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Motorcycle Flasher Circuit validation

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Joe_echo:
Evening all,

Would you kind people be able to pick over my design and let me know if there are any issues you can foresee.

I have a motorcycle that has been badly wired with all cables and wire taps over the place. I am integrating a single 12-14V DC supply from the battery into a PCB and having it feed the lighting circuits through the handle bar switchgear.

As part of this I have designed the attached Flasher circuit to supply the LED indicators, these draw around 1W front and rear. So 2W per side and grounded through the indicator itself. The indicator switch on the handle bar feeds the flasher output to the LED, so high side switching is required.

I have a 555 timer set to 50% duty cycle and a frequency of 1.5Hz, the output of which goes to the base on a PNP transistor, when the 555 is high the PNP doesn't conduct, when low the PNP is in saturation. Please ignore the Cap and resistor values in the schematic, they are just for the pcb design footprints.

The actual values are as follows.

R1 = 10K
R2 = 100K
R3 = 1K
R4 = 5.1K
C1 = 47uF
C2 = 100nF

Would there be an issue with the collector of the PNP effectively being floating unless the indicators are on and grounded?

bson:
Because of the gate pullup resistor the 12V supply will never float if switched off.

The easiest solution would be to power your turn signal circuit from the same 12V switched supply, so if it's not used it's not powered.

Is 12V from the battery terminals or rectifier/regulator?  If so, be aware it's going to be more like 11-14.6V with nasty transients, and not very kind to small-signal components.

Joe_echo:
The supply is from the battery not the regulator/rectifer. If needed I can protect from transients with a zener.

The 12v switched is the power supply rail from a NO relay that is switched using the ignition, thus when the bike isn't running the entire board is powered down.

Hopefully the below makes a little more sense. The relay output will also have the horn and a auxillary dash on it.

moffy:
You might want to drop the value of R3 just to ensure that the 2N2907 saturates fully.

Joe_echo:
Will do, will likely drop it to around 700 Ohm which will give around 15mA of base current.

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