SSR, EMR

[Starwax]

Hi

I’m trying to create a capacitor switching circuit using a bank of SSR's as the switching component. The signal is at 13.56Mhz. The problem I’m having is that the output capacitance of the SSR's is too high. There’s 8 of these devices in a row which when all turned off are creating a minimum capacitance of about 120pf. The spec is of course a lot lower so I’m assuming the frequency is causing the devices to have a higher output capacity? Would I be correct? I can get around the problem by replacing them with reed EMR's but ideally I would have SSR's as they are generally cheaper and would result in a smaller circuit. Is there any way to reduce the output capacitance or am I going to have to use EMR's to solve the solution?

Thanks

 

[VEBill]

You're trying to drive Solid State Relays (SSRs) at 13.56 MHz?

 

[VEBill]

You're suggesting to use reed Electromechanical Relays (EMRs) at 13.56 MHz?

 

[VEBill]

Sorry for the repeated posts...

Is the 13.56 MHz the 'switched' signal or the 'switching' signal?

 

[Starwax]

My mistake. The 13.56 is the signal being switched. The switch itself is controlled by an external source so is operating at nowhere near that speed.

 

[VEBill]

Okay.

13.56 MHz is "RF", and I don't recall seeing SSRs being used to switch RF. There are many technologies that can be used to switch RF, reed relays will work just fine carrying low power HF frequencies - if that's the approach that works best for your application.

 

[itsmoked]

What IS the switching frequency?
What is driving the switch?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Starwax]

Its driven by a micro controller. This I can set to whatever speed I need so isn't a problem, Its a automated tuning circuit for a HF RFID antenna and the response isn't that crucial. Im not an RF engineer so this is a new area to me, after a bit of reading online I came to the conclusion (though apparently a wrong one) that SSR's were normally used,this would have also been beneficial for my space concerns and reducing the EMF (opto-coupled). However yesterday after starting this post I found this:

http://uk.rs-online.com/web/p/reed-relays/6220799/

Which I think will probibly do exactly the same thing. The circuit is low power so should be fine and I can reduce the EMF in other ways.

Cheers for your help anyway