JPH06197555A - Lamp turn-on circuit - Google Patents

Abstract

PURPOSE:To prevent the occurrence of beats by connecting in parallel with a lamp turn-on circuit the tertiary windings of two inverter circuits containing a first and second switching elements, the turned-on/off states of which are alternately switched by means of each terminal voltage of the tertiary windings. CONSTITUTION:The tertiary windings 413 of a first and second inverter circuits 4a and 4b are connected in parallel with the turn-on circuit and an oscillation circuit 21 outputs a triangular-wave voltage Vosc conforming to the frequency of the output voltage of a first chopper circuit 3a. Driving of the first and a second chopper circuits 3a and 3b are controlled by switching the levels of the output signals A1 and A2 of operational amplifiers 23a and 23b between high and low levels in accordance with the magnitudinous relation between the voltage Vosc and voltages Vd1 and Vd2. Therefore, the inverter circuits 4a and 4b are intermittently conducted through their corresponding chopper circuits 3a and 3b. As a result, the occurrence of frequency beats can be prevented, because the frequencies generated from the plurality of inverter circuits can be made the same.

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 for lighting a plurality of lamps by using a plurality of self-excited inverter circuits.

[0002]

2. Description of the Related Art Conventionally, a lamp lighting circuit for lighting a plurality of lamps such as cold cathode fluorescent lamps has been known as a backlight for a liquid crystal panel or the like, and an example using an inverter circuit is known. As an example of this, an example of a circuit for lighting two lamps is shown in FIG. In the figure, 1 is a DC power supply, 2 is a chopper drive control circuit, and 3a and 3b are first
Also, the second chopper circuit, 4a and 4b are first and second inverter circuits, and 5a and 5b are first and second current detection circuits.

The chopper drive control circuit 2 includes an oscillator 21,
Amplifier circuits 22a and 22b, operational amplifiers 23a and 23b used as comparators, resistors R1 to R4, variable resistors VR1 and VR2, and NPN-type transistor 2
It is composed of 4a and 24b. The oscillator 21 outputs a triangular wave signal synchronized with a synchronizing signal input from the outside, and this voltage Vosc is applied to the inverting input terminals of the operational amplifiers 23a and 23b.

The resistors R1 and R2 and the variable resistor VR1 are connected in series, and the voltage Vrf1 output from the current detection circuit 5a is divided into a voltage Vd1. This voltage Vd1 is supplied to the operational amplifier 23a via the amplifier 22a. Applied to the non-inverting input terminal. In addition, the output voltage V1 of the operational amplifier 23a
Is applied to the base of the transistor 24a, and the emitter of the transistor 24a is connected to the negative electrode of the DC power supply 1.

Similarly, the resistors R3 and R4 and the variable resistor VR2 are connected in series, and the voltage Vrf2 output from the current detection circuit 5b is divided into a voltage Vd2, which is the voltage Vd2.
Is applied to the non-inverting input terminal of the operational amplifier 23b via the amplifier 22b. The output voltage V2 of the operational amplifier 23b is applied to the base of the transistor 24b, and the emitter of the transistor 24b is connected to the negative electrode of the DC power supply 1.

Both the first and second chopper circuits 3a and 3b are field effect transistors (hereinafter referred to as FETs).
31, a resistor 32, 33, a diode 34 and a choke coil 35, the source of the FET 31 is connected to the cathode of the diode 34 and one end of the choke coil 35, and the anode of the diode 34 is connected to the negative electrode of the DC power supply 1. There is.

Further, the FET 3 of the first chopper circuit 3a
The gate of No. 1 is connected to the collector of the transistor 24a via the resistor 32, and its drain and the positive electrode of the DC power supply 1 via the resistor 33. The gate of the FET 31 of the second chopper circuit 3b is connected to the resistor 32a. Is connected to the collector of the transistor 24b via the resistor, the drain thereof and the positive electrode of the DC power source 1 via the resistor 33, respectively.

First and second inverter circuits 4a and 4b
Are both configured by a well-known self-excited resonance type push-pull multivibrator circuit. That is, a transformer 41 having a primary winding 411 having an intermediate tap 411a, a secondary winding 412 and a tertiary winding 413, and NPN type transistors 42, 4
3, resistors 44 and 45, and a capacitor 46. A capacitor 46 is connected in parallel with the primary winding 411, and a transistor 42 is connected to one end side 411b of the primary winding 411.
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 emitters of the transistors 42 and 43 are
The transistor 4 is connected to the negative electrode of the DC power source 1 and
The second base is connected to the other end side 413a of the tertiary winding 413, and the base of the transistor 43 is connected to one end side 413b of the tertiary winding 413.

Further, the intermediate tap 411a of the primary winding 411 of the first inverter circuit 4a is connected to the other end of the choke coil 35 of the first chopper circuit 3a, and a transistor 42 is connected via a resistor 44. Is connected to the base of the transistor 43 through the resistor 45, and the intermediate tap 411a of the primary winding 411 of the second inverter circuit 4b is connected to the other end of the choke coil 35 of the second chopper circuit 3b. It is connected to the base of the transistor 42 via the resistor 44 and to the base of the transistor 43 via the resistor 45.

Both the first and second current detection circuits 5 are composed of a half-wave rectification circuit consisting of a resistor 51, a diode 52 and a capacitor 53, and one end of the resistor 51 of the first current detection circuit 5a has a first Secondary winding of the inverter circuit 4a
It is connected to one end of 412 and the negative electrode of the DC power supply 1, and the other end is connected to one end of the lamp 6a and the anode of the diode 52. Further, the cathode of the diode 52 is connected to the negative electrode of the DC power supply 1 via the capacitor 53, and the voltage Vrf1 is output from the cathode of the diode 52. Further, one end of the resistor 51 of the second current detection circuit 5b is the second
Is connected to one end of the secondary winding 412 of the inverter circuit 4b and the negative electrode of the DC power supply 1, and the other end is connected to one end of the lamp 6b and the anode of the diode 52. Further, the cathode of the diode 52 is connected to the negative electrode of the DC power supply 1 via the capacitor 53, and the voltage Vrf2 is output from the cathode of the diode 52.

The other end of the lamp 6a has a capacitor C1.
Is connected to the other end of the secondary winding 412 of the first inverter circuit 4a, and the other end of the lamp 6b is connected to the other end of the secondary winding 412 of the second inverter circuit 4b via the capacitor C2. Has been done.

Further, the output voltage of the first chopper circuit 3a, that is, the voltage at the other end of the choke coil 35 is input to the oscillator 21 of the chopper drive control circuit 2 as a synchronizing signal.

Next, the operation of the lamp lighting circuit having the above structure will be described. In the initial state, when the first and second chopper circuits 3a and 3b are in the ON state and the inverter circuits 4a and 4b are energized, for example, in the first inverter circuit 4a, the values of the resistors 44 and 45 are Also, due to the difference in characteristics between the transistors 42 and 43, either of the transistors 42 and 43 is turned on first. If the transistor 42 is turned on first, the transformer 41
The positive feedback drive is performed by the induced voltage of the tertiary winding 413 of the above so as to stabilize the ON state of the transistor 42. The transistor 42 operates at the resonance frequency of the resonance circuit determined by the inductance of the transformer 41, the capacitance of the capacitor 46, the capacitance of the resonance capacitor C1, the winding capacitance of the transformer 41, and the like. The self-excited resonance is performed by a push-pull operation in which the on / off states of the transistors 42 and 43 are inverted every half cycle of the resonance frequency, and the transistor 43 is in the off state when the transistor 42 is on. As a result, an AC voltage is generated in the secondary winding 412 of the transformer 41 and the lamp 6a is turned on. The lamp 6b is similarly turned on in the second inverter circuit 4b.

Further, the current flowing through the secondary winding 412 of each of the inverter circuits 4a and 4b is the current detecting circuit 5 corresponding thereto.
It is detected by a and 5b and is converted into voltages Vrf1 and Vrf2. These voltages Vrf1 and Vrf2 are applied to the resistor R
1, R2 and variable resistor VR1, or resistors R3, R
4 and the variable resistor VR2 to divide the voltage Vd1,
Converted to Vd2. The resistors V1 to V4 and the variable resistors VR1 and VR2 are set so that the voltages Vd1 and Vd2 have values between the maximum value and the minimum value of the output voltage Vosc of the oscillator 21 at the input terminals of the operational amplifiers 23a and 23b. Is set, and the values of the variable resistors VR1 and VR2 are set to values at which a sufficient dimming effect can be obtained. As a result, the operational amplifiers 23a and 23b are connected to the transistors 24a and 24b.
Current is supplied to the transformer 41 of the corresponding inverter circuit 4a, 4b via the FET 31 of each chopper circuit 3a, 3b only while the low-level signal is output to the variable resistor VR1, VR2. The brightness of the lamps 6a and 6b can be adjusted by changing the resistance value and changing the pulse width of the output signals of the operational amplifiers 23a and 23b.

[0015]

However, in the above-mentioned conventional lamp lighting circuit, the oscillation frequency f3 of the oscillator 21 and the operating frequency f of the first inverter circuit 4a are set.
Although they match with 1, these frequencies f1 and f3
And the operating frequency f2 of the second inverter circuit 4b are different, beats of these frequencies occur. Since this beat is generated over a number of times and contains multiple frequency components, it may cause audible noise, or may cause interference with the frame frequency of the liquid crystal display when used for lighting the backlight of the liquid crystal display. Causes screen beats, flicker, etc. Furthermore, when combined with other higher-level devices, due to interference with the natural frequency of the higher-level device,
There is a problem in that the host device may malfunction.

It is also conceivable to set the oscillation frequency f3 of the oscillator 21 and the operating frequencies f1 and f2 of the inverter circuits 4a and 4b to frequencies that do not affect the host device, but these frequencies f1 to f3 are individually set. To ambient temperature,
It is difficult to set these frequencies because the beat spectrum changes due to the fluctuations due to drift over time.

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

In view of the above problems, it is an object of the present invention to provide a lamp lighting circuit which prevents the occurrence of beats.

[0019]

In order to achieve the above-mentioned object, the present invention provides a transformer having a primary winding with an intermediate tap, a secondary winding and a tertiary winding; At least two inverter circuits that are interposed between each of both ends and ground and that include first and second switch elements that are alternately turned on and off by terminal voltages of the tertiary winding, and a primary winding of each inverter circuit. In a lamp lighting circuit comprising a current supply circuit for energizing a line center tap and lighting a plurality of lamps connected to the output of each inverter circuit, a lamp lighting circuit in which a tertiary winding of each inverter circuit is connected in parallel is provided. suggest.

[0020]

According to the present invention, since the tertiary windings of each inverter circuit are connected in parallel, the switching cycles of the on / off states of the first and second switch elements of each inverter circuit are the same. As a result, the oscillation frequency of each inverter circuit becomes the same.

[0021]

1 is a block diagram showing an embodiment of the present invention. In the figure, the same components as those of the above-described conventional example are designated by the same reference numerals and the description thereof will be omitted. Further, the difference between the conventional example and the present embodiment is that the tertiary windings 413 of the first and second inverter circuits 4a and 4b are connected in parallel.

That is, one end of the tertiary winding 413 of the first inverter circuit 4a is connected to one end of the tertiary winding 41 of the second inverter circuit 4b.
3 and the other end of the tertiary winding 413 of the first inverter circuit 4a is connected to the other end of the tertiary winding 413 of the second inverter circuit 4b via the resistor R.

Further, the first and second inverter circuits 4
In a and 4b, a resistor Ra and a capacitor Ca connected in parallel are interposed between the base of the transistor 42 and one end of the resistor 44 and the other end 413a of the tertiary winding 413, and the base of the transistor 43 and the resistor Ca are interposed. A resistor Rb connected in parallel between one end of 45 and one end 413b of the tertiary winding 413.
And the capacitor Cb is interposed.

Next, the operation of this embodiment having the above configuration will be described. As described above, the oscillation circuit 21 outputs the triangular wave voltage Vosc that matches the frequency of the output voltage of the first chopper circuit 3a, and the levels of the output signals A1 and A2 of the operational amplifiers 23a and 23b are the voltage Vosc and the voltage Vd.
1 and Vd2 are switched between a high level and a low level according to the magnitude relationship with Vd2, and the first and second chopper circuits 3
Drive control of a and 3b is performed. As a result, the first and second
The corresponding inverter circuits 4a and 4b are intermittently energized through the chopper circuits 3a and 3b.

In the initial state, the first and second chopper circuits 3a and 3b are in the ON state, and the inverter circuit 4
When a and 4b are energized, for example, in the first inverter circuit 4a, resistors 44, 45, Ra, Rb
And the difference in the characteristics of the transistors 42 and 43,
Either of the transistors 42 and 43 is turned on first. When the transistor 42 is turned on first, the induced voltage of the tertiary winding 413 of the transformer 41 drives the positive feedback so as to stabilize the on state of the transistor 42. The transistor 42 operates at the resonance frequency of the resonance circuit determined by the inductance of the transformer 41, the capacitance of the capacitor 46, the capacitance of the resonance capacitor C1, the winding capacitance of the transformer 41, and the like. The self-excited resonance is performed by a push-pull operation in which the on / off states of the transistors 42 and 43 are inverted every half cycle of the resonance frequency, and the transistor 43 is in the off state when the transistor 42 is on. As a result, an AC voltage is generated in the secondary winding 412 of the transformer 41 and the lamp 6a is turned on.

The same oscillation is also performed in the second inverter circuit 4b, an AC voltage is generated, and the lamp 6
b is turned on. Furthermore, the tertiary winding 413 of the first inverter circuit 4a and the tertiary winding 41 of the second inverter circuit 4b.
Since 3 is connected in parallel via the resistor R, it is equivalent to that in which the resonance circuits of the inverter circuits 4a and 4b are connected in parallel, and the resonance frequency of the inverter circuits 4a and 4b, that is, the operating frequency f1. , F2 are equal.

Here, the resistors Ra and Rb in each of the inverter circuits 4a and 4b correspond to the corresponding transistors 42 and 4, respectively.
3, the capacitors Ca and Cb function to speed up the switching of the transistors 42 and 43. In addition, the resistor R is for each lamp 6
The current change due to the voltage difference of the tertiary winding 413 caused by the deviation of the tube voltage of a and 6b and the tube current is limited.

As described above, according to this embodiment, the oscillation frequency f3 of the oscillation circuit 21, the operating frequencies f1 and f2 of the first and second inverter circuits 4a and 4b, and the first and second chopper circuits 3a and 3a, Since the operating frequencies of 3b are the same, beats at these frequencies do not occur, so that audible noise is generated as in the conventional case, or even when used for lighting the backlight of a liquid crystal display, the liquid crystal It does not cause screen beats, flicker, etc. due to interference with the frame frequency of the display.
Further, even when it is combined with other higher-level devices, interference with the natural frequency of the higher-level devices does not cause malfunction of the higher-level devices.

The oscillation frequency f3 of the oscillation circuit 21 and the operating frequencies f1 and f2 of the inverter circuits 4a and 4b are
These synchronized states are maintained even if they change due to ambient temperature, drift over time, and the like. Further, the lighting frequency of the lamp, the backlight, etc. can be set to an efficient frequency of about 30 to 60 KHz, and the efficiency of the entire device can be improved.

Although the lamp lighting circuit having two inverter circuits is constructed in this embodiment, the present invention is not limited to this, and the same effect can be obtained even if the lamp lighting circuit has three or more inverter circuits. Needless to say.

[0031]

As described above, according to the present invention, since the oscillation frequencies of a plurality of inverter circuits can be set to the same frequency, beats at these frequencies do not occur. Generate audible noise,
Alternatively, even when used for lighting the backlight of a liquid crystal display, screen beats, flicker, etc. due to interference with the frame frequency of the liquid crystal display are not caused. Further, even when it is combined with other higher-level devices, interference with the natural frequency of the higher-level devices does not cause malfunction of the higher-level devices. In addition, the operating frequency of the plurality of inverter circuits,
These synchronized states are maintained even if they change due to ambient temperature, drift over time, and the like. Further, the lighting frequency of the lamp, the backlight, etc. can be set to a highly efficient frequency of about 30 to 60 KHz, which is a very excellent effect that the efficiency of the entire apparatus can be improved.

[Brief description of drawings]

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

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

[Description of Reference Signs] 1 ... DC power supply, 2 ... Chopper drive control circuit, 21 ... Oscillator, 22a, 22b ... Amplifier, 23a, 23b ... Operational amplifier, 24a, 24b ... Transistor, R1 to R4 ... Resistor, VR1, VR2 ... variable resistor, 3a ... first chopper circuit, 3b ... second chopper circuit, 31 ... FET,
32, 33 ... Resistor, 34 ... Diode, 35 ... Choke coil, 4a ... First inverter circuit, 4b ... Second inverter circuit, 41 ... Transformer, 411 ... Primary winding, 412 ...
Secondary winding, 413 ... Tertiary winding, 42, 43 ... Transistor, 44, 45, Ra, Rb ... Resistor, Ca, Cb ... Capacitor, 5a, 5b ... Current detection circuit, 51 ... Resistor,
52 ... Diode, 53 ... Capacitor, 6a, 6b ... Lamp, C1, C2 ... Capacitor.

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H05B 41/24 F 9249-3K U 9249-3K 41/29 C 9249-3K

Claims (1)

[Claims] 1. A transformer having a primary winding provided with an intermediate tap, a secondary winding, and a tertiary winding, and a transformer interposed between each end of the primary winding and ground and each of the tertiary windings. Each of the inverters includes at least two inverter circuits including first and second switch elements whose on / off states are alternately switched depending on a terminal voltage, and a current supply circuit for energizing a primary winding intermediate tap of each inverter circuit. A lamp lighting circuit for lighting a plurality of lamps connected to an output of a circuit, wherein a tertiary winding of each inverter circuit is connected in parallel.