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Fahime said:I see that the IC 555 gets hot when it's running. I guess it's because of the half wave rectification. So I changed it to a full-wave rectifier. But it's getting warm yet. Actually not as hot as before. Is it a clue of a problem in the circuit or not? Should I use a voltage regulator or it's not the matter to get warm?
Dear Nigel,Nigel Goodwin said:More likely it's getting warm because you're feeding the realy directly from it!.
Fahime said:Dear Nigel,
What do you mean of "feeding directly"?
The resistance of relay's coil= 400 ohmsem2006 said:Check and post the resistance of relay's coil (use am ohmeter).
Check and post the supply voltage of 555 (pin 8).
Fahime said:The resistance of relay's coil= 400 ohms
the supply voltage is alternating between 13V and 15V.(It's not too smooth)
I also measured the current that relay draws. I=27 mA
I looked for the allowable current that can be drawn from 555 in the datasheet but I couldn't find any. Is it at most the mentioned 15mA in the 3th page of the datasheet that I attach it?
Dear em2006,em2006 said:Check also, if the timing resistor (pin 7) is not too low (must be over 1KOhm)
Yes, I tried it with 2 more new ICs. They get less warm but they do so.em2006 said:I think not.
Did you tried to replace the IC with another one?
That's it!audioguru said:...The max power dissipation without a load is 15V x 15mA= 225mW which will make it warm...
I agree.audioguru said:The output of a 555 has a 1.4V loss when it is high and the load current is low. The diode in series with the output adds another 0.7V loss so the 12V relay gets only 9.9V and it might not work...
Thanks for your shematic, Em2006. My last circuit is the same as yours. But I can't figure out the operation of C4 that you inserted between V+ and ground!? I don't have it!em2006 said:Fahime, is this the final schematic wich you tried (attach) ?
If not, try it, and decrease the supply voltage to 12V.