Why my transistor is heating up to failure

[CHILLFACTOR]

 

[Nigel Goodwin]

At that rate, I'd rather grab an old LM386 audio amplifier, wire it as a comparitor and drive the relay coil directly from the output.

As always, an LM386 isn't an opamp, it's a power amp - however, the 741 circuit just needs an attenuator on the output of the 741, the two diodes are a horrible idea

As I'm sure almost everyone here knows, it's a VERY simple and basic circuit, and has been done perfectly fine with 741's for decades - and can be found in many (all?) of the countless 741 books.

However, why use an antique 741?, there are numerous cheaper and much better 'modern' opamps, far better to use one of those.

 

[crutschow]

the 741 circuit just needs an attenuator on the output of the 741, the two diodes are a horrible idea

Not optimum perhaps, but hardly "horrible".

 

[ZipZapOuch]

As always, an LM386 isn't an opamp, it's a power amp - however, the 741 circuit just needs an attenuator on the output of the 741, the two diodes are a horrible idea

As I'm sure almost everyone here knows, it's a VERY simple and basic circuit, and has been done perfectly fine with 741's for decades - and can be found in many (all?) of the countless 741 books.

However, why use an antique 741?, there are numerous cheaper and much better 'modern' opamps, far better to use one of those.

Of course it's not a op amp and, in this case the OP is best off with a comparitor - in any case, that's the beauty of the LM386. It's a power amp and can be used to directly drive the relay's coil. There is an old TI (National Semi) application note of where you can use the TI386 to minimize component count and board space in your designs. Even shown for small speed control of brushed-DC motors.

 

[Tony Stewart]

At that rate, I'd rather grab an old LM386 audio amplifier, wire it as a comparitor and drive the relay coil directly from the output.

Why do you need a relay with that?