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There is touch sense circuit that controls a SMPS circuit drives a power LED at output. When disconnect the energy while LED ON, if I reconnect the energy LED must start be as ON state. I need a cheap, logic circuit. Thank you for your help.

schematic

simulate this circuit – Schematic created using CircuitLab

Here is a simple referance design. Touch IC'output state is initially active high, because of them there is a NOT circuit made by NPN. Circuit should save ON state at least 30 minutes.

U2 is IQS127D

Dave Tweed
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IHK
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  • What you need is some form of nonvolatile memory, not merely a logic circuit. This could be anything from an EEPROM or flash to a latching relay. Do you have any preferences? – Cristobol Polychronopolis Aug 12 '20 at 19:05
  • I thought there should be a logic circuit which drives a capacitor somehow. That capacitor should have large discharge time so that it should provide enough voltage to output left high in case of reconnecting. @CristobolPolychronopolis – IHK Aug 12 '20 at 19:28
  • Do you have a requirement to guarantee that the state is preserved for a specific amount of time (undetermined thereafter)? If so, what's the time constraint? – Cristobol Polychronopolis Aug 12 '20 at 19:51
  • @CristobolPolychronopolis It should be min. 5 min. – IHK Aug 12 '20 at 19:59
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    Does this answer your question? [How to make 1 bit permanent memory circuit?](https://electronics.stackexchange.com/questions/188314/how-to-make-1-bit-permanent-memory-circuit) – Dave Tweed Aug 12 '20 at 20:07
  • @DaveTweed Yes, but I won't use 555 to control button. I have touch sense IC that gives toggled output according to touch input. I want to combine that memory circuit with my touch sense ckt. – IHK Aug 12 '20 at 20:43
  • If you want to make the memory in an existing circuit nonvolatile, you need to show us the circuit! – Dave Tweed Aug 13 '20 at 01:11
  • @DaveTweed Dave nonvolatile circuit is not define my requirement exactly. We can say time-limited memory. This circuit should save high state at least 5 min. – IHK Aug 13 '20 at 06:56
  • Unless you also specify a maximum time, we have to assume that it's arbitrarily large -- nonvolatile. – Dave Tweed Aug 13 '20 at 10:22
  • @DaveTweed Dave I specified max. time as 5 minutes, but customer changed as at least 30 min. – IHK Aug 13 '20 at 11:19
  • "At least" is a minimum time. not a maximum time. You also need to tell us what "U2" actually is. – Dave Tweed Aug 13 '20 at 11:54
  • @DaveTweed IQS127D00008 Touch IC toggles output between GND-VDD+0.3V with respect to input. Sorry, there is no limit for max. time. – IHK Aug 14 '20 at 14:30

2 Answers2

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Here's a circuit using a ratchet relay.

enter image description here

vu2nan
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Maxim has an app note on this subject that seems a bit overkill but here ya go:

https://www.maximintegrated.com/en/design/technical-documents/app-notes/4/4624.html

vir
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