MOSFET regulated thermoelectric cooling circuit -PCB

[geoland]

Hi. This is my first post on this forum.

I have been working on a temperature regulated thermoelectric cooling system to cool the CMOS sensor of a Canon DSLR camera for astrophotography work.

I'm using aTeensy 2.0 (Teensyduino) to pwm a logic level n-channel mosfet (very low rds on ~1.3milliohms), to switch current through the TEC. EMI has been a significant problem interfering with camera electronics. This is partly solved by bonding the camera chassis and the copper conducting plate fixed to the back of the camera sensor and then connecting to ground.

I resolved the remaining EMI (mosfet switching), with the use of ground planes and voltage planes instead of traditional snubber circuits, which were not at all effective for this application. Separating analog and digital ground sources, as well.

I want to run heating supplies off the same board using 3 switchable and trimmable voltage regulators - 5 pin SIP. These have an on/off logic pin and I want to activate heating at 6 Celcius - Arduino code is no problem. The Eagle CAD PCB attached shows SMD pads overlayed with vias to create holes - this is a hack because there was no part in Eagle, and I have not yet learned how to create parts.

datasheet http://www.ledsales.com.au/pdf/MDC_OKR-T-1.5-W12-C.A01.D5-214787.pdf

I am looking for guidance on how to integrate these switchable voltage regulators into the circuit so that they are controllable. The prototype board is not working and I have damaged one Teensy - there seems to be a feedback problem which is preventing the Teensy USB and the board from operating.

The solution might be a simple matter of isolating the inputs to the voltage regulators with diodes. However before continuing, at risk of breaking another board, I would really appreciate feedback on what I have created here. Another symptom is positive voltage in the analog ground section. I didn't have these issues prior to adding the switchable regulators.

Thank you - looking forward to a response

EDIT: added schematic

 

[geoland]

I have edited the post and it should be clearer. I have also added a second PCB image showing the components and a link to the voltage regulator datasheet.

 

[Headroom]

A schematic would actually be more helpful than a board layout in this case.
As to available parts libraries, Adafruit and Sparkfun provide pretty extensive free Eagle libraries for a wide variety of packages/parts.

What do you mean with "controllable" in reference to these DC/DC converters ?

 

[geoland]

Thanks for the reply.

Controllable - I want to turn them on and off, based on ambient temperature.

I will post a schematic shortly.

 

[geoland]

Added schematic. No access to home computer for a while, so cant get to Fritzing or Eagle. Working from Android using Droid Tesla SPICE program - some parts not available and improvised with TMP36 sensors and DC-DC converters. Also had to do a little artwork, post screenshot, to group Teensy pins and DC-DC converter pins. The 5V supply is powered from the 12V.

Analog ground and digital ground are separate and tied with a 100R resistor. Common ground is Teensy board. This configuration interferes with USB (Teensy external power set up - trace cut).

Will this do for the exercise.