element 6 is limited to a given level, and electromagnetic energy stored at the choke 5 is limited. Then, an electric charge stored in the capacitor 8 is also limited.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boost chopper circuit used in a discharge lamp lighting device or the like.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram of a conventional boost chopper circuit. In the figure, 1 is an AC power supply, 2 is a choke for a noise filter, and 3 is a full-wave rectification circuit for full-wave rectifying the AC power supply 1, which is composed of a diode bridge. The AC power supply 1, the choke 2 for the noise filter,
The full-wave rectifier circuit 3 constitutes a DC power supply 4.

Reference numeral 5 is a choke, and 6 is a switching element, which is a metal oxide film field effect transistor (MOSFET).
It is composed by. The choke 5 and the switch element 6 are connected in series between the output terminals of the DC power supply 4. A series circuit of a diode 7 and a capacitor 8 is connected in parallel to both ends of the switch element 6, and the switch element 6 is turned on and off at a high frequency to accumulate electromagnetic energy in the choke 5 and transfer the energy to the diode 7 The voltage is discharged to the capacitor 8 via the capacitor 8 and the voltage higher than the voltage obtained by full-wave rectifying the AC power supply 1 by the full-wave rectifier circuit 3 is stored in the capacitor 8.

Reference numeral 11 denotes a switch control circuit for on / off controlling the switch element 6, which is an output signal of the multiplier 12, the control amplifier 13, the comparator 14, the NAND circuits 15 and 16, the RS flip-flop 17, the AND circuit 18, and the AND circuit 18. And a drive circuit 19 for adjusting Switch control circuit 11
Outputs a high voltage (H) or a low voltage (L) from the drive circuit 19, turns on the switch element 6 when the output signal from the drive circuit 19 is H, and the output signal from the drive circuit 19 is L. At this time, the switch element 6 is turned off.

Then, the switch control circuit 11 detects the current flowing through the switch element 6 by the resistor 21, and when the current flowing through the switch element 6 reaches the threshold value corresponding to the peak value of the desired choke 5 current, the comparison is made. The output signal from the drive 14 is inverted and the output signal from the drive circuit 19 changes from H to L.
Is configured to be. The threshold is the multiplier 12
Switch element 6 detected by resistors 25 and 26
Input voltage waveform to the control amplifier 1 and the output voltage of the capacitor 8 detected via the resistors 27, 28 and 29 are input.
3 and the amplitude of the output voltage of 3.

In addition, the NAND circuit 15 outputs high voltage (H) or low voltage (L) from the secondary winding 22 provided in the choke 5.
When the NAND circuit 15 inputs L from the secondary winding 22, the output signal from the drive circuit 19 changes from L to H.
The diode 7 is kept off until the current of the diode 7 becomes zero. To detect the zero crossing of the current of the diode 7, the voltage of the choke 5 is taken out by the secondary winding 22, and the voltage of the secondary winding 22 of the choke 5 becomes positive when the switch element 6 is turned on, and the energy of the choke 5 is reduced. When the release is completed, it returns to zero.

Therefore, when the currents of the choke 5 and the diode 7 become 0, the switch element 6 is turned on, and when the current flowing through the switch element 6 reaches the threshold value corresponding to the desired peak value of the choke 5 current, the switch element 6 is turned on. The switch control circuit 11 controls the switching element 6 to be turned on and off at a high frequency so that a stable DC voltage is obtained on the capacitor 8 side.

However, the DC voltage charged in the capacitor 8 may exceed the predetermined voltage due to a sudden change in the load impedance or a delay in the detection signal of the resistor 21 or the like. Therefore, in order to prevent this, the voltage of the capacitor 8 is detected. Zener diode 3 separately from the resistors 27, 28 and 29
The reference voltage of 1 is provided, and the two voltages are compared by the comparator 32 and converted into H and L output signals. At the normal set voltage, the output signal of the comparator 32 is set to L,
When the overvoltage is charged, the output signal of the comparator 32 is set to H, and the H signal is input to the NAND circuit 15 of the switch control circuit 11 to stop the on / off operation of the switch element 6 so that the capacitor 8 does not become overvoltage. It was protected.

[0009]

However, in the conventional case,
In order to protect the capacitor 8 from overvoltage, the comparator 32 and the reference voltage are required, and the entire circuit configuration becomes very complicated. In view of the above-mentioned problems, the present invention is to prevent the output voltage of the boost chopper circuit from becoming an overvoltage with a simpler circuit.

[0010]

According to the technical means of the present invention for solving this technical problem, a choke 5 and a switch element 6 are connected in series between output terminals of a DC power source 4, and both ends of the switch element 6 are connected. , A series circuit of a diode 7 and a capacitor 8 is connected in parallel, and a switch control circuit 11 for on / off controlling the switch element 6 is provided. The on / off operation of the switch element 6 accumulates electromagnetic energy in the choke 5 to generate the energy. In a step-up chopper circuit for discharging DC to a capacitor 8 via the diode 7 to obtain a DC voltage, an overvoltage protection circuit for stopping the ON / OFF operation of the switch element 6 when the current flowing in the switch element 6 is a certain value or more. 39 is provided.

[0011]

The current flowing in the switch element 6 is detected by the resistor 21, and when the added voltage of the voltage of the diode 35 and the voltage of the resistor 21 becomes larger than the voltage between the base and the emitter of the transistor 36, the transistor 36 is turned on. Then, when the transistor 36 is turned on, driving of the switch control circuit 11 is stopped, and the switch element 6 is held in the off state. In this way, when the current of the switch element 6 is limited to a certain level, the electromagnetic energy stored in the choke 5 is limited, and as a result, the electromagnetic energy stored in the capacitor 8 is limited and the charge stored in the capacitor 8 is limited. Is also limited.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, the resistor 21 added to the ground side of the switch element 6 is connected to the base terminal of the transistor 36 via the diode 35.
The emitter of is connected to ground. The collector of the transistor 36 is connected between the resistors 25 and 26. When the current flowing through the switch element 6 by the diode 35 and the transistor 36 exceeds a certain level, the switch control circuit 11 is stopped to drive the switch element 6
An overvoltage protection circuit 39 is configured to stop the on / off operation of.

According to the configuration of the above embodiment, the current flowing in the switch element 6 is detected by the resistor 21, and the diode 3
5 is added to the voltage of the resistor 21 and the voltage between the base and the emitter of the transistor 36 are compared, and the added voltage of the voltage of the diode 35 and the voltage of the resistor 21 is calculated between the base and the emitter of the transistor 36. When the voltage exceeds the voltage, the transistor 36 is turned on. That is, the magnitude of the current flowing through the switch element 6 is determined.

When the current of the switch element 6 is larger than a predetermined level, the transistor 36 turns on and the transistor 3
When 6 is turned on, the output of the switch control circuit 11 to the multiplier 12 is changed to a low voltage (L), so that the output of the multiplier 12 becomes L and the output of the comparator 14 also becomes L. Therefore, the output of the RS flip-flop 17 is inverted, the output signal of the drive circuit 19 changes from H to L, the drive of the switch control circuit 11 is stopped, and the switch element 6 is held in the OFF state.

In this way, when the current of the switch element 6 is limited to a certain level, the electromagnetic energy stored in the choke 5 is limited, and the electromagnetic energy stored in the capacitor 8 is limited and stored in the capacitor 8. The charge is also limited.

[0016]

According to the present invention, it is possible to prevent the output voltage of the boost chopper circuit from becoming an overvoltage by a simpler circuit without the need for a comparator and a reference voltage as in the conventional case.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing a conventional example.

[Explanation of symbols]

 1 AC power supply 3 Full wave rectification circuit 4 DC power supply 5 Choke 6 Switch element 7 Diode 8 Capacitor 12 Multiplier 13 Control amplifier 14 Comparator 15 NAND circuit 16 NAND circuit 17 RS flip-flop 18 AND circuit 19 Drive circuit 21 Resistance 35 Diode 36 Transistor

Claims (5)

[Claims] 1. A choke 5 is provided between the output terminals of the DC power supply 4.
And the switch element 6 are connected in series, and the switch element 6
A series circuit of a diode 7 and a capacitor 8 is connected in parallel at both ends of the switch, and a switch control circuit 11 for controlling the on / off of the switch element 6 is provided. The on / off operation of the switch element 6 accumulates electromagnetic energy in the choke 5. In a step-up chopper circuit in which the energy is released to a capacitor 8 via the diode 7 to obtain a DC voltage, an overvoltage for stopping the on / off operation of the switch element 6 when the current flowing in the switch element 6 is a certain value or more. A boost chopper circuit, which is provided with a protection circuit 39. 2. The step-up chopper circuit according to claim 1, wherein the DC power supply 4 includes an AC power supply 1 and a rectifying circuit 3 that full-wave rectifies the AC power supply 1. 3. The switch control circuit 11 comprises a multiplier 1
2, control amplifier 13, comparator 14, NAND circuits 15 and 1
6. The step-up chopper circuit according to claim 1, further comprising: 6, an RS flip-flop 17, an AND circuit 18, and a drive circuit 19 that adjusts an output signal of the AND circuit 18. 4. A choke 5 is provided between the output terminals of the DC power supply 4.
And the switch element 6 are connected in series, and the switch element 6
A series circuit of a diode 7 and a capacitor 8 is connected in parallel at both ends of the switch, and a switch control circuit 11 for controlling on / off of the switch element 6 is provided, and electromagnetic energy is accumulated in the choke 5 by the on / off operation of the switch element 6. In the step-up chopper circuit, in which the energy is released to the capacitor 8 via the diode 7 to obtain a DC voltage, a resistor 21 for detecting a current flowing through the switch element 6 is provided, and the switch detected by the resistor 21 is provided. A step-up chopper circuit, which is provided with an overvoltage protection circuit 39 for stopping the drive of the switch control circuit 11 when the current flowing through the element 6 is above a certain level. 5. The overvoltage protection circuit 39 includes a diode 35 and a transistor 36, and the resistor 21 for detecting a current flowing through the switch element 6 is connected to the base terminal of the transistor 36 via the diode 35. The boost chopper circuit according to claim 4, wherein the boost chopper circuit is connected.