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Voltage Reg. With Pass Transistor

M

Thread Starter

mayhemsm

Joined Mar 25, 2009
2
Hi I was wondering if anyone could look at this and tell me what I might be doing wrong, I seem to have killed the transistor.

I was running it with a heat sink on both the LM317 and the transistor at about 12v / 4amps, and the transistor was hitting about 230 Deg. Fahrenheit in open air which is still inside the max temp for the transistor.

Thanks

 
SgtWookie

SgtWookie

Joined Jul 17, 2007
22,230
What was your input voltage to the 2N3055? 12v is the output, right?

It has a thermal resistance from the junction to the case of 1.5°C per Watt, so the junction is considerably hotter than the case.
 
M

Thread Starter

mayhemsm

Joined Mar 25, 2009
2
SgtWookie said:
What was your input voltage to the 2N3055? 12v is the output, right?

It has a thermal resistance from the junction to the case of 1.5°C per Watt, so the junction is considerably hotter than the case.
Click to expand...
Yeah 12v was the output, input was 15-16v.

If I did over heat the junction would adding a fan likely be enough to keep it cool enough? Possibly adding a 2nd transistor?

Also I've been looking at some other schematics, and I've seen several using a PNP type transistor like the schematic below rather than a NPN, is there any advantage to this?


 
S

santonel

Joined Feb 28, 2010
6
mayhemsm said:
Hi I was wondering if anyone could look at this and tell me what I might be doing wrong, I seem to have killed the transistor.

I was running it with a heat sink on both the LM317 and the transistor at about 12v / 4amps, and the transistor was hitting about 230 Deg. Fahrenheit in open air which is still inside the max temp for the transistor.

Thanks

Click to expand...
Shouldn't 1 and 2 be your power in/out and 3 and 4 be ground? Or am I misreading the schematic?
 
Audioguru

Audioguru

Joined Dec 20, 2007
11,248
Your first circuit used the 2N3055 transistor as an emitter-follower so the output voltage was poorly regulated.

The next two circuits have the transistor as a current booster so the output voltage is properly regulated.
 
Bychon

Bychon

Joined Mar 12, 2010
469
These circuits are right out of the text book. That means, "good". The only problem is in melting the transistors. Do you need help with the math for heat, temperature, and cooling?
 
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