Re: 2N3055 failure (power supply)


Ben Jackson wrote:

I tracked down the fault in a failed power supply to a failed 2N3055
power transistor. It's conducting from C->B in a gang with 4 other
transistors driven by a TIP31. The net result was that the failure
caused the supply to jump to 22V+, far higher than its typical max
voltage, and with no current limiting. Are there any obvious mods
I should consider while I'm fixing it?

___
|
TIP31 | ___
LM723 ___ |/ |
[Vout>-|___|-o-----| |
22R | |> o---o---o---o---o
| | | | | | |
| ___ | | | | | |
'-|___|-o |/ |/ |/ |/ |/ 2N3055
2k2 '-----|---|---|---|---|
|> |> |> |> |>
| | | | |
.-. .-. .-. .-. .-.
| | | | | | | | | |
0.1R | | | | | | | | | |
5W '-' '-' '-' '-' '-'
| | | | |
o---o---o---o---o---->>>

(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

--
Ben Jackson AD7GD
<ben@xxxxxxx>
http://www.ben.com/

I cant read this circuit very well, it appears to be an emmiter
follower. If thats the case then you have 2 basic problems. Firstly
your output is not inside the regulation loop so your regulation will
be poor. Secondly you have no short circuit protection, or indeed any
current control. Both these problems are easily solved by looking at
the application notes for the 723.

.