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Forum Index : Electronics : TL431 crowbar problem
| Author | Message | ||||
| davef Guru  Joined: 14/05/2006 Location: New ZealandPosts: 499 |
I built the precision crowbar circuit found on this page here During testing on a 28V 1Amp bench supply I noticed a 20us pulse when power was applied to the circuit. This is not good a 0.5A test fuse blows! I found that placing a 22uF electro from Vcc to ground "fixed" this issue. Is this a manifestation of contact bounce? Now, when I connect it to my 24V 440Amp/Hour battery a 5amp fuse blows instantly. Has anyone successfully connected a crowbar circuit to a 24V battery without it blowing up? |
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| VK2MCT Senior Member  Joined: 30/03/2012 Location: AustraliaPosts: 120 |
A pulse response graph for the TL431 in the TI specs, seems to show that the device output ramps up from 2v to 2.5v approx over 0.5us. Maybe there are enough pulses when cct is connected, to extend this time enough to conduct the transistor. John B. |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
John, Didn't realise, until now, that the post had been edited! Investigations have focused on this start-up issue. My solution is to put a 1K resistor across the fuseholder pins so that when you connect it to the 24Volt battery (still with the 22uF electro on the supply) that the ramp-up of the supply voltage is slow enough not to trigger the TL431. After 1 second or so, I then plug the fuse in. I assume that in most applications the supply voltage comes up slow enough not to cause this problem ... or one would expect some fixes out there on the internet! Perhaps, this suggests using a more modern device, ie Linear Technology power management devices. Perhaps here or the LTC4366-1 Cheers, Dave |
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