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| Protecting against Voltage Regulator failure? |
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| 2N3055:
Board was speced at 5V for dispation not maximum input voltage. If you put in 9 V unreg you prbably fed it 12V. So 5-3.3V=1.7 V. 12-3.3=8.7V. . That is 5 times more dissipation than speced. I wonder why it did not smoke within 60 seconds. This board should be powered by 5V stabilized PSU. Like the USB ones or one of bricks. Even high quality ones by Meanwel are cheap. And you can use it for all other uses too. |
| Ian.M:
--- Quote from: magic on March 05, 2019, 09:26:13 am --- --- Quote from: Ian.M on March 04, 2019, 11:33:13 pm ---This is easy for rails 5V and upwards - see the classic TL431 + TRIAC crowbar circuit in the full TL431 datasheet - but with only a 3.3V rail, a TL431 wont have enough headroom to trigger a TRIAC reliably. --- End quote --- There are similar chips with 1.25 reference which may replace the 431 in low voltage applications. Something like TLV431, TLC431, TL431LV, I don't remember. Multiple types exist from many vendors. Some tolerate only 6V, others 12V, maybe even 18V. --- End quote --- Yes, but a TLV431 is only rated for 10mA Ik max vs 100mA for a TL431, so its nowhere near as good at firing large TRIACs. One can work around that by adding a PNP medium power transistor as a saturated switch between the TLV431 and the TRIAC to increase the available gate drive, which also lets you use ordinary SCRs as the gate drive is then positive going. |
| magic:
--- Quote from: Ian.M on March 05, 2019, 10:08:33 am ---TLV431 is only rated for 10mA Ik max vs 100mA for a TL431, so its nowhere near as good at firing large TRIACs. One can --- End quote --- ... spend a minute in TME parametric search to come up with vendors better than TI, like SC431L and AZ431L :P |
| perieanuo:
Hi, a good way to protect is an voltage supervisor who cuts power (5V from usbport in your case) when limits are exceeded.quick and efficient,there are some implementations like this on some projects, but is overkill for your board. You can protect cheapies like this one with archaic methods like puting diodes all over the place to cut some induction,reverse polarity covered sometimes partially in the chips but with limited power absorbing diodes Regards,pierre Envoyé de mon iPad en utilisant Tapatalk |
| Zero999:
--- Quote from: Ian.M on March 05, 2019, 10:08:33 am --- --- Quote from: magic on March 05, 2019, 09:26:13 am --- --- Quote from: Ian.M on March 04, 2019, 11:33:13 pm ---This is easy for rails 5V and upwards - see the classic TL431 + TRIAC crowbar circuit in the full TL431 datasheet - but with only a 3.3V rail, a TL431 wont have enough headroom to trigger a TRIAC reliably. --- End quote --- There are similar chips with 1.25 reference which may replace the 431 in low voltage applications. Something like TLV431, TLC431, TL431LV, I don't remember. Multiple types exist from many vendors. Some tolerate only 6V, others 12V, maybe even 18V. --- End quote --- Yes, but a TLV431 is only rated for 10mA Ik max vs 100mA for a TL431, so its nowhere near as good at firing large TRIACs. One can work around that by adding a PNP medium power transistor as a saturated switch between the TLV431 and the TRIAC to increase the available gate drive, which also lets you use ordinary SCRs as the gate drive is then positive going. --- End quote --- A couple of points: Only a short pulse is required, so there's no harm in exceeding the current rating of the TLV431 by a fair margin. A surge of 100mA or so for the short length of time it takes to trigger the TRIAC will not damage it. It depends on the TRIAC. There are sensitive gate TRIACs which can adequately trigger with under 10mA. https://www.onsemi.com/pub/Collateral/MAC15S-D.PDF |
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