Motorbike light controller output stage - Page 1
Forum section: electronics / projects

author: SysAd
author_rank: Newbie
timestamp: June 26, 2021, 03:10:52 pm
content: Hi everybody,I'm designing a controller for my motorbike aftermarket led lights, those have position lights (or brake lights) built-in togheter with blikers, and here is not possible to have the position lights and blinkers on at the same time.My idea is to bypass the blinker relay and take the blinker switch status, control everything with an mcu (ATMEGA328P or PIC16F876A/628A), and to insulate it with optocouplers for I/O and an insulated DC-DC converter (TRACO POWER TDN 1-1211WI); My doubt is about the output stage: I thought to use the 6N137 and MJE5852G in the configuration below but i see that the optocoupler has maximum VCC about 7V, so I think to use the old 4N25 and leave the idea to use PWM and adopt simply ON/OFF. At this point will be better to use P-MOS instead PNP transistor?

author: Zero999
author_rank: Super Contributor
timestamp: June 26, 2021, 05:00:30 pm
content: The circuit can be simplified significantly. Ditch the BJTs and use a photovoltaic opto-coupler, such as the APV2111V and a MOSFET to switch the lamps.

author: Andreas
author_rank: Super Contributor
timestamp: June 26, 2021, 06:27:02 pm
content: Quote from: SysAd on June 26, 2021, 03:10:52 pmI would use a high side automotive switch.Something like a BTS621.With short cirquit protection.Why is there a photocoupler?with best regardsAndreas

author: Zero999
author_rank: Super Contributor
timestamp: June 26, 2021, 09:23:09 pm
content: Another simple solution is a relay, which can be driven by a small BJT, or MOSFET. It obviously needs to be rated for at leat 2A, at 12VDC. Note that it's more difficult to break DC, than AC, so don't assume an AC relay will have the same DC rating.

author: SysAd
author_rank: Newbie
timestamp: June 27, 2021, 04:54:30 am
content: Quote from: Zero999 on June 26, 2021, 09:23:09 pmI evaluated also relays but the occupied space is bigger than BJT/MOSFETQuote from: Andreas on June 26, 2021, 06:27:02 pmThe optocoupler is there to avoid spike interference to the MCUThanks for the replies, I'll check all the components datasheet

author: Zero999
author_rank: Super Contributor
timestamp: June 27, 2021, 11:50:02 am
content: Quote from: SysAd on June 27, 2021, 04:54:30 amUse a DC solid state relay, such as the VO14642AT.http://www.farnell.com/datasheets/2244849.pdf

author: SysAd
author_rank: Newbie
timestamp: June 28, 2021, 08:21:20 am
content: BTS621 is really nice it feature a lot of stuff like the open drain detection and short-circuit detection (really useful to detect open bulb or died led) and with 100mof Ron, I could simply couple the digital pins with HCPL2731.By the way, VO14642AT is a really simple and small device, with built-in insulation and 250mof RonI think I'll use the BTS621 in SMD package, it can drive two loads in one IC and has diagnostic output pinAnother doubt I have is about the ESD protection for the digital inputs, I'm taking in consideration to use TVS diodes to protect the optocouplers, could be useful or completely useless?Thank you very much for your suggestions

author: Zero999
author_rank: Super Contributor
timestamp: June 28, 2021, 04:19:05 pm
content: Quote from: SysAd on June 28, 2021, 08:21:20 amThe is actually better than that. It has two MOSFETs in its output stage. If they're connected in series, for AC operation, the on resistance is 250mΩ, but if they're connected in parallel, it's a quarter of that.QuoteGood choice.QuoteHow are the digital inputs connected? Presumably by opto-couplers? If so, a diode in reverse parallel with the opto-coupler's LED is a good idea, to protect it from reverse voltages.

author: Terry Bites
author_rank: Super Contributor
timestamp: June 28, 2021, 07:19:19 pm
content: Yeah, use a high side swich and save yourself from problems. eghttps://www.ti.com/power-management/power-switches/high-side-switches/products.htmlAvoid metting Joseph Lucas the prince of darkness.

author: SysAd
author_rank: Newbie
timestamp: June 29, 2021, 09:37:14 pm
content: Quote from: Zero999 on June 28, 2021, 04:19:05 pmCorrect, I think to use the same optocouplers and driving their led directly from the switch (directly connected to the battery) but I'v not idea about the tvs diode rating to consider in this scenario