Search for board voltage filter 12V automotive - Page 1
Forum section: electronics / repair

author: snapper
author_rank: Contributor
timestamp: August 28, 2022, 10:28:03 pm
content: HiThe following problem: With an engine control unit for an injection systemit happens again and again that a fixed voltage regulator type TLE4274 5Vis defective although there is a TVS diode on the on-board voltage side is used.The TLE is said to be able to handle an input voltage of max. 40V !?Unfortunately the ECU is completely potted so that you can only swap the 5v regulatorby cutting a window in the aluminum housing (see video) and major internal changesto the circuit are not possible, a circuit diagram does not exist either.I'm looking for an extern filter that reliably eliminates interference in the vehicle electricalsystem such as load dump, overvoltage, superimposed AC voltages, negative voltages, etc.(component, assembly group, circuit diagram...)Anyone have an idea?greetings

author: SMdude
author_rank: Frequent Contributor
timestamp: August 28, 2022, 11:06:31 pm
content: You could fit another TVS externally, but you really need to track down the source of the fault, not put another bandaid on it.It is most likely caused by a voltage spike during/after cranking.Check the grounding and power connections to your starter motor and vehicle body/engine, any connections on your battery terminals, your battery ESR could also contribute if it is old.Where is your main ECU power connected to? Battery or starter? Check and clean all main connections.The only other thought is to put a TVS or zener on the 5v output of the Reg in case something is getting it from the regulated side.I really hate stuff that is potted like that.

author: David Hess
author_rank: Super Contributor
timestamp: August 28, 2022, 11:51:09 pm
content: I would use a power MOSFET source follower circuit to limit the voltage to 12 volts. The MOSFET would require about 15 volts of gate drive which could be provided by a small capacitor-diode charge pump. A circuit like this can be designed to hold off 100s of volts with a suitably large power MOSFET.

author: snapper
author_rank: Contributor
timestamp: August 29, 2022, 12:12:05 am
content: @SMdudeI think it's very unlikely that there will be an interference voltage on the internal 5v side of the ic's.I once attached the circuit diagram of the scooter, I noticed that the 12v relays(3x switched via mosfets within the ECU, fuel pump, cooling fan and aux-relay, starter relay switched via aux-relay)have no protection diode!The supply voltage for the ECU comes directly from the battery via a 5A fuse.Since I don't know the exact data of the TVS DIODE, the question now is which one can I use externally,are there unidirectional and bidirectional and what voltage?

author: snapper
author_rank: Contributor
timestamp: August 29, 2022, 12:50:47 am
content: Quote from: David Hess on August 28, 2022, 11:51:09 pm"power MOSFET source follower with small capacitor diode charge pump" sounds good,but unfortunately that doesn't help me, I'm unfortunately not a circuit designer, if so I need a circuit diagram for it.THX

author: SMdude
author_rank: Frequent Contributor
timestamp: September 01, 2022, 10:45:51 am
content: If it is a 12v system I'd suggest trying around 20v given that the Regulator that fails is rated up to 60v, surely this should protect it.The worst that will happen is it blows and the regulator blows again.