OVP for battery powered circuit - Page 1
Forum section: electronics / beginners

author: rakeshm55
author_rank: Regular Contributor
timestamp: December 19, 2018, 02:45:14 pm
content: I look forward to implementing an over voltage protection (OVP) for my power input circuit.My max input current requirement is 5A ...... Input voltage range is 24V to 33.6V..... Components at the input side can operate upto 42V....My plan for over voltage is to have a fuse followed my unidirectional TVS diode....fuse -----> TVS diodeI tried searching for TVS diodes with a reverse standoff voltage of 33V ...Diodes start their breakdown operation at about 36V and clamping voltage at 53V... I would like to blow before achieving 42V..... How to do this?? Choosing a high Peak to peak current device will it solve the problem??Any suggestions ....Is there any other solution ??

author: mvs
author_rank: Frequent Contributor
timestamp: December 19, 2018, 08:25:41 pm
content: Quote from: rakeshm55 on December 19, 2018, 02:45:14 pmYou may use SCR crowbar circuit instead of TVS.... It can be build with precision threshold and it will clamp to few volts only.

author: David Hess
author_rank: Super Contributor
timestamp: December 20, 2018, 01:17:46 am
content: A shunt regulator has a much sharper knee than a TVS and can be more accurate. Or a shunt regulator can be combined with an SCR to make a very accurate crowbar circuit which is a simplification of a reference and comparator driving an SCR crowbar.

author: Zero999
author_rank: Super Contributor
timestamp: December 21, 2018, 04:54:56 pm
content: Are you looking for a circuit to blow the fuse, when a certain voltage threshold is exceeded? A crowbar would do that but beware they can be prone to nuisance tripping. One way is to use both a crowbar and a clamping circuit. The crowbar can trip at a higher voltage, than the clamp, but have an RC circuit, giving a delayed response so it will go if the voltage clamp is on for a long time. See the thread linked below:https://www.eevblog.com/forum/beginners/2n7000-strange-behaviour/msg1185894/#msg1185894

author: spec
author_rank: Frequent Contributor
timestamp: December 22, 2018, 10:03:57 am
content: Hi rakeshm55Quote from: rakeshm55 on December 19, 2018, 02:45:14 pmAs the other members say, TVS' breakdown voltage is not terribly accurate, compared to 1% zener diodes for example, but sufficient for your application I would suggest.The Vishay 5KP33A through hole or SMC5K33A surface mount, Transorbs will probably do your job:https://www.vishay.com/docs/88308/88308.pdfhttps://www.vishay.com/docs/87742/smc5k10a.pdfJust to explain, the 5KP33A/SMC5K33A Transorbs have maximum clamp voltages which looks rather high on the data sheet, but this clamp voltage is measured at 93.8 amps. At 5 amps, the clamp voltage would be much lower, low enough to protect your equipment I would think.The other thing is that Transorbs are designed to catch fast voltage transients so they will provide good protection from fast over voltage-transients which probably would not blow the fuse. In the forward direction 5KP/SMC5K Transorbs behave like 100A diodes, so they will give good protection from fast negative transients too.Although the 5KP/SMC5K Transorbs will handle 5kW for a short duration, they will only handle around 4W continuous in practical terms, so your idea of proceeding the TVS by a fuse is a good one and will work fine.You have not asked about this, but you may also be interested in resettable fuses:https://www.littelfuse.com/products/resettable-ptcs.aspxhttps://www.littelfuse.com/~/media/electronics/datasheets/resettable_ptcs/littelfuse_ptc_rline_catalog_datasheet.pdf.pdf