Zero current voltage regulator (or limiter) - Page 1
Forum section: electronics / projects

author: sporubcan
author_rank: Newbie
timestamp: April 06, 2024, 06:42:35 pm
content: Hello,I need some voltage regulator for limiting Vgs of MOSFET transistor (I can not regulate the gate driver power supply). Problem is, that gate driving source must be not loaded more than several microamps and solution must be very simple. Target Vgs voltage is around 2.5-2.8V. Solution must be very cheap (intended for mass production) and space-saving.My ideas which will unfortunately not work:Resistor + Zener diode (Zener voltage is very inaccurate for small currents).Resistor + 4x standard 0,7V drop diodes in series - would be good, but takes too much space, even SOD packages used.Use TL431 or similar - according to datasheet not applicable for me, because needs cathode current higher than 100uA-1mAI found thishttp://www.dicks-website.eu/nocurrentregulator/enindex.htm, but it is not easy to find right and cheap transistor available on JLC which would match selected output voltage range.Any help is appreciated!Thank you very much!Sam

author: VinzC
author_rank: Frequent Contributor
timestamp: April 06, 2024, 06:56:13 pm
content: The target value for Vgs that you indicated seems odd. What is the model of your MOSFET? It's the Vgs value in the Absolute Maximum Ratings we are interested in.EDIT:Also a bit... no, way more context is necessary to provide you with an elaborated answer.Can you share a schematic?What is that MOSFET supposed to act for?Are you sure the functionality in which you're trying to integrate that transistor is not already available in a jellybean integrated circuit?

author: sporubcan
author_rank: Newbie
timestamp: April 06, 2024, 07:05:40 pm
content: Hello,my MOSFET is logic-level and of course it has much higher Vgs(MAX). But what I exactly need is to keep Rds(ON) approximately constant at various gate driver supply voltage. The problem is that I can not stabilize gate driver supply voltage due to some reasons, so I want limit its output.EDIT: Unfortunately I am not allowed to share schematic. I apologize.Thank you!Sam

author: temperance
author_rank: Super Contributor
timestamp: April 06, 2024, 07:33:54 pm
content: It would help if you specify the requirements. Does the mosfet has to switch and how fast?For a low knee current zener take a look at the ZRC250.https://www.diodes.com/assets/Datasheets/ZRC250.pdfFor static drive you might be able to use a low quiescent current LDO and drive the input with the gate signal.

author: sporubcan
author_rank: Newbie
timestamp: April 06, 2024, 07:37:22 pm
content: Switching is relatively slow, several Hz...

author: sporubcan
author_rank: Newbie
timestamp: April 06, 2024, 07:39:35 pm
content: Btw. that ZRC250 is very interesting!

author: temperance
author_rank: Super Contributor
timestamp: April 06, 2024, 07:42:52 pm
content: I've searched around and you have more options. If a little over 60 µA is not a problem is the LM4040 which you can obtain from a few manufacturers.You can search for shunt regulators to find more options.Edit: I mean shunt voltage references.

author: Wolfgang
author_rank: Super Contributor
timestamp: April 06, 2024, 07:44:25 pm
content: Tried TLVH431?

author: sporubcan
author_rank: Newbie
timestamp: April 06, 2024, 07:53:13 pm
content: Wolfgang TLVH431 has too high cathode current requirement. 100uA is too much for my application and would need three external resistors, what is also con. But thank you for your attempt.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: April 06, 2024, 07:57:06 pm
content: Quote from: sporubcan on April 06, 2024, 07:05:40 pmErr,whyexactly do you want to attempt this ?You do know that gate-controlled RDS varies wildly with gate threshold and temperature ?A simple voltage clamp will only give a targeted RDS for a single FET sample, and a single temperature.QuoteYou can get up to 6 diodes in a single SMD package, SOT363 or smaller.

author: sporubcan
author_rank: Newbie
timestamp: April 06, 2024, 08:32:59 pm
content: Quote from: PCB.Wiz on April 06, 2024, 07:57:06 pmI know that Rds(ON) is temperature dependent and varies piece-by-piece. My intention is only approximate Rds(ON) stabilization. Thank you for important answer, that multiple diodes in SOT363 are available.

author: MasterT
author_rank: Frequent Contributor
timestamp: April 06, 2024, 10:23:18 pm
content: LED?

author: BrianHG
author_rank: Super Contributor
timestamp: April 07, 2024, 01:24:28 am
content: Use a single N channel J-fet. (Most popular type)Tie the Gate to GND, tie the Drain from anywhere 2.8v to 25v/45v/75v (depends on Jfet's max voltage, rare 250v Jfets do exist) and the Source pin is the output which will be a regulated ~2.8v.(Output voltage is the J-fet's ~VGs cuttoff voltage listed in it's data sheet)Some J-fets will give you 1.2v, others as high as 7.5v. The output voltage play from J-fet to J-fet of the same part number is around +/- 0.1v so long as you keep using the same manufacturer.The quiescent current on the Gate's GND connection will be in thenanoamprange. You will not find a regulator which will consume less current than this. A simple 1nf-100nf cap from output to Gnd will make the output clean. Do not draw more than a few ma, or you will loose regulation. The dropout voltage is ~0v! Low noise audiophile grade voltage reference.Examples:Digikey overpriced N-JFets

author: VinzC
author_rank: Frequent Contributor
timestamp: April 07, 2024, 12:25:41 pm
content: Quote from: sporubcan on April 06, 2024, 07:05:40 pmWell... that is unfortunate as I definitely smell an X-Y problem here. Not being able to give the slightest detail about what you're trying to achieve is not really the best way to get help on any forum, I guess (hope) you're aware of that. Consequently anything else will only be speculation and conjecture...