JP3029728B2 - Lamp lighting circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a lamp lighting circuit capable of dimming a lamp or the like by pulse width modulation of an applied voltage.

[0002]

2. Description of the Related Art Conventionally, there has been known a lamp lighting circuit capable of dimming a lamp or the like by pulse width modulation of an applied voltage. As an example, a lamp lighting circuit using an inverter circuit is known. An example of this is shown in FIG. In the figure, 1 is a DC power supply, 2 is a chopper control unit, 3 is a chopper unit, 4 is an inverter unit, and 5 is a current detection unit.

The chopper control unit 2 includes an oscillator 21, an amplifier circuit 22, and an operational amplifier 2 used as a comparator.
3, composed of resistors 24 and 25, a variable resistor 26 and an NPN transistor 27. The oscillator 21 outputs, for example, a triangular wave signal. The resistors 24 and 25 and the variable resistor 26 are connected in series, and divides the voltage Vrf output from the current detection unit 5 into a voltage Vd.
d is applied to the non-inverting input terminal of the operational amplifier 23 via the amplifier 22. The output voltage V1 of the operational amplifier 23 is applied to the base of the transistor 27, and the emitter of the transistor 27 is connected to the negative electrode of the DC power supply 1.

The chopper section 3 includes a field effect transistor (hereinafter, referred to as a transistor) 31, resistors 32, 3
3, a diode 34, choke coils 35 and 36, and a capacitor 37. The gate of the transistor 31 is connected to the collector of the transistor 27 through the resistor 32.
Further, it is connected to its drain and the positive electrode of the DC power supply 1 via a resistor 33, respectively. Further, the source of the transistor 31 is connected to the cathode of the diode 34 and one end of the choke coil 35, and the other end of the choke coil 35 is connected to one end of the choke coil 36 and one end of the capacitor 37. Further, the anode of the diode 34 and the other end of the capacitor 37 are connected to the negative electrode of the DC power supply 1.

[0005] The inverter unit 4 is composed of a known lower circuit. That is, the transformer 41 includes a primary winding 411 having an intermediate tap 411a, a secondary winding 412 and a tertiary winding 413, NPN transistors 42 and 43, resistors 44 and 45, and a capacitor 46. ing.
A capacitor 46 is connected in parallel with the primary winding 411,
The collector of the transistor 42 is connected to one end 411b of the primary winding 411, and the collector of the transistor 43 is connected to the other end 411c of the primary winding 411. further,
The respective emitters of the transistors 42 and 43 are connected to the negative electrode of the DC power
The second base is connected to the other end 413a of the tertiary winding 413, and the base of the transistor 43 is connected to one end 413b of the tertiary winding 413. Further, an intermediate tap 411a of the primary winding 411 is connected to the other end of the choke coil 36 and a transistor 42 is connected via a resistor 44.
Of the transistor 43 through the resistor 45
Each is connected to the base.

[0006] The current detecting section 5 is composed of a half-wave rectifier circuit including a resistor 51, diodes 52 and 53, and a capacitor 54. That is, the resistor 51 is connected to the secondary winding 41.
2 are connected in series, and a current is supplied to a lamp or the like (not shown) to be lit via a resistor 51. One end of the resistor 51 connected to the secondary winding 412 is connected to the anode of the diode 52 and the cathode of the diode 53, and the other end of the resistor 51 is connected to the anode of the diode 53 and the capacitor 5
4 and the negative electrode of the DC power supply 1. Further, the cathode of the diode 52 is connected to the other end of the capacitor 54, and the voltage V
rf is output.

Next, the operation of the lamp lighting circuit having the above configuration will be described. While current is supplied to the transformer 41 via the transistor 31 and the choke coils 35 and 36 of the chopper 3, current flows through the primary winding 411, and when the transistor 42 reaches the saturation region from the unsaturated region. ,
Transistor 42 turns off. As a result, the transistor 4 is connected to one end 413b of the tertiary winding 413 by the back electromotive force.
3 is turned on, and the transistor 43 is turned on. Thus, while the transistor 43 remains on, the collector current increases linearly up to the saturation region. Here, the transistor 43 is turned off and the transistor 42 is turned on, and this relationship is repeated. As a result, an AC voltage is generated in the secondary winding 412, and the lamp is turned on.

Further, the current flowing through the secondary winding 412 is detected by the current detection circuit 5 and converted into a voltage Vrf. This voltage Vrf is divided by the resistors 24 and 25 and the variable resistor 26 and is converted into a voltage Vd. As for the value of the voltage Vd, the values of the resistors 24 and 25 and the variable resistor 26 are set so that the value at the input terminal of the operational amplifier 23 is between the maximum value and the minimum value of the output voltage Vosc of the oscillator 21. Further, the value of the variable resistor 26 is set to a value at which a sufficient dimming effect can be obtained. As a result, only when the low-level signal is being output from the operational amplifier 23 to the transistor 27, the transformer 41
Is supplied to the variable resistor 26, the luminance of the lamp can be adjusted by changing the resistance value of the variable resistor 26 and changing the pulse width of the output signal of the operational amplifier 23.

[0009]

However, in the above-described conventional lamp lighting circuit, the oscillation frequency of the oscillator 21 and the operating frequency of the inverter section 4 are different.
Beats of these frequencies occur. Since this beat occurs over many orders and includes a plurality of frequency components, it generates audible noise or, when used for lighting a backlight of a liquid crystal display, interference with the frame frequency of the liquid crystal display. Causes screen beats, flicker, etc. Furthermore, when combined with other higher-level devices, there is a problem that interference with the natural frequency of the higher-level device causes a malfunction or the like of the higher-level device.

It is also conceivable to set the oscillation frequency of the oscillator 21 and the operating frequency of the inverter unit 4 to a frequency that does not affect the host device.
Each of these is accompanied by fluctuations due to the ambient temperature, drift over time, etc., and the beat spectrum changes due to these fluctuations, so that setting these frequencies is difficult.

Further, as a lighting frequency of a lamp, a backlight or the like, a frequency of about 30 to 60 KHz is often used, and as a countermeasure against the audible noise, the lighting frequency is set to 300 to 600 KHz and a beat component of the audible frequency is reduced. It is conceivable to set a higher order, but in this case, there is a problem that the overall efficiency is reduced.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lamp lighting circuit capable of preventing occurrence of a beat in view of the above problems.

[0013]

According to the present invention, a transformer having a primary winding having an intermediate tap and a secondary winding is provided. First and second switch elements respectively connected to both ends of the first switch element, switching control means for alternately switching on and off states of the first and second switch elements, and voltage application to the intermediate tap. In a lamp lighting circuit including a third switch element for switching on / off and a voltage control unit for controlling the on / off state of the third switch element, the switch control units are synchronized with each other and have the same predetermined cycle. An oscillation circuit that outputs a substantially triangular wave signal and a binary signal; a first state control circuit that controls an on / off state of the first switch element; and an on / off state of the second switch element. And a second state control circuit Gosuru, first connected between the one end and the center tap of the primary winding
And a second charge / discharge circuit connected between the other end of the primary winding and the intermediate tap, and the first state control circuit is configured so that the binary signal is one of: The first switch element is turned on based on the charge polarity of the first charging / discharging circuit while the second level control circuit is at the one level. The second switch element is turned on based on the charging polarity of the second charging / discharging circuit, and the voltage control means detects a current flowing through a secondary winding of the transformer; A voltage conversion circuit that converts a detection current value of the current detection circuit into a voltage, arbitrarily changes and outputs the voltage value within a predetermined range, and an output voltage of the voltage conversion circuit and a voltage of the triangular wave signal. Based on the on / off state of the third switch element, Suggest lamp lighting circuit comprising a third state control circuit changing Ri.

According to a second aspect of the present invention, there is provided the lamp lighting circuit according to the first aspect, wherein the current detection circuit includes a voltage doubler full-wave rectifier circuit.

[0015]

According to the first aspect of the present invention, in the initial state, each of the first and second charge / discharge circuits is in an uncharged state, so that the binarized signal output from the oscillation circuit has one level. , One of the first and second switch elements is turned on and the other is turned off due to a difference in electrical characteristics. For example, when the first switch element is turned on and the second switch element is turned off, the primary winding of the transformer is energized through the first switch element that is turned on. Accordingly, the first and second charge / discharge circuits are charged. Here, since the potentials at one end and the other end of the primary winding are different, the first and second potentials are different.
Has a different polarity on the primary winding side.

When the binarized signal is inverted to the other level, the first and second switch elements are both turned off by the first and second state control circuits, and thereafter,
When the binary signal is inverted to the one level, the first switch element is continuously turned off by the first state control circuit based on the charge polarity of the first charge / discharge circuit, Further, the second switch element is turned on by the second state control circuit based on the charge polarity of the second charge / discharge circuit. As a result, electricity is supplied to the primary winding via the second switch element. The energizing direction at this time is reverse to the direction when the first switch element is in the ON state, and the potential at one end and the potential at the other end of the primary winding are inverted. The charge polarity of the charge / discharge circuit is inverted. Thereby, when the binary signal is inverted to the other level and further inverted to the one level, the first switch element is turned on by the first and second state control circuits. , The second switch element is turned off. Therefore, the transformer, the first and second switch elements, the first
And a second state control circuit, and a first and second charge / discharge circuit constitute a self-excited oscillation circuit, and the off state of the self-excited oscillation circuit is controlled in synchronization with the binarized signal, The direction of current supply to the primary winding is reversed in synchronization with the binarized signal, and an AC voltage is generated in the secondary winding of the transformer.

Further, the ON / OFF of the application of the voltage to the intermediate tap of the primary winding is switched by a third switch element. Further, a current detection circuit detects a current flowing through the secondary winding, and the detected current value is converted to an arbitrary voltage value within a predetermined range by a voltage conversion circuit, and output from the voltage and the oscillation circuit. The on / off state of the third switch element is switched by the third state control circuit based on the voltage of the triangular wave signal.

According to the present invention, the current detecting circuit is constituted by a voltage doubler full-wave rectifier circuit. This makes it possible to reduce the resistance value when converting the current flowing through the secondary winding into a voltage value.

[0019]

FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention, and FIG. 3 is a circuit diagram. In the figure, 110 is a DC power supply (hereinafter referred to as a power supply), 120 is a switch circuit,
130 is a reference voltage generation circuit, 140 is an oscillation circuit, 150 is a chopper drive control circuit, 160 is a low input lockout circuit, 170 is a chopper drive circuit, 180 is a chopper circuit, 190 is an overvoltage protection circuit, 200 is an inverter circuit, 22
0 is a current detection circuit, and 230 is a voltage conversion circuit.

The switch circuit 120 includes a switch 121, resistors 122 and 123, a PNP transistor 124, and a capacitor 125. One end of the switch 121 is connected to the negative electrode of the power supply 110, and the emitter of the transistor 124 is connected to the positive electrode of the power supply 110. Have been. Further, the base of the transistor 124 is connected to the other end of the switch 121 via the resistor 122, and to the positive terminal of the power supply 110 via the resistor 123, respectively. The capacitor 125 is connected in parallel with the power supply 110. Thus, when the switch 121 is turned on, the base potential of the transistor 124 becomes low level, and the transistor 124 is turned on.

The reference voltage generating circuit 130 comprises a Zener diode 131, an NPN transistor 132, a resistor 133 and a capacitor 134. The base of the transistor 132 is connected to the collector of the transistor 132 and the collector of the transistor 124 via the resistor 133. With Zener diode 131
Connected to the cathode. In addition, transistor 13
2 is connected to the negative electrode of the power supply 110 via a capacitor, and the anode of the Zener diode 131 is connected to the power supply 110.
Is connected to the negative electrode. Thereby, the transistor 13
The constant voltage Vref based on the control voltage of the Zener diode 131 is output to the emitter 2.

The oscillation circuit 140 is composed of a well-known astable self-running multivibrator, and includes an operational amplifier 141 used as a comparator, resistors 142 to 146, and a capacitor 147.
It is composed of The inverting input terminal of the operational amplifier 141 is connected to its output terminal via a resistor 142,
It is connected to the negative electrode of the power supply 110 via the capacitor 147. Further, the output terminal of the operational amplifier 141 is connected to the resistor 143
Is connected to the non-inverting input terminal of the transistor 132 via a resistor 144 and to the emitter of the transistor 132 via a resistor 144. The non-inverting input terminal of the operational amplifier 141 is a resistor 145
Is connected to the emitter of the transistor 132 via the resistor 146 and to the negative electrode of the power supply 110 via the resistor 146. The oscillation frequency fos is determined by charging and discharging of the capacitor 147, and the voltage Vcf of the capacitor 147 has a substantially triangular waveform. The amplitude level of this voltage Vcf and the operational amplifier
The pulse width of the output signal A at 141 is determined by the values of the resistors 142 to 146 and the capacitor 147.

The chopper drive control circuit 150 includes an operational amplifier 151 used as a comparator and resistors 152 to 152.
154 and capacitors 155 and 156.
A voltage Vd1 obtained by dividing the reference voltage Vref is applied to the inverting input terminal of
In addition, the inverting input terminal is a capacitor 155 connected in series,
It is connected via a resistor 152 to the inverting input terminal of the operational amplifier 141 and via a capacitor 156 to the negative terminal of the power supply 110. A voltage Vd2 output from a voltage conversion circuit 230 described later is applied to a non-inverting input terminal of the operational amplifier 151. As a result, the voltage Vcf of the triangular wave generated in the capacitor 147 of the oscillation circuit 140 is removed (DC cut) by the capacitor 155 after the DC component is removed.
It is AC-coupled to the voltage Vd1 by the operational amplifier 151. The resistor 152 adjusts the amplitude level of the voltage Vcf and sets the gain of the operational amplifier 151. Further, since the voltage Vcf of the triangular wave is differentiated by the resistor 152 and the capacitor 155, the waveform is corrected by integrating by the capacitor 156. Further, the time constant of the capacitor 156 and the resistor 153 allows a soft start at the time of startup.

The low input lockout circuit 160 comprises a PNP transistor 161, a Zener diode 162, and resistors 163 and 164. The base of the transistor 161 is connected via a resistor 163 to its emitter and the output terminal of the operational amplifier 151. Zener diode 16 via resistor 164
2 anodes. Further, the cathode of the Zener diode 162 is connected to the collector of the transistor 124 of the switch circuit 120. As a result, the on / off control of the switch 121 and the power supply 110
It is possible to avoid a malfunction of the oscillation control at the time of a low input from the controller. That is, since the output of the operational amplifier 141 is low when the input is low, the output voltage of the chopper circuit 180 described later momentarily becomes overvoltage when the switch 121 is turned on and off, and the output current of the inverter circuit 200 may increase. For this reason, when the collector voltage of the transistor 124 of the switch circuit 120 is lower than a predetermined value, the chopper drive circuit 170 described later is controlled by the transistor 161 and the chopper circuit 80 is turned off.

The chopper drive circuit 170 includes an NPN transistor 171, a PNP transistor 172, and resistors 173 to 175.
Is connected to the base of transistor 172, to the collector of transistor 171 and the positive electrode of power supply 110 via resistor 173, and to the collector of transistor 161 via resistor 174, respectively. Further, the emitter of the transistor 172 is connected to the emitter of the transistor 171, and the collector is connected to the negative electrode of the power supply 110 via the resistor 175.

The chopper circuit 180 includes an N-channel field effect transistor (hereinafter, referred to as a transistor) 181.
, Diode 182, choke coil 183, capacitor 1
The drain of transistor 181 is connected to power supply 110.
The gate is connected to the emitter of the transistor 171 and the source is connected to the cathode of the diode 182 and one end of the choke coil 183, respectively. The other end of the choke coil 183 is connected to one end of the capacitor 184, and the anode of the diode 182 and the other end of the capacitor 184 are connected to the negative electrode of the power supply 110.

The overvoltage protection circuit 190 comprises a zener diode 191 and a resistor 192 connected in series, and the cathode of the zener diode 191 is connected to the choke coil 183.
And the other end of the resistor 192 are connected to a voltage conversion circuit 230 described later.

The inverter circuit 200 includes a transformer 210, P-channel field effect transistors (hereinafter referred to as transistors) Q1 and Q2, and NPN transistors Q3 and Q3.
Q6, PNP transistors Q4, Q5, diodes D1 to D4, resistors R1 to R4, and capacitors Ca,
Cb.

One end 211a of the primary winding 211 of the transformer 210 is connected to the drain of the transistor Q1, the cathode of the diode D4 and one end of the resistor R2, and the other end of the primary winding 211
211b is connected to the drain of the transistor Q2, the cathode of the diode D3, and one end of the resistor R1. The intermediate tap 211c of the primary winding 211 is connected to the transistor Q
3 and Q6, and to the other end of the choke coil 183. The source of the transistor Q1 is connected to the source of the transistor Q2, the collectors of the transistors Q4 and Q5, and the negative electrode of the power supply 110. A resistor R3 is connected between the base and the collector of the transistor Q3, and the emitter of the transistor Q3 is connected to the gate of the transistor Q1 and the emitter of the transistor Q4. The base of transistor Q4 is the anode of diodes D1 and D3, transistor Q3
The cathode of the diode D1 is connected to the cathode of the diode D2 and the output terminal of the operational amplifier 141. Also,
The other end of the capacitor Ca is connected to the other end of the resistor R1.

A resistor R4 is connected between the base and the collector of the transistor Q6, and the emitter of the transistor Q6 is connected to the gate of the transistor Q2 and the emitter of the transistor Q5. The base of the transistor Q5 is connected to the anodes of the diodes D2 and D4, the base of the transistor Q6 and one end of the capacitor Cb, and the other end of the capacitor Cb is connected to the other end of the resistor R2.

The current detection circuit 220 comprises a half-wave rectifier circuit, and includes a resistor 221, diodes 223 and 224, and a capacitor 22.
It consists of 4,225. The resistor 221 is connected to the transformer 21
0 is connected in series with the secondary winding 212, and the secondary winding 212 is connected to the load via the resistor 221. A capacitor 224 is connected in parallel to the resistor 221, and one end of the resistor 221, that is, the secondary winding 212 side is connected to the cathode of the diode 222 and the anode of the diode 223, and to the other end of the resistor 221. Is connected to the anode of the diode 222 and one end of the capacitor 225. Further, the cathode of the diode 223 is connected to the other end of the capacitor 225. As a result, the current supplied to the load is converted into a voltage by the resistor 221, and this voltage is half-wave rectified and smoothed by the diodes 222 and 223 and the capacitor 225, and output as a voltage VA. Also diode
Reference numeral 221 denotes a bypass diode for preventing the current in the negative cycle of the half-wave rectification from flowing through the resistor 221, thereby reducing the detection loss. The capacitor 224 is a bypass capacitor for avoiding a detection error caused by a change in surge current due to a temperature characteristic of a load.

The voltage conversion circuit 230 includes resistors 231 to 234,
Consisting of a variable resistor 235 and a capacitor 236, the resistor 231
Is connected to the cathode of the diode 223,
The other end is connected to the other end of the resistor 192 of the overvoltage protection circuit 190 and one end of the resistors 232 to 234, respectively. The other end of the resistor 232 is connected to one end of the variable resistor 35, and the other end and the variable terminal of the variable resistor 235 are connected to one end of the capacitor 236 and the negative terminal of the power supply 110. In addition, resistor 23
3 is connected to the other end of the capacitor 236 and the operational amplifier 15.
Connected to 1 non-inverting input terminal. In addition, resistors
The other end of 234 is connected to the collector of the transistor 124. As a result, the voltage VA output from the current detection circuit 220 is divided by the resistors 231 and 232 and the variable resistor 236, converted into a voltage Vd2 corresponding to the resistance value of the variable resistor 235, and output. Further, the above-described chopper drive control circuit 150 controls the chopper drive circuit 170 so as to keep the output current of the inverter circuit 200 constant with respect to the voltage fluctuation of the power supply 110, but the gain of the operational amplifier 151 is the voltage of the triangular wave. This voltage level is determined by Vcf and cannot be reduced below a predetermined value due to noise margin or the like.
4, the input voltage is fed forward from the switch circuit 120.

Next, the operation of the present embodiment having the above configuration will be described with reference to the waveform diagram shown in FIG. As described above, the oscillating circuit 140 is composed of an astable free-running multivibrator circuit, and its oscillating frequency is determined by the capacitor 147 and the resistor 14
2, the voltage Vcf applied to the inverting input terminal of the operational amplifier 141 changes into a substantially triangular waveform. The level of the output signal A of the operational amplifier 141 is switched between high level and low level in accordance with the time constant.

In the initial state, when the chopper circuit 180 is on and the inverter circuit 200 is energized, each of the capacitors Ca and Cb of the inverter circuit 200 is in an uncharged state and each of the transistors Q3 and Q6 A high level voltage is applied to the bases of the transistors Q1 and Q2 through the resistors R3 and R4, and the transistors Q3 and Q6 are turned on. When the output signal A of the oscillation circuit 140 is at a high level, the transistors Q1 and Q2 The gate voltages C and D are at a high level, and the transistors Q1 and Q2 are turned on when the on-voltage is lower, and turned off when the transistors Q1 and Q2 are different in the on-voltage between the gate and the source.

For example, when the transistor Q1 is turned on and the transistor Q2 is turned off, the voltage between the drain and the source of the transistor Q1 which has been turned on decreases to the on-voltage between the gate and the source. Through the primary winding 211 of the transformer 210. Here, the potentials E and F at one end 211a and the other end 211b of the primary winding 211 of the transformer 210 are different. That is,
The potential E of one end 211a of the primary winding 211 becomes lower than the potential of the intermediate tap 211c, and the potential F of the other end 211b of the primary winding 211 becomes higher than the potential of the intermediate tap 211c. As a result, the base voltage of the transistor Q6 is set to the low level via the diode D4, the transistor Q6 is turned off, and the transistor Q2 is turned off. Further, the base voltage of the transistor Q3 is set to a high level via the diode D3, and the transistor Q3 is turned on, so that the on state of the transistor Q1 is stabilized. Further, the capacitor Ca is connected to the transistors Q3 and Q3.
The base side of Q4 is charged as a negative electrode and the capacitor Cb
Is charged with the bases of the transistors Q5 and Q6 as positive electrodes.

When the output signal A of the oscillation circuit 140 is inverted to a low level, the transistors Q4 and Q5 are both turned on, and a low level voltage is applied to the gates of the transistors Q1 and Q2. Q
1 and Q2 are both turned off. This prevents a cross current in which the transistors Q1 and Q2 are simultaneously turned on.

Thereafter, when the output signal A of the oscillation circuit 140 is inverted to a high level, the transistors Q4 and Q5 are both turned off, and the transistor Q3 is turned off based on the charging polarity of the capacitor Ca. Transistor Q1 is continuously turned off. Further, based on the charging polarity of the capacitor Cb, the transistor Q6 is turned on, and the transistor Q2 is turned on. As a result, the primary winding 211 is energized via the transistor Q2. At this time, the energizing direction is opposite to that when the transistor Q1 is in the ON state, and the potentials at one end and the other end of the primary winding 211 are inverted.
The charge polarity of Cb is inverted.

Thus, the inverter circuit 200 includes the transformer 210, the transistors Q1 to Q6, and the diodes D1 to D6.
4 and a self-excited oscillation circuit composed of capacitors Ca, Cb, etc., and the OFF state of the inverter circuit 200 is controlled in synchronization with the output signal A of the oscillation circuit 140. Is inverted to a low level and further inverted to a high level, the transistor Q1 is similarly turned on, the transistor Q2 is turned off, and the transformer is synchronized with the output signal A of the oscillation circuit 140. The direction of current supply to the primary winding 211 of the transformer 210 is reversed, and an AC voltage G is generated in the secondary winding 212 of the transformer 210.

On the other hand, when changing the brightness of a lamp or the like connected to the secondary winding 212 of the transformer 210, the voltage conversion circuit 230
The resistance value of the variable resistor 235 may be changed. That is,
The current flowing through the secondary winding 212 of the transformer 210 is a current detection circuit.
The voltage is changed to a voltage by a resistor 221 and further half-wave rectified and smoothed to obtain a voltage VA. This voltage VA is supplied to the resistors 231 and 232 of the voltage conversion circuit 230 and the variable resistor 235
, And is output to the chopper drive control circuit 150. Here, as described above, the switch circuit 120 is connected via the resistor 234 to correct the voltage fluctuation of the power supply 110.
The input voltage is fed forward from.

The voltage Vd2 output from the voltage conversion circuit 230
Is input to the chopper drive control circuit 150, and is compared with the triangular wave voltage Vcf by the operational amplifier 151.
From 151, the voltage Vcf becomes the voltage Vd1 as the output signal Vcnt.
At this time, a low-level signal is output, and when the voltage Vcf is lower than the voltage Vd1, a high-level signal is output. When the signal Vcnt is low, the transistor 16
The base voltages of the transistors 171 and 172 are set to the low level via 1, the transistor 171 is turned off, and the transistor 172 is turned on. As a result, the inverter circuit 200 is energized via the transistor 181. When the signal Vcnt is at a high level, the transistor 16
1,172 is turned off and the transistor 171 is turned on. Thus, the transistor 181 is turned off, and the power supply to the inverter circuit 200 is cut off. Therefore,
By changing the value of the variable resistor 235 of the voltage conversion circuit 230, the signal V
By changing the cnt pulse width, the inverter circuit 20
Since the energization time to 0 can be changed, dimming of the lamp can be performed.

As described above, according to this embodiment, since the oscillation frequency of the oscillation circuit 140, the operation frequency of the inverter circuit 200, and the operation frequency of the chopper circuit 180 are synchronized, a beat of these frequencies may be generated. Therefore, no audible noise is generated as in the prior art, and no screen beat, flicker, and the like due to interference with the frame frequency of the liquid crystal display are caused even when used for lighting the backlight of the liquid crystal display. Furthermore, even when combined with another higher-level device, interference with the natural frequency of the higher-level device does not cause a malfunction or the like of the higher-level device.

Even if the oscillating frequency of the oscillating circuit 140 and the operating frequency of the inverter circuit 200 fluctuate due to ambient temperature, drift over time, etc., their synchronized state is maintained.

Further, the lighting frequency of a lamp, a backlight or the like can be set to an efficient frequency of about 30 to 60 KHz, and the efficiency of the entire apparatus can be improved.

Next, a second embodiment of the present invention will be described.
FIG. 5 is a circuit diagram showing a second embodiment. In the figure,
The same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted. In addition, the first embodiment and the second embodiment
The difference from this embodiment is that the current detection circuit 220 is constituted by a voltage doubler full-wave rectifier circuit, the voltage obtained by voltage doubler full-wave rectification is converted, and the operation of the chopper drive control circuit 150 is performed via a shunt regulator. Amplifier 151
To be entered.

That is, the current detection circuit 220 includes the resistors 221 and
The voltage doubler full-wave rectifier circuit includes diodes 222 and 223 and capacitors 224 to 227. The output voltage VA of the current detection circuit 220 is
After being divided by the resistors 231 and 232 and the variable resistor 235 connected in series to a voltage Vd3, the voltage is input to the inverting input terminal of the operational amplifier 151 via the shunt regulator 157, the resistor 158 and the capacitor 159. Further, a reference voltage Vref is applied to the inverting input terminal via the resistor 152, and a triangular wave voltage Vcf is input to the non-inverting input terminal.

According to the second embodiment, when the half-wave rectifier circuit is used for the current detection circuit 220 as in the first embodiment, the operational amplifier of the chopper drive control circuit 150 is used.
Since the input voltage to 151 must be, for example, about 2.5 V, it is necessary to increase the resistance value of resistor 221 to increase the detection voltage, and the detection loss is (square of current value) ×
(Resistance value), but the current detection circuit 220 is configured by a voltage doubler full-wave rectifier circuit.
221 can be set small, and the detection loss can be reduced.

Since the output frequency of the inverter circuit 200 is half the frequency of the oscillation circuit 140, when a half-wave rectifier circuit is used, the output ripple is amplified,
The output of the inverter circuit 200 may be tuned,
By configuring the current detection circuit 220 with a voltage doubler full-wave rectifier circuit, this can be prevented and a stable operation can be maintained.

[0048]

As described above, according to the first aspect of the present invention, since the oscillation frequency of the oscillation circuit and the operating frequencies of the first to third switch elements are synchronized, the beats of these frequencies are synchronized. Causes no audible noise as in the past, or causes screen beats, flicker, etc. due to interference with the frame frequency of the liquid crystal display even when used for backlighting of the liquid crystal display. There is no. Furthermore, even when combined with another higher-level device, interference with the natural frequency of the higher-level device does not cause a malfunction or the like of the higher-level device. Further, even if the oscillation frequency of the oscillation circuit and the operating frequencies of the first to third switch elements fluctuate due to ambient temperature, drift over time, and the like, these synchronized states are maintained. Furthermore, as a lighting frequency of a lamp, a backlight or the like, an efficient 30 to 60 KHz
The frequency can be set to about the same, and the efficiency of the entire apparatus can be improved.

According to the second aspect, in addition to the above effects, the current detection circuit can reduce the resistance value when converting the current flowing through the secondary winding of the transformer into a voltage value. Therefore, the detection loss can be reduced. Further, the output frequency of the transformer is １ ／ of the frequency of the oscillation circuit.
Therefore, when a half-wave rectifier circuit is used, the output ripple is amplified and the output may be tuned.However, this is achieved by configuring the current detection circuit with a voltage doubler full-wave rectifier circuit. This is a very excellent effect that it can be prevented and stable operation can be maintained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention.

FIG. 2 is a waveform chart for explaining the operation of the conventional example.

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

FIG. 4 is a waveform chart for explaining the operation of the first embodiment of the present invention.

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

[Explanation of symbols]

110: DC power supply, 120: Switch circuit, 130: Reference voltage generation circuit, 140: Oscillation circuit, 141: Operational amplifier, 142 to
146… Resistor, 147… Capacitor, 150… Chopper drive control circuit, 160… Low input lockout circuit, 170…
Chopper drive circuit, 180 ... Chopper circuit, 190 ... Overvoltage protection circuit, 200 ... Inverter circuit, 210 ... Transformer,
211: primary winding, 212: secondary winding, Q1, Q2: field-effect transistor, Q3-Q6: transistor, D1-D
4: Diode, R1 to R4: Resistor, Ca, Cb: Capacitor, 220: Current detection circuit, 221: Resistor, 222, 22
3… Diode, 224,225… Capacitor, 230… Voltage conversion circuit, 231-234… Resistor, 235… Variable resistor, 236
... capacitors.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 7/538 H02M 3/28 H02M 7/537 H05B 39/04

Claims (2)

(57) [Claims] A transformer having a primary winding having an intermediate tap and a secondary winding, first and second switch elements respectively connected to both ends of the primary winding, Switching control means for alternately switching on and off states of the first and second switch elements, a third switch element for switching on and off of voltage application to the intermediate tap, and controlling on and off states of the third switch element A lamp lighting circuit provided with a voltage control unit that performs a switching operation, wherein the switching control unit synchronizes with each other and outputs a substantially triangular wave signal and a binarized signal having the same predetermined cycle; and the first switch element. Control the on / off state of the
A state control circuit for controlling the on / off state of the second switch element;
A first charge / discharge circuit connected between one end of the primary winding and an intermediate tap; and a second charge / discharge circuit connected between the other end of the primary winding and the intermediate tap. The first state control circuit controls the first switch element based on the charge polarity of the first charge / discharge circuit while the binary signal is at one level. And the second state control circuit turns on the second switch element based on the charge polarity of the second charge / discharge circuit while the binarized signal is at one level, The voltage control means is a current detection circuit that detects a current flowing through a secondary winding of the transformer, and converts a detection current value of the current detection circuit into a voltage,
A voltage conversion circuit that arbitrarily changes the voltage value within a predetermined range and outputs the voltage value; and a third switching device that switches an on / off state of the third switch element based on an output voltage of the voltage conversion circuit and a voltage of the triangular wave signal. And a state control circuit. 2. The lamp lighting circuit according to claim 1, wherein said current detection circuit is constituted by a voltage doubler full-wave rectifier circuit.