Need help with a circuit! Proper coordination of bulb, relay, regulator

[DPluss]

I've put together the circuit, but the transistor is smoking as hell... what am I doing wrong?

 

[c_mitra]

You have put the other end of the relay coil to 12V; the relay coil is rated for 5V and the transistor is taking too much current. The transistor base is also permanently tied to ground- that is not correct. The 12V source on the left side is also connected to the ground...

 

[DPluss]

You have put the other end of the relay coil to 12V; the relay coil is rated for 5V and the transistor is taking too much current. The transistor base is also permanently tied to ground- that is not correct. The 12V source on the left side is also connected to the ground...

Would you please help me out with my mistakes? I'm really not familiar with transistors yet :/

 

[CataM]

Schematics are already showed in post #9 and #20. Your schematic is veryyyy different than those schematics. Some resistors are missing.

 

[DPluss]

Schematics are already showed in post #9 and #20. Your schematic is veryyyy different than those schematics. Some resistors are missing.

I've tried recreating the same simulation with the same values and also adding my bulb to the relay. It doesnt seem to work, the coil is always energized



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I think I figured it out... the CLK gives half second 12V pulses, the relay coil remains energized for about a second, or if I dont switch off CLK

 

[BradtheRad]

I think I figured it out... the CLK gives half second 12V pulses, the relay coil remains energized for about a second, or if I dont switch off CLK

View attachment 130493

You have the right idea. My simulation had scope traces which showed the capacitor discharging slightly between pulses (CLK). If the pulses stop, the capacitor discharges completely.

Your second schematic has no bias resistor. It's a good idea to include one, so your transistor does not get ruined by overmuch current in the base-to-emitter junction.

 

[DPluss]

You have the right idea. My simulation had scope traces which showed the capacitor discharging slightly between pulses (CLK). If the pulses stop, the capacitor discharges completely.

Your second schematic has no bias resistor. It's a good idea to include one, so your transistor does not get ruined by overmuch current in the base-to-emitter junction.

Bias resistor as in resistor that is before the transistor? Im gonna play with the simulation hopefully the physical one will be as good as it Also one more question, if I dont use a transistor for the circuit, I would need a reeeeally big capacitor dont I?

 

[CataM]

if I dont use a transistor for the circuit, I would need a reeeeally big capacitor dont I?

If you do not have the transistor then the RLC circuit you will have will "ring" (i.e. oscillate) a bit and then will be always ON, meaning the relay is no more controlled.

 

[BradtheRad]

if I dont use a transistor for the circuit, I would need a reeeeally big capacitor dont I?

Yes, if you were to use the DRC pulse extender by itself, to drive the relay coil. By adding the transistor it allows you to use a smaller capacitor. You could go further and make the transistor a darlington combination, allowing an even smaller capacitor, if you wish.

There is probably a way to get a 555 timer IC to work in the mode you are discussing. It would also be based on the principle of a capacitor holding a charge between pulses.

 

[DPluss]

Yes, if you were to use the DRC pulse extender by itself, to drive the relay coil. By adding the transistor it allows you to use a smaller capacitor. You could go further and make the transistor a darlington combination, allowing an even smaller capacitor, if you wish.

There is probably a way to get a 555 timer IC to work in the mode you are discussing. It would also be based on the principle of a capacitor holding a charge between pulses.

I was once told to use a 555 timer but since i never really learned electronics(apart from the very basics which are required for a car mechanic) I dumped the idea when I saw how complicated the 555 timer actually is(alll those pins) to be honest I am very interested in learning these things as I learned a lot in a few weeks, a couple a weeks ago I didnt even knew how a capacitor worked

 

[c_mitra]

555 timer is a very simple and useful IC; first you wire it to see that it can flash a LED. Then you can replace the LED with a relay coil and a diode. The CLK signal should be applied only to the base of the transistor via the resistor capacitor network.