Badboy running warmer than expected?

[Th232]

I'm using a Badboy with a 1.8 ohm resistor for 28 mA, and it's running 6x 3 mm LEDs in series using a fresh 123A primary. I've noticed that after about half a minute of use, the driver board gets fairly warm. I'd guess about 60 deg C, but that's a very rough guess. No heatsinking on any of the driver's components.

By my count, assuming each LED has a Vf of 3.3 V, the BB has an efficiency of 82% and delivers 0.028 A, then the LEDs draw a total of 0.555 W, driver inefficiencies consume 0.122 W. Maybe I need to check up on my knowledge of heat and all, but it seems to me that something doesn't add up with those numbers and the resultant temperature is too high.

Or is this normal, and it's just that I need to dig out my textbooks again?

Edit: My sense of touch is screwed, more like 60 deg instead of 40...

 

[dat2zip]

Can you read the sense resistor and verify it is really 1.8 ohms. It is possible the resistor is not 1.8 ohms and you are driving the LEDs harder than expected and if that is the case then the BB may be warmer than expected.

Your calculations are correct and with the setup you have the BB should be running on the cool side as this configuration is not pushing the BB very hard.

If you have a DMM and can measure the LED current or the battery current you can confirm the setup is working as expected or not. You can also measure the Vf of one of the LEDs and if it much higher than 3.3V then that would be a good indicator of overdrive.

Wayne

 

[Th232]

Just took a quick look at the resistor... 0.18 ohms.

I'm an idiot...

... and what have I been doing to those poor LEDs?!?