cupoftea
Advanced Member level 5
Hi,
We are doing a Dual Synch Buck for 18-30vin to 26vout and 400W and 450kHz.
We have a FET with parallel resistor to do inrush limitation at the input at startup.
My and my boss originally put forward a circuit which had a mini boost converter which provided the hi side drive to turn on the
inrush FET after the inrush had already rushed in. There was then a delay circuit, and then the Synch Buck was enabled.
In this way, the inrush fet never conducted any high current when it was in the transitioning linear region, and the inrush resistor
never ported any power current of the synch buck.
But the owners forced me and the gaffer to change to a much cheaper inrush circuit involving a charge pump which works from the switching of the synch buck fets...but what this means is that whilst the inrush fet is in the linear region, a high startup current pulse ends up going through it.
This causes loads of dissipation in the inrush fet.
So a cheap double BJT + Zener circuit was added to make the synch buck controller disabled until 15V was on the input capacitors.
But the problem then, is that if the customer ever ends up with a Vin which lingers around 15vin, then the buck controller will be constantly
enabling and disabling, and making the inrush fet suffer repeating high current pulses when its in the linear region.
So do you have any cheap inrush modules which don't suffer this?
I mean, the cheap mini booster circuit works fine, but they
say its too expensive.
We are doing a Dual Synch Buck for 18-30vin to 26vout and 400W and 450kHz.
We have a FET with parallel resistor to do inrush limitation at the input at startup.
My and my boss originally put forward a circuit which had a mini boost converter which provided the hi side drive to turn on the
inrush FET after the inrush had already rushed in. There was then a delay circuit, and then the Synch Buck was enabled.
In this way, the inrush fet never conducted any high current when it was in the transitioning linear region, and the inrush resistor
never ported any power current of the synch buck.
But the owners forced me and the gaffer to change to a much cheaper inrush circuit involving a charge pump which works from the switching of the synch buck fets...but what this means is that whilst the inrush fet is in the linear region, a high startup current pulse ends up going through it.
This causes loads of dissipation in the inrush fet.
So a cheap double BJT + Zener circuit was added to make the synch buck controller disabled until 15V was on the input capacitors.
But the problem then, is that if the customer ever ends up with a Vin which lingers around 15vin, then the buck controller will be constantly
enabling and disabling, and making the inrush fet suffer repeating high current pulses when its in the linear region.
So do you have any cheap inrush modules which don't suffer this?
I mean, the cheap mini booster circuit works fine, but they
say its too expensive.