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fchouza
Joined: 07 Jun 2008
Posts: 3
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 01 Oct 2008 15:25 High voltage linear power supply (0-400V) |
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Hello, im building this power supply:
 
In the simulation with PSpice the circuit works well, but when i build it i have this problem:
With out charge i set the output voltage at 100V (voltage setting input at 1.25V). When i charge the circuit with 5K, the output voltage down to 95V(aprox).
Then, with out charge i set the output voltage at 300V (voltage setting input at 3.75V). When i charge the circuit with 5K, the output voltage down to 275V (aprox).
Apparently, the regulation is not working well...
Possible solutions?
Thanks a lot
PS: Sorry for my English...
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FvM
Joined: 22 Jan 2008
Posts: 2635
Helped: 431
Location: Bochum, Germany
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| 01 Oct 2008 16:22 High voltage linear power supply (0-400V) |
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I can't imagine, that the circuit works well in simulation. It's using a P controller with small gain, thus supply and load regulation are rather poor.You can change the controller into a PI type by addig a series capacitor to R4.
The current limiting circuit isn't connected correct and has no effect, B.T.W.
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fchouza
Joined: 07 Jun 2008
Posts: 3
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| 01 Oct 2008 16:40 Re: High voltage linear power supply (0-400V) |
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| FvM wrote: |
| I can't imagine, that the circuit works well in simulation. It's using a P controller with small gain, thus supply and load regulation are rather poor.You can change the controller into a PI type by addig a series capacitor to R4. |
Thank you! Where i can read more about P and PI controllers? What is the size of the R4 series capacitor?
I attach the PSpice design...
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FvM
Joined: 22 Jan 2008
Posts: 2635
Helped: 431
Location: Bochum, Germany
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| 01 Oct 2008 17:06 High voltage linear power supply (0-400V) |
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| Add an IPULSE source to your simulation and try yourself. I guess, 1 nF to 10 nF can work, but it depends e.g. on the output load.
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fchouza
Joined: 07 Jun 2008
Posts: 3
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| 03 Oct 2008 14:10 Re: High voltage linear power supply (0-400V) |
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I put a 2.2n capacitor and the power supply works good!  (thank you!!!). But i have another problem. With 0V input, i set the LM317 bias for 0V output. After, i increment a little bit the control voltage input and i have 18V output, then i increment another little bit the control voltage and the output voltage down to 10V, then i increment the voltage control input and i have a normal operation.
I have something like this (the voltages are approximated):
 
Added after 33 minutes:
Sorry, the problem is not the power supply. I generate the voltage control with a resistor divider voltage, apparently the potentiometer is not working well. I measured (again, with a more precise tester range) the voltage control again, and the same curve is repeated in the input control voltage. I will buy another potentiometer and post results.
Thank you for the help .
PS: The current output of the power supply is about 200 mA. I'm not sure if parallelize two MOSFET for improve the power dissipation may be a problem...
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