Zener + Emitter Follower voltage regulator - diyAudio
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Old 29th April 2004, 02:13 PM   #1
Alcaid is offline Alcaid  Norway
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Default Zener + Emitter Follower voltage regulator

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

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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?
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Old 29th April 2004, 02:20 PM   #2
Bricolo is offline Bricolo  France
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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
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Old 29th April 2004, 02:26 PM   #3
Werner is offline Werner  Europe
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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 ...
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Old 29th April 2004, 02:32 PM   #4
Alcaid is offline Alcaid  Norway
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Ok so the schematic will work when R13 is removed?

Any suggestions for a good "audiophile" transistor with a higher output current?
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Old 29th April 2004, 02:33 PM   #5
Bricolo is offline Bricolo  France
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how much current do you need?
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Old 29th April 2004, 02:34 PM   #6
Alcaid is offline Alcaid  Norway
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In the case of a transistor with higher current:
Should it be heatsinked?
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Old 29th April 2004, 02:37 PM   #7
Bricolo is offline Bricolo  France
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How much current?
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Old 29th April 2004, 02:38 PM   #8
Alcaid is offline Alcaid  Norway
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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.
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Old 29th April 2004, 02:44 PM   #9
Bricolo is offline Bricolo  France
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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.
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Old 29th April 2004, 02:54 PM   #10
Alcaid is offline Alcaid  Norway
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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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