Blinking lamp

181

04:28:45

Blinking lamp

published 7 years ago

Robert_Kidd

7 years ago

You need a little more voltage to allow for transistor collector to emitter drop or change relay pull-in voltage.

BillyT

7 years ago

The relay pull in Voltage should be 1/2 VCC, and drop out voltage a little bit less than 1/2 VCC

hurz

7 years ago

right @BillyT pull in at about 1/2 Vcc maybe, but why for drop out only a little below? Relays do have a big hysteresis and drop out is for most relays maybe even below 1/3 supply. Anyway right, the problem here is just the relay configuration while the transistor Collector Emitter voltage drop here is as low as possible with such a high base current, over saturated i would call that. As there will be always a little voltage drop across a transistor even a switch with 1mOhm will drop a few uV it can never reach the 5V. e.g. 4.9999999999999V wont be enough to pull in this relay

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