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email dave@allmon.com

To run the camera from a 12V source, a converter is required. Typically the noise from a switchmode converter is higher than the camera can tolerate. I chose to use a switcher as a pre-regulator, and use standard linear regulators for the final voltage regulation.

To keep the radiated noise down, the switcher is contained within a shielded enclosure inside the main enclosure. The pre-regulated +/- 17 VDC output then feeds the regulators mounted in the main enclosure.
 

The switcher uses a National LM2524D controller. I chose that part for two reasons - it is easy to use, and I am familiar with it. It is used as a push-pull converter. The transformer is driven by a pair of IRF-520 MOSFETS. A bit over the requirement, but the low on-resistance contributes to the 85% overall efficiency of the pre-regulator.
 

The linear regulator section is just a pair of fixed voltage regulators - one each 7815 and 7915 - bypassed out the kazoo.
 

The temperature control is a proportional control which uses the difference between the set temperature and the actual temperature to determine the amount of current to feed to the TEC. The gain is such that 0.1 degree of error will produce the maximum current in the TEC, while a 0.05 degree error will produce half of the maximum current. In this way, the temperature should be regulated to within 0.1 degree of the set point. The maximum current is adjustable.

The temperature is set and read via a digital panel meter which reads the temperature as a positive value - that is 0C will read "0", while -25C will read "25". The temperature range is 0 to -50 degrees C.

Two parallel IRF-520 MOSFETS drive the TEC. They are paralleled to decrease the on resistance at full-tilt. This is required since I am using a 12V TEC in place of the 7.5V TEC originally used in the camera. Power loss goes down with the paralleled devices.