High Voltage LED buck for ebikes

[georges80]

So, after seeing a request for a high voltage capable LED driver I figured I needed to look into appropriate driver electronics and whether there was a market. Looks like the ebike crowd has been left a little behind so off I went to do some R&D and we now have - wait for it.... ta da... CC_HV (Constant Current High Voltage).

Capable of driving up to 1A of LED load (fully current regulated) with input voltage of up to 70V.

I did some quick tests with nominal 750mA output and the efficiency looks pretty reasonable. More tests to do, but a couple of spot values:

2 LEDs (6.64V total Vf) at 770mA with 39.6V input I measured 86% efficiency
4 LEDs (14.0V total Vf) at 770mA with 39.6V input I measured 94% efficiency

Obviously the efficiency improves as the input/output voltage differential comes closer - typical of all buck or boost converters.

The driver is single sided and can be thermally mounted to a heatsink using the same kind of thermal pad material as used on hipFlex.

Current selection is via 2 onboard sense resistors and I plan to support 750mA and 1A as standard shipping options, but obviously many different combinations are possible.

Of course we must have photos

Close up of the board, R2/R3 are the paralleled sense resistor locations. The board is 1.2" x 1" and components only on the top side:

I need a higher input voltage test, 39.7V is the max my HP supply will put out. I'll need to series it up with my other power supply:

Test load of 4 LEDs:

Ok, hookup the 2 power supplies in series for some serious testing

39.7 + 18.99 = 58.7V total. Efficiency now close to 93%

Still happily driving the 4 series LEDs:

cheers,
george.

 

[VKruger]

This would be great for me. I have 3 ebikes; 2 @ 36v and 1 @ 48v. I have to charge 3 separate batteries every night on my home built commuter. 36V LiFePO4 for motor, Li-poly for trinewt bar LED, and nicd for HID helmet light. I only use 7 of my 14 Ah of my 36v each day, but can almost drain the light batteries during the short days of winter. Powering everything from one battery with 2 high voltage bucks would be great. Can't wait to buy a couple.

This would also help me convert my wife's 36v ebike to 48v and still use all the accesories (horn and lights).

 

[georges80]

Yep, I think it should be popular with the ebike folk. Saves having to run separate batteries or having to use a DC-DC converter to drop the ebike battery voltage down to a LED driver friendly voltage.

I've put up some preliminary tech info on my website:

http://www.taskled.com/techcchv.html

cheers,
george.

 

[ktronik]

Nice work in this new board...

I do a lot of ebike work...

the voltages we use are: 24v,36v,48v is most popular & 72v (2x 36v packs)

if its @ 70v max, then you count out the 72v guys...not a heap of people running 72v +, so maybe does not matter, but do I know guys that use 100v & 122v as well...

http://www.endless-sphere.com/forums/

this is the best forum for e-bike stuff I reckon...

best

Ktronik

 

[georges80]

Nice work in this new board...

I do a lot of ebike work...

the voltages we use are: 24v,36v,48v is most popular & 72v (2x 36v packs)

if its @ 70v max, then you count out the 72v guys...not a heap of people running 72v +, so maybe does not matter, but do I know guys that use 100v & 122v as well...

http://www.endless-sphere.com/forums/

this is the best forum for e-bike stuff I reckon...

best

Ktronik

I think once you get up to 70V+ you really don't want wiring running around the bike to the front lights - we're getting into lethal voltage range and I certainly would rather a DC-DC converter to step things down to a safer level for general distribution at that point...

cheers,
george.

 

[ktronik]

Good point, don't want anyone to get hurt...

48v is the most popular anyway, so all good... :thumbsup:

K

 

[ktronik]

Q: So if max input is say 65v (spec on your site) any reason why I could NOT run up to 15 LEDs in series?? (65v / 4v + overhead) or am I missing something here??

K

 

[georges80]

Q: So if max input is say 65v (spec on your site) any reason why I could NOT run up to 15 LEDs in series?? (65v / 4v + overhead) or am I missing something here??

K

15 x 3.5 x 1000mA ~53W total output. Assuming say 95% efficiency (since we have a close Vin to total Vf) you have about 2.7W dissipated in the driver. That is too much for the switcher IC to dissipate, the junction temps will force the IC to go into thermal protection.

Most of the bottom of the PCB is ground plane which is what the thermal pad of the driver IC connects to - so a nice wide thermal interface for keeping it cool. The bottleneck will be to 50C/W thermal resistance of the IC package.

I see the driver being nice for a 3 x MC-E 4S configuration for a 48V ebike. That gives 12 die in series at say 3.5V each -> 12 x 3.5 = 42V which is a great match to a 48V system. Driven at 750mA per die (a little overdrive of the MC-E) would be 48 x 0.75 = 36W, so around 1.8W dissipated. So, 1.8 x 50C = 90C higher junction temperature than heatsink. So, heatsink at say 40C means 130C junction, well below the 150C max junction temp spec. That would be a LOT of light already - more than needed for normal road use on an ebike...

cheers,
george.

 

[ktronik]

Ok so 12 LED die's in series...that just great!!!

thanks for that!

Best

Ktronik

 

[Whitedog1]

Hi george,

is there also a high voltage boost circuit in planning?

For powering 4MCE 4s4s at approx. 1Amp per die with one driver?
Boosts from an 18.5 or even higher Battery to the 48V needed?

To power 4 MCE's with the hipflex or hipcc only the parallel wiring is possible, therefore only the 700mah per die......

greetings
Whitedog

 

[georges80]

No higher boost planned, CCHIPO is the limit there.

You won't see any appreciable different in light output from an MC-E at 1000mA versus 700mA. With all the heat in the LED die (degrading light output) and the human eye response (mostly logarithmic) all you will 'see' is shorter runtime...

Also, 4 MC-E is 4S4S would be closer to 16 x 3.5 = 56V.

cheers,
george.

 

[Whitedog1]

thanks for the answer!

in this case, i'll stick to the 4s4p configuration with the hipflex