Low power BJT's

gareth

Member
2008-01-31 3:38 pm
Hi,

Just a quick question regarding low power BJT's. A couple of years ago I read somewhere that you can parallel low power devices to get higher output currents.

Is this true ? If so what are the pro's and con's of doing this ? And is it, on the whole, a worthwhile route to take ?

Thanks
Gareth
 
Hi

The obvious con is more parts involved. Maybe better Ft from the small signal devices?? It depends on application, but IMO if more power is the goal, it is better to use a larger device. Although, it is common to parallel many small signal J-fets for better noise performance. Theoretically, I suppose you could parallel enough small signal J-fets to make a power amp, but that would take a lot of resources and effort.:dodgy:

BTW, anybody actually ever tried that???:smash: :devilr:
 
It's quite common to parallel transistors.
Commonly power outputs because as you spread out the power/currect/etc. you can get better performance (consistent current gain (less beta droop) iow more linearity) and greater reliability.

It'll work with smaller xistors too.
Input xistors are paralleled to reduce overall noise.
 

gareth

Member
2008-01-31 3:38 pm
.
Commonly power outputs because as you spread out the power/currect/etc. you can get better performance (consistent current gain (less beta droop) iow more linearity) and greater reliability.

It'll work with smaller xistors too.
Input xistors are paralleled to reduce overall noise. [/B][/QUOTE]


Hi,

So would the electrical characteristics of these devices work out the same as other electrical devices, series and parallel, or are they going to react differently because of the nature of the component ?

Also would the better current gain less beta droop and more linearity make it easier in matching npn and pnp transistors ?

Thanks
Gareth
 
gareth said:
.
Hi,

So would the electrical characteristics of these devices work out the same as other electrical devices, series and parallel, or are they going to react differently because of the nature of the component ?

Also would the better current gain less beta droop and more linearity make it easier in matching npn and pnp transistors ?

Thanks
Gareth


Yep.
even internal divice capacitance.
So beware ;)
 
gareth said:
Hi,

Just a quick question regarding low power BJT's. A couple of years ago I read somewhere that you can parallel low power devices to get higher output currents.

Is this true ? If so what are the pro's and con's of doing this ? And is it, on the whole, a worthwhile route to take ?

Thanks
Gareth

Hi Gareth

If a Vce of 60 to 80 Volts is enough for you; Check this type of ON Semi ;)

D44H - D45H

Also from two pairs and above there is need for matching them as for their beta (hFE).

Fotios
 

gareth

Member
2008-01-31 3:38 pm
Hi,
So how would I be able to effectively test and match the gain of the transistors ?

How critical is it as I would like to make a low(ish) power Class A amp for my first build and I thought that I could use parallelled low power BJT's in the VA stage.

Thanks
Gareth