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I'm sorry for the bugger up with the .rar files...as I said I packed them with winrar then renamed the extension to zip....I didn't give this a 2nd thought.
Current thru the heater device is dependent upon the PWM mark-space ratio ...which is adjusted by the pot. Basically adjusting this gives a higher or lower average level to the gate of the FET which is thus turned on more or less.
Which in turn supplies more or less Current thru the heater.
Since the ambient temperature is lower than the OTA then we need to constantly add energy to the heaters to keep dew at bay.
Place your heater straps behind the optics on the OTA so the heat is supplied to the OTA and re-radiated at an IR energy levels to the optics. I prefer the commercial dew heater straps.
This design is about to be updated soon. I have found I can source the newer international Rectifier current feedback FETs in Australia. These are designed for Automotive operation...ie switching lamps and are ideal for this design. They also have current feedback input pin...an on die measurement of the current thru the FET.
This means I can set max current parameters with 1 resistor..... do not need a fuse!
Stay tuned.
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