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Hall effect ignition weird behaviour

tomcer34

Nov 20, 2021
18
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Hi, my circuit is working when is of the bike and when I put it on, there is weird behaviour. It's giving signal properly for 3s~20s. Then output of hall effect stays high, even when magnet is close to it. I'm using not gate, because hall effect which I'm using has sinking putput. Hall effect is 55100-3H-02-A. I tried even pnp style ignition, but it had same problem. For power I'm using L7805c and L7812c linear regulation. When I unplugg ignition coil it's working properly.
51737-0ffb0e2d925b2cde9f9490d285d2292f.jpg
 

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Harald Kapp

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Your circuit may experience adverse effects from the flyback voltage of the ignition coil. When the power transistor is turned off, a high positive voltage will occur at the common connection of the ignition coil (collector of the power transistor). This voltage peak may feed back into the circuit and create havoc.
Usually the power transistor would be protected from the high voltage spike by a flyback diode as e.g. in this variant of the driver circuit.
Sometimes a so called snubber capacitor is used instead of the diode as e.g. in this circuit.
Plus I found also variants which use both a snubber capacitor and a diode.
Also adding a bypass capacitor across the 5 V power supply (100 nF) may help to keep noise away from the 5 V circuit. A high capacity electrolytic capacitor (100 µF ... 1000 µF, whatever you have at hand) is also a good idea to supply current peaks without dropping the 5 V.

Btw: I rotated the image for better readability.
 

tomcer34

Nov 20, 2021
18
Joined
Nov 20, 2021
Messages
18
Your circuit may experience adverse effects from the flyback voltage of the ignition coil. When the power transistor is turned off, a high positive voltage will occur at the common connection of the ignition coil (collector of the power transistor). This voltage peak may feed back into the circuit and create havoc.
Usually the power transistor would be protected from the high voltage spike by a flyback diode as e.g. in this variant of the driver circuit.
Sometimes a so called snubber capacitor is used instead of the diode as e.g. in this circuit.
I used power darlington. There is protective diode. Is it possible even with diode there is flyback voltage? I will try what u suggested.
Thank u very much.[/QUOTE]
 

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Harald Kapp

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I see. I didn't look into the datasheet :(
I hope one of the other suggestions improves the circuit.
 
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