Hello everyone, I am currently working on a project, where I want to use a thyristor as a static switch that once turned on stays in its on (conductive) state. The problem is, that I can't find any information about the thyristors remaining collector emitter resistance once triggered. The datasheets don't provide that value. Also no shop provides any sort or filter option regarding this value. I would like to choose the component with the minimum resistance/ voltage drop in conductive mode. I asked a question regarding this topic quite some time ago but it could not really be solved and now returning to this project I am stuck again. I hope you can help me. Thanks a lot :-)
Guest
#6209707
Physics did not change meanwhile. And so you will find an output saturation voltage specified in every data sheet, but no on-resisistance - this is no MOSFET.
Guest
#6209712
the voltage drop is with any thyristor somewhere around 1V, the sum of one BE-equivalent junction and the saturation voltage of the opposite CE-equivalent junction The exact value depends on your current, also the doping levels where there is a trade off between switching speed and voltage As an example i am refering to the BT145 that i recently used, https://de.rs-online.com/web/p/thyristoren/4842836/ where datasheet figure 10 lists the on-state voltage as a function of current
Thanks a lot for your answers!! Pointing me to the datasheet and telling me what to look for with "on-state voltage" I could now figure out more what I have to search for. As you said all thyristors I could find have a voltage drop of around 1V so it doesn't seem to make sense for me to use them in my 12V and relatively low current application. I was now thinking about using alternatively a MOSFET and somehow create a self-holding circuit for it. My problem in general is that I want to build a one cable solution meaning the switching MOSFET and its controlling circuit should sit on the cable that powers (+) the load without any direct connection to ground despite through the load itself. Can someone think of a way to do this? Maybe with a charge pump and using the on state resistance of the MOSFET? Also please excuse my late reply. I invested some time getting familiar with LTspice and trying to come up with a solution myself. I'm looking forward to possible answers :-)
Guest
#6213452
Too much prose, draw a schematic!
Here is a basic schematic of the problem. The idea is that the switch should be not conductive at power up so the µC can boot. Then once triggered by the µC, the switch should stay conductive until power is cut.
Attached files:
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one_cable_solution.png
(8.2 KB)
Guest
#6214028
I would consider a latching (polarized) magnetic relay.