Over Voltage Protection Crowbar Circuit

OK, it seems to work well with an LTSpice simulation:

I had missed the second page of your pdf. But I still think the circuit should be made more robust.

I read the fuse blower discussion, and agree that it's best, as you also

concurred.

But I don't really see the need for your circuit, and for all that complexity it might as well include regulation and overcurrent protection.

Paul

It exists because of a request by a poster on this group.

It is simply an extension of a charge/discharge controller chip I did for a LiIon battery charge.

Then, with a little bit of sensing circuitry, you can prevent over charging or discharging. ...Jim Thompson

You're getting a bit off-topic for me. I avoid administrative bullshit where possible. If you can do it simply by inflating an estimate, there's skin off anyone's nose.

Again, you probably got you paid for. Hiring someone for a project after a few minutes, because he 'exuded competence', is a pretty good example of administrative bullshit, if ever I've heard it. Competence is demonstrated, not discharged through the skin, or smelled.

Next time, just widen your search, based on recommendation and realize before-hand that one man does not a power design lab make and that other inputs are required before you can switch from out-sourcing to in-house development of some kinds of hardware.

RL

On a sunny day (Sun, 2 Dec 2012 10:56:05 -0800 (PST)) it happened snipped-for-privacy@gmail.com wrote in :

fuse -

There is likely no universal solution. Question to be asked first is: WHAT do you want to protect. I remember a technician wiring the mains to a 24 volt bus of a big PLC system. It killed many many expensive PLC cards. If your crowbar only kills primary circuit, then it does NOT protect the load against external voltage sources. And in installation this is a much more likely error condition than in normal operation a voltage going high. Also it depends on the kind of supply, in case of a switcher with output transformer separation, maybe you can simply switch the control chip off as protection against over voltage.

eradicate/prevent.

Transient load testing isn't exactly rocket science; the whole thing sounds fishy to me.

'Failing to act' early and the use of the term random doesn't suggest that a lot of expertise went into field or return failure analysis.

Sounds more like tight money and toxic communications - not an unusual combination.

RL

( Not a great demonstration of proof-reading skill here.)

If you can avoid administrative bulshit by pricing yourself out of it, then there's no skin off anyone's nose.

Again, you probably got what you paid for. ........

Inheriting a design group and their work is not an easy job. It takes great skill, to avoid losing people, product and customers.

RL

eradicate/prevent.

And since when has there been a flyback controller chip without current sense shut-down protection or provisions for slow-start? Sounds like junk to me too.

It does, thanks for noticing.

I've been thinking about how to respond to some of your other inputs. I've decided that the polite thing to say is, "I'm speechless."

Yup.

Two-hundred-buck PSU toast - pick up the phone.

Ten thousand buck load toast - fifteen aspirin headache.

Pas du tout.

The purpose of the crowbar is to protect the load. When the SCR fires, the load voltage drops to the SCR's Vt in a few microseconds. The load is protected.

How long after, or whether at all, the fuse ruptures, depends on the PSU. If it has foldback protection, the fuse (selected for full-load current) will handle the reduced current. If there is no such protection,or it has failed, the fuse will rupture after t>I^2t/I^2. What happens to the PSU afterward depends on its design and how well its input is protected.

The PSU is the sacrificial item, not the load. We must assume that it has been designed or selected with all possible fault conditions of itself considered.

The purpose of the crowbar is to protect the load by 1) reducing output to voltage to zero AND 2) activating the overcurrent protection.

If you don't blow a fuse or trip a breaker, you don't have a crowbar. And f or each of those devices you need a crowbar current in excess of 10x pass c urrent rating unless you want to wait the better part of a second in the ca se of a fuse and minutes in the case of a breaker. If your source does not supply that kind of current then you need an energy storage device to do it .

has

Your work may be of that caliber and some others around here, but to project that competence on all other engineers and their management is surely specious.

?-)