Soft start query

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#1 Soft start query

Post by iansr »

From what I’ve seen most soft start modules comprise an NTC and a relay that bypasses the NTC once the trafo is charged up as it were. My query is why is it preferable to bypass the NTC? I’m sure it will still offer some resistance once up to temperature, but enough to mean the PS caps are not kept topped up? Or is there some other reason for taking the NTC out of the circuit?
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#2 Re: Soft start query

Post by Nick »

Assuming the power supply is doing more than keeping the caps charged up, i.e. something is drawing power and discharging the caps, the power supply will have to supply current, that current will pass trough the NTC and generate heat and unwanted losses in the process. The goal is to keep the power supply impedance as low as possible.

Though if its bipased with a relay then not sure what advantage a NTC will offer. I just use some power resistors and bipass them with a relay after a few tenths of a second.
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