Quote:
|
Originally Posted by 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)
|
I think I disagree with this. The added resistance will just slow down the switching, causing the MOSFET to spend more time in its linear region. This has two side-effects: 1) More energy will be dumped into the MOSFET, which is not what you want to do. 2) the MOSFETS output slew-rate will suffer, causing loss of signal fidelity in the beacon waveforms. The zener won't help much if the gate gets hit with a 15KV shock (Human ESD model).
Quote:
|
Originally Posted by Dale(294engr]
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
|
Doesn't the beacon already run for a few hours on one battery? Isn't consistant infrared intensity important?
Quote:
|
Originally Posted by Dale(294engr]
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 !
|
This isn't a problem because the resistors are already sized for continuous operation of the LEDs
Quote:
|
Originally Posted by Dale(294engr]
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 !!
|
No, this isn't true. While there is unregulated battery voltage on the fourth pin of the header, if a PWM cable is attached as intended, there is +5 volt regulated power on the red lead.
Quote:
|
Originally Posted by Dale(294engr]
(2 cases: unknown if Orig design assumes 8to7.2Unreg or 5v Reg EDU use)
|
As all the documentation shows, the circuit is designed to operate from five volts.
With just a couple of weeks left, the last thing we need to be doing is, as my (also an engineer) wife says, "keep fixing it until it's broken".
-Kevin