The collector. Here is the link to the schematic I followed. I have also included the image. https://www.elprocus.com/darlington-transistor-pair-circuit-with-working/

 

Please see my previous post. I added a picture of the schematic I followed. Thanks.

 

Please see my previous post. I added a picture of the schematic I followed. Thanks.

Couldn't find it - a Darlington could have a gain like 50,000 if you're lucky. Divide load current by gain and work out if sticking your finger on those pads will cause the required base current to flow.

With a MOSFET - the only current is through the gate bleed resistor, about 1M should work but you could probably go to 2M2.

Most TO220 style MOSFETs need at least 6V on the gate unless you use a logic level type - don't forget your skin resistance and the gate bleed form a voltage divider. Not all of Vcc is going to reach the gate.

 

Ian, thanks for that. So I could use a single MOSFET, logic level type? Would it accept the voltage from an op amp, stepping it up? Or would that have too much noise?

 

It might be a good idea to include an op-amp then you can guarantee solid on/off switching.
With a simple touch pad and a transistor (BJT or MOSFET) if you touch gently the transistor will be only partly on and so will disipate more power and get hot.

 

It might be a good idea to include an op-amp then you can guarantee solid on/off switching.
With a simple touch pad and a transistor (BJT or MOSFET) if you touch gently the transistor will be only partly on and so will disipate more power and get hot.

Op-amp or comparator - with a smidge of positive feedback.

 

Would putting two darlington pairs, in parallel increase the available current?

 

Yes, but not the voltage drop, which is more likely the problem.

Bob