Electronics > Beginners

help, oscilating circuit

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GigaJoe:
Hello,

here is my el. DC load:
it oscillating very stable, around 140KHz , even if I increase back-feed caps (C1, C4) to 0.3uf it oscillating on 2KHz. Need some help.
C5,R3 -no effect
I'm out of ideas, unfortunately, due to lack of experience, microscopic brain, no imagination, and so ..
Upd: with R2 = 100K , I'm able to enforce oscillating it in a simulator, about the same as on real circuit,  but it means not enough speed to change mosfet condition. or I'm not right ...



MarkF:
You might try putting a 100 \$\Omega\$ resistor in series with the MOSFET gate.

Similar to my Elec Load.  I used a large 6.2K resistor to protect the Op-Amp.
The 10nF capacitor in the feedback loop also helps with oscillations.

   

MarkF:
I totally missed that you ARE using Op-Amps.  Your schematic is very hard to read.  It would be helpful to use the standard Op-Amp symbol and place them is sequence from left to right instead of vertical.

I've seen the feedback loop with the RC in series instead of in parallel.  I found that I didn't need the resistor.


Edit-   Your shunt resistor seems to be very small.  My 0.33 \$\Omega\$ shunt is designed for 0.5V at max across it for a current range of 0 to 1.5A

Kilroywashere:
I dunno if this helps  But when I want to know how something is working before i build it i like to use this 

https://www.falstad.com/circuit/

Its been really helpful to me and i have learned a lot

Its really a great site

You can build your circuit on that and adjust it ....


I hope that its helpful !!!

Kilroywashere:
Also if your making an oscillating circuit Why not use a 555 timer? they have a  fixed frequency of up to 500kHz do they not?

Maybe its not good enough .... i dunno

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