Limit in-rush current for DCDC

Question

We are using a Isolated Fixed-Ratio DC-DC Converter from Vicor (http://www.vicorpower.com/documents/datasheets/ds_BCM4414xG0F4440yzz.pdf) that is powered through a 600VDC accumulator.

The DCDC powers the entire low voltage system of a electric vehicle. It's somewhere between 10-16 Amps depending on the state of charge and which systems are active. The DCDC has problems starting up and I believe it is because we are on the limit of the output capacitance for the DCDC and unplugging some systems at start-up seems to fix the problem. Usually we have to start it without cooling fans being connected, and then connect them once it has finished starting up.

I am waiting for parts to connect to the DCDC through the PMBus to monitor the current and other parameters at start-up.

I was wondering if there exist a nice solution for slewing the output current of the DCDC?

By the way, this is a student project if it seems like a strange issue.

Answer 1

You may be able to use a component specifically designed for this problem, the Inrush Current Limiting NTC Thermistor. In the following article, "How to Use NTC Thermistors for Inrush Current Limiting", it states:

An NTC thermistor limits an inrush current with its high initial resistance, and then its temperature rises because of energization and its resistance falls to a few percent of its level at room temperature, thus achieving a power loss that is lower than when a fixed resistor is used.

So, it's a temperature-dependent current-limiting resistor that heats up and then takes itself out of the equation. Just the thing to help a DC-to-DC converter start up into a challenging load. :-)

For greater efficiency, you could put a MOSFET having low Rds(on) around the inrush NTC, and turn the MOSFET on once the inrush current-limiting has been accomplished.

Answer 2

If all else fails, and if you can reliably start the thing up with peripherals unplugged and then plug them in later, then you could intentionally stage the turn-on of the peripherals. Just have them on timed relays (or relays controlled from a microprocessor) that sequence them on in a way that doesn't challenge the power supply too much.