Help with circuit using SOB 1000 driver

[dieselsmoke]

I planned to create the following simple circuit, have all the parts on the bench:

I'd like to add an ability to dim the emitters to somewhere around 300ma as an option to the full 1a mode. Will the following circuit work by replacing the SPST with an SPDT and resistor ? Am I going about this the right way or is there a better way to do it ? Thanks.

 

[Justin Case]

Essentially, you are doing what the McC2S and McE2S 2-stage tailcap switches do. You could also get a Shark Buck with Remora.

 

[Greg G]

I second the Shark Buck and Remora, or a pot.

I tried to run 3 Crees off an SOB once. It lasted a few minutes.

 

[Justin Case]

I'm using an SOB1227 to drive a 2S2P MC-E, and the SOB is holding up fine (it is potted with Arctic Alumina thermal compound to dissipate the heat to the heat sink). To drive 3 Crees, you'd have to generate over 10W of power and dissipate over 1W of heat, perhaps even 2W. A little board like the SOB isn't going to like that unless your thermal management is good. I assume that your SOB cooked itself, which is interesting since in theory the SOB's IC controller is supposed to have thermal protection (shutdown at 150C). Or maybe some other component, like a diode, roasted itself?

 

[dieselsmoke]

I second the Shark Buck and Remora, or a pot.

I tried to run 3 Crees off an SOB once. It lasted a few minutes.

So do I understand that I could use a pot in place of the switch and resistor, effectively providing gradient dimming rather than the two set levels that I've proposed ?

If that's right, I guess a 1a pot would do, but I'm not sure what resistance range I would be looking for (that was going to be my next question with the resistor as well.)

Thanks for the insight, I'm definitely green when it comes to electrical circuits and have learned more hanging around here over the last few weeks than in my entire life prior. :twothumbs

 

[Justin Case]

The Shark Buck has a trim pot already installed. You can also remove it and install an external pot.

 

[dieselsmoke]

I like the Shark Back/Remora combo also, but needed to keep costs down for this project. I just received the SOB and man is it small, I see why you mentioned the heatsinking which I'll certainly do.

So now I'm on to the calculation of the needed resistor which I will use if I can't find an appropriate pot.

From my calculations, I'll need a 15 Ohm 2w resistor. Does these seem to be a reasonable solution ?

And does this math look correct ?

Thanks again

Vin = 11.1
Vf = 6.4 (emitters measured at 3.19 and 3.21)
desired current = 300ma

- so -

(11.1-6.4)/.3 = 15.67 Ohm (rounded down to 15 Ohm since I don't need exact)

.3 x .3 x 15.67 = 1.4 watt

 

[Justin Case]

Assuming that your two Vf values of 3.21V and 3.19V are for a forward current of 300mA and the 11.1V of your battery pack is the voltage under the corresponding load, then your calculations look correct.

The resistor should drop the SOB driver out of regulation and then you will be running in direct drive. Thus, you need to dissipate the extra juice from your battery pack through a current limiting resistor, similar to what folks have to do when they build direct drive 3D Maglites using a Seoul P7 LED.

 

[dieselsmoke]

The resistor should drop the SOB driver out of regulation and then you will be running in direct drive. Thus, you need to dissipate the extra juice from your battery pack through a current limiting resistor, similar to what folks have to do when they build direct drive 3D Maglites using a Seoul P7 LED.

hmmm, does that mean I need another resistor in addition to the one in the lower circuit diagram in post #1 ? I've searched for the 3D mag mods that you mentioned and haven't foudn the detail yet.

sorry for the naive questions, and thanks for the help.

 

[Justin Case]

hmmm, does that mean I need another resistor in addition to the one in the lower circuit diagram in post #1 ? I've searched for the 3D mag mods that you mentioned and haven't foudn the detail yet.

sorry for the naive questions, and thanks for the help.

No you don't need another resistor. I was commenting on what the resistor you were considering would be doing to the SOB driver. It would drop the SOB out of regulation and act as a current limiting resistor.

I might put the switch and resistor between the batt negative and the SOB GND though (not between the driver LED- and the emitter negative).

Here is one link for selecting a resistor in a Mag direct drive mod:

http://www.candlepowerforums.com/vb/showpost.php?p=2835228&postcount=7

 

[dieselsmoke]

It worked great ! AA'd the SOB to a slug, and wired the resistor across the two throws of the SPDT switch. I'm getting exactly 1a on high and 200ma on low, just what I wanted :twothumbs

Thanks for the guidance !

 

[Justin Case]

That's great!

You probably could have soldered your orange wire to the center anode pad, as an alternative to soldering it to the small Vin hole. And the black wire probably could have been soldered to the outer ground trace ring, as an alternative to soldering the wire to the GND hole.

Let's see more photos of the build and some beam shots. :twothumbs

 

[dieselsmoke]

Got it finished last night and have posted some various build pics below.

 

[dieselsmoke]

And some beamshots. Low mode runs at about 200ma, depending on battery voltage, and on runs right on 1a. It's not so noticeable from the shots, but there's a very different beam pattern coming from the two LED's. I really think that I have either two different R2's, or an R2 and a Q5, although both were purchased from DX in a single batch as R2 WG's.

I took the shots this morning with the digital Elph, and I'm sure that if I waited until night and used the DSLR they would show better, but its enough to get the idea.

Low mode, 1 meter ceiling bounce.

High mode

Low mode from 5 meters

High mode