Switch 12-28 VDC and VAC up to 1-2A and not use relay? - Page 1
Forum section: electronics / projects

author: nardev
author_rank: Unknown
timestamp: March 15, 2023, 12:26:47 am
content: Hey guys, i need to switch on/off, nothing fast. Nothing below 1s at a time, to connect 12-28 VDC/VAC but to avoid using relays.Any suggestions?And jes, the controller which i use is 5V logic so, i wold prefer that it works with 5V logic.thnx

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 15, 2023, 12:48:27 am
content: You could use a pair of back-to-back MOSFETs and driver circuitry. Essentially building your own solid state "relay"...Something like this, but with beefier FETs

author: nardev
author_rank: Unknown
timestamp: March 15, 2023, 01:01:37 am
content: How about Thyristor? I should also mention it's a coil that i have to turn on/off.I just never used this in the application, i have no idea about pros/cons. Is there something important to say about Thyristor?How stable/safe it is?

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 15, 2023, 01:03:20 am
content: Or, even simpler,something like this.The problem with a Thyristor (SCR) or Triac, is they'll latch on if you use DC... Didn't you say you need to switch BOTH AC and DC?

author: nardev
author_rank: Unknown
timestamp: March 15, 2023, 01:23:44 am
content: Yea.. right.. latching is the issue.. I would have to use two pins to unlatch it?This Photorelay looks so interesting. It's bit expensive but should fit nicely. Just have to find those that are always in stock.Quote from: Kim Christensen on March 15, 2023, 01:03:20 am

author: coromonadalix
author_rank: Super Contributor
timestamp: March 15, 2023, 02:03:45 am
content: SSR solid state relay no contacts 5v logic ??

author: nardev
author_rank: Unknown
timestamp: March 15, 2023, 02:19:05 am
content: Quote from: coromonadalix on March 15, 2023, 02:03:45 amIt's usually quite big for this application.

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 15, 2023, 02:33:46 am
content: Quote from: nardev on March 15, 2023, 02:19:05 amThe TLP241A that I posted could also be described as a "solid state relay". That's how I found it on Digikey. You may be able to find something similar from a local supplier if you searched for solid state relay.If you just want to switch DC only, then single MOSFET could work if the MCU and load share the same power source. It's the AC capability that adds the complication and cost.

author: nardev
author_rank: Unknown
timestamp: March 15, 2023, 02:55:22 am
content: Quote from: Kim Christensen on March 15, 2023, 02:33:46 amI'm thinking.. but i don't know how "stupid" it is, to have separate versions of the device. DC and AC one....

author: nardev
author_rank: Unknown
timestamp: March 15, 2023, 02:56:24 am
content: p.s. just realized, TLP241A is not that expensive. Similar to cheap telecom relays.thnx, good idea...

author: tinfever
author_rank: Regular Contributor
timestamp: March 15, 2023, 03:21:11 am
content: Silly idea: Could you put a FET and triac in series? Assuming you can deal with the triac power dissipation?

author: BrianHG
author_rank: Super Contributor
timestamp: March 15, 2023, 03:55:43 am
content: Quote from: nardev on March 15, 2023, 02:19:05 amBig? How so? Are you looking for an SOT-23 device?Everything I listed below are around a 4 to 6 pin dip package, all within your specs...DC/AC 4 amp Solid state relays aren't too big, only a 4 pin DIP, example:https://www.digikey.com/en/products/detail/toshiba-semiconductor-and-storage/TLP3553A-F/94723595 amp, 6 pin smt/dip device:https://www.digikey.com/en/products/detail/toshiba-semiconductor-and-storage/TLP3543A-TP1-F/853991830v doesn't leave you with any headroom, so you may better choose a 3amp 60v device in a 6pin dip package:https://www.digikey.com/en/products/detail/toshiba-semiconductor-and-storage/TLP3545-F/3056611The price is now increasing, bu here is a 40v, 4.5amp device in dip 6 package:https://www.digikey.com/en/products/detail/bright-toward-industrial-co-ltd/AA28/13556940And in a funky SMD package, here is 6amp 60v:https://www.digikey.com/en/products/detail/ixys-integrated-circuits-division/CPC1907B/3908816I am not sure how small you want to go as you said SSRs are too big, but you wont get too much smaller with multiple discrete back to back mosfets and an opto-photo-voltaic to directly drive the gates, though with this, you can easily achieve 100-500v, 50 to 500amps. Such solutions will be larger in circuits and complexity than all the SSR ICs I listed above.

author: nardev
author_rank: Unknown
timestamp: March 15, 2023, 03:59:04 am
content: Thank you so much.This is plenty to start.My quick search into ssr (i didn't have much experience with those) was showing some tall and wide relays... I was trying to avoid that.10x5x8mm for example is more than good size.I already included 30-40% of overhead with 28V. So it's safe...