Hi

To glow an LED which is best as a switch BJT or FET ?
Can anyone help me with reason and circuit diagram for resistor calculation ?

Thanks

 

Sounds like a homework question. Is it?

 

Sounds like a homework question. Is it?

yes,

I am using it for at the output of dc-dc to indicate the supply is on or off.
Can you please tell me which is better to use bjt or fet ?

Thanks

 

I am using it for at the output of dc-dc to indicate the supply is on or off.

Why do you need a switch?
Can't you connect the LED with its limiting resistor directly to the dc-dc output?

 

Why do you need a switch?
Can't you connect the LED with its limiting resistor directly to the dc-dc output?

Because the output voltage is 0.8v and mostly all led requires more than 1.1v forward voltage?

 

So what voltage do you have to power the LED?

If you have only 0.8V to control the switch, then a look at the turn-0n characteristics of typical BJT's and FET's will tell you which is better for your application.

 

So what voltage do you have to power the LED?

If you have only 0.8V to control the switch, then a look at the turn-0n characteristics of typical BJT's and FET's will tell you which is better for your application.

hi,

Thanks for your reply
But i am not able to distinguish between FET and BJT ? Which should i use to turn on LED?And what are the parameter to chose ?

Thanks again

 

Look at the threashold voltage for FETs. Do any meet your input voltage requirements ? What forward voltage is required for the base emitter junction of a BJT to conduct ?

Les.

 

Here is one source for selection.
Max.

 

But i am not able to distinguish between FET and BJT ?

I don't understand.
The data sheet or wherever you purchase them will tell you that.