FEDEVEL
Platform forum

Gaskoin , 10-11-2024, 12:13 PM

Hi!
I am desining a rocket computer for flight stability, altitude measurement, tracking, recovery and so on. I need all components to be relatively small so the less ICs the better. Power lines looks here like below:

- 1s to 4s LiPo battery input (3,7 V - 14,8 V)
- 500 mA 3,3 V rail for MCU, sensors and telemetry
- 4A 6 V rail for servos

I have considered few solutions but I do not know what is the best approach to take here:
- 2 x buck-boost for each rail
- 1x buck-boost for 6V and then LDO for 3.3 V. I would need some higher current IC as TPS63070 is 4A only
- 1x double-output DC-DC converter (couldn't find the IC though)
- resign from 1s LiPo support and use only buck converters with one of above setups as they are usually higher current rated. I want to avoid that if possible

Schematic attached for broader view. Thanks!

Robert Feranec , 10-11-2024, 03:51 PM

I would probably use separate power supplies, both powered from battery - just to be sure currents from servos will not influence the control circuit. but this is not the kind of circuit I normally design, so maybe someone else can also share their opinion. In both cases I would probably use switching PWR as the input voltage range is wide.

QDrives , 10-11-2024, 08:00 PM

If your batteries give more than 6V, why would you add a buck regulator?

Gaskoin , 10-11-2024, 08:54 PM

not all of them do, and if they do buck is for downregulating voltage

QDrives , 10-11-2024, 08:57 PM

I know what a buck regulator does. My rhetorical question is why you want to add one for the servo motors?

Gaskoin , 10-11-2024, 09:22 PM

I do not understand. I've added buck-boost regulator for 3,7 up to ~15V regulation.

Gaskoin , 10-11-2024, 09:22 PM

as servo needs around 6V

User , 10-12-2024, 09:03 PM

His battery voltage can go down to 3.7V if I understand correctly

QDrives , 10-12-2024, 10:28 PM

Yes, but a servo is like an inductor. You can use PWM to 'reduce' the voltage.
What you cannot do is increase it. But voltage for a motor is like speed and current equals torque.