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comparison FC-handset-spec @ 74:e4eebf9ffce3

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FC-handset-spec: Vf=2.9 V on both HaoRan and Formike LCD modules
author Mychaela Falconia <falcon@freecalypso.org>
date Thu, 16 Sep 2021 06:26:35 +0000
parents eb68975e1b81
children c458b7159fbd
comparison
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73:eb68975e1b81 74:e4eebf9ffce3
206 the backlight consists of 3 white LEDs wired in parallel, joined either at the 206 the backlight consists of 3 white LEDs wired in parallel, joined either at the
207 anode or at the cathode - although as we shall see momentarily, we require an 207 anode or at the cathode - although as we shall see momentarily, we require an
208 LCD module where the 3 LEDs are joined at the anode, with the 3 cathodes brought 208 LCD module where the 3 LEDs are joined at the anode, with the 3 cathodes brought
209 out separately. LCD module datasheets call for 15 mA current through each LED 209 out separately. LCD module datasheets call for 15 mA current through each LED
210 at maximum intensity, for 45 mA total, and the LED forward drop voltage (Vf) at 210 at maximum intensity, for 45 mA total, and the LED forward drop voltage (Vf) at
211 this rated current seems to range between 2.9 V (what I actually measured on one 211 this rated current seems to range between 2.9 V (what I actually measured on
212 candidate LCD module) to 3.2 V (what the datasheets list as typical) to perhaps 212 both Formike and HaoRan LCD modules) to 3.2 V (what the datasheets list as
213 as high as 3.4 V (what one datasheet lists as the maximum). 213 typical) to perhaps as high as 3.4 V (what one datasheet lists as the maximum).
214 214
215 Given the parallel (as opposed to series) wiring of the 3 LEDs and the 215 Given the parallel (as opposed to series) wiring of the 3 LEDs and the
216 relatively low Vf, there is no need to use any kind of boost converter as part 216 relatively low Vf, there is no need to use any kind of boost converter as part
217 of the LED driver circuit for this backlight - any boost converter will only add 217 of the LED driver circuit for this backlight - any boost converter will only add
218 inefficiency (more current will be drawn from the battery for the same LED 218 inefficiency (more current will be drawn from the battery for the same LED