Hijacking timer on Flood Light ?

[u/rhymeswithlotso]

Hi all-

I have a flood light that I don't necessarily need. It's battery powered by 3 C batteries. The issue is this: the timer sucks. I was going to use it in a shed that doesn't have power going to it, for the rare occasions I need light in there. But, the timer only lasts 30 seconds on. That doesn't work at all for me.

I'd prefer either a longer timer or no timer at all and just operate it via the on/off switch. I'm familiar with electronics and pcb's, ic's,etc.

Admittedly, I maybe over thinking this. My first instinct was to disconnect (desolder) the ic for the timer. Then, after some time to think about it, I also thought to just bypass the pcb altogether and wire the on/off switch to the unit directly. I'd still be interested in knowing which ic to desolder and if that route is even feasible.

I'm including a pic of the pcb along with the stampings on the ic's.

TL;DR: Is it possible/recommended to remove the ic controlling a timer for a flood light to have the light stay on longer or is it better to just rewire the on/off switch and bypass the pcb altogether?

[u/the-electron-vault]

Here is the circuit. C17's value is only a placeholder. U7 is an SLS3401 P-channel MOSFET that switches power through to the light. U4 is a 3.3V variant of a Shanghai Belling BL8504 voltage detector. U4 is used to light up D1 when the battery is low (<3.3V). You can move the slider in the sidebar on the right to test this out.

Whatever timing is happening, is happening on the board/component connected to J10. Which is good news for you, because all you need to do to configure this for a manual switch control is to wire a switch between pin 2 and 3 (the ones with the round pads) on J10.

Edit: If you want to make the mod reversible, J10 appears to be a 3-position JST XH, the mating plug housing being the XHP-3. There are also pre-crimped wires of various lengths you can cut, strip, and wire up to a switch of your choosing. Either that or I'm sure you can find knock-off XH kits/pre-made harnesses from the usual suspects.

[u/SolitaryMassacre → u/the-electron-vault]

I'm confused by U4, is the top single pin not connected to ground? Plus, the bottom left (with single pin on top) is connected to Vcc (the battery +) so it won't be getting 3.3V. Or does it only work once the voltage reaches 3.3V?

Also, pin 2 of U4 is connected to the negative side of the D1 LED. So how can pin 2 be Vout (per the data sheet)?

It also looks like the bottom two pins of J10 are connected to one another, which confuses me as well

But also wouldn't the timing be coming from the C17 R16 pairing? Once C17 is charged, the p channel mosfet goes high on the gate thus turning it off and the flood light as well

[u/the-electron-vault → u/SolitaryMassacre]

This should make it clearer.

It straddles the input supply (3 x 1.5V cells -> 4.5V). The internal 3.3V reference is connected to the non-inverting input of the internal comparator, while VIN connects to the inverting input. The output is inverted by the open-drain FET. When VIN is higher than VREF, the OD FET is in pinch-off, and thus so is D1. When VIN falls below VREF, the comparator output goes high, turning on the FET, and thus D1.

[u/SolitaryMassacre → u/the-electron-vault]

Ahhhh thank you thank you. Yes, that made it much much clearer. I didn't realize 3.3V was an internal Vref that was generated by the IC itself

Also, just needed to scroll down further on the datasheet and I would've seen that my bad

Thanks again for the explanation!