Replacing relays with MOSFET and TRIAC

Thread Starter


Joined Sep 30, 2017
Hi Guys Im back again.

First of all thanks to everyone who helped out in my last post, great help much appreciated.
I got a few basics questions so thought i'd lump them in one go.
So i want to swap out relays in my circuit for triacs and mosfets.

here is what im thinking.

1) In the left circuit is a 'car door lock actuator' the ones used for remote door locking- cheap - from china- with 5 wires, it works just fine and its rated at (so the seller says) 2.2A. The other 3 wires are just a switch where a centre wire is connected to either of the remaining 2 wires depending on the actuator position.

Before i put D1 in i was having a problem with it resetting the arduino(sharing common ground and VCC). The trip would happen at the moment of the actuator triggering and would not even actuate. Now there is quite a hefty load (spring) attached to return the actuator, but i reckon its no more force than what a door lock uses (i have experience here) but could be wrong. Whatever's going on doesn't so with the diode in place. don't ask me to hook up a DMM i'm waiting for replacement fuses - i keep blowing them for some reason.
Any thoughts?

2) The MOSFET Q1 i presume is wired correctly and presuming a current draw of 5A (being that i don't really know) means i'll probably be looking at a TO-220 package. Is it good practice to put in additional diode protection from ground to source given the existing issue? The actuator is only meant to switch for a few hundred milliseconds but my application may keep it open for lets say 3-10 seconds (bad for the motor i know but hey - lets see how long it lasts) is it possible then to use the mosfet in pulse mode to achieve this higher amperage, before the field in the motor collapses?(or is this bad for a motor?). This of course is not my intention (i could just get a bigger MOSFET) but would like to know if it is plausible application.

3) is there some sort of IC that switches polarity (to reverse the motor). This will negate the spring and hence the problems thus identified - or could i make use of that switch talked about in 1).

4) because the actuator is grounded at its position its easier for my application to switch before the load rather than after. what are the implications of using P channel ?- other than the gate needing to be on for the MOSFET to be off.

5) the middle circuit shows a solenoid powered by 2 sources. In order to protect each source, is the diode arrangement acceptable and is this common practice?

6) Again would like to use a Transistor for switching with arduino, I am unsure how best to achieve this, being that i cant move the ground, Any ideas?

7) the circuit on the right is the ignition coil. the primary gives out 2-300VAC but very low power, Im looking at a TRIAC for this application although probably using a opto in front. Is this achievable with a triac, and any thoughts about the AC grounding with the arduino, they share the same ground and there has been no problems so far, just wanted to know of anything to be aware of.

the connections of components my be incorrect - i have no intention of implementing this circuit until i know what is what.