JPH07296984A - Fluorescent lamp circuit and power supply device installed in fluorescent lamp circuit - Google Patents

Abstract

PURPOSE:To construct a circuit and device in small sizes, preclude temperature rise of a switching element on the primary side of a converter transformer at the time of dimming, and avoid generation of noises. CONSTITUTION:A secondary winding n2 with an intermediate tap and a main winding n4 for a fluorescent lamp are furnished on the secondary side of a multi-output converter transformer T1, and the primary side is subjected to switching control using a switching element SW1 so that the output voltage of the main winding n4 becomes constant. Choke coils L2, L3 for limiting the lamp current are connected between one end of the secondary winding n2 and its intermediate tap and one end of the fluorescent lamp FL1. The dimming operation is performed by changing the on/off timings of bidirectional switch means DB3, SW3. According to this constitution, the impedance of the lamp current limiting choke coil viewed from the primary side can be made greater than conventional, and the current passing through the primary side switching element SW1 can be lessened, and it is feasible to construct the device in a small size.

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 device with a fluorescent lamp circuit suitable for a copying machine, a printer and the like.

[0002]

2. Description of the Related Art A conventional device of this type has a structure as shown in FIG. 4 and uses a choke coil L2 for limiting the 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, by controlling the on / off duty of the dimming switch SW2,
Dimming and preheating.

Further, 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 charging device of a copying machine or a CRT (CRT) and a low voltage for controlling a logic and a motor.

[0004]

In FIG. 4, since there is the choke coil L2, its inductance value L1 'when viewed from the primary side of the transformer T1 is obtained by converting the inductance of the choke coil L2 to the primary side. The value L2 'and the inductance L1 of the primary winding of the transformer T1 are connected in parallel, resulting in a considerably small value L1'. Therefore, in order to set the resonance frequency to a certain value f1, it is necessary to set the value of the resonance capacitor C1 to a large value. Then, the resonance current Ires. Becomes bigger, the transformer T
Considering the heat generation of the switching element SW1 and the like, the transformer T1 and the switching element SW1 are uneconomical because large elements are required.

Due to the characteristics of the fluorescent lamp, the fluorescent lamp FL1 does not start discharging for a certain period of time at the moment when the switching element SW2 is turned off during dimming. During 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 zero voltage of the switching element SW1 on, and problems such as temperature rise of the switching element SW1 and generation of noise occur.

The present invention has been made in order to solve such a problem, and can downsize a circuit and a device,
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 temperature rise 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 term "fluorescent lamp circuit" is used as a general term for fluorescent lamp dimming circuits.

[0008]

In order to achieve the above-mentioned object, the present invention provides two choke coils and a two taps with an intermediate tap.
By using the secondary winding (in this specification, the meaning of including two independent secondary windings), the inductance value of the lamp current limiting choke coil when viewed from the primary side of the converter transformer is sufficient. The circuit configuration is made so that it looks large, the resonance current is reduced, and the fluctuation of the resonance frequency during dimming is sufficiently reduced to reduce the load on the resonance circuit.

Specifically, the fluorescent lamp circuit is described in the following (1),
(3), (5) and (7), and the fluorescent lamp circuit-equipped power supply device is configured as described in (2), (4), (6) and (8) below.

(1) A voltage resonance type switching power supply for switching the 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 secondary winding. A fluorescent lamp circuit including a second choke coil and a bidirectional switch means connected in series between the intermediate tap and one end of the fluorescent lamp.

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

(3) The fluorescent lamp circuit according to (1), wherein the bidirectional switch is a saturable reactor.

(4) The power supply device with a fluorescent lamp circuit according to (2), wherein the bidirectional switch is a saturable reactor.

(5) 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.

(6) The power supply device 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.

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

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

[0018]

With the configurations (1) to (8), the resonance current of the converter transformer can be reduced. With the configurations (7) and (8), dimming can be performed in a state in which 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" according to a first embodiment. As shown in the figure, one end of the primary winding n1 of 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. The resonance capacitor C1 is a switching element SW1.
Connected in parallel with the multi-output converter transformer T1 1
It resonates with the secondary inductance L1, thereby forming a voltage resonance type power supply. Due to the 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. It should be noted that n2 represents a winding applied to both ends of the fluorescent lamp FL1, n3 is an intermediate tap winding of n2, and n2> n3.
Is. One end of the secondary winding n2 is connected to one end of the fluorescent lamp FL1 through the choke coil L2 and is connected to the secondary winding n2.
The other end of is connected to the other end of the fluorescent lamp FL1. The fluorescent lamp FL1 can be turned on or off by turning on / off both ends by the diode bridge DB2 and the switching element SW2. 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 composed of a diode bridge DB3 and a switching element SW3.

The secondary winding n4 is a main winding for supplying electric power to a load other than the fluorescent lamp, and the PWM control circuit 1 is used to stabilize the voltage obtained by rectifying and smoothing the output of the switching element SW1. The switching duty of is changed.

The circuit operation will be described below. When the switching element SW3 is off and when the switching element SW3
It will be described separately when is 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,
When viewed 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 seen from the primary side of the transformer T1 is L2' = {(n1 / n2) ↑ 2} * L2 (1) Expression (↑ indicates exponentiation, * indicates multiplication) Becomes After all, the primary side of the transformer is L which is a parallel connection of L2 'and L1.
It is a series resonance circuit of {L1 // L2 '} and the resonance capacitor C1.

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 winding n3. When viewed from the primary side of the transformer T1, the inductance L3 ′ of the choke coil L3 is L3 ′ = {(n1 / n3) ↑ 2} * L3 (2) Equation (1) and the primary of the transformer T1 of the choke coil L2 is The inductance L2 ″ seen from the side is expressed by the following equation: L2 ″ = [{n1 / (n2-n3)} ↑ 2} * L2 (3). After all, the primary side of the transformer is a parallel connection of L3 ', L2 "and L1. It is a series resonance circuit of L {L1 // L3' // L2"} and the resonance capacitor C1.

In the circuit of FIG. 1, when viewed from the fluorescent lamp FL1, in the case of, if VRES is the resonance voltage generated in the resonance capacitor C1, then V () = (VRES-Vin) * (n2 / n1) ...... The voltage that becomes the formula (4) is the fluorescent lamp lighting start voltage Vth <V
If the number of turns of the winding n2 is selected so as to be (), the fluorescent lamp FL1 starts discharging and the discharge current I () is given by I () ≈V () / (ωL2) (5) Become.

In the case of, V () = (VRES−Vin) * (n3 / n1) (6) is the voltage which becomes the fluorescent lamp lighting start voltage Vth> V.
After the state of (), the discharge can be continued, and the discharge current I () is expressed by I () ≈V () / ωL3 (7).

An example will be described below using specific numerical values.

In the conventional example of FIG. 4, n2 = 4 * n, L
2 = L4 * L (n and L represent specific turns and inductance), in the first embodiment, n2 = 4 * n3 =
If 4 * n, L2 = 10 * L, and L3 = L, then the result is as follows.

Substituting n2 = 4n into equation (4) gives V
() Is V () = (VRES −Vin) * (4 * n) /
It becomes n1. Therefore, with the same value as the conventional example, the fluorescent lamp F
L1 can be turned on. Substituting n3 = n into equation (6) gives V
() Is V () = (VRES −Vin) * n / n1
However, if the voltage exceeds the lighting maintaining voltage Vkp of the fluorescent lamp FL1, the lighting can be maintained immediately after the state of V (), and the lamp current is I () = V () / ωL3 = V.
() / Ω (4 * L), and the same lamp current as in the conventional example can be secured.

On the other hand, I () is L2 = 10L (5)
Substituting into the formula, I () = V () / ω (10 * L)
And becomes 0.4 times I (). Therefore, dimming can be performed by switching the switching element SW3 on and off, or by changing the on / off timing, that is, the duty.

By the way, regarding the inductance value seen from the primary side of the transformer T1, in the case of, n3 = n and L3 = L are substituted into the equation (2), and L3 'is L3' = {(n1 /
n) ↑ 2} * L.

Letting L3 'be LL, n2 = 4 * n
Substituting 3 = 4 * n and L2 = 10 * L into the equation (3), L
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

In the case of, n2 = 4 * n, L2 = 10 * L
Substituting in the equation (1), L2 ′ is L2 ′ = [{n1 / (4 * n)} ↑ 2] * (10 * L) = 10/16 * LL. Since L1 = LL, parallel connection of 10/16 * LL and L1 = 10/26 * LL (B).

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

That is, under the condition that the same lamp current is obtained, in the circuit of the present embodiment, the switching element SW3 is controlled so as to be in the state after the state of, so that the fluorescent lamp FL1 is turned on. In addition, since the inductance value seen from the primary side of the transformer T1 can be approximately doubled as compared with the conventional example in the case of the above-described example, the resonance capacitor C1 can operate at the same resonance frequency. The capacity can be halved.

By doing so, the resonance impedance (L
/ C) ↑ (1/2) can be increased and the resonance current can be decreased. That is, the current values of the switching element SW1 and the converter transformer T1 are reduced, and the size can be reduced.

Further, since the dimming can be performed while maintaining the discharge of the fluorescent lamp, the moment when the current of the winding n2 becomes zero is completely eliminated, the zero voltage of the switching element SW1 can be kept ON, and the switching element SW1 rises. The problem of temperature and noise generation can be avoided.

(Embodiment 2) FIG. 2 is a circuit diagram of a "power supply device with a fluorescent lamp circuit" according to a second embodiment.

In this embodiment, a saturable reactor is used as the bidirectional switch means. In this case, the saturable reactor L4 remains until the fluorescent lamp FL1 is turned on.
Shows a large L value, and the saturable reactor L4 saturates after lighting and shows a small L value. In this way, the resonance current can be reduced and the device can be downsized, as in the first embodiment, with a simple circuit. Note that dimming cannot be performed with the circuit of this embodiment as it is, but dimming can be performed by providing a control winding on the saturable reactor to control the timing of saturation.

(Third Embodiment) FIG. 3 is a circuit diagram of a "power supply device with a fluorescent lamp circuit" according to a third embodiment.

In the present 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 taken.

Note that dimming cannot be performed by the circuit of this embodiment as it is, but dimming can be performed by providing a bias circuit in the circuit of the switching element SW3 to control the bias.

(Modification) In each of the above embodiments, a partial output of the multi-output converter transformer is used in the fluorescent lamp circuit, but the present invention is not limited to this, and the converter transformer is dedicated to the fluorescent lamp circuit. It can also be implemented in the form. Further, although the feedback control is performed in each embodiment, 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 device with the fluorescent lamp circuit can be downsized. Further, the problems of temperature rise and noise of the primary side switching element during dimming are solved.

[Brief description of 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 third embodiment.

FIG. 4 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 T1 Converter transformer

Claims (8)

[Claims] 1. A voltage resonance type switching power supply for switching the 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 a secondary winding of the secondary winding. A fluorescent lamp circuit comprising: a second choke coil connected in series between the intermediate tap and one end of the fluorescent lamp; and a bidirectional switch means. 2. A primary side of a converter transformer having a secondary winding for a fluorescent lamp and a secondary winding other than the secondary winding on the secondary side,
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; an intermediate tap of the fluorescent lamp secondary winding; and the fluorescent lamp. A power supply device with a fluorescent lamp circuit, comprising a second choke coil connected in series with one end and bidirectional switch means. 3. The fluorescent lamp circuit according to claim 1, wherein the bidirectional switch is a saturable reactor. 4. The power supply device with a fluorescent lamp circuit according to claim 2, wherein the bidirectional switch is a saturable reactor. 5. The fluorescent lamp circuit according to claim 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. 6. A power supply device with a fluorescent lamp circuit according to claim 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. 7. The fluorescent lamp circuit according to claim 1, wherein the dimming is performed by changing the on / off timing of the bidirectional switching means. 8. The power supply device with a fluorescent lamp circuit according to claim 2, wherein the dimming is performed by changing the on / off timing of the bidirectional switching means. .