LTspice voltage controlled switch not working for me

Thread Starter

AlbertHall

Joined Jun 4, 2014
8,860
In the attached asc file I was attempting to use a voltage controlled switch in a push on/push off switch. The switch is open at the start and so the transistors should start in the 'off' condition - but they don't. If I disconnect the switch from R2 then the transistors are off.

What am I doing wrong?
 

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Thread Starter

AlbertHall

Joined Jun 4, 2014
8,860
One problem seems to be the MOSFET. I selected a BSS84 which works much better than the default pmos.
The other thing I found is that if I select start DC supplies at 0V it works as I would expect.
Does that setting also affect the pulsed source feeding the switch?

[EDIT] I have also changed the default NPN to 2N3904 but that didn't change anything.
 

Thread Starter

AlbertHall

Joined Jun 4, 2014
8,860
hi A,
On this correct circuit, how can we help with any changes.?
E
It seems to be OK now. Just some fine tuning to do. The principal problem was the MOSFET.

The other thing I found is that if I select start DC supplies at 0V it works as I would expect.
Does that setting also affect the pulsed source feeding the switch?
Can you answer that question?
 
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