JPH10294195A - Power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power unit preventing application of great stresses to the switching elements of an inverter circuit during startup. SOLUTION: The input of power is detected by a voltage detector circuit 12. A capacitor C14 is charged gradually, the collector-emitter current of a transistor Q11 is decreased, and the collector-emitter current of a transistor Q12 is smoothly decreased for turning off. Since the apparent resistance values of a resistance R14 and the emitter and collector of the transistor Q12 increase gradually, the apparent impedance of the parallel circuit of resistances R1, R14 increases smoothly and a control circuit 4 is finally controlled by the resistance value of only the resistance R1. Since a current flowing in the resistance R1 increases even if currents flowing in the drain and source of a field effect transistor Q1 are of the same value, the output of a step-up chopper circuit 3 is reduced to eliminate overshoot during the input of power so as to prevent application of great stresses to field effect transistors Q2, Q3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a power supply having a chopper circuit and an inverter circuit.

[0002]

2. Description of the Related Art Conventionally, as a power supply device of this type, for example, a configuration shown in FIG. 3 is known. In the power supply device shown in FIG. 3, a noise filter circuit 1 is connected to a commercial AC power supply e. The noise filter circuit 1 has a capacitor C1, a common mode choke Tr1, and a capacitor C2. Is connected to an input terminal of a full-wave rectifier circuit 2 such as a diode bridge, and an output terminal of the full-wave rectifier circuit 2 is connected to a step-up chopper circuit 3 which is a DC conversion circuit.

The boost chopper circuit 3 includes a primary winding Tr of a transformer Tr2 between output terminals of the full-wave rectifier circuit 2.
2a, a series circuit of a field effect transistor Q1 and a resistor R1 is connected, and a diode D1 and a smoothing capacitor C3 are connected in parallel with the field effect transistor Q1 and the resistor R1.
Are connected in series. Note that a series resonance circuit is configured by the primary winding Tr2a of the transformer Tr2 and the capacitor C3. A resistor is provided between the output terminals of the full-wave rectifier circuit 2.
A series circuit of R2 and R3 is connected, and the connection point of these resistors R2 and R3 is connected to the multiplier M of the control circuit 4.
ULT terminal, and a series circuit of resistors R4 and R5 is connected in parallel with the capacitor C3.
The connection point of the resistor R5 is connected to the feedback FB terminal of the control circuit 4, and the connection point of the field effect transistor Q1 and the resistor R1 is connected to the CS terminal of the current sense amount of the control circuit via the resistor R6. Circuit 4 is further connected to the gate terminal of field effect transistor Q1. An error amplifier is connected to the FB terminal.
The field effect transistor Q1 of the boost chopper circuit 3 is controlled so that the voltage input to the B terminal is always constant.

The boost chopper circuit 3 is connected to a high frequency series resonance type half-bridge type inverter circuit 5 which is a frequency converter. The inverter circuit 5 includes a field-effect transistor Q2 and a field-effect transistor Q3 connected in series.
The control circuit 6 is connected to the gates of Q2 and the field effect transistor Q3. In addition, field effect transistors
A fluorescent lamp as a discharge lamp is connected to both ends of Q3 via a ballast choke L1 and a capacitor C4 for DC cut.
One ends of the filaments FLa and FLb of the FL are connected, and a starting capacitor C5 is connected between the other ends of the filaments FLa and FLb.

[0005] First, the AC voltage of the commercial AC power supply e is full-wave rectified by the full-wave rectifier circuit 2 via the noise filter circuit 1. The control circuit 4 chops the field effect transistor Q1, stores the DC voltage full-wave rectified by the full-wave rectifier circuit 2 in the transformer Tr2 when the field-effect transistor Q1 is on, and stores the energy in the transformer Tr2 when the field-effect transistor Q1 is off. The energy of the transformer Tr2 is released. further,
Capacitor smoothed by diode D1 and capacitor C3
The voltage of C3 is a DC voltage. According to the boost chopper circuit 3, the output voltage of the full-wave rectifier circuit 2 is directly chopped by the field effect transistor Q1 and smoothed by the diode D1 and the capacitor C3. As a result, the power factor is improved and the ripple can be reduced, so that the flicker of the fluorescent lamp FL can be reduced.

Further, the divided voltage of the resistors R4 and R5 is fed back to the control circuit 4 so that the output of the step-up chopper circuit 3 is kept constant by the control circuit 4.

[0007]

However, in the conventional example shown in FIG. 3, when the power is turned on, an overshoot occurs in the output of the boost chopper circuit 3 due to the delay of the feedback input to the FB terminal, and the boost chopper circuit 3 Output voltage of the inverter circuit 5 causes a large stress to be applied to the field effect transistor Q2 and the field effect transistor Q3 of the inverter circuit 5 at the time of startup, or the field effect transistor
Elements having high withstand voltage must be used for Q2 and the field effect transistor Q3, which causes a problem that the cost is increased and the device may be enlarged.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a power supply device capable of preventing a large stress from being applied to a switching element of an inverter circuit at the time of startup without increasing costs or increasing the size of the device. The purpose is to do.

[0009]

A power supply device according to the present invention comprises a chopper circuit for boosting and outputting a power supply voltage, an inverter circuit for converting the output of the chopper circuit into an alternating current by the operation of a switching element, A start-up control means for gradually increasing the output of the chopper circuit. Then, the power supply voltage is boosted and output by the chopper circuit, and the boosted output voltage is AC-converted by the switching element of the inverter circuit. When the power is turned on, the startup control means gradually increases the output of the chopper circuit, A large stress is prevented from being applied to the switching element of the circuit.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the power supply device of the present invention will be described below with reference to the drawings. The parts corresponding to the conventional example shown in FIG.

As shown in FIG. 1, a noise filter circuit 1 is connected to a commercial AC power supply e. The noise filter circuit 1 has a capacitor C1, a common mode choke Tr1, and a capacitor C2. Is connected to an input terminal of a full-wave rectifier circuit 2 such as a diode bridge, and an output terminal of the full-wave rectifier circuit 2 is connected to a boost chopper circuit 3 which is a DC conversion circuit.

The boost chopper circuit 3 includes a primary winding Tr of a transformer Tr2 between output terminals of the full-wave rectifier circuit 2.
2a, a series circuit of a field effect transistor Q1 and a resistor R1 is connected, and a diode D1 and a smoothing capacitor C3 are connected in parallel with the field effect transistor Q1 and the resistor R1.
Are connected in series. Note that a series resonance circuit is configured by the primary winding Tr2a of the transformer Tr2 and the capacitor C3. A resistor is provided between the output terminals of the full-wave rectifier circuit 2.
A series circuit of R2 and R3 is connected, and the connection point of these resistors R2 and R3 is connected to the multiplier M of the control circuit 4.
Connected to the ULT terminal, a series circuit of a resistor R4, a resistor R5 and a resistor R11 is connected in parallel with the capacitor C3, and a connection point of the resistors R4 and R5 is connected to a feedback FB terminal of the control circuit 4. The connection point between the field effect transistor Q1 and the resistor R1 is connected to the CS terminal of the current sense amount of the control circuit via the resistor R6, and the control circuit 4 is further connected to the gate terminal of the field effect transistor Q1. An error amplifier is connected within the FB terminal, and controls the field effect transistor Q1 of the boost chopper circuit 3 so that the voltage input to the FB terminal is always constant.

The boost chopper circuit 3 is connected to a high frequency series resonance type half-bridge type inverter circuit 5 which is a frequency converter. This inverter circuit 5 is a field effect transistor as a switching element
Q2 and a field effect transistor Q3 are connected in series, and a control circuit 6 is connected to the gates of the field effect transistor Q2 and the field effect transistor Q3. Further, at both ends of the field effect transistor Q3, the filaments FLa and FLb of the fluorescent lamp FL serving as a discharge lamp are connected via a ballast choke L1 and a DC cut capacitor C4.
Is connected, and a starting capacitor C5 is connected between the other ends of the filaments FLa and FLb.

Further, when the power is turned on, the boost chopper circuit 3
Is connected to the start-up control means 11 for gradually increasing the output. The start-up control means 11 includes a voltage detection circuit 12 for detecting a predetermined time after power-on, and a timer circuit 13 for varying the apparent impedance of the resistor R1 for a predetermined time according to the voltage detection circuit 12. I have.

The voltage detection circuit 12 has a series circuit of a capacitor C11 and a capacitor C12 connected in parallel with the field effect transistor Q3, and a capacitor C1.
2, a rectifying diode D11 and a diode D12 are connected in parallel, a capacitor C13 is connected in parallel to the series circuit of the diode D11 and the diode D12, and a constant voltage Zener diode ZD1 is connected in parallel.

The timer circuit 13 includes a Zener diode
Capacitor C14 and diode D13 in parallel with ZD1
The resistor R11 is connected in parallel with the diode D13.The junction of the capacitor C14 and the diode D13 is connected to the base of the transistor Q11.The collector of the transistor Q11 is connected via the resistor R12. The emitter of the transistor Q11 is connected to the negative electrode of the full-wave rectifier circuit 2 via the resistor R13. Further, the base of the transistor Q12 is connected to the emitter of the transistor Q11, and the emitter of the transistor Q12 is connected to the resistors R1 and R1 via the resistor R14.
The collector of the transistor Q12 is connected to the negative terminal of the full-wave rectifier circuit 2.

Next, the operation of the above embodiment will be described.

First, the AC voltage of the commercial AC power supply e is full-wave rectified by the full-wave rectifier circuit 2 via the noise filter circuit 1. Further, the control circuit 4 chops the field effect transistor Q1 and the full-wave rectified DC voltage is supplied to the transformer Tr2 when the field effect transistor Q1 is turned on.
And discharges the energy of the transformer Tr2 when the field effect transistor Q1 is turned off. Then, the current flowing through the field effect transistor Q1 is connected to the resistor R1 or the resistor R1.
And the resistance of the resistor R14 is detected by the series circuit.
The control circuit 4 changes the on-duty and the like of the field-effect transistor Q1 to make the current flowing through the field-effect transistor Q1 constant, thereby making the output constant and the diode D1 and the capacitor
After smoothing by C3, the voltage of the capacitor C3 becomes a constant DC voltage.

The voltage detection circuit 12 detects when the power is turned on. That is, the voltage of the field-effect transistor Q3 is divided by the capacitors C11 and C12 and
The current is rectified by D11 and diode D12 to charge capacitor C13. After the capacitor C13 is charged with a predetermined charge, the voltage of the capacitor C13 is made constant by the Zener diode ZD1.

Then, the capacitor C14 is gradually charged,
When the capacitor C14 is not sufficiently charged, the transistor Q11 is turned on, and the collector and emitter current of the transistor Q11 gradually decreases due to the class A operation. Due to the decrease in the collector and emitter currents of the transistor Q11, the base current of the transistor Q12 gradually increases in accordance with the charging of the capacitor C14. As shown in FIG. 2, the base current of the transistor Q12 increases and the current between the collector and the emitter increases. As the apparent impedance gradually increases, the collector and emitter currents of the transistor Q12 gradually decrease and then turn off.

That is, the resistor R14 and the transistor Q1
Since the apparent resistance of the emitter and collector of 2 gradually increases, the apparent impedance of the parallel circuit of the resistor R1 and the resistor R14 gradually increases, and eventually the resistor R1
The control circuit 4 is controlled by only the resistance value.

Therefore, when the power is turned on, a parallel circuit of the resistor R1 and the resistor R14 is formed, and the combined resistance value of the resistor R1 and the resistor R14 becomes smaller than that of the case where only the resistor R1 is used. The current flowing into the CS terminal of the control circuit 4 increases even if the currents flowing through the drain and the source have the same value, and the drain and source currents of the field effect transistor Q1 apparently increase. The on-duty of the effect transistor Q1 is changed to operate so as to lower the output of the boost chopper circuit 3, and as shown in FIG. It rises gently. After that, resistance
The current flowing through the field effect transistor Q1 is detected only by R1, and the detection is performed as usual.

Therefore, no overshoot voltage is applied to the field effect transistor Q1 and the field effect transistor Q2, so that a large stress is not applied and the withstand voltage can be reduced.

According to the boost chopper circuit 3, the output voltage of the full-wave rectifier circuit 2 is directly chopped by the field effect transistor Q1 and smoothed by the diode D1 and the capacitor C3. Since the impedance is increased, the power factor is improved, and the ripple can be reduced, the flicker of the fluorescent lamp FL can be reduced.

Then, the control circuit 6 turns on the field effect transistors Q2 and Q3 alternately.
By turning off, a high-frequency AC voltage is applied to the fluorescent lamp FL, and the fluorescent lamp FL is lit at high frequency.

[0026]

According to the power supply apparatus of the present invention, the starting control means gradually increases the output of the chopper circuit when the power is turned on, so that the switching element of the inverter circuit can be switched without using a switching element having a high withstand voltage. This prevents a large stress from being applied to the element.

[Brief description of the drawings]

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

FIG. 2 is a waveform chart showing voltages of a transistor Q12 and a chopper circuit according to the first embodiment.

FIG. 3 is a circuit diagram showing a conventional power supply device.

[Explanation of symbols]

3 Boost chopper circuit 5 Inverter circuit 11 Start-up control means Q2, Q3 Field-effect transistor as switching element

Claims (1)

[Claims] 1. A chopper circuit for boosting and outputting a power supply voltage, an inverter circuit for converting an output of the chopper circuit into an alternating current by an operation of a switching element, and a starter for gradually increasing the output of the chopper circuit when power is turned on. A power supply device comprising: a time control unit.