Strategies for powering an ATtiny micro controller and 40W peltier from mains


I'm trying to power an ATtiny1634 at 5VDC and a 50W peltier element at 12VDC. The microcontroller will, amongst other things, turn on the peltier via a 5VDC non-latching relay. I want to use an embedded SMPS that will convert mains power to DC suitable for powering the aforementioned two devices. Also, I would prefer all components except the peltier to be PCB mounted as the components need to fit within a tight space.

  1. What different approaches are there to powering these devices?

    In terms of simplicity I'm leaning towards a simple 5VDC 1W SMPS to power the micro controller and a 12VDC 40W SMPS for the peltier. The problem I have with this approach is that it becomes prohibitively expensive to put together. For PCB mounted power supplies in the 40W range, manufacturers like Tracopower charge ~USD 95, add in the 5VDC SMPS and that's over USD 100 just to power the devices.

  2. Would using the 40W SMPS to power both sub-circuits be a viable option? If so, how?

It is still expensive to spend the USD 95 for the 40W SMSPS but it is an option if push comes to shove.

Best Answer

Would using the 40W SMPS to power both sub-circuits be a viable option? If so, how?

Yes, that sounds likely. Your microcontroller circuit is likely to draw very little current. Unless energy efficiency is paramount, this means you can use a cheap linear regulator like a 7805 to get 5V from a 12V supply.

The biggest draw on the 5V circuit is likely the relay coil. To solve that problem, I'd suggest not using a 5V relay. Instead, use a 12V relay, and drive it via a transistor, like this:


simulate this circuit – Schematic created using CircuitLab

This way, the current necessary to run the relay coil is drawn from the efficient 12V supply, and your 7805 won't get hot.