Hey all, I have a question for you U2 gurus/experts:
...So, I'm having this conversation last night with another fellow CPF'er about his Surefire U2. No doubt we're agreeing the U2 per design has a boost circuit. Whether Vin from the battery is 1x 18650 (4.2V) LiIon or 2x CR123s (6V), Vf at the led is typically always higher for even the lowest available xxxS (maybe -R?) bin Lux V.
But then he's also trying to convince me that the circuit can act in buck mode, at the lower levels.
I've always thought of the U2 as a boost circuit only, so I'm arguing back, and although it makes perfect sense to me in the 1x LiIon battery config (with Vin always lower than Vf, whatever the dropped-down level may be), I can't really prove my point with the 2x CR123s original battery config, since Vf on low setting can be lower than Vin (He's measured his Vf at the Led at the lowest setting (100mA?) to be around 5.2V < 6V).
"Vf is lower than Vin and the output is regulated, so it's a buck!", he says.
As I can't really disagree with him, I still don't get it then that you couldn't use 3x CR123s or maybe 2x LiIons, or heck, even maybe just swap the led for a LuxIII then?
Wouldn't a real boost/buck converter allow that much range? Or is the circuit in the U2 doing much more that meets the eye? Does somebody know how the circuit actually behaves in those lower levels, does it switch to buck mode if needed?
Maybe if PK could chime in...
Please post your thoughts on this as you probably have a better clue than I do right now! Thanks.
...So, I'm having this conversation last night with another fellow CPF'er about his Surefire U2. No doubt we're agreeing the U2 per design has a boost circuit. Whether Vin from the battery is 1x 18650 (4.2V) LiIon or 2x CR123s (6V), Vf at the led is typically always higher for even the lowest available xxxS (maybe -R?) bin Lux V.
But then he's also trying to convince me that the circuit can act in buck mode, at the lower levels.
I've always thought of the U2 as a boost circuit only, so I'm arguing back, and although it makes perfect sense to me in the 1x LiIon battery config (with Vin always lower than Vf, whatever the dropped-down level may be), I can't really prove my point with the 2x CR123s original battery config, since Vf on low setting can be lower than Vin (He's measured his Vf at the Led at the lowest setting (100mA?) to be around 5.2V < 6V).
"Vf is lower than Vin and the output is regulated, so it's a buck!", he says.
As I can't really disagree with him, I still don't get it then that you couldn't use 3x CR123s or maybe 2x LiIons, or heck, even maybe just swap the led for a LuxIII then?
Wouldn't a real boost/buck converter allow that much range? Or is the circuit in the U2 doing much more that meets the eye? Does somebody know how the circuit actually behaves in those lower levels, does it switch to buck mode if needed?
Maybe if PK could chime in...
Please post your thoughts on this as you probably have a better clue than I do right now! Thanks.