JPS6139416Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is a slide projector (including an overhead projector) whose light source lamp can be dimmed.
The present invention relates to a power supply circuit for a light source.

Some conventional power supply circuits for light sources of this type dim the light source lamp by controlling the output voltage using, for example, a commercial power transformer or resistor. The efficiency was low because it passed a current equal to the wavelength, and the weight was large, which was an obstacle to reducing the overall weight of the slide projector.It also had the drawbacks of high manufacturing costs.Furthermore, phase control using triacs, SCRs, etc. Some devices dimmed the light source lamp by controlling the output voltage, but this had the disadvantage that it generated a lot of heat and was not suitable for large-capacity devices.

The present invention aims to provide a power supply circuit for a light source that eliminates the above-mentioned drawbacks.This will be explained based on an embodiment shown below. The power supply circuit is shown, where D ₁ is a rectifier circuit connected to input terminal a, C ₁ is a capacitor connected between the output terminals of rectifier circuit D ₁ , and T ₁ is the middle point of primary winding L ₁ . An output transformer Q 1 connected to the + side terminal of the capacitor C ₁ and whose secondary winding L ₂ is connected to the output terminal b _which is to be connected to a light source lamp (not shown).
is a transistor connected between one end of the primary winding L _{1 of the output transformer T 1 and} the negative terminal of the capacitor C ₁ , and Q ₂ is the primary winding of the output transformer T ₁ .
The transistors T ₂ and T ₃ are connected between the other end of L ₁ and the negative terminal of the capacitor C ₁ , and the respective secondary windings L ₂ ′ and L ₂ ″ are connected to the transistors Q ₁ and Q ₂ . Output transformers connected between each base emitter, A is each primary winding of output transformers T ₂ and T ₃
L ₁ ′, L ₁ ″ are connected to the primary windings L ₁ ′, L ₁ ″ to alternately apply input pulses, and the pulse width of the input pulses can be changed manually. It is a control circuit.

Since the light source power supply circuit according to the present invention is configured as described above, when AC input is applied to the input terminal a, it is converted to DC by the rectifier circuit D ₁ and applied to the capacitor C ₁ . ₁
Then, a current with a wavelength as shown in FIG. 2 is output. On the other hand, since input pulses are alternately applied to the output transformers T ₂ and T ₃ by the control circuit A, outputs are alternately generated from the transformers T ₂ and T ₃ . Therefore, the transistor
Since Q ₁ and Q ₂ are turned on alternately, currents with different directions are generated alternately in the primary winding L ₁ of the output transformer T ₁ , and as a result, an AC power source is induced in the secondary winding L ₂ . . In this case, if the pulse width of the output wave at the capacitor C ₁ is T and the pulse width of the input pulse to the output transformers T ₂ and T ₃ is τ, then the output terminal b
The output waveform at is as shown in FIG. Therefore, if the effective value of the voltage of this AC output is Erms, then Erms=τ/T×E, so if T is kept constant and τ is varied in the range from O to T by control circuit A, the effective value is value
Erms can be changed. Since the voltage applied to the light source lamp is thus controlled, the light source lamp can be dimmed. In addition, the proposed light source power supply circuit uses a high-frequency AC-AC converter and controls the output voltage by pulse width control, so that only the current corresponding to the wavelength corresponding to the desired output voltage can flow. Therefore, it is extremely efficient. Moreover, since it is extremely light in weight, it helps to reduce the weight of the entire slide projector, and the manufacturing cost is also low. Furthermore, since it generates less heat, a large capacity one is suitable.

As described above, the light source power supply circuit according to the present invention has extremely important advantages such as being highly efficient, helping to reduce the overall weight of the slide projector, having low manufacturing costs, and being suitable for large-capacity projectors. There is.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an embodiment of the power supply circuit for the light source of a slide projector according to the present invention, Fig. 2 is an output waveform diagram at the capacitor of the above embodiment, and Fig. 3 is an output at the output terminal of the above embodiment. FIG. a...Input terminal, _D1 ...Rectifier circuit, _C1 ...Capacitor, _T1 , _T2 , _T3 ...Output transformer, _Q1 ,
Q ₂ ...transistor, A...control circuit, b...output terminal.

Claims (1)

[Scope of utility model registration request] A rectifier circuit connected to an AC power source, a capacitor connected between the output terminals of the rectifier circuit, and the intermediate point of the primary winding connected to one output end of the capacitor, and the secondary winding used as a light source. The first connected to the lamp
and second and third transformers each having a secondary winding connected via a transistor between the other output end of the capacitor and the primary winding of the first transformer; a control circuit connected to the primary windings of the second and third transformers and capable of changing the pulse width of input pulses applied to the second and third transformers; A power supply circuit for a light source of a slide projector, characterized in that the light source lamp can be dimmed by controlling the effective value of the voltage.