Does anyone know of methods to have effective isolation between logic and power (handling inductive loads, such as small motors, solenoids, etc.) in hybrid solutions where it is possible to power the board either by battery (so the entire circuit must consume as little power as possible) or by an external power supply.

I usually see two approaches used in industrial applications:


1. Isolate the logic supply from the power supply via isolated DC/DC converters, using the isolated part to supply the loads.
2. Isolate the logic supply from the power supply via isolated DC/DC converters, using the isolated part to supply the logic.

Communication between the two isolated parts is done via optical coupling or via isolated gate drivers.

In my case, I did not find practical solutions to maintain high reliability by anticipating interference from inductive loads, especially when PWM-driven.

Isolation via isolated DC/DC modules is incompatible with a
battery application as the standby current will be within ten milliamperes
at best.

Is anyone familiar with this type of issue?

To do goal, the solution would be to have the ability to control inductive loads (2A) in PWM at a typical frequency of 25Khz combined with fully protected MOSFET solutions that are easy to find on the market. This is for reasons of PCB space.

 

Usually, the load uses more power than the logic, so that efficiency points toward isolating the logic portion. IN ADDITION, the amount of isolation required depends on how sensitive the logic is. so always an evaluation is in order. Understand the logic sensitivity and the load's disruptive levels.

WHAT would be controlling the PWM signal?? A variable pot with a knob works well, control from a processor gets more complex. The simple scheme uses a556 (Dual555timer )and a high gain t0-220 power transistor. The first timer generates a ramp voltage while the second timer serves as a comparator.