JP3294429B2 - Fluorescent lamp circuit and power supply unit with fluorescent lamp circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorescent lamp circuit and a power supply unit with a fluorescent lamp circuit, which are suitable for copying machines, printers and the like.

[0002]

2. Description of the Related Art Conventionally, this type of apparatus has a configuration as shown in FIG. 3 , and uses a choke coil L2 for limiting a lamp current. The number of turns of the secondary winding n2 of the multi-output converter transformer T1 is a predetermined number of turns determined by the lighting start voltage Vth of the fluorescent lamp FL1. The value of the choke coil L2 is determined by the maximum lamp current, resulting in a relatively small inductance value. Further, the on / off duty of the dimming switch SW2 is controlled to
Dimming and preheating.

The multi-output converter transformer T1, the resonance capacitor C1, the switching element SW1, and the like constitute a voltage resonance type switching regulator.
It is widely used as a device for generating a high voltage such as a horizontal deflection voltage of a charger of a copying machine or a CRT (CRT) or a low voltage for logic and motor control.

[0004]

In FIG. 3 , because of the presence of the choke coil L2, when viewed from the primary side of the transformer T1, its inductance value L1 'is obtained by converting the inductance of the choke coil L2 to the primary side. The value L2 'is connected in parallel with the inductance L1 of the primary winding of the transformer T1, resulting in a considerably small value L1'. Therefore, in order to set the resonance frequency to a certain value f1, it is necessary to increase the value of the resonance capacitor C1, and if so, the resonance current Ires. Becomes larger and the transformer T
1. Considering the heat generated by the switching element SW1 and the like, the transformer T1 and the switching element SW1 require large elements, which is uneconomical.

Also, due to the characteristics of the fluorescent lamp, the discharge of the fluorescent lamp FL1 does not start for a certain period of time at the moment when the switching element SW2 is turned off during dimming. In that period, the inductance value L1 'of the transformer T1 viewed from the primary side is only the inductance L1 of the primary winding, and the resonance frequency is f2 (f1 >> f) smaller than f1.
2), it becomes difficult to keep the switching element SW1 at zero voltage ON, and problems such as a rise in temperature of the switching element SW1 and generation of noise occur.

The present invention has been made to solve such a problem, and can reduce the size of circuits and devices.
It is an object of the present invention to provide a fluorescent lamp circuit and a power supply device with a fluorescent lamp circuit that can avoid the rise in temperature of the switching element on the primary side of the converter transformer and the generation of noise.

In this specification, a fluorescent lamp lighting circuit,
The expression "fluorescent lamp circuit" is used as a generic term for the fluorescent lamp dimming circuit and the like.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides two choke coils and two taps with an intermediate tap.
By using the secondary winding (in this specification, it is used to include two independent secondary windings), the inductance value of the lamp current limiting choke coil as viewed from the primary side of the converter transformer is sufficiently increased. In order to reduce the load on the resonance circuit, the circuit configuration is made so as to look large, the resonance current is reduced, and the fluctuation of the resonance frequency during dimming is sufficiently reduced.

More specifically, the fluorescent lamp circuit is described in the following (1),
The power supply unit with the fluorescent lamp circuit is configured as described in ( 3 ) and ( 5 ), and as described in (2), ( 4 ) and ( 6 ) below.

(1) A voltage resonance type switching power supply for switching a primary side of a converter transformer, a first choke coil and a fluorescent lamp connected in series to a secondary winding of the converter transformer, and the first choke coil
A fluorescent lamp circuit comprising: a second choke coil connected in series between one end of the fluorescent lamp connected to the second coil and an intermediate tap of the secondary winding; and bidirectional switch means.

(2) A voltage resonance type switching power supply device for switching a primary side of a converter transformer having a secondary winding for a fluorescent lamp and another secondary winding provided on a secondary side, wherein a first choke coil and the fluorescent lamp connected in series to the secondary winding for the lamp, the first Cho
A second terminal connected in series between one end of the fluorescent lamp connected to the coil and an intermediate tap of the secondary lamp for the fluorescent lamp.
Power supply device with a fluorescent lamp circuit, comprising a choke coil and a bidirectional switch means.

[0012]

[0013]

( 3 ) The fluorescent lamp circuit according to (1), wherein a current transformer is connected in series with the fluorescent lamp, and the bidirectional switch means is driven by the output of the current transformer.

( 4 ) The power supply unit with a fluorescent lamp circuit according to (2), wherein a current transformer is connected in series with the fluorescent lamp, and the bidirectional switch means is driven by the output of the current transformer.

( 5 ) The dimming is performed by changing the on / off timing of the bidirectional switching means (1), ( 3 ).
The fluorescent lamp circuit according to any one of the above.

( 6 ) The dimming is performed by changing the on / off timing of the bidirectional switching means (2), ( 4 ).
The power supply device with a fluorescent lamp circuit according to any one of the above.

[0018]

According to the constitutions (1) to ( 7 ), the resonance current of the converter transformer can be reduced. In the configurations of ( 5 ) and ( 6 ), dimming can be performed in a state where the fluctuation of the resonance frequency is small.

[0019]

The present invention will be described in detail with reference to the following examples.

Embodiment 1 FIG. 1 is a circuit diagram of a “power supply device with a fluorescent lamp circuit” which is Embodiment 1. As shown, the multi-output converter transformer T1
Is connected to one end Vin of the DC power supply, and the other end is connected to the drain of the switching element SW1. The source of the switching element SW1 is connected to the other end of the DC power supply and is grounded. Resonant capacitor C
1 is connected in parallel with the switching element SW1, and resonates with the primary side inductance L1 of the multi-output converter transformer T1, thereby constituting a voltage resonance type power supply. By switching of the switching element SW1, a desired voltage is generated in the secondary windings n2, n3, and n4 according to the turn ratio with the primary winding n1. Note that n2 is the fluorescent lamp F
L3 represents a winding applied to both ends of L1, where n3 is an intermediate tap winding of n2, and n2> n3. One end of the secondary winding n2 is connected to one end of the fluorescent lamp FL1 through the choke coil L2, and the other end of the secondary winding n2 is connected to the fluorescent lamp FL.
1 is connected to the other end. Turning on / off both ends of the fluorescent lamp FL1 by means of the diode bridge DB2 and the switching element SW2 determines whether to turn on or off. n3 is an intermediate tap winding of n2, which is connected to the fluorescent lamp FL1 through a choke coil L3, a bidirectional switch means constituted by a diode bridge DB3 and a switching element SW3.

The secondary winding n4 is a main winding for supplying power to loads other than the fluorescent lamp, and uses a PWM control circuit 1 to stabilize a voltage obtained by rectifying and smoothing the output of the secondary winding n4. Is changed.

Hereinafter, the circuit operation will be described. Switching element SW3 is OFF and switching element SW3
Will be described separately for the case where is turned on. The inductances of the choke coils L2 and L3 are shown as L2 and L3 for convenience.

When the switching element SW3 is off,
As seen from the fluorescent lamp FL1, the choke coil L2 and the fluorescent lamp FL1 are connected in series to the n2 winding. The inductance L2 'of the choke coil L2 viewed from the primary side of the transformer T1 is: L2' = {(n1 / n2) {2} * L2 (1) (where ↑ indicates a power and * indicates multiplication) Becomes As a result, the primary side of the transformer has L {L1 // L2 ′}, which is a parallel connection of L2 ′ and L1, and the resonance capacitor C1.
Is a series resonance circuit.

When the switching element SW3 is on,
As seen from the fluorescent lamp FL1, the inductance of the choke coil L3 and the fluorescent lamp FL1 are connected in series to the n3 winding. When viewed from the primary side of the transformer T1, the inductance L3 'of the choke coil L3 is given by the following equation: L3' = {(n1 / n3)} 2} * L3 (2) The inductance L2 ″ viewed from the side is L2 ″ = [{n1 / (n2-n3)｝ ↑ 2] * L2 (3) After all, the primary side of the transformer is a series resonance circuit of L {L1 // L3 ′ // L2 ″}, which is a parallel connection of L3 ′, L2 ″ and L1, and the resonance capacitor C1.

In the circuit shown in FIG. 1, when the switching element SW3 is turned off, assuming that the resonance voltage generated in the resonance capacitor C1 is VRES, the winding voltage V () of n2 becomes V. () = a (VRES -Vin) * (n2 / n1) ...... (4) equation. If the number of turns of the winding n2 is selected so that the fluorescent lamp lighting start voltage Vth <V (), the fluorescent lamp FL1 can
Start discharging . The winding voltage V () of n2 is almost
The discharge current I () applied to the yoke coil L2 is expressed by the following formula : I () ≒ V () / (ωL2) (5)

[0026] In the case where the switching element SW3 is turned on, the winding voltage V of n3 () is, V () = a (VRES -Vin) * (n3 / n1) ...... (6) equation. Even after the fluorescent lamp lighting start voltage Vth> V (), the discharge sustaining voltage Vkp <
If V (), the discharge can be continued . n3 winding voltage V
() Is almost applied to the choke coil L3, and the discharge current I () is expressed by the following equation: I () ＩV () / ωL3 (7)

An example will be described below using specific numerical values.

In the conventional example of FIG . 3 , n2 = 4 * n, L
2 = 4 * L (where n and L indicate a specific number of turns and inductance), and in the first embodiment, n2 = 4 * n
If 3 = 4 * n, L2 = 10 * L, and L3 = L, the following is obtained.

[0029] n2 = 4 * n (4) is substituted into the formula Sui
N2 winding voltage V when switching element SW3 is off
() Is as follows: V () = (VRES−Vin) * (4 * n) / n1 Thus the fluorescent lamp FL1 can be started lighting at winding voltage in the conventional example and the same value. Further, when n3 = n is substituted into the expression (6) , n3 when the switching element SW3 is on is obtained.
Winding voltage V () is, V () = (VRES -Vin ) * n / n1 and becomes, taking the winding voltage V () than sustaining voltage Vkp fluorescent lamps FL1, V () Immediately after the state, the fluorescent lamp FL1 can maintain lighting, and the lamp current becomes I () = V () / ωL3 = V () / ω (4 * L). Can be secured.

On the other hand, when the switching element SW3 is off,
The lamp current I () in this case is I () = V () / ω (10 * L) by substituting L2 = 10 * L into the equation (5), and is 0.4 times I (). . Therefore, dimming can be performed by switching on / off of the switching element SW3 or by changing the on / off timing, that is, the duty.

By the way, the inductance value viewed from the primary side of the transformer T1 when the switching element SW3 is ON <br/>, by substituting n3 = n, L3 = L in (2), one
Inductance L of choke coil L3 viewed from the next side
3 ′ becomes L3 ′ = {(n1 / n)} 2} * L.

If L3 'is LL, n2 = 4 * n
3 = 4 * n, L2 = 10 * a L (3) are substituted into equation one
Inductance L of choke coil L2 viewed from the next side
2 ″ is L2 ″ = [{n1 / (3 * n)｝ ↑ 2] * (10 * L) = 10/9 * LL Therefore, L ｛L3 ′ // L2 ″｝ = 10/19 * LL, and when L1 = LL, parallel connection of 10/19 * LL and L1 = 10/29 * LL (A) Becomes

When the switching element SW3 is off ,
Substituting n2 = 4 * n and L2 = 10 * L into equation (1),
Inductance L of choke coil L2 viewed from the primary side
2 ′ is L2 ′ = [{n1 / (4 * n)｝ ↑ 2] * (10 * L) = 10/16 * LL Since L1 = LL, the parallel connection of 10/10/16 * LL and L1 = 10/26 * LL (B).

On the other hand, in the conventional example, since the inductance L2 'of the choke coil L2 viewed from the primary side of the transformer T1 is n2 = 4 * n, L2 = 4 * L, L2' = [｛n1 / (4 * n)｝ ↑ 2] * (4 * L) = 1/4 * LL, and since L1 = LL, the parallel connection of 1/4 * LL and L1 = 1/5 * LL ... ( C). As is clear from the above (A), (B), and (C), in each case, it can be seen that the primary side inductance is larger than that of the conventional example.

That is, under the condition that the same lamp current is obtained, in the circuit of this embodiment, the switching element SW3 is switched so that the state of the switching element SW3 is turned on after the state of the switching element SW3 is turned off. By controlling, the fluorescent lamp FL1 can be turned on, and the inductance value viewed from the primary side of the transformer T1 can be approximately twice that of the conventional example in the above-described example. At the frequency, the capacitance of the resonance capacitor C1 can be reduced to half to operate.

By doing so, the resonance impedance (L
/ C) ↑ (１ ／) can be increased, and the resonance current can be reduced. That is, the current values of the switching element SW1 and the converter transformer T1 decrease, and the size can be reduced.

Further, since the dimming can be performed while maintaining the discharge of the fluorescent lamp, there is no moment when the current of the winding n2 becomes zero, the zero voltage ON of the switching element SW1 can be maintained, and the rise of the switching element SW1 can be maintained. The problem of temperature and noise generation can be avoided.

[0038]

[0039]

Embodiment 2 FIG. 2 is a circuit diagram of a “power supply device with a fluorescent lamp circuit” according to Embodiment 2 .

In this embodiment, the lamp current is detected by the current transformer CT, and the switching element SW3 is turned on by the detection signal. In this circuit configuration, the on / off timing of the switching element SW3 is automatically set.

Although dimming cannot be performed with the circuit of this embodiment, dimming can be performed by providing a bias circuit in the circuit of the switching element SW3 so as to control the bias.

(Modification) In each of the embodiments described above, a part of the output of the multi-output converter transformer is used for the fluorescent lamp circuit. However, the present invention is not limited to this. It can also be implemented in form. In each embodiment, the feedback control is performed. However, the feedback control may be performed without performing the feedback control.

[0044]

As described above, according to this embodiment, the fluorescent lamp circuit and the power supply unit with the fluorescent lamp circuit can be reduced in size. Further, the problem of temperature rise and noise of the primary side switching element at the time of dimming is eliminated.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a first embodiment.

FIG. 2 is a circuit diagram of a second embodiment.

FIG. 3 is a circuit diagram of a conventional example.

[Explanation of symbols]

 C1 Resonant capacitor DB3, SW3 Bidirectional switch means FL1 Fluorescent lamp L2, L3 Choke coil

Claims (6)

(57) [Claims] 1. A voltage resonant switching power supply for switching a primary side of a converter transformer, a first choke coil and a fluorescent lamp connected in series to a secondary winding of the converter transformer, and the first choke coil Contact
A fluorescent lamp circuit comprising: a second choke coil connected in series between one end of the fluorescent lamp and an intermediate tap of the secondary winding; and bidirectional switch means. 2. The primary side of a converter transformer having a secondary winding for a fluorescent lamp and another secondary winding provided on the secondary side,
1. A voltage resonance type switching power supply device for switching, comprising: a first choke coil and a fluorescent lamp connected in series to the fluorescent lamp secondary winding ;
A fluorescent lamp circuit, comprising: a second choke coil connected in series between one end of the fluorescent lamp connected to the fluorescent lamp and an intermediate tap of the secondary lamp for the fluorescent lamp; With power supply. 3. The fluorescent lamp circuit according to claim 1, wherein a current transformer is connected in series with the fluorescent lamp, and an output of the current transformer drives the bidirectional switch means. 4. The power supply unit with a fluorescent lamp circuit according to claim 2, wherein a current transformer is connected in series with the fluorescent lamp, and an output of the current transformer drives the bidirectional switch means. On the 5. A bidirectional switching means, according to claim 1, characterized in that the changing dimming timing off the fluorescent lamp circuit according to claim 3. 6. The bidirectional switching means ON, claim 2, characterized in that the changing dimming timing off the fluorescent lamp circuit with power supply device according to claim 4.