Simulated circuit does not work as real circuit does

[madmart]

Hi this is a noob question, I am evaluating version 12.

I am trying to simulate a circuit that works fine in real life but not in simulation. Each section works but not altogether!

Any suggestions?

[Kev_R]

Hi madmart, 

Thank you for posting to our forum. My name is Kevin, I am an application's engineer for NIUK and I will be assisting you with this query. I have taken a look at the circuit you attached, can you give me some more information. What are you expecting to see? What is the expected behavior?

I look forward to hearing from you 

Kind Regards

[madmart]

hi Kevin,

the cct is from a step up voltage generator. R8 is in place of a transformer primary which steps up from 24v to 760v.what should happen is Q1 should turn on until the current through the sense resistors R1,R2,R3 bias Q2 on and turns Q1 off Q3 is an override control to stop the oscillations.

a pulse waveform should be visable at the scope chnl A.

the individual parts work as expected but not the circuit as a whole ,any suggestions would be good!!

madmart

[madmart]

kevin attached is a clearer diagram.

[Kev_R]

Hi madmart, 

When you say the individual parts work, what do you mean? What are the individual parts? 

Do you have a circuit diagram, of your real world circuit? So that we can compare the real world (working circuit) with the simulated circuit. 

I look forward to hearing from you

[madmart]

hi kevin,

S1 is the output of a micro it starts when low and stops Q1 oscillatingwhen high. When the current through R8 is sufficent the voltage on Q2 base turns Q2 on and shorts the gate of Q1 effectivley to zero ,turning off Q1 until the charge on C1 dissapates and Q1 turns back on and repeats the cycle.If the micro output is high then it stops the oscillation.

The circuit is part of a high voltage generator which steps up the 24v supply to 760v to charge a 30uF 1200v cap.

There is voltage feedback from the 30uF cap to stop the oscillations whe the voltage is reached.

i have included another diagram to clafiy the end circuit.

so we should have at the drain of Q1 a repetative square wave until it is stopped by Q3

r8 value was chosen to give enough current to generate the voltage to turn Q2 on.

madmart

[madmart]

Kevin

can you look at my last post my trial is about to run out!

[Kev_R]

Hi madmart, 

Sorry for the delay inmy reply.  

You have set this circuit up (physically) and everything works? Are you able to send me, a circuit diagram of the actual circuit. So I can ensure you have placed down the correct components.

I do not see any reason why this circuit is not giving you the correct behavior, I would like to compare it to the actual circuit to find out what is different. 

I am able to run your circuit, and when I switch S1 on and off I am seeing a square wave on the scope. Is this the correct behavior?

How much longer do youu have on your trial?

Kind Regards

[madmart]

hi kevin,

the circuit is in production as part of some equipment, many hundres are installed.the circuit is correct although i replaced the transformer with a resistor , it should just switch on and off producing a square wave on the scope and repeat until stopped.for me it only works once, the mosfet turns on the current flows and when the voltage across the sense resistors is sufficent Q2 turns on and switches off the mosfet Q1.

there are 10 days left on the trial. i wanted to see how the program dealt with this circuit to compare results that i get in real life!

best regards

madmart

[madmart]

okay if your cicuit shows a square waveon the scope then why does it not on mine??

madmart