2N3055's and heat

[BobK]

A center tapped transformer cannot be wired for double the current at half the voltage. A transformer with 2 windings (4 wires) can. If your transformer is like that, you could have a switch to have 2 ranges of voltage and you would save power on any voltage < 18V when using the lower range.

If it is really centered tapped, you can still do the same, but you will not double the current output.

Bob

 

[John Potter]

A reply to all - I hope that's OK
The other reason I chose a linear device was because a friend said it was better. The reason - he's a radio ham and is paranoid about interference. When I told him i was making a Joule thief he went purple. I then said i would make a 100W one and add a 100 foot aerial. Not a titter.

In regard to the quality of 2N3055's mine are all steel. However there are a lot of fakes around. Good little video on Youtube - chap cuts the case off a good one and a fake. The fake one is almost empty, these are failing at 30V and 1A. I have 4 x 2N3055's from the US and 4 from CPC UK.

If the idea I have proposed above works then this linear regulator gets nearer reality and more than a learning challenge. Come to think of it it might even work.
I shall be dropping from 26V to 2V =24V or 52V to 26V = 26V ?
That's better than 52V to 2V = 50V.
3.33A x 26V = 86W spread over 4 x 2N3055's. The fan cooling and the heat sinks I have looked at are just under 1C/W - roughly 22C + ambient.
If that = 50C then the 2N3055 junction is going to be 76C. ( I have read it's 1.52 x case C Max).

Thanks shrtrnd. It looks like I may well have to use your advice if what I have goes fut.

I do thank you all. It's not always easy to follow all of some comments but I'm running at better than 90% which for an old f**t isn't too bad.

Tonight I am having an early night, it's 22.47 hrs and the dog needs her beauty sleep.
Thanks again all.

 

[John Potter]

Back again
Hi Bobk.
Mine has 4 output wires It does run at 18V and 36V when 2 of the wires are joined. CPC say that each section is 18V at 4.44A

http://cpc.farnell.com/multicomp/mcta160-18/160va-toroidal-2x18v/dp/FF01565

I hope this is OK
Thanks.