Maybe I'm not looking hard enough, but it's a long time since I saw a power supply design including a crowbar. Is it just an idea that's just come and gone? If that is the case, any idea why? It seems like a good last-ditch protection mechanism for gear with a small overvoltage margin, which includes nearly all digital stuff.
Is there another protection mechanism against regulator failure that's applied nowadays, or it just a case of wearing the risk?
"Bruce Varley"
** Many plug-pak style SMPSs have zener crowbars on the output.The zener is intended to fail short if the output voltage goes high and so protect the load.
** Still common enough to see damaged ( written off) digital devices when the SMPS goes haywire.I have personally added SCR crowbars to the +5 volt supply on Yamaha digital effects processors - notably SPX90s and REV5s cos the SMPS is a notorious lemon.
Most PC power supplies have over voltage protection in the form of DC rail monitoring and shut down if out of range.
.... Phil
I had a Data General minicomputer which had a built in UPS with crowbar over voltage protection. It had eight 2 volt Gates cells in series parallel to give 8 volts which was series regulated down to 5 volts through 14 power transistors in parallel. It had a 200 amp HRC fuse in line with the buss bars and across the buss bars was a large SCR. It had a switch mode power supply rated at 5 volts at 135 amps.
On Thu, 11 Aug 2011 23:44:07 +1000, Barry OGrady put finger to keyboard and composed:
Nova? Eclipse?
I still have several of those PSUs, although mine have +/-12V and -5V rails.
- Franc Zabkar
On Thu, 11 Aug 2011 18:41:20 +0800, "Bruce Varley" put finger to keyboard and composed:
Many devices have overvoltage protection in the form of TVS (transient voltage suppression) diodes. These work like zeners, but they respond much faster. In fact I answer about 3 questions per week in various forums where the OPs have overvolted their external hard drives with a
19V laptop adapter. The fix in the majority of cases is to simply cut out the shorted 12V TVS diode.See
- Franc Zabkar
I don't recall the model but it was a rack style with two "washing machine" hard drives.
Mine had a separate power supply for the 12 volts.
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