How to build 220 Volts Flashing Lamps

Especially designed for Christmas tree lamps
Replaces old thermally-activated switches

Circuit diagram

Parts:

• R1 100K 1/4W Resistor
• R2,R5 1K 1/4W Resistors
• R3,R6 470R 1/4W Resistors
• R4 12K 1/4W Resistor
• C1 1000μF 25V Electrolytic Capacitor
• D1-D4 1N4007 1000V 1A Diodes
• D5 P0102D 400V 800mA SCR
• Q1 BC327 45V 800mA PNP Transistor
• Q2 BC337 45V 800mA NPN Transistor
• PL1 Male Mains plug
• SK1 Female Mains socket

Device purpose:

This circuit is intended as a reliable replacement to thermally-activated switches used for Christmas tree lamp-flashing. The device formed by Q1, Q2 and related resistors triggers the SCR. Timing is provided by R1,R2 & C1. To change flashing frequency don't modify R1 and R2 values: set C1 value from 100 to 2200μF instead.
Best performances are obtained with C1=470 or 1000μF and R4=12K or 10K. Due to low consumption of normal 10 or 20 lamp series-loops intended for Christmas trees (60mA @ 220V typical for a 20 lamp series-loop), very small and cheap SCR devices can be used, e.g. C106D1 (400V 3.2A) or TICP106D (400V 2A), this last and the suggested P0102D devices having TO92 case.

Important Note:

For proper operation it's absolutely necessary to employ high Gate-sensitive SCRs. If you are unable to find these devices you can use Triacs instead. In this case the circuit operates also with relatively powerful devices. A recommended Triac type is the ubiquitous TIC206M (600V 4A) but many others can work.Note that in spite of the Triac, diode bridge D1-D4 is in any case necessary.
This circuit was awarded with publication in ELECTRONICS WORLD "Circuit Ideas", June 2000 issue, page 458

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