This electric lamp flasher which may be used as a warning light works directly on 230V-AC mains. - The diodes Dl to D4 in convert the alternating voltage into pulsating DC voltage. Components Rl, Cl, R2 and C2 form the timing circuit to control the flashing rate. When the charged voltage across the capacitor C2 exceeds the neon’s (Nl) firing voltage, the neon fires and provides the required triggering current to SCR. Then the SCR also fires and acts as a short, connecting the lamp across the AC mains. Finally, when the voltage across capacitor C2 falls below the maintaining voltage of the neon, the neon stops conducting and the SCR also returns to its non-conducting state, thus disconnecting the lamp from AC mains. The capacitor C2 starts charging again and the cycle repeats.
The lamp flashes in this circuit once every second. The rate can be varied, if required, by adjusting R2. The circuit of Fig. 2 is a simpler and a more economical arrangement. lt uses only one diode instead of four for rectification. ln fact, an SCR itself is a rectifier and power halving is done by it. The diode Dl is however required because without it the timing period will get disturbed during negative cycles. Incidentally, it helps to increase the reverse voltage ratings of the SCR and also protects the electrolytic capacitors by providing a proper polarity voltage. ln this arrangement the lamp flashes at a reduced brightness. Thus the circuit acts as a lamp flasher-cum-wattage halver.
A 100W bulb used in this circuit, acts as a 50W lamp flasher. The lamp flasher may be light-controlled by adding an LDR across the timing capacitor C2. An LDR has high resistance in darkness and has little effect on the circuit functioning. When light falls on it (during day time), its resistance becomes sufficiently low to prevent the capacitor from charging to the neon lamp firing voltage. Instead of LDR a simple switch or reed relay contacts can also be used to short-circuit the capacitor C2 when the flasher is not required. Thus, by controlling low current path of triggering circuit, the high load current of the lamp can be switched on and off very conveniently. Caution: Since the flasher uses a SCR, RF interference can be a problem. lt is therefore advised to use a filter for eliminating the interference.
The lamp flashes in this circuit once every second. The rate can be varied, if required, by adjusting R2. The circuit of Fig. 2 is a simpler and a more economical arrangement. lt uses only one diode instead of four for rectification. ln fact, an SCR itself is a rectifier and power halving is done by it. The diode Dl is however required because without it the timing period will get disturbed during negative cycles. Incidentally, it helps to increase the reverse voltage ratings of the SCR and also protects the electrolytic capacitors by providing a proper polarity voltage. ln this arrangement the lamp flashes at a reduced brightness. Thus the circuit acts as a lamp flasher-cum-wattage halver.
A 100W bulb used in this circuit, acts as a 50W lamp flasher. The lamp flasher may be light-controlled by adding an LDR across the timing capacitor C2. An LDR has high resistance in darkness and has little effect on the circuit functioning. When light falls on it (during day time), its resistance becomes sufficiently low to prevent the capacitor from charging to the neon lamp firing voltage. Instead of LDR a simple switch or reed relay contacts can also be used to short-circuit the capacitor C2 when the flasher is not required. Thus, by controlling low current path of triggering circuit, the high load current of the lamp can be switched on and off very conveniently. Caution: Since the flasher uses a SCR, RF interference can be a problem. lt is therefore advised to use a filter for eliminating the interference.
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