Buck driver board
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TorchBoy
Flashlight Enthusiast
A buck driver probably isn't what you should be looking for, since a single Li-ion cell won't have enough voltage. The best buck drivers have about 0.5 V overhead - that's the amount the battery voltage is over the Vf of the LED - so a single cell runs out of voltage pretty quickly for a typical LED driven by a buck driver.
The AMC7135 has just 0.12 V overhead, so it's very probably more suitable. It's a linear regulator, not a buck driver, and drops out of regulation gracefully. They can be very efficient with a single Li-ion driving a single white LED, and are very popular in that situation.
I see that many of the boards linked by old4570 are boost boards, not buck boards or buck/boost, and have limited or no information on efficiency. You can find buck/boost boards (they do both, so can cope with battery voltages above or below the LED Vf) but if a driver just boosts it'll be direct drive when the battery voltage exceeds the LED Vf. That might be bad because the LED may try to draw too much current at the supplied voltage, causing itself to burn out. An unprotected Li-ion cell might also be damaged.
Another reason a boost driver would be bad to use with an unprotected Li-ion cell is because draining one too much (to too low a voltage) can also damage it.
You might like to consider what sort of regulation you want. Constant current until the battery is dead, or a gradually reducing current as the battery dies, etc.
The AMC7135 has just 0.12 V overhead, so it's very probably more suitable. It's a linear regulator, not a buck driver, and drops out of regulation gracefully. They can be very efficient with a single Li-ion driving a single white LED, and are very popular in that situation.
I see that many of the boards linked by old4570 are boost boards, not buck boards or buck/boost, and have limited or no information on efficiency. You can find buck/boost boards (they do both, so can cope with battery voltages above or below the LED Vf) but if a driver just boosts it'll be direct drive when the battery voltage exceeds the LED Vf. That might be bad because the LED may try to draw too much current at the supplied voltage, causing itself to burn out. An unprotected Li-ion cell might also be damaged.
Another reason a boost driver would be bad to use with an unprotected Li-ion cell is because draining one too much (to too low a voltage) can also damage it. You might like to consider what sort of regulation you want. Constant current until the battery is dead, or a gradually reducing current as the battery dies, etc.
old4570
Flashlight Enthusiast
Its a mix / bit of this n that ...
No8 / I use a lot . Most of the others are new ..
No8 / I use a lot . Most of the others are new ..
Justin Case
Flashlight Enthusiast
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- Mar 19, 2008
- Messages
- 3,797
As TorchBoy clearly presented, a buck driver generally will have too high of a voltage overhead to run in full regulation on 1xLi-ion. There are a few low voltage overhead buck drivers that might work -- they all have an overhead of about 0.5V. With an XP-E, you might get lucky and get a low Vf of around 3.2V at 1A drive (note, the XP-E is actually spec'ed at a max of 700mA; if this is an issue, you might consider an XP-G instead). Thus, a relatively large sized Li-ion like an 18650 probably can hold its voltage under load long enough to get some useful run time in regulation. But a smaller cell like a 16340 might not. And if you get a more typical Vf of say 3.3V to 3.4V at 1A, then you start to cut into your run time in regulation even when using big Li-ions.
As a concrete example, I can tell you that the buck driver in choice #5 in post 2 uses a buck IC with a recommended min input voltage of 5V. That isn't going to work very well with 1xLi-ion. I've tested several other buck drivers (different from choice #5) also based on the same buck IC and I've typically gotten a voltage overhead of about 1V to reach regulation. That's too much for 1xLi-ion.
For any of the boost drivers that were suggested in post 2, they won't work well either with 1xLi-ion. The driver won't be in boost mode, except at the end of the Li-ion's run time life when its voltage under load falls below the LED's Vf. But you probably won't want to drive the Li-ion to such a low voltage anyway, which is bad for cycle life. Instead, you will be direct-driving the XP-E for probably 100% of the battery's operational life. And with the low Vf of that LED, you will be overdriving it by a fair amount. See this post for example. If you have an XP-E with Vf of about 3.4V at 1A drive current, then pushing the XP-E with 3.7V (the nominal voltage for a Li-ion) means over 2A drive current. The XP-E will be very unhappy with that unless you have really good thermal management.
I've used many AMC7135-based drivers in 1xLi-ion applications and they work very nicely -- fully regulated output from 1xLi-ion with long and efficient run time. I've used these drivers to run Cree XR-Es, XP-Es, and XP-Gs. Most of these were single LED setups but some of them include triple XP-Es and XP-Gs.
As a concrete example, I can tell you that the buck driver in choice #5 in post 2 uses a buck IC with a recommended min input voltage of 5V. That isn't going to work very well with 1xLi-ion. I've tested several other buck drivers (different from choice #5) also based on the same buck IC and I've typically gotten a voltage overhead of about 1V to reach regulation. That's too much for 1xLi-ion.
For any of the boost drivers that were suggested in post 2, they won't work well either with 1xLi-ion. The driver won't be in boost mode, except at the end of the Li-ion's run time life when its voltage under load falls below the LED's Vf. But you probably won't want to drive the Li-ion to such a low voltage anyway, which is bad for cycle life. Instead, you will be direct-driving the XP-E for probably 100% of the battery's operational life. And with the low Vf of that LED, you will be overdriving it by a fair amount. See this post for example. If you have an XP-E with Vf of about 3.4V at 1A drive current, then pushing the XP-E with 3.7V (the nominal voltage for a Li-ion) means over 2A drive current. The XP-E will be very unhappy with that unless you have really good thermal management.
I've used many AMC7135-based drivers in 1xLi-ion applications and they work very nicely -- fully regulated output from 1xLi-ion with long and efficient run time. I've used these drivers to run Cree XR-Es, XP-Es, and XP-Gs. Most of these were single LED setups but some of them include triple XP-Es and XP-Gs.
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old4570
Flashlight Enthusiast
There are many drivers out there that will maintain 1000mA output , 2 mode , 3 mode , 5 mode , and single mode ..
No 8 does not overdrive , it maintains 1A as long as it can .. Yes use protected batts or AA's with it .
I have run XP-E @ 1A and they seem to handle it OK , just dont go over 1A , ive gone as high as 1.4A , they just get hot .
700mA
2mode
3Groups
I have used the 2 mode , its a nice driver .
No 8 does not overdrive , it maintains 1A as long as it can .. Yes use protected batts or AA's with it .
I have run XP-E @ 1A and they seem to handle it OK , just dont go over 1A , ive gone as high as 1.4A , they just get hot .
700mA
2mode
3Groups
I have used the 2 mode , its a nice driver .
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TorchBoy
Flashlight Enthusiast
That's 1,000 mA output - current, not capacity. Similarly for the 700 mA driver.
Justin Case
Flashlight Enthusiast
- Joined
- Mar 19, 2008
- Messages
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The 2 mode and the 3 groups drivers are all AMC7135-based multimode drivers. The 2 mode driver looks like it uses an ATMEL controller to implement the multimodes. The 3 groups driver looks like it uses a PIC controller.
Have you used the "700mAh" driver? I'm guessing it is a direct drive PWM controller, and the product description is a little bit "off".
For driver #8, have you verified that it is a constant current driver? It looks like CC may be implemented via what looks like a PIC controller and possibly a current sense resistor on the side with the spring. A challenge appears to be selection of the boost-buck component values (e.g., inductor, capacitor values) for Vout. The problem is that Vout isn't a constant. It would be interesting to test this board's performance when hooked up to different LEDs of varying Vf.
Have you used the "700mAh" driver? I'm guessing it is a direct drive PWM controller, and the product description is a little bit "off".
For driver #8, have you verified that it is a constant current driver? It looks like CC may be implemented via what looks like a PIC controller and possibly a current sense resistor on the side with the spring. A challenge appears to be selection of the boost-buck component values (e.g., inductor, capacitor values) for Vout. The problem is that Vout isn't a constant. It would be interesting to test this board's performance when hooked up to different LEDs of varying Vf.
old4570
Flashlight Enthusiast
There you go
old4570
Flashlight Enthusiast
The 700mA driver , no ... Its new I think , and I have no need of 700mA drivers , but for a XP-E ? , so I included a link to it .
Some of those new drivers look interesting .
