Backlight Power Measurement
xaaronc at gmail.com
Wed Oct 14 23:58:52 CEST 2009
2009/10/14 Werner Almesberger <werner at openmoko.org>:
> Aaron Carroll wrote:
>> BL is the backlight, with I measured across R1763, and V at C1764.
>> BL = 14.38 V, 28.53 mA, 410.26 mW
> Is the BL voltage what you measure at LED+ relative to GND or have
> you already subtracted LED- ? In the former case, your result would
> be about 10% high with maximum backlight.
LED+ to GND, because I want to include the power lost in R1763.
>> IN is measured at the battery with no other external connections,
>> with the current measured via a 100mohm resistor in series with (+).
>> The power is just the product of the quoted V/I.
>> IN = 4.01 V, 252.89 mA, 1014.09 mW
> Which side is IN - battery side of the shunt resistor or Neo side ?
> In the former case, you'd be another 6% high.
I can't see which shunt resistor you are refering to, but the
measurement is taken at the battery connector (i.e. CON1701).
> Regarding expected efficiency, the 50633 manual is silent about it,
> the 50606 manual has the following data:
> Current Conversion
> (mA) 3.6 V -> 1.8 V 3.6 -> 3.3 V
> 1 75% 92%
> 10 85% 95%
> 100 85% 96%
> Up conversion seems to have similar characteristics as down
> conversion, but the voltages given don't make sense (Vi = 5.0 V
> and Vp = 1.8 V. That's a down conversion !)
> So we should expect an overall conversion loss of not much more
> than 25%.
The 50606 converter has a much lower peak voltage/higher peak
current... can we make a meaningful extrapolation here?
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