Magic smoke...

[dat2zip]

I believe in the BB case one would turn off the BB and restore connection before re-applying power since this is mostly used in a flashlight type situation.

I see no real need for concern since this is a stopgap situation.

YOU SHOULD NEVER POWER THE BB WITHOUT A LOAD.

Of course during constuction things can happen and it would be nice to not blow the converter board during constuction.

I hope to try to get the two resistors implemented in the next pass. Since a 5W Vf should never get past somewhere around 7.2V or so. I suggest setting the voltage divider for a worst case of 8V-9V. That would give 1V of headroom margin of the 10V output capacitor. I do worry more than anything of frying the capacitor which is rated at 10V.

Whether you can run it to 100% of tated voltage is unknown by me. I don't think the 60% rated voltage of tantulums apply. But, for high value ceramic constuction, I don't have and data or specifications of what you can actually expect.

Wayne

 

[Mednanu]

Hi Wayne,

What type of load would be the minimum safe load for a BB module (sorry to ask you this if you've already posted it elsewhere on the forum). I was kind of thinking of hooking my BB700 up with a 10 or 20k resistor in parallel with the Luxeon. It shouldn't take much energy if the luxeon is working fine (ie- it would be like a resistor logic gate ....sort of). With the luxeon at a logic value of '1', the resistor should be pulled down to a '0' (I would think) because the Luxeon is the path of least resistance for the current. But if the luxeon blew or became disconnected, the luxeon would then represent a '0' and the resistor would 'turn on' and become a '1' (thus saving the BB module I would hope).

Perhaps a better setup would be to simply use a transistor with a lower resistance value applied to it's base in order to ensure that enough load is placed on the BB unit, but this might significantly lower efficiency and waste too much power.

What would the minimum safe load be for a BB module ?

 

[Mednanu]

...

 

[CM]

Wayne, thanks for the capacitor voltage rating info. I'm gonna have to dial down the voltage limit since I thought the cap was 16V. BTW, ceramic caps do not need to be derated for voltage like tantalums do. I think a 10V cap is good for 1W and 5W LED applications. I think it would be great to incorporate this voltage limit on the next turn of the board. While you're at it /ubbthreads/images/graemlins/smile.gif bringing out the Iadj pin to a cuttable trace on the board that would normally be grounded but can be isolated by cutting the trace would allow some of the more creative dudes here to put their own dimmer in the circuit. This is merely a suggestion /ubbthreads/images/graemlins/grin.gif

Mednanu, a BB700 with 10K resistor with no LED is 7000V. POOF, Magic Smoke. Best to use the voltage limit feature of the switcher. It's only two resistors. It's cheap, and it's simple.

CM

 

[JSWrightOC]

Re: Magic Smoke

My BB400 has survived brief applications of power with no load--this happened when one of the leads broke on me. After fixing the broken lead, it seems to operate fine.

From what I understand Tantalum caps like to be operated close to their WV rating.

I like the idea of the Iadj option, I have run into some applications where a variable brightness would be nice. The extra voltage limit resistor is a good saftey.

Mednanu,

A zener diode would make an excellent saftey device, especially for testing. Just make sure it's rated for the power it would have to dissipate (400/700/750mA * Vr of zener). A good option if you already have an existing module without the voltage protection.

 

[AilSnail]

Re: Magic Smoke

"bringing out the Iadj pin to a cuttable trace on the board that would normally be grounded but can be isolated by cutting the trace would allow some of the more creative dudes here to put their own dimmer in the circuit. This is merely a suggestion "

I second (or actually first) that. I have already broken one Iadj pin, but managed to solder the stub. /ubbthreads/images/graemlins/smile.gif

The best solution I believe, if the geometry allows it, would be to pull the Iadj straight through to the underside, and taking it from there to J6. Easy to cut, easy to solder in the hole.

 

[CM]

Re: Magic Smoke

AilSnail, you're one of the "dudes" I was referring to. I was gonna try to mod Iadj on mine but thought it would be too mechanically fragile. Wayne should consider these suggestions as long as it doesn't compromise the primary requirements of the BB circuit. Out of the box, it's a very nice little circuit that has gotten a lot of mileage in many, many lights, mods as well as others. Evolving the circuit is fine if it doesn't detract from it's main mission.

 

[AilSnail]

Re: Magic Smoke

^ 'zactly. you're right; can't bend it many times before it snaps.