EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: Mike Warren on August 11, 2020, 03:31:56 am
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Either my Google skills are not working today or nothing close to what I want exists.
In a perfect world, this is what I want:
- 5V output (anything from 3 to 5V would be fine)
- Very low quiescent current
- At least 10mA (I may get away with 6mA)
- Output voltage within +/- 10%
- Can handle up to 30V input
- Low dropout
- No external components (apart from decoupling caps)
- Surface mount (preferably SOT23 or similar)
- Sub $2 (cheaper the better)
- Easily sourced
Does anyone know of a part that at meets most of these specs?
I have successfully used an LM358 and zener in the past. regulation wasn't too critical in that case, and the same here. That was the best solution for that project because I also needed a level converter and the other channel of the LM358 did that job.
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TPS70950
1uA is pretty high.
If you need low quiescent current, and 0v dropout, a simple 30v-50v n-channel JFet would get the job done with quiescent current in the pA or fentoamps. Though, the regulation is a little worse. One of my old projects which targeted 3.0v left me with and acceptable 2.9 to 3.1v output within a hundred JFets. They were excellent regulating 2x CR1616 I had mounted in wearable electronic glasses.
Careful, the VGS is different between JFet types. The cheapest 8cent ones usually work best.
Some Jfets go as high 7v while many part # operate between 4v & 5v.
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TPS70950
$0.27 on LCSC @ 100pcs. $0.4 one-off.
Thanks.
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If you need low quiescent current, and 0v dropout, a simple 30v-50v n-channel JFet would get the job done with quiescent current in the pA or fentoamps.
Thanks for your reply. I've never done that. Do you have a link to a circuit?
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Careful, the VGS is different between JFet types. The cheapest 8cent ones usually work best.
Some Jfets go as high 7v while many part # operate between 4v & 5v.
Hello,
which JFets did you use for 6-10 mA?
In one of my cirquits I use a BF245C / BF545C to get around 4 V with up to 25V input.
My load is around 1 mA peak.
But I would not load a BF245C with more than 3 mA since the voltage drops with increasing load.
The bad thing is that JFets are getting more and more obsolete.
with best regards
Andreas
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If you need low quiescent current, and 0v dropout, a simple 30v-50v n-channel JFet would get the job done with quiescent current in the pA or fentoamps.
Thanks for your reply. I've never done that. Do you have a link to a circuit?
Somebody else just asked in a PM, so, here was my answer:
It is nothing more that tying the 'GATE' to the GND, and tying the source to you unregulated DRAIN and the SOURCE as your output voltage. You may also swap the source and drain for this type of regulator circuit.
I've operated at typically 2v output drawing up to 0.5ma with a high source voltage, 2ma-10ma with lower source voltages like 9-6v.
To increase above the 2v at the expense of some minor quiescent current, you may use a simple signal diode like 1N914/1N4148 connected between GND & the GATE, with a 20Megaohm resistor on the output VCC tied to the gate effectively raising the gate reference voltage. This should increase the output voltage by 0.5v. Or, find another J-fet with a higher VGS and go back to the absolute minimum quiescent current.
I typically used 0.1uf decoupling on the output, but, you can use more at the expense of a slower charge up time during powerup.
As you can see this was not designed to drive a lot of current, but, I guess you can add a emitter-follower NPN transistor like a 2N3904 to get up to 50ma out. Though, on the base, I would add a 20Megaohm resistor to GND to prevent run-away and now you will have a 0.5v drop when using this addition to your regulator. A number of matched J-Fets running in parallel would offer higher current with that sweet 0v input to output v-drop. But for this to work, you will need to bin multiple Jfets relatively matching their VGS.
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Thanks for your reply. I've never done that. Do you have a link to a circuit?
I am using this within my battery monitor in AD587LW cirquit
https://www.eevblog.com/forum/metrology/ad587lw-10v-precision-travel-standard/msg1449488/#msg1449488 (https://www.eevblog.com/forum/metrology/ad587lw-10v-precision-travel-standard/msg1449488/#msg1449488)
See:
https://www.eevblog.com/forum/metrology/ad587lw-10v-precision-travel-standard/?action=dlattach;attach=402886 (https://www.eevblog.com/forum/metrology/ad587lw-10v-precision-travel-standard/?action=dlattach;attach=402886)
Essential is to use at least 100nF on input and output in case of the FET.
There is a laternative population with a XC6216 regulator (which needs 1uF)
with best regards
Andreas