230 Volts Flashing Lamps
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 do not 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 @ 230V 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 cases.
Important Note:
For proper operation it is 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. Please 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.