IR Beacon circuit optimizations (8-7.2v unreg, 5v reg)

[Dale(294engr]]

Engineer Dale recommends for:

all beacons: add ESD protection to the Logic level MOSFET gate:
10K series + 1M parallel; optional 15V zener cathode to gate, anode gnd)

EDU controller, exclusive use with (8v charged) to 7.2V unreg battery:

wire 4 IR Beacon LEDs all in series w/15 ohms for.11Apk, or 10ohms for.2Apk
(1.34v forward Vdrop measured across each LED at .111A_avg)

benefit: fewer parts, lower pk/avg current power w/ identical operation AND
lower power = less inefficiency (less generated heat)
= longer battery life

Note if the EDU program corrupts & PWM pin stays 100%ON LEDs get vy HOT
due to the highest ON duty cycle (100% fault Vs 5% @1mS, 10% @2mS)

(1mS on *50% 40kHz duty =.5mS on, 9.5mS off @100Hz =100*.5/10 = 5%)
(2mS on*50% 40kHz duty =1mS on, 9mS off @100Hz = 100*1/10 = 10%)

OR if the MOSFET source and drain are crossed, int. Fwd biased body diode
keeps LEDs ON, ignoring gate drive input from EDU, anyone been there !

some engineering calcs:
Vfwd LED =1.34V (.11A =33 ohms @5-1.34v, my init assumption for Beacon)

Discovery:
NOTE EDU PWM connector = Unreg Battery =8V charged to 7.2V discharged
For 5V regulated use must break out Red lead and connect to DIG +5 pin !!

(2 cases: unknown if Orig design assumes 8to7.2Unreg or 5v Reg EDU use)

UnReg: Orig design I per LED=8-1.34v/33=.202Apk*4 LEDsParallel=.808Apk !
Power used = IE = .804*1.34 =1.08Wp (*2mS*.5=.1dutyCycle= .11Wavg
Power consumed as heat in resistors = I^2R = 21.54Wp * .1 = 2.2Wavg

Reg: Orig design I per LED =5v-1.34v/33=.11Apk*4 LEDsParalleled =.44Apk !!
Power used = IE = .44*1.34 =.6Wp (*2mS*.5=.1dutyCycle= .06Wavg
Power consumed as heat in resistors = I^2R = 14.5Wp * .1 =1.5Wavg

4 LEDs in series: one R justification 4 *1.34 = 5.36v > 7.2 to 8v batt supply
Ipk per LEDseries = .202A Rnew=7.2v(end.of.life)-5.36/.212A=9.1 ohms

Ipk per LEDseries = .111A Rnew=7.2v-5.36/.111A=16.6 ohms

To replace EDU contoller with Hardware Timer design:
for use w/3 AA alkalines (4.5v) or 4 NiCads/NiMH (4.8 to 5.3v)

use ICM7556 dual timer
Optional add CMOS timer, auto power off ~15 min after button press

2 series IR LED strings w/15 ohms each, strings in parallel

R_led.string.1opt =4.5-2.68v/.111A =16.4 ohms
R_led.string.2opt =4.5-2.68v/.202A = 9 ohms

R_led.string.1opt =5-2.68v/.111A =21 ohms
R_led.string.2opt =5-2.68v/.202A =11.5 ohms

(allows varying 40KHz to check 4840 sensivity to frequency)