Interesting Q3 driver observation

While doing a emitter swap on a Nuwai Q3 today I discovered something new. The driver board is giving off heat even without a emitter. I desoldered the old emitter and wanted to verify polarity on the star before installing the SSC P4. The phone rang and I left the body with battery in it and the switch on. When I returned, I noticed the body was quite warm. I thought I had shorted out something, so I checked with a multimeter. Everything was fine and the new emitter was installed without a hitch. I was probably in a incandescent frame of mind thinking no bulb = no heat.

Still learning:twothumbs

btw I found copper plumbing tubing is .032 wall thickness. I used a 9/32 hole punch to make a spacer for the SCC P4. The slug is perfect for the emitter to sit on. A whack with a hammer reduced it to .030:naughty:. I turned down the base of the reflector by .031 on the lathe to compensate for the spacer.

Try this with other boost driver boards and you will find out, that most of them would get hot too ... but only for a couple of seconds and then never again .

The driver of the Q3 is simple and obviously forgiving, but it´s always a very bad idea to fire up a boost driver without a load, unless it´s explicitly stated that it has a open-circuit-protection. Most of the boost drivers, including "good" ones like fatman, vip & badboy, will get damaged, if you try somethings similar with them ...

The Q3's Zetex driver is different from most boost drivers. Its difference is also the reason for its lower efficiency than most boost drivers. Unlike most boost drivers where current is only drawn from the battery on the on cycles to the LED, the Q3's circuit continues to sink current to gnd during the off cycles also. Basically, when the LED is on, the output transistor is off, but to stop current to the LED, the Zetex chip turns on the output transistor shunting the current to gnd, so it's always on with respect to the driver circuit itself.

jsr said:

Unlike most boost drivers where current is only drawn from the battery on the on cycles to the LED, the Q3's circuit continues to sink current to gnd during the off cycles also.

Click to expand...

oooh, that's an ugly picture. Any upside to all that except low price ?

So will a lock out tailcap that breaks the ground connection stop the battery drain during "off" mode?

Thanks for the info guys!:thumbsup:

Guess I'll check polarity before removing the old emitter from now on. I'm too green to know current was being drawn by the board even without a load.

NA8 - no, no benefit aside from cost.

nein - I think you misunderstood. The driver doesn't draw current when the light is off. A Switch Mode Power Supply of any type has on and off cycles and essentially pulses voltage (and resultant current) to the load. When there is no voltage pulse, that is considered the "off" cycle of the driver. When you click the light off, everything is off and there is no current draw.

jsr said:

nein - I think you misunderstood. The driver doesn't draw current when the light is off. A Switch Mode Power Supply of any type has on and off cycles and essentially pulses voltage (and resultant current) to the load. When there is no voltage pulse, that is considered the "off" cycle of the driver. When you click the light off, everything is off and there is no current draw.

Click to expand...

Ah thanks for the clarification, I think I get it now. Is it like PWM pulses at a frequency on-on-off but the Q3 does it onLOAD-onLOAD-onGROUND?

Yeah, similar to PWM. Not sure what you mean by on-on-off. The output of a switch-mode-power-supply is always on-off-on-off... What CPFers refer to as "current regulation" is a filtered output to smooth out the on-off transitions. Current regulation is still PWM. So the Q3's circuit goes onLED-onTransistor-to-GND sequence. But from the battery's standpoint, current is always being drawn.