Incandescent lamp protection device. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Lighting

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I solved the problem of frequently burning incandescent lighting lamps by assembling the protection device offered to the attention of readers. Lamps equipped with such devices have been operating without replacement for two years.

The scheme of the device is shown in fig. 1. Here EL1 is the protected lamp, SA1 is its switch. Through a rectifier on the diode bridge VD1, a composite transistor VT1VT2 is connected to the lamp circuit. At the moment of closing the contacts of the switch SA1, the capacitor C1 is discharged and the composite transistor is closed. Therefore, only a small charging current of the capacitor C1 flows through the lamp, depending on the value of the resistor R1.

Fig. 1

The graph in fig. 2 shows the dependence of the voltage across the capacitor on the time elapsed since switching on. When the voltage reaches a value sufficient to open the composite transistor, the current flowing through the lamp gradually increases to the nominal value, as shown in the graph of Fig. 3. A further increase in the voltage across the capacitor stops, because the base section of the transistor VT1 - the emitter of the transistor VT2 acts as a kind of stabistor.

Fig. 2

Transistor VT2 should be installed on a heat sink with an area proportional to the power of the protected lamp or several lamps connected in parallel. Their total power should not exceed 240 W, while the area of ​​the dissipating surface of the heat sink should be at least 400 cm2. It is allowed to replace the KT840A transistor with KT828A or KT828B. Imported diode bridge D3SB can be replaced by any other for voltage 300V and current 1...3A.

Fig. 3

When you first turn on the protective device, measure the voltage between the collector and emitter of the transistor VT2 in steady state. If it is more than 15 ... 25 V, it is necessary to replace the resistor R1 with another one of a smaller rating. The turn-on delay can be changed by selecting the capacitor C1. Please note that between turning off the lamp and turning it on again, enough time must pass so that the capacitor C1 has time to discharge. Otherwise, the protective effect of the device will be incomplete.

Author: V. Skublin, Karaganda, Kazakhstan; Publication: radioradar.net

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