Author Topic: Control El-Wire with FET  (Read 578 times)

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Offline Apothus

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Control El-Wire with FET
« on: October 27, 2018, 05:09:18 am »
As part of a project i am working on I want to control electroluminescent segments with a FET. I realise the typical solution is to use a flyback transformer to generate the high AC voltage and switch this with triacs. However I am trying to shrink my footprint and I have a lot of signals I wanted to control. My thought was to generate 200V DC with a boost converter, then switch each segment at ~1kHz with a logic evel signal driven FET.

However... from what i understand the model of EL segments is a series resistor and capacitor effectively filtering the DC aspect of my circuit. So I am needing help in working out what I need to switch this load, my simulation skills and AC knowledge are sadly lacking.
 

Offline mvs

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Re: Control El-Wire with FET
« Reply #1 on: October 27, 2018, 08:06:02 am »
My thought was to generate 200V DC with a boost converter, then switch each segment at ~1kHz with a logic evel signal driven FET.
El wire is essentially a capacitor. To get some current throught it, you will need to apply AC voltage. So you will need at least half-bridge with some kind of gate driver (HV MOSFETs are usually not logic level) to make it glow.

You can get TRIACs in TO-92 or SOT-223 packages, which will make you circuit small. Why to bother with MOSFETs for switching AC?
 

Offline Apothus

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Re: Control El-Wire with FET
« Reply #2 on: October 28, 2018, 09:31:42 pm »
I want to drive 18 individual channels so 18 SOT-223 chips would take up a lot of real estate. So being able to get down to SOT-23 would have been a good step. The original idea for using FETs came from the HV509 however I wanted to see if I could do it without the IC, especially considering the package it comes in (fussy arent I!). Although having looked at it further I see what you are saying about the half bridge and HV drive circuitry. Whilst it would be nice to have developed something from scratch I think this is another case of just use the IC :-\
 


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