Monolithic latching and UN-latching transistor? - Page 1
Forum section: electronics / projects

author: MustardMan
author_rank: Contributor
timestamp: June 08, 2025, 12:14:15 am
content: I'm not talking about SCRs, or triacs, or flip-flops, or any sort ofcircuitthat can implement the functionality - I'm thinking about a single chunk of silicon...Small (likereallysmall) FETs with a gate that can retain a static charge even when powered off have been available for a couple of decades now - it's called flash memory.Is anyone aware if any attempt to 'scale up' these types of devices has been attempted? To where the "flash memory" FET is able to conduct amps?I'm thinking of an application where the usual solution would be a latching relay... retaining its' on/off state regardless of if the control signal disappears or power is removed.However, it might be asking too much that polarity of the controlled circuit is ignored like one can with a relay!Cheers,MM

author: coppercone2
author_rank: Super Contributor
timestamp: June 08, 2025, 12:26:02 am
content: every fet ever does this if its a fetits not done because sensitive electronics suck, fry easily, non robust, etc.

author: Someone
author_rank: Super Contributor
timestamp: June 08, 2025, 12:38:30 am
content: There is one company claiming they have the technology but it isn't available yet:https://www.isocom.uk.com/news/latching-solid-state-relays-launchhttps://www.isocom.uk.com/news/how-our-latching-solid-state-relays-will-impact-space-industryDo you have the XX million dollars to jumpstart the product?

author: moffy
author_rank: Super Contributor
timestamp: June 08, 2025, 03:11:55 am
content: A very large low leakage capacitor and a low gate leakage MOSFET, but then it depends upon how long it needs to hold its state.

author: MustardMan
author_rank: Contributor
timestamp: June 08, 2025, 07:47:46 am
content: @someoneThank you for the pointer to Isocom - it looks like they have commercialized the product, although I have yet to find a supplier that will list a price. I had a closer look at the datasheet for the Isocom CSMRLGXXP1 (others available too), but it would seem that the "latching" of the output only remains latched as long as power is applied... when the power is removed, the relay (the "LSSR" - really just a fancy SSR) returns to its' default state -notthe state it was last in. Boo.@moffyAlthough I will remain keeping my eye out for a genuine LSSR (latching solid state relay), I agree that most people would just make a circuit to emulate the function: a micro with in-built flash memory controlling a FET/triac would be it - then the "powered off" time could be years! A SOT-23 or equivalent micro would do the trick nicely, and then the selection of a power device would be at the designers whim (instead of relying on a very limited selection offered by a company such as Isocom).Edit: Still not as nice as where do you get the power for the micro? It can't be siphoned off the output... because when the FET is on, the voltage drop across it is way to small even for a joule thief (and where else can you siphon from for a genuine 'relay' type operation).Thank you for the replies.

author: moffy
author_rank: Super Contributor
timestamp: June 08, 2025, 08:27:23 am
content: A solution with current components, use a long life button cell to power a low power SR latch which then drives a low leakage MOSFET gate, could last several years.

author: Someone
author_rank: Super Contributor
timestamp: June 08, 2025, 12:11:47 pm
content: Quote from: MustardMan on June 08, 2025, 07:47:46 amDo link or attach the data sheet(s) if you can, haven't seen anything from them so far.

author: mawyatt
author_rank: Super Contributor
timestamp: June 08, 2025, 01:00:54 pm
content: Quote from: MustardMan on June 08, 2025, 12:14:15 amA large Memresistor, or bunch in parallel?Best

author: MustardMan
author_rank: Contributor
timestamp: June 10, 2025, 08:36:49 am
content: @someonelink to datasheet:https://www.rhopointcomponents.com/wp-content/uploads/2024/11/isocom-csmrlgxxp1-hermetically-sealed-latching-solid-state-relay-datasheet-issue-2.pdfPage 5 contains the disappointing news... the NO and NC states should return to what they were after the loss and restoration of "XV bus".And having an "XV bus" is cheating - as noted in a previous post, implementing aproperLSSR with access to an "XV bus" is trivial!@mawyattI haven't paid much attention to the hype surrounding memristors, but thememistordoes get close (although not truly a silicon device by the words on Wikipedia: "Reproducible elements have been made which are continuously variable ... and cover this range in about 10 seconds with several milliamperes of plating current" - "plating current" gives it away). It seems as though all development effort in relation to Floating-Gate MOS (FGMOS) went smaller to make stupidly large storage devices the size of your thumbnail possible, and not the other way. No demand I suppose.