[SOLVED] Problem with circuit simulated with LTSpice IV

[torakaru]

Dear folks,

I have been trying to simulate the DC behaviour of a voltage protection circuit with LTSpice, but I cannot achieve the expected results. If you take a look, the VBAT_CLAMP output voltage should be clamped at +15V due the zener diode D2, but in my simulation this is not happening (the output is near the same as the input voltage; near +20V), and I cannot understand why :sad:.

Could you help me, please?

FYI, you can download the free LTSpice IV from:

https://ltspice.linear.com/software/LTspiceIV.exe

And my circuit (to avoid you to re-draw it) from the attachment. Or take a look to the picture:



Thanks a lot in advance by your support!

 

[FvM]

The circuit surely won't work as a clamp, but should switch of the output above about 15.5 V input voltage. You'll need to connect at least a resistance at the output to see the effect.

 

[torakaru]

I tried your suggestion and it works! (Now I can see how the output voltage(Vbat_clamp) is switched off above Vbat=+15.5V) ;-)

Thanks a lot!