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Old 24th January 2006, 03:20 PM   #1
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Default Low noise current source

Hello
What's the best way to make a low noise adjustable current source.
In fact I'm looking for a low noise adjustable tension source to drive a mosfet gate. I've tried 9V1 zener diode paralleled by a 10K multitour adjustable, but what a noise.......

Do you have some ideas? LED, TL431???????

Thanks
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Old 24th January 2006, 03:53 PM   #2
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Just an idea you can try:

Zener diodes are very noisy and should be bypassed with a capacitor or two to help filter out their noise. Try an electrolytic cap in parallel with a small film cap for bypassing.

Also, you can try using regular diodes for your refernce voltage. Let's say you wanted to make a 5V reference, you can use about 7 forward biased diodes instead of one reverse biased zener diode. Forward biased diodes tend to produce less noise than reverse biased ones.

==> Just so you know (although I don't think this will help you much), transistors tend to be noisy current sources because they amplify their own noise. Can you make some sacrifices and use simple resistors for this project?
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Old 24th January 2006, 06:28 PM   #3
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This thread could be the logic following step of the very recent and first class one :
Some noise measurements for LEDs and zener diodes

~~~~~ Forr

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Old 24th January 2006, 11:05 PM   #4
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Thanks a lot for the link,

Do you think that adding an adj in parallel with the voltage reference will increase noise?

Thanks
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Old 25th January 2006, 02:51 AM   #5
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Yes, if you start to bypass current around the zener to the point where it's not being fully turned on, they get real noisy. Try taking an LM334 adjustable current source to bias the zener while watching the noise across it with a scope, as you bring the current up it will get real noisy until you get a miliamp or more going through it. I've used this technique to chose where to bias them for lowest noise.
Are you looking for a current source or a quiet voltage source? your original post is a bit unclear...

Mike
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Old 25th January 2006, 10:50 PM   #6
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In fact I have to drive the gate of mosfet with an adustable voltage source (the less noisy, of course) to make a current source.

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