Making high side switch 5V trigger 12V supply

Thread Starter

n8clamp

Joined Mar 29, 2020
2
Hi, electronics dabbler here, (only self taught, which is like being one's own lawyer) I am working on a reclaimed scooter that had previously been underwater. As such, all the electronics are shot, although hub motor and wiring harness are both fine. I put in a third party motor controller, and that all works fine, The last thing I am trying to get to work is the brake lights.
The scooter power source is 36/42V system, but the back running/brake lights are 12V. I know this because 1) there is a sticker on the inside that says 12V 2) when i feed them 12V they work. Two hots and a ground. One hot is brake one is running. I gave a buck converter from the 36V supply so I can get running lights no problem. What I want to do is have the brake hall sensor (5V system) trigger the 12V brake light system. because of the brake light load sharing the same ground wire as the running light load I have (perhaps wrongly) figured out I need a high side switch. I have looked here and elsewhere on ways to do it. I gather using an NPN transistor to drive a PNP transistor is the way to do it. like the diagram in this other thread. I try and make sure I have my collector straight form my emitter etc. but all I get is magic blue smoke.
https://forum.allaboutcircuits.com/threads/controlling-12v-circuit-with-5v-control-with-high-side-switch.140996/

I also tried something like the last diagram here: https://www.baldengineer.com/low-side-vs-high-side-transistor-switch.html
And I get intermittent behavior that "almost" works. or it works for a bit then stops, like a burned something up. like it turns on the brake signal but then it will not reliably go off.

I'm guessing the hall sensor is much like an SS49E (that was what was in a similar scooter brake assembly) but in any case it is a hall sensor. the generic controller does come with a dash that tells me when it thinks brakes are being applied, so that works as it should. I do not know the load of the brake lights, as there is no other markings on the housing and it is glued shut so I can't see the innards. I have confirmed 12.0V from buck converter. Hall sensor does not get above 4.5v if I recall, but I would be happy getting it to trip at a lower voltage as I want the brake light to go on more or less when any brakes are applied.
Please help. and feel free to assume you have to talk to me as a child, as I am clearly missing something.
 

Thread Starter

n8clamp

Joined Mar 29, 2020
2
sorry, that was supposed to be "from" not form. I just meant I made sure I wasn't plugging the transistor in backwards. I looked up data sheet so I knew which end was the emitter and which was the collector.
The diagram on the first thread I used same transistors, but used 2.2K ohm and 470 ohm instead of what it called for 2.7K and 680 i think, again, mainly as it was what I had on hand. I also used a different diode, as it was also what I had on hand.... Which upon looking that component up, may be my problem. it was a Zener diode, not a regular diode. Again, I suppose I should have known better, but there you go. So I guess I could order the proper diode and try again. Although I don't really know the actual load amps so I am not sure how to calculate the resistors. So any help on my second go round would be appreciated.
 
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