Re: IR2110 gate driver issues.

Terry Given wrote:

> Pooh Bear wrote:
> > Winfield Hill wrote:
> >
> >
> >>Pooh Bear wrote...
> >>
> >>>I'm using an IR2110 high and low side gate driver in a smps that
> >>>I mentioned some time back in the group under the thread 'should
> >>>I use a SG3525'.
> >>>
> >>>I've had some 'odd' power device failures that I didn't expect in
> >>>entirely benign situations, such as the half bridge output simply
> >>>driving the primary of my transformer.
> >>
> >> Device failure meaning damaged components, or meaning, a FET that
> >> didn't do what you expected under a certain circumstance, but yet
> >> wasn't actually damaged.
> >
> >
> > Device going short. Either just the high side device or both. I've
> > established to my satisfaction that there are 2 failure scenarios.
> >
> > 1. Ramping the voltage down on the variac ( quickly ) . E.g. after
> > I've been testing @ line voltage. There's a bzzt and the high side device
> > goes short. I suspect a mixture of the UVLO mismatches and possible
> > 'mis-track' of the main bus and supervisory rail. Doesn't happen if I
> > ramp the volts down slowly ( or so it seems ). Hence my thoughts about
> > the droop of the rails.
> >
> > 2. Both devices fail - this first happened after I'd been running the
> > transformer primary only for about 1/2 hour just to establish likely
> > practical core temp rise. It ran fine for ages - I turned my back to do
> > some calcs and the thing bzzt'ed at me. It was still working so I thought
> > I was hearing things ! Did it terminally 3 mins later. Looking closely
> > I'm seeing the high side drive terminate prematurely under circumstances
> > I have yet to exactly determine the cause of. Maybe insufficient
> > bootstrap C ? Was looking at this last thing today. Will investigate
> > further tomorrow wrt all the drive waveforms.
> >
> >
> >
> >>>I realised that it happened a couple of times when I wound down the
> >>>input volts ( I'm supplying the board via a variac and isolating
> >>>transfomer for development ).
> >>>
> >>>The IR2110 has undervoltage lockout. Fine! I checked it carefully
> >>>today and the UVLO for the low side and high side aren't linked.
> >>>Indeed a careful look at the data *** does indeed show that
> >>>there's no connection. The low side drive activates at about 8V
> >>>and the high side about a volt higher.
> >>
> >> IR has to separately detect the low-side and high-side voltages,
> >> because the latter is the voltage across the flying capacitor.
> >
> >
> > True. I wish they'd OR the UVLOs though.
> >
> >
> >> The mismatch you observed sounds good: the high side should stop
> >> working well before the low side, thereby preventing any shoothro
> >> current, which could be disasterous.
> >
> >
> > I'd prefer it if both terminated together !
> >
> >
> >
> >>>Needless to say this creates 'issues'!
> >>>Anyone here used this part and care to comment?
> >>
> >> Let's hear about your issues.
> >
> >
> > Well, the devices failing for one !
> >
> > The 2110 UVLO is sensitive to line ripple. It appears to result in a
> > effect that's like weird duty cycles when it's hovering around the UVLO
> > threshold(s).
> >
> >
> >> BTW, recognizing the need for low-voltage protection, and the need
> >> for a benign response to low-voltage conditions, you could easily
> >> add a comparator operating at lower voltages, plus shutoff gates
> >> managing the IR2110's three logic inputs, per your special needs.
> >
> >
> > That's what I imagine I may indeed have to do. Or I can shutdown the
> > 3525.
> >
> > Was curious if anyone had experienced similar when using the 2110.
> >
> > Cheers, Graham
> >
> > p.s. I now understand why smps design has always had a reputation for
> > being 'tricky'. Also why when quizzed about them - some vendors go all
> > shy when talking about the reliability of smps versions of their audio
> > amps ! I have no plans to put anything into production that's marginal.
>
>
> what caps are you using for your bootstrap supplies?

Box polyester film. You gonna say I should be using ceramic ?

Graham

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