JP2797461B2 - Light emitting element drive circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for a light-emitting element used for driving a light-emitting element such as an illuminated push-button switch with a commercial AC power supply.

<Prior Art and Problems> Conventionally, for example, when a light emitting diode (hereinafter, referred to as an LED) of an illuminated push button switch is driven by a commercial AC power supply, as shown in FIG.
100V AC or 20V AC to the LED external terminals 102 and 103
A measure is taken to insert and use an AC drive unit 104 having a built-in transformer (not shown) for stepping down 0V.

However, in the case where the AC power supply voltage is stepped down by a transformer, there is a disadvantage that the AC drive unit 104 becomes large in size, which hinders downsizing and downsizing of the illuminated push button switch 101.

There is also a unit in which a current limiting resistor and a rectifier (both not shown) are built in the unit 104. However, this unit consumes 10 to 20 mA to the LED, so that the power consumption is 1 unit.
22 W, which is relatively large, and as a result, it is difficult to reduce the size of the unit 104.

<Object of the Invention> The present invention has been made to eliminate the above-mentioned drawbacks of the conventional one, and has as its object to provide a light-emitting element driving circuit which consumes less power and can be downsized.

<Structure and Effect of the Invention> A driving circuit for a light emitting element according to the present invention includes a rectifying circuit for rectifying an AC power supply voltage, and a rectifying circuit that is interposed between an output terminal of the rectifying circuit and the light emitting element. A semiconductor switching element with a control electrode for controlling energization, and a control circuit interposed between an output terminal of the rectifier circuit and the semiconductor switching element for driving the semiconductor switching element only for a period of a predetermined level or less of the rectified output. It is provided with.

According to the present invention, since the AC power supply voltage is directly rectified without being stepped down, a step-down transformer is not required, and the unit can be miniaturized. Do not shed
Power consumption can be reduced.

<Description of Embodiment> An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example in which a drive circuit of a light emitting device according to the present invention is applied to an AC drive unit of an illuminated push button switch.

Referring to FIG. 1, reference numerals 1 and 2 denote a pair of power terminals to which an AC power supply 3 such as 100 V AC or 200 V AC is connected, and 4 denotes an illuminating section of a push button switch. It comprises a diode 5 and a resistor 6.
Reference numeral 7 denotes a bridge rectifier circuit for full-wave rectification connected to the power supply terminals 1 and 2. A semiconductor switching element with a control electrode is provided between an output terminal of the bridge rectifier circuit 7 and the illuminating section 4 side. For example, the collector-emitter of the first switching transistor 8 is interposed and connected.

Reference numeral 9 denotes a control circuit inserted between the switching transistor 8 and the output terminal of the bridge rectifier circuit 7. The control circuit 9 includes, for example, a resistor 10, a Zener diode 11, and a resistor 12, and is connected in parallel between the output terminals of the bridge rectifier circuit 7; A switching transistor for driving the switching transistor when the voltage level at the voltage dividing point on the anode side of the diode is below a predetermined value;
And a resistor 15 connected between the bases.

Reference numeral 16 denotes a rectifying diode interposed between the emitter of the switching transistor 8 and the illuminating unit 4 side.
Is a smoothing capacitor connected to the cathode side of the rectifying diode 16, and 18 is a Zener diode for surge protection connected in parallel between the output terminals of the bridge rectifier circuit 7.

 Next, the operation of the above configuration will be described.

The AC power supply voltage is full-wave rectified by the bridge rectifier circuit 7 as shown by the waveform C in FIG. 2, and then divided by the voltage divider 13 in the control circuit 9. During the period when the full-wave rectified voltage exceeds a certain level of potential E determined by the Zener diode 11, the potential of the voltage dividing point d causes the switching transistor.
Since 14 is turned on, no base current flows through the first switching transistor 8, and the switching transistor 8
OFF.

During the period when the full-wave rectified voltage is equal to or lower than the constant level potential E, the second switching transistor 14 is turned off.
F, a base current flows through the first switching transistor 8, and the switching transistor 8 is turned on.
The emitter voltage is as shown in waveform f in FIG. This voltage is rectified and smoothed by the rectifying diode 16 and the capacitor 17 as shown by a waveform g. That is, the light emitting diode 5 is turned on and driven by the DC voltage generated at both ends of the capacitor 17.

Here, the current is allowed to flow only for a period of time equal to or lower than the constant level potential E of the full-wave rectified voltage. Therefore, a transformer for stepping down the AC power supply voltage is not required, and the unit can be easily reduced in size. In particular, since current does not flow during the period in which the potential E exceeds the certain level of potential E, a device with low power consumption can be easily obtained.

 FIG. 3 shows another embodiment of the present invention.

In the figure, reference numeral 31 denotes a second terminal connected to the output terminal of the bridge rectifier circuit 7 via a diode 32 to smooth the rectified output.
Is a smoothing capacitor. A second voltage dividing circuit 33 is connected in parallel with the smoothing capacitor 31 and includes resistors 34 and 35 and a Zener diode 36. By using the Zener diode 36, the potential at the point b when the AC power supply voltage is 200 V is set to be smaller than twice the potential at the point b when the AC power supply voltage is 100 V (see FIG. 4).

A comparing circuit 37 compares the potential at point b of the second voltage dividing circuit 33 with the potential at point d of the first voltage dividing circuit 38. For example, the second switching transistor 14, the third switching transistor 39, a resistor 40 and the like. Reference numeral 41 denotes a diode interposed between the point b of the voltage dividing circuit 33 and the base of the third switching transistor 39. The first and second voltage dividing circuits 38 and 33, the comparing circuit 37, and the like constitute a control circuit 42 for the switching transistor 8.

Here, in the above-described first embodiment, as shown in FIG. 5, when the AC voltage is 100 V, the output voltage is 200 V AC compared to the waveform width t ₁ of the output voltage which is the emitter potential f ₁ of the _first switching transistor 8. the output waveform width t ₂ of the voltage f ₂ decreases upon irradiation, this potential across g of the first smoothing condenser 17
And the luminance of the light emitting diode 5 is different.

On the other hand, in the second embodiment, the full-wave rectified voltage c from the bridge rectifier circuit 7 is supplied to the smoothing capacitor 31.
, And the potential a at both ends is divided by the voltage dividing circuit 33. At this time, the potential at the point b of the voltage dividing circuit 33 changes according to the AC power supply voltage applied at that time. In other words, the potential at point b when AC 200 V is applied in addition to AC 100 V is increased. On the other hand, the potential at the point d in the first voltage dividing circuit 38 changes according to the rectified voltage c, and is compared with the potential at the point b by the comparison circuit 37. When the potential at the d point is b
During a period greater than the point potential, the second switching transistor 14 is turned on, and the third switching transistor 39 is turned on.
When the switch is turned off, the first switching transistor 8 is turned off, and no current flows to the light emitting diode 5 side. When the potential at the point d is smaller than the potential at the point b, the second switching transistor 14 is turned off, the third switching transistor 39 is turned off, the first switching transistor 8 is turned on, and the first switching transistor 8 is turned on. The light emitting diode 5 is driven by the DC voltage g smoothed by the smoothing capacitor 17.

Thus, in this example, the emitter potential f ₂ of the first switching transistor 8, since the waveform width t ₂₁ is large at the time of application of AC200V, the difference in brightness of the light emitting diode 5 as compared with the time of application of AC100V There are advantages that can be reduced.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing an example in which a drive circuit of a light emitting device according to the present invention is applied to an AC drive unit of an illuminated push button switch. FIG. 2 is a signal waveform diagram of a main part of the drive circuit. FIG. 4 is an electric circuit diagram showing another embodiment of the present invention. FIG. 4 is an explanatory diagram of a set potential by a zener diode in FIG. 3, and FIG. 5 is a diagram of a switching transistor when AC100V is applied and AC200V is applied. FIG. 6 is a perspective view showing a conventional illuminated push button switch and an AC drive unit. 1 AC power supply 5 Light emitting element 7 Rectifier circuit 8
…… Semiconductor switching element, 9,42 …… Control circuit.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 33/00

Claims (1)

(57) [Claims] A rectifying circuit for rectifying an AC power supply voltage, a semiconductor switching element with a control electrode interposed between an output terminal of the rectifying circuit and a light emitting element for controlling energization of the light emitting element; A driving circuit for driving the light emitting element, the control circuit being interposed between the output terminal of the rectifier circuit and the semiconductor switching element and driving the semiconductor switching element only for a period of a predetermined level or less of the rectified output. circuit.