Does anyone know of an easy mod for this driver before I make it DD only? It’s from a CrazyFire C4 that can take 18650 or 2xCR123A and has 5 modes. It only does 1A on 18650 and about .5A on 2xCR123A.
The buck PS control chip is the QX9920. Datasheet here: http://www.qxmd.com.cn/?product/QX9920.html
Piggyback some additional resistors on top of the 0.18ohm resistor if you want to increase the output current. This will reduce the effective sense resistance. The formula for output current is I = 0.25V / R. Put another way, each additional 1 ohm resistor in parallel will add 250mA to the output.
Thanks! Does that also mean I can safely bridge it to get DD and still have other modes?
I’ve never actually done that, but I suppose if you bypass the sense resistor with either a big blob of solder or a short copper wire, it will effectively become direct drive with modes. Before you do this, make sure you REALLY want to do this. How many LEDs are there? What is the power source? You don’t want to burn out the LEDs.
Ronin42 - that uses the same chip. The sense resistor is the one marked R500. I can see there are actually two resistors stacked, most likely to get 0.25ohm for the sense resistance and result in a 1A output. The same advice applies.
Yes, you can bridge it and keep modes, but after bridging I wouldn't use it anymore with anything but a single 18650. Also, if you've got an aluminum MCPCB you will probably fry it with a hot cell.
My small iron quit working and I ended up destroying it with a larger one as solder went where I didn’t intend. I lost patience trying to remove it and messed up the traces. :_( It still might be fixable with some helping hands/magnifying glass and smaller tip.
Thanks
Whoops! Been there, done that. Depending on how many traces got destroyed, you may want to just chuck it and get a new driver. They’re fairly cheap.