(updated due to remark of ChrisStratton).
I am wondering if it is a good idea to use two regulators in series.
What I want: using 2 12V Nema17 motors (using 12V, 1.7A each). Using a microcontroller board (STM32F103C8T6 in most cases, 5V input voltage). However, I'm not sure what to add (except DMX possibly also a nRF24L01+ 2.4 GHz transceiver), multiple LEDs (5 mA each). So assume I need max. 200 mA.
Than my power dissipation if I would use a single 7805 would be (12 V - 5 V) * 0.2 A = 1.4 W
I heard above 0.8 or 0.9 W a heatsink is adviced. However, what if I use two regulators in series:
- 7809: power dissipation: (12 V - 9 V) * 0.2 A = 0.6 W
- 7805: power dissipation ( 9 V - 5 V) * 0.2 A = 0.8 W
Would this work? And if so, should I place them with some distance not to heat each other?