TV-B-Gone battery droop

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rubidium
 
Posts: 43
Joined: Sun Nov 18, 2012 10:36 am

TV-B-Gone battery droop

Post by rubidium »

I did a little test the other day and took a standard Adafruit TV-B-Gone with 2x AA batteries and put a scope across the battery pack output terminals. As the code executes, the waveform that I observe indicates that the voltage supplied by the battery pack droops by about 1 volt during the duration of each firing of the LEDs. I read somewhere that Duracell alkaline AA's have an ESR of about 0.12 ohm, so that 2 in series would give an effective ESR for the pack of about 0.24 ohm. That leads me to believe that each of the 4 LEDs is drawing a peak current of about 1 amp. Considering the "absolute maximum rating" of 600mA for PN2222 collector current, I would have thought these transistors in saturation would prevent anything as high as 1A from ever flowing. Or am I interpreting my measurement incorrectly?

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adafruit_support_bill
 
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Re: TV-B-Gone battery droop

Post by adafruit_support_bill »

Actual ESR changes with temperature and discharge. You will probably get more reliable numbers measuring current directly.

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