Will this circuit work?

Thread Starter

ScorpFire

Joined Jun 4, 2009
13
I have this certain setup. I have very a very limited time with trainer boards at school so i need to confirm this before i try it out physically.

i used just 1 BC547 transitor before but it was not enough to turn on the relay. Will this now turn on the relay?

 

bertus

Joined Apr 5, 2008
19,942
Hello,

Is the -12 Volts ground level?
As drawn the power supply is 24 Volts.
The relays is most times connected at the collector side of the transistor.
There should also be a diode accross the relayls coil to prevent back EMF to destroy the transistor.
This diode has the cathode to the plus-side of the relays.

Greetings,
Bertus
 

Thread Starter

ScorpFire

Joined Jun 4, 2009
13
How can i determine if the -12v is ground level?. The 12v is coming from an external relay module board which has a +12 -12v.

WIll the current be a bit too high for the base of the BD139?
 

bertus

Joined Apr 5, 2008
19,942
Hello,

What is the voltage difference between the - 12 Volts and the input base connection (2.8 Volts)?
That is why I asked if the -12 volts is your ground reference.

Greetings,
Bertus
 

Wendy

Joined Mar 24, 2008
21,840
The drop on the transistors Collector-Emitter will be 1.2V. It is basically a Darlington Pair configuration.

You didn't tell use the voltage of the relay, it matters.

If you want to reduce this CE drop you can use a Sziklia Pair.
 
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