Low power voltage reference? Or reduce energy consumption from TL431? - Page 1
Forum section: electronics / beginners

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: January 01, 2025, 09:49:17 pm
content: Trying to design a battery-powered device to have a runtime of over 1-month, and I need a dedicated 2.5v voltage reference for the project, with an output power of *at most* 5mA from the voltage reference, but a likely standby of 0.1mA.Messing with the TL431 in Falstad, I can't really get the I.C to below 1mA consumption? Am I just using the wrong voltage reference, or are they generally this inefficient? How else should I generate a 2.5v reference, with minimal wasted energy?TL431 circuit

author: magic
author_rank: Super Contributor
timestamp: January 01, 2025, 10:04:43 pm
content: You will obviously never get 5mA output and 0.1mA standby current from a shunt reference. And TL431 does require at least 1mA bias current for guaranteed correct operation.Go to your component supplier, click "voltage references", select 2.5V output, whatever tolerance you need, look for anything that says "low power" in the description. If something like 1~2% accuracy is acceptable, you may even consider LDOs too.

author: Andreas
author_rank: Super Contributor
timestamp: January 01, 2025, 10:09:49 pm
content: Its not clear to me what you really want.TL431 is a shunt referenceIf you want to get out 5 mA of it you need at least 6 mA total current.The low power version is the LM385-2.5 but for 5 mA output you need at least 5.1 mA total current.For real low quiescent power you need a series reference like REF34 or REF3425.with best regardsAndreas

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: January 01, 2025, 10:13:37 pm
content: Woops, completely forgot about the existence of series-voltage references, and see if they'll work for me. I'll also take a look into LDO's, as I'd imagine some exist with standby power's less than 0.1mA?

author: jwet
author_rank: Frequent Contributor
timestamp: January 01, 2025, 10:15:21 pm
content: The TL431 is a "two terminal" type reference-<I know it has three terminals>, its biased like a zener and shunts whatever leftover current is surplus to your needs. A shunt reference will be very inefficient (0%) if its is unloaded since it has to sink the max current you might require. If the load on your reference is highly variable, three terminal reference should be used. These are like a voltage regulator but more precise- in fact just small voltage regulators might be accurate enough- they're a couple of percent.Maxim and many others like TI makes some nice three terminal references, some draw 10 uA unloaded. Digikey's search is best place to find one as last poster said.

author: Zero999
author_rank: Super Contributor
timestamp: January 01, 2025, 10:29:39 pm
content: LT6656https://www.analog.com/media/en/technical-documentation/data-sheets/lt6656.pdf

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: January 01, 2025, 10:39:22 pm
content: The NCP51460 is less than $1/each and looks like it'll work for my application. It's far from being the most efficient, but it's much better for my application in comparison to the TL431 or other cheap LDO's.Thanks for the help everyone!

author: tchicago
author_rank: Regular Contributor
timestamp: January 02, 2025, 04:41:31 am
content: C'mon, you are engineer, use your skills.If something takes too much power continuously, you don't have to keep it on all the time. Use some extremely low power microcontroller that would control the MOSFET to occasionally open and give power to your TL431. Do your measurements during that time and go back to idle. Having it on for like 100ms once every minute will reduce the overall power consumption by 600 fold. Turning 6mA into 10uA average.