Today's Message Index:
----------------------
1. 09:06 AM - Re: Next generation Crowbar OVM (Eric Page)
2. 03:06 PM - Re: Next generation Crowbar OVM (Robert L. Nuckolls, III)
Message 1
| INDEX | Back to Main INDEX |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Next generation Crowbar OVM |
nuckolls.bob(at)aeroelect wrote:
> ...go for any event exceeding 16.0+/-0.5Volts AND 500+/-0.50Seconds; well inside
design goals cited by DO160/MIL-Std-704.
> [...]
> I'd go for the whole 500 MSec enchilada.
Copy all; thanks. I'll update my schematic accordingly. Hitting that target will
be a lot easier than it was to hit exactly 3mS!
> At the moment, I'm rather enamored of the NEC NP110N03PUG FET. This little guy
will grunt over 200A at low temperatures with a Vgs of only 5V.
Looks good, but... does the 30V max Vds present a risk of avalanche breakdown
during a short-duration (i.e. not long enough to trip the timer) OV transient?
The BUK962 that I mentioned above has a max Vds of 60V and the transfer characteristic
chart looks even better.
But... depending upon what the crowbar pulse looks like, it might fall outside
the bounds of the Safe Operating Area chart for either of those FETs.
What is it that this task demands that isn't met by an available SCR?
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=511286#511286
Message 2
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Next generation Crowbar OVM |
>Thanks Bob, that's a handy device if one doesn't happen to have a
>zener on hand with desired voltage, even if it doee require two resistors.
>
>I'd forgotten that LM311's can have open collector outputs (when
>tying output transistor emitter to ground). Still have several in my
>old parts bins but more than four decades since last used one.
>
>I'm thinking the SCR is still the better choice for a crowbar
>circuit. But if we're changing the OVP circuit to a relay disconnect
>between alternator and battery/bus a FET or other device that can
>drive the relay may be OK. Assuming the OVP monitors alternator
>voltage and not bus voltage.
Those two voltages are generally the same as
long as we're talking about the main bus.
Yeah, the SCR configuration has some really
desirable features, namely it's an AC device
that inherently 'latches' in DC service. Don't
need to worry about gate drive latency.
So for the moment, I'm trying to stuff a more
modern NFET into that slot. But if I could find
a suitable SCR not likely to disappear in the
next few years . . . yeah, let us lament the
evolution of selenium rectifiers.
The 'crowbar' approach that opens the control
power source yields a kind of universal configuration
in the spirit and intent of the original CBOVM-14
products. Yet it may well be that 'progress'
in component evolution makes that a
goal-too-far.
Good input sir!
Bob . . .
////
(o o)
===========o00o=(_)=o00o========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
================================
In the interest of creative evolution
of the-best-we-know-how-to-do based
on physics and good practice.
Other Matronics Email List Services
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|