JPH01157100A - Power source - Google Patents

Abstract

PURPOSE:To attain simplification of construction for dimming, power saving and the like by providing secondary output with DC rectifying output and fluorescent lamp lighting circuit, and controlling ON/OFF operation of a fluorescent lamp through the change of switching frequency. CONSTITUTION:A DC stabilizing output V0 is controlled with ON-OFF duty of a switching transistor 1 according to a formula, while ON/OFF operation of a fluorescent lamp 4 is realized by variably controlling switching frequency (f). Namely, OFF conditions are realized by enabling full increase comparing the frequency (f) with resonance frequency, while ON conditions are attained around the resonance frequency. When voltage of a power supply varies in the ON conditions, the frequency (f) is changed to control characteristic impedance of the formula, and to feedback the signal of photosensor 6, so as to stabilize current in a constant level. It is thus possible to realize simplification of construction for dimming, energy saving and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a power supply device applicable to, for example, a copying machine.

[Prior art]

Conventionally, as an example of a power supply device for a copier or the like that uses a fluorescent lamp as a light source, a DC constant voltage secondary output of a line operation type switching power supply as shown in Fig. 2 is used.
In recent years, it has become generally known to prepare an input type fluorescent lamp ballast separately, or to use a power supply configuration in which the secondary output of a push-pull inverter is provided with a DC rectified output and a fluorescent lamp drive output, as shown in Figure 3. Ta.

However, the configuration shown in Figure 2 is expensive, and in Figure 3, there is a power loss problem in regulator 2 to obtain a DC stabilized output, and when it is necessary to dim the fluorescent lamp, transistor 1 must be controlled by PwM. Therefore, a means to control the fluorescent lamp tube current was needed, and a more advanced technology was required.

[Object of the present invention]

The present invention has been made in view of the above points, and an object thereof is to provide a power supply device that makes it possible to simultaneously realize circuit simplification, cost reduction, and energy saving.

〔Example〕

FIG. 1 shows an embodiment of the present invention. Consists of a line operation type simple end converter,
Switching transistor 1 has ON-OFF duty
The ratio and frequency are controlled to transmit the output to the secondary winding of transformer 2. One of the outputs is half-wave rectified in a forward manner, and then resistors R, , R are connected so that the output voltage is stabilized.
The voltage divided by 2 is fed back.

It is indicated by. Here, VIN is the input voltage after AC rectification,
N1 is the number of transformer primary winding turns, and N2 is the ON duty of the transformer lamp transistor l.

That is, for example, when the input voltage increases, feedback control is performed to reduce D, thereby making it possible to perform constant voltage control.

Next, the lighting output of the fluorescent lamp I, which is another output, will be explained. When a fluorescent lamp is lit, it can be considered a resistor.

Therefore, the fluorescent lamp circuit of FIG. 1 can be replaced with a constant-low circuit as shown in FIG. 4. The series impedance +21 in FIG. 4 is the minimum. That is, the current reaches its maximum at the resonance angular frequency W0. FIG. 5 shows IY1=□.

ro=v-1yl ・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・ (3) shows how the current flows.

In the present invention, an inductance ballast is used in the fluorescent lamp circuit as shown in FIG.
ZI becomes large, and at W-+■, IZ1 → wL, and there is only an inductance load, and V Fl shown in Fig. 4,
approaches Ov (i.e., the fluorescent lamp remains off).

As mentioned above, the present invention uses DC stabilized output.

From equation (1), the ON-O of the switching transistor is
It is controlled by the duty of FF, and on the other hand, turning off and turning on the fluorescent lamp is realized by variable control of the switching frequency f.As mentioned above, r is turned off by the resonance frequency, and turned on near fo. be able to.

Furthermore, if power supply voltage fluctuation occurs in the lighting state, f
By changing the characteristic impedance shown in equation (1), it is possible to control the current flowing through the fluorescent lamp to a constant value. For example, when the power supply voltage increases, the lamp current increases and the amount of light increases. Therefore, as shown in FIG. Then, a feedback circuit is configured to finally control the switching frequency to a high level through a voltage-frequency converter, and as a result, control is applied so that the lamp current does not increase.

〔Effect of the invention〕

As explained above, according to the present invention, the secondary output is equipped with a DC rectified output and a fluorescent lamp lighting circuit, and the lighting and extinguishing of the fluorescent lamp is controlled by changing the switching frequency. Simplification of the configuration, energy saving, etc. are achieved.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the circuit configuration of the present invention, Figs. 2 and 3 are diagrams showing the conventional circuit configuration, Fig. 4 is an equivalent circuit diagram of the fluorescent lamp circuit portion of Fig. 1, and Fig. 5 is a diagram showing the conventional circuit configuration. FIG. 2 is a diagram showing the relationship between frequency and admittance of the fluorescent lamp circuit portion of FIG. 1; 1 ・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・ Transistor Xta 2 ・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・ Trance 4・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・Fluorescent lamp 6.
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
...Photo sensor Figure 5

Claims (4)

[Claims] (1) In a separately excited type switching power supply device, the output has at least a fluorescent lamp circuit consisting of a DC rectifier circuit and an LC series resonant circuit, and switching of the fluorescent lamp on and off is controlled by switching the switching frequency of the separately excited means. A power supply device characterized by: (2) The power supply device according to claim 1, wherein the switching frequency is variably controlled so that the amount of light of the fluorescent lamp is controlled to a predetermined value while the fluorescent lamp is turned on. (3) In claims 1 and 2, the separately excited means includes a transistor, and the output voltage of the DC rectifier circuit is kept constant by controlling the ON-OFF duty ratio of switching of the transistor. A power supply device characterized in that it is controlled as follows. (4) In claim 1, the lighting of the fluorescent lamp is controlled by controlling the switching frequency in the vicinity of the resonance frequency f_o of the LC series resonant circuit, and in a sufficiently large frequency band with respect to the resonance frequency f_o. A power supply device characterized in that the fluorescent lamp is controlled to turn off by controlling the fluorescent lamp.