Hi everyone,
I'm having hard time in specifying the secondary output of a DC/DC stage which is supposed to supply a set of half-bridges for a BLDC motor.
The half-bridges are switching +/-45V at 72 kHz for a max current on each phase of 2A peak-to-peak and from simulation we see how much current we are surging at each commutation and the time constants involved. The current drive on each phase is varying very slowly (few tens of Hz).
We clearly see the secondary output (sitting on another board and more than few cm away from the loads) cannot provide the necessary charge rapidly enough therefore it does not make any sense to specify it's output impedance up to 72 kHz.
In order to provide all the switching surge we are thinking about including local energy storage with ceramic caps close to the loads. We are also including a pi filter upstream to minimize the current ripple seen by the DC/DC secondary output but I'm having hard time to decide what to specify for each of these blocks:
- secondary output impedance
- pi filter characteristics
- local energy storage
Today we have 1. around few kHz (~10kHz) with few ohm (