10A Buck Switching Regulator

[luckybucket]

Finding a switcher that is designed ground up for current regulation (modern LED driver chips) simplifies things a lot. For the current levels you're looking at you would likely need a 'controller' and use an external power FET.

cheers,
george.

I like the idea of a simple solution. With a sharkcage or even individual shark sinks from the shoppe the fet's could be sinked to the side of the light, even multiple ones if necessary. None of my lights are overdriven and its time to step it up and make a real light. Im thinking sst-90 at 12 amps on high, but a conservative 3 amps for normal use. This would require a very versatile regulator and pushing 4 sharks to their limit kinda worries me. IMO things run better when their is some headroom.

 

[stinky]

I use very simple design - LDO10C as a voltage regulator with decreasing voltage with increasing temperature.

It contains one thermistor (1kohm) parallel with 510ohm resistor and serial with 100ohm trimmer for exact setup trim pin of LDO10C driver.

Would you mind sharing some more details on your design for us newbs? I'm thinking that this LDO06C-005W05-SJ might be a good item for the SST-50. 6A should be sufficient for that emitter, and avnet has them in stock for around $11, with min order of 1. Paired with either the KTY83/110 or the KTY83/122 (specs are very close). http://www.mouser.com has those in stock for under $1 also with min order of 1.

In your picture I see the emitter clearly, but not the driver.

Thanks!

 

[pepko]

Would you mind sharing some more details on your design for us newbs? I'm thinking that this LDO06C-005W05-SJ might be a good item for the SST-50. 6A should be sufficient for that emitter, and avnet has them in stock for around $11, with min order of 1. Paired with either the KTY83/110 or the KTY83/122 (specs are very close). http://www.mouser.com has those in stock for under $1 also with min order of 1.

In your picture I see the emitter clearly, but not the driver.

Thanks!

This is my design, but it's only first version ...


Police (maglite) 2D with KD 52mm aspherical lens ...

http://www.mypicturehost.com/show.php/60336_DSC7302.jpg.html


DX 2mode switch - low mode with 82ohm resistor (about 0.8A from batteries), off with 10kohm resistor (stand-by = 0.050A consumption)

http://www.mypicturehost.com/show.php/60337_DSC7309.jpg.html

LDO10C with 100ohm trimmer and 510ohm resistor parallel to thermistor KTY83-110

http://www.mypicturehost.com/show.php/60338_DSC7310.jpg.html

LDO10C pin 'enable' is not used ...

http://www.mypicturehost.com/show.php/60339_DSC7311.jpg.html


Solarforce L900M modded with 6x Cree XRE Q5

http://www.mypicturehost.com/show.php/60340_DSC7295.jpg.html


Police Maglite SST90 current 9A - wide focus

http://www.mypicturehost.com/show.php/60341_DSC7297.jpg.html


Police Maglite SST90 current 9A - narrow focus

http://www.mypicturehost.com/show.php/60342_DSC7298.jpg.html

 

[stinky]

This is my design, but it's only first version ...

LDO10C with 100ohm trimmer and 510ohm resistor parallel to thermistor KTY83-110

http://www.mypicturehost.com/show.php/60338_DSC7310.jpg.html

LDO10c pin 'enable' is not used ...

http://www.mypicturehost.com/show.php/60339_DSC7311.jpg.html

Thanks pepko! I also found this design (diagrams and equations) in the docs for the chip here, for those who are interested (see p.7-8):

http://www.powerconversion.com/assets/an_ldo03c_06c_10c_1199502565_appnote.pdf - Powered by Google Docs

the specs for chip are very nice. seems like you could just solder or embed the whole thermistor right into the heatsink without damage to ensure good thermal transfer. using different resistor combinations, you could have very wide or extremely narrow Vout ranges at differing temperatures. does anyone know the formula for how the Vout drops on SST chips as the temp rises? with that info, in theory at least, it shouldn't be too hard to figure out the components for a nice driver for these chips

 

[LED Boatguy]

Very nice. Now we just need the SST90 in warm or neutral white...

 

[Mike cz]

Beautiful work. SST-90 is with the aspherical lens great ...:twothumbs

Appendix:
Idea of the thermistor was mine, but I did not know about this forum ... During production (2.9.2009) Romisen@6xSSC P7 (published 17.9.2009 here http://forum.fotonmag.cz/index.php?showtopic=436&st=40 and now here https://www.candlepowerforums.com/posts/3131681#post3131681) I used 30Amps voltage DC-DC schwith and I needed something to compensate for temperature, because it is a voltage DC-DC schwith. So I added a thermistor to control DC-DC switch. Then was created this thread... Then Pepko used a similar DC-DC switch with termistor for SST-90.:thumbsup: I and pepko are friends from the Czech forum: http://forum.fotonmag.cz/index.php?

 

[pepko]

Beautiful work. SST-90 is with the aspherical lens great ...:twothumbs

Appendix:
Idea of the thermistor was mine, but I did not know about this forum ... During production (2.9.2009) Romisen@6xSSC P7 (published 17.9.2009 here http://forum.fotonmag.cz/index.php?showtopic=436&st=40 and now here https://www.candlepowerforums.com/posts/3131681#post3131681) I used 30Amps voltage DC-DC schwith and I needed something to compensate for temperature, because it is a voltage DC-DC schwith. So I added a thermistor to control DC-DC switch. Then was created this thread... Then Pepko used a similar DC-DC switch with termistor for SST-90.:thumbsup: I and pepko are friends from the Czech forum: http://forum.fotonmag.cz/index.php?

That's right, this was your theory and your experiences were very helpful for me. Thanks for your advice.

Now I'm trying to use SMD thermistor KTY82 (2kohm) paralel to 470ohm resistor. I think I don't have to use trimmer with that. And I want to place it directly under PCB of LED and minimize thermal transfer between thermistor and LED chip.

 

[Alan B]

Good thread here. Some suggestions and thoughts:

1) the initial posting indicates 18.8V max in the text, this is a typo. Clearly 13.8V elsewhere. Might be worth fixing that.

2) I found a similar part at Mouser for $12. Murata LSS-T/10-W12. 50W 6V 10A output. They also had another similar part for a higher price.

3) There is a 2V Vin to Vout minimum on the Murata part so Vbatt minus losses needs to be at least 5.6V. Still likely ok for 2 Li-Ions if other various voltage drops are kept to a low enough value.

4) I'm considering driving one of these regulators with a microprocessor. Have it close the current loop. Since this is effectively a thermal compensation loop it does not need high bandwidth. The LED current can be read by a hall effect current sensing chip so no shunt resistance is required, or a low value shunt can be used. Many of the microprocessors have built in high gain differential channels on their ADCs for reading small value shunts.

The interface between the micro and these regulators would then be the issue. The regulators do not appear to take a voltage control input directly but an FET can be biased with a pwm derived voltage to replace the trim resistor. This setup can be used to get dimming control as well as current regulation.

 

[Justin Case]

DX 2mode switch - low mode with 82ohm resistor (about 0.8A from batteries), off with 10kohm resistor (stand-by = 0.050A consumption)

A 50mA parasitic draw seems rather high to be practical, depending on what batteries you are using. In one day, you'll burn 1200mAh. Even for a 10000mAh capacity D cell, the shelf life seems somewhat short.

 

[Alan B]

Not sure what others were planning, but I'm planning to remove power from the regulator when the light is off.

 

[Justin Case]

A flashlight without an immediate source of power is like a 1911 that's not in Condition 1.

 

[Alan B]

A flashlight without an immediate source of power is like a 1911 that's not in Condition 1.

I will use an FET controlled by the micro. No delay.

 

[OldNick]

Thanks pepko! I also found this design (diagrams and equations) in the docs for the chip here, for those who are interested (see p.7-8):

http://www.powerconversion.com/assets/an_ldo03c_06c_10c_1199502565_appnote.pdf - Powered by Google Docs

the specs for chip are very nice. seems like you could just solder or embed the whole thermistor right into the heatsink without damage to ensure good thermal transfer. using different resistor combinations, you could have very wide or extremely narrow Vout ranges at differing temperatures. does anyone know the formula for how the Vout drops on SST chips as the temp rises? with that info, in theory at least, it shouldn't be too hard to figure out the components for a nice driver for these chips

Interesting thread indeed.

It's the regulator you need to match, and let it take care of the LED (??)

How about using a trimpot in parallel with the thermistor, as well as the one in series? Then you could set for as little voltage drop or as much as required (???), within reason. Use the parallel trimpot to set it up, testing on a simple resistive load, controlling the thermistor with controlled temps.

 

[ahx66]

I was wondering if anyone has put a potentiometer in series with the trim resistor? You could choose your POT to be the max setting around the 9 A, and dial down the brightness.

 

[lolzertank]

This is an old thread, but I believe I have a way to make the LDO10C current regulated well enough for LEDs.

The regulator voltage can be controlled by having an additional resistor and a voltage source connected to the trim pin. It's not too tricky to see how this works with the resistor divider, and it doesn't mess with the feedback loop so long as the voltage source is reasonably stable. The voltage source will be supplied by a microcontroller through PWM and a low-pass filter, which should allow current and temperature sensing and multiple modes among other things. Basically it's simulating a really slow op-amp to avoid any instability, with some extra intelligence behind it.

 

[mpf]

having tried both constant current (voltage boost) and constant voltage (buck/boost) switching regulators with out success. Could not get them stable. I have resorted to designing my own buck regulator uC controlled which does both constant voltage and constant current. Not very well regulated but good enough for feeding my torch as a table lamp and charging the batteries.

Will post the details later (much later at the rate I am working on it). Or contact me at www.forward.com.au if you want the present circuit.

p.s. mine is only a 2 to 3A buck so not actually in this league.