Zener + Emitter Follower voltage regulator

Alcaid · 29th April 2004, 01:13 PM

I have a couple of questions regarding the Zener + Emitter Follower voltage regulator on www.tnt-audio.com.

1. What is the max output current of a regulator like this?
2. What type of zener to use for an output of 15V? (15V, xW zener?)
3. Can cap C8 & C7 be polarized?
4. Is the schematic under the right way to make a dual supply?

Bricolo · 29th April 2004, 01:20 PM

The max current will be defined by the transistor max current.
Here, with a CD550 I think it's 100mA

the output voltage is Vzener-0.7V, you don't need a high power zener

yes, the caps are polarized (they are electrolytics)

it seems correct

Werner · 29th April 2004, 01:26 PM

R13 in the original schematic should not be there, of course, or at least not with such a high value.

It seems I did a lot of copy and paste from a shunt reg schematic for this one ...

Alcaid · 29th April 2004, 01:32 PM

Ok so the schematic will work when R13 is removed?

Any suggestions for a good "audiophile" transistor with a higher output current?

Bricolo · 29th April 2004, 01:33 PM

how much current do you need?

Alcaid · 29th April 2004, 01:34 PM

In the case of a transistor with higher current:
Should it be heatsinked?

Bricolo · 29th April 2004, 01:37 PM

How much current?

Alcaid · 29th April 2004, 01:38 PM

Don't actually need more than 44-55mA (2x OPA627 and 2x BUF634T in wide BW), but the trafo will be a 2x18V 50VA, so why not? So I can use it for other designs.

Bricolo · 29th April 2004, 01:44 PM

for 50mA the BC550 will be fine, just take care that you don't have more than 10V between the collector and the emitter (otherwise you'll exceed the maximum power dissipation)

If you need more than 70mA, a BD140 will be nice. I think it can dissipate +-1W without heatsink.
But if it's for less than 70mA, i suggest you to stey with the BC550
Generally, transistors that can handle more power have a lower beta. And a higher beta gives a better regulation.

Alcaid · 29th April 2004, 01:54 PM

Yes the BC550C/BC557C combo has a good beta.

BC557C can only dissipate 0.5W though while the BC550C can dissipate 1.5W. What trasistor should I use instead of the BC557C which can dissipate 1.5W with the same (or better?) beta?

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29th April 2004, 01:20 PM	#2
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	The max current will be defined by the transistor max current. Here, with a CD550 I think it's 100mA the output voltage is Vzener-0.7V, you don't need a high power zener yes, the caps are polarized (they are electrolytics) it seems correct

29th April 2004, 01:26 PM	#3
Werner diyAudio Member Join Date: Jan 2002 Location: Belgium	R13 in the original schematic should not be there, of course, or at least not with such a high value. It seems I did a lot of copy and paste from a shunt reg schematic for this one ...

29th April 2004, 01:32 PM	#4
Alcaid diyAudio Member Join Date: Nov 2003 Location: Klepp	Ok so the schematic will work when R13 is removed? Any suggestions for a good "audiophile" transistor with a higher output current?

29th April 2004, 01:33 PM	#5
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	how much current do you need?

29th April 2004, 01:34 PM	#6
Alcaid diyAudio Member Join Date: Nov 2003 Location: Klepp	In the case of a transistor with higher current: Should it be heatsinked?

29th April 2004, 01:37 PM	#7
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	How much current?

29th April 2004, 01:38 PM	#8
Alcaid diyAudio Member Join Date: Nov 2003 Location: Klepp	Don't actually need more than 44-55mA (2x OPA627 and 2x BUF634T in wide BW), but the trafo will be a 2x18V 50VA, so why not? So I can use it for other designs.

29th April 2004, 01:44 PM	#9
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	for 50mA the BC550 will be fine, just take care that you don't have more than 10V between the collector and the emitter (otherwise you'll exceed the maximum power dissipation) If you need more than 70mA, a BD140 will be nice. I think it can dissipate +-1W without heatsink. But if it's for less than 70mA, i suggest you to stey with the BC550 Generally, transistors that can handle more power have a lower beta. And a higher beta gives a better regulation.

29th April 2004, 01:54 PM	#10
Alcaid diyAudio Member Join Date: Nov 2003 Location: Klepp	Yes the BC550C/BC557C combo has a good beta. BC557C can only dissipate 0.5W though while the BC550C can dissipate 1.5W. What trasistor should I use instead of the BC557C which can dissipate 1.5W with the same (or better?) beta?