Right. I did think of this (a mechanical switch). But ultimately I really want to be able to trigger the SCR with a wireless remote control. Which is easy enough in principle - I will replace the switch with a mosfet.
I could also use the remote receiver to activate a physical NC relay, so that it isolates the booster module when it's switched on. However, the relay would activate slightly too late - I need it to switch on just before the capacitor discharges. Is there a way to delay the discharge? (I mean I can do it with a ATTINY85 or something but that seems unnecessarily complicated)

 

Than would something like this work?
https://www.amazon.com/Wireless-Tra...44&sprefix=wireless+relay,aps,226&sr=8-5&th=1

use one relay for you're SW1 and another for your SW2 Remove the need for complex circuitry with existing off the shelf modules.

 

Yes those would work but I already have a load of wireless modules without relays which are a lot smaller and quieter

 

Right. I did think of this (a mechanical switch). But ultimately I really want to be able to trigger the SCR with a wireless remote control. Which is easy enough in principle - I will replace the switch with a mosfet.
I could also use the remote receiver to activate a physical NC relay, so that it isolates the booster module when it's switched on. However, the relay would activate slightly too late - I need it to switch on just before the capacitor discharges. Is there a way to delay the discharge? (I mean I can do it with a ATTINY85 or something but that seems unnecessarily complicated)

Hi,

Can you use a MOSFET for the booster switch too then?
It's easy to create a delay if you are using MOSFETS. Just use an RC low pass filter to trigger the SW1 MOSFET. The booster MOSFET will be turned off directly, while the SW1 MOSFET will be turned off a bit later. You might also get away with disconnecting the ground of the booster rather than the positive output, that would be simpler I think.
You should probably try it with two switches first just to make sure the idea works.

One thing seems certain and in unusual circuits this can be a very good thing, and that is that disconnecting the booster should work no matter what, unless a high voltage spike can jump the switch or MOSFET being used for the booster cut switch. The booster circuit can not blow out if it is disconnected. The only other possibility then is that a fast rising electromagnetic field can couple to the inductor used in the booster and cause some over current or over voltage to blow out the switch device or control circuit. In that rare case you would have to also add some damping to that boost circuit.

 

Use a DPDT relay.

One set of contacts connects the power supply through the NC contact. The other triggers the SCR through the NO contact.

 

Use a DPDT relay.

One set of contacts connects the power supply through the NC contact. The other triggers the SCR through the NO contact.

Hi,

Just to be clear, you have to specify what the relative timing of each contact is because there are different types.
For this application, the NC contacts would have to open before the NO contacts close.
This might require using a relay contact adjusting tool to slightly bend the contacts to force this behavior unless you can purchase one like that.
A normal relay may work though if it is made properly.