Solution for large inrush currents

[Landsbytosse]

Hi there,

I have a power supply with a filter, diode bridge and a large cap to hold the voltage close to DC. A NTC is mounted to minimise inrush but this is not enough due to its lose (Thinking Green )

When powering up large inrush currents are seen. Is there a cheap and easy way to elimnate this problem.

Using Relays acroos the NTC is not an option due to pysical sice of components.

Can i use a Triac triggered byt my 5V supply or uP? Or is a SCR the way to go? If anyone has a active solution or ider im all ears.

Cheers

 

[FvM]

Inrush Limitier

A relay is usually smaller than a triac, considering the required heat sink. A triac has a least 1 V drop, it's losses can't be
actually expected lower than of a NTC.

A couple of "oversized" MOSFET in an anti-serial circuit can work as an almost ideal electronic switch.

 

[M!k]

Re: Inrush Limitier

There's a nice application note from Motorola: Active Inrush Current Limiting Using MOSFETs (AN1542)
Unfortunately this document isn't available from ON anymore.
Found it here: https://application-notes.digchip.com/010/10-13155.pdf

 

[Tahmid]

Inrush Limitier

Hi,
You should use a relay and upon power up, use the microcontroller or control circuit to isolate the load from the supply using the relay for a specified time, x seconds, after which you turn the relay on.

You could use a triac or SCR, but I think the relay is a better choice.

Hope this helps.
Tahmid.

 

[Landsbytosse]

Re: Inrush Limitier

Hi,
You should use a relay and upon power up, use the microcontroller or control circuit to isolate the load from the supply using the relay for a specified time, x seconds, after which you turn the relay on.

You could use a triac or SCR, but I think the relay is a better choice.

Hope this helps.
Tahmid.

The problem with this solution is size, i will not fit inside the case. So its not an option.

I thinkt the optimal solutions would be a MOSFET used as a relay to short a resister after X mS, but i have yet to get it to work when coupled up to the 5V supply insted of a microprocessor.

 

[FvM]

Inrush Limitier

You should mention the circuit's current rating. A reasonable solution depends on it, particularly required power component sizes. I also wonder where you get 5V DC. Do you use an additional transformer power supply?

 

[Landsbytosse]

Re: Inrush Limitier

I draw around 0.9A.

I have a microprocessor and 5V to control start of different fans. No trafo is used just a SMPS.

But the large cap needed after the filter to supply these fans draws very large current killing off Relays used to power the system on/turn it off.