# easiest asjustable precision reference...

Discussion in 'Homework Help' started by dtvonly, Nov 4, 2013.

1. ### dtvonly Thread Starter Member

Dec 14, 2012
43
0
Hi. there are so many reference voltage circuits available, I just want to use the easiest one - to allow me to adjust from 0 to 3.3V. Please advise on circuit. Thank you.

2. ### wayneh Expert

Sep 9, 2010
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There are many choices because different applications call for different things. Current at the output? Temperature stability? Degree of accuracy and precision? How close to zero?

3. ### dtvonly Thread Starter Member

Dec 14, 2012
43
0
Current output: 25mA; accuracy: 5%; 0.1V to 3.3V output.

4. ### wayneh Expert

Sep 9, 2010
15,512
5,738
With that much current and a need for 5% accuracy, I would rule out a simple voltage divider (which requires a reference voltage anyway).

You've posted this in Homework. Is it?

What things have you been considering?

5. ### MikeML AAC Fanatic!

Oct 2, 2009
5,444
1,073
What is the input voltage from which the reference is to be derived?

6. ### Alec_t AAC Fanatic!

Sep 17, 2013
9,172
2,163
For 5% accuracy you might (depending on the temperature range experienced) get away with a zener followed by a pot followed by an emitter-follower or source-follower.

Last edited: Nov 5, 2013
7. ### ScottWang Moderator

Aug 23, 2012
6,480
1,001
You may using a resistor + 4V zener to be a reference voltage, and using a VR1 10K potential meter cross on the two pin of Zener, and using one stage of transistor to amplify the Base current, and Vout from E, and E connecting a 1K resistor to GND to be a false LOAD.

You can also in series with two resistors, one with pin1 and another one with pin3 of VR1 to set the low limited voltage 0.1V and high limited voltage 3.3V.

8. ### tubeguy Well-Known Member

Nov 3, 2012
1,157
198
I seem to recall that a 6.2 volt zener in series with a 1n4001 diode make a relatively stable voltage reference because the temperature coefficients cancel each other. I'm not sure if it's the 6.2 volt or one of the other close values (like 5.6 or 6.8 volt) zeners.

9. ### WBahn Moderator

Mar 31, 2012
23,550
7,206
A 5.6V zener has very little temperature coefficient because the zener and avalache modes are in balance and offset each other. But for reasons I haven't bothered to look up, a 6.2V zener is apparently more stable over time and has a tempco of about +2mV/°C which is equal and opposite the normal tempco of a forward biased silicon diode, so you can put them in series and get comparable tempco performance while keeping the long-term stability.

tubeguy likes this.
10. ### bountyhunter Well-Known Member

Sep 7, 2009
2,498
510
There are tons of references like LM336 or LM385 and others with all ranges of precision.

Mar 31, 2012
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