Common on converter boards?

[mrme]

Do the converter boards have a lead common to the power in and the LED out? It would simplify my project immentsely if they did share a common on the Downboy.

I need a backup battery since my Li-ion battery just up and shuts off with little warning. I would like to run a Luxeon off the Li-ion and the regulator and have have a DD samll battery hookup to the same Luxeon. The switch would be a 1-2-3-0 clicky. I can't see any other way to do it as I don't have room for a second LED in the light.

Thanks

 

[mrme]

I take it a lack of responses contitutes a no.

 

[jaids]

My downboy doesnt have a common ground as far as I can see so I guess not

 

[StoneDog]

Common power in and LED out? I'm no EE but is that even possible?

Jon

 

[knifebright]

it seems like if they did share the same in and out then you would circumvent the circuit board all together.
jimmy

 

[mrme]

It would only circumvent the power if BOTH positive and negative were common. Most devices will have a negative common, also known as a ground. Your car, for example, has a negative ground (common). All the devices in the car from the battery, charging system, ignition system, lights and even the spark plugs all connect to the same negative ground, the body of the car.

However, several devices use a positive common, such as Willey Hunt's LVR regulators for incan bulbs.

If I could find a schematic, it would be obvious if there was a common. However, I don't trust a visual inspection nor a DMM test to tell me if making a common would short out some parts.

 

[chimo]

Many current regulated converters use a small sense resistor on the negative lead that feeds the LED. It may measure like a short (common resistance values are in the order of 0.1 ohms) with a DMM but this resistance is needed as it provides a voltage drop that is amplified and passed to a feedback pin on the converter IC. If this resistor is shunted the regulator board may not work properly. You also have to worry about the potential (no pun intended) for reverse feeding the circuit by the DD battery.

Some converter boards also use a current sense resistor on the positive output side. A slightly different type of proportional (V/V) amp is used to convert the voltage dropped across Rsense to send to the Feedback pin.

Having said all this your proposal could be done if you can isolate the converter board from the luxeon with the proper switch when you run on DD. Hope this helps.

Paul

 

[dat2zip]

Madmax, Badboy, Wizard2 and Nextgen all have common Ground.

Downboy has different Grounds. The LED is floating relative to GND and tying LED- to GND will destroy the converter board. The Wizard1 board also is floating.

Wayne

 

[mrme]

That's what I needed to know. Thanks.