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Nite Rider swift 300 Headlamp Problem-Solved!

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Nite Rider swift 300 Headlamp Problem-Solved!

Old 12-22-21, 01:29 AM
  #1  
cjenrick
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Nite Rider swift 300 Headlamp Problem-Solved!

i would charge this light up and the next day it be dead. what do i do?

trace out the circuit and take a stab at it.

couple of surface mount caps had given up the ghost. i just clipped them out and the light works like new.

those 0.1uf caps are probably to squelch noise or keep the circuit stable, but i notice no instability. squelch noise for what? maybe to limit interference blue tooth devices and such.

looks like they use a square wave generator with variable duty cycle to limit power for the various settings. this saves power over using resistors to vary brightness. the human eye responds to peak brightness and there is a storage factor going on, this is why we do not see frames during the movie or the old tv set flipping those 30 cps images.
i built a light a long time ago using the same concept with the variable square wave, only i had a pot instead of a momentary switch so that i had an infinite amount of brightness settings. the pot was mounted on the handlebars with a thumbwheel, very handy when you need ultra low light for sneaking past the ranger station to get to your favorite single track at night.
i also had a 10 segment LED bar graph that indicated battery life.
and a condenser mic was built in so that i could shout loudly into it during a vicious downhill and the brights would come on, why? so i did not need to ride one handed on a bumpy hi speed descent.


i do not feel bad about posting their circuit as there is a custom chip built for Nite Rider so nobody can clone this thing unless they reverse the chip which is highly unlikely.

if by chance you have had a similar failure, just clip out those caps (circled in red).

the battery is protected so that the shorted caps did not damage the battery. and that battery is available from 7 to 10 bucks on evilbay. be careful when soldering.

Last edited by cjenrick; 12-22-21 at 01:53 AM.
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Old 12-29-21, 10:43 AM
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U2 looks like a PWM switching driver made for exactly this purpose. From the view of the supply it's a pulsing load with high switching currents, so should be thoroughly decoupled, although 0.1F x2 (or is it one per IC) seems a little small. Are you sure one isn't larger? If not decoupled the high switching current spikes will go to the battery, and batteries don't like high ripple currents. It will shorten their life span significantly. The supply line will also form a loop current with the ground return, which acts as an inductor and antenna for emissions, which can be problematic and make the product fail emissions testing. Finally, the supply rail if the load isn't decoupled would ripple under the switching load, which means switching edges to the Q1 BJT (?) transition slower, increasing power dissipation in Q1.

Are you sure Q1 is a BJT and not a P-channel MOSFET? The latter would make more sense, but would also present higher switching currents.
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