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Ahhhhhh......Jo. I have been working on a solution. In my case, the noise/lines is generated by the switching of the MOSFET gate.
Make sure you have grounded the camera chassis and the cold finger and the case.
The capacitor is preventing the MOSFET gate from going low enough to switch off. This means the MOSFET is being driven linearly and gets hot as well as being difficult to maintain temperature control.
A solution that seems to be working is to keep the MOSFET gate from going too low when in its low state. I have had success by setting two voltage sources to the gate. One 5V and the other ~2.5v and alternating them on and off at about 1khz. The MOSFET runs cold.
PWM works much the same by keeping the low voltage above zero. I will post the circuit following more testing.
Last edited by rcheshire; 25-11-2013 at 10:32 PM.
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