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Unread 09-02-2004, 23:10
Dale(294engr]'s Avatar
Dale(294engr] Dale(294engr] is offline
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FRC #0294 (Beach Cities Robotics)
Team Role: Engineer
 
Join Date: Jan 2004
Rookie Year: 1998
Location: Redondo Beach, CA
Posts: 92
Dale(294engr] is a glorious beacon of lightDale(294engr] is a glorious beacon of lightDale(294engr] is a glorious beacon of lightDale(294engr] is a glorious beacon of lightDale(294engr] is a glorious beacon of lightDale(294engr] is a glorious beacon of light
Re: IR Beacon circuit optimizations (8-7.2v unreg, 5v reg)

Hi Kevin,
1. Are you saying the logic level FET is not extra ESD sensitive ?

How then is it protected ?
(logic level gate threshold =very thin gate oxide =lower destruct V/energy)

My suggested 10K ohm in series with the gate does NOT slow down
the FET (check it out on a scope)
Series resistance isolates the gate a bit & if used aids zener effectiveness.
The 1M parallel keeps the FET gate drained, i.e. off.

A very much higher series resistor than 10k would indeed slow turn on,
but I do not suggest that.

Zener (or even a reversed diode)
presents junction protection of HiZ MOSFET unprotected gate
offering a reasonable and increased degree protection given likely frequent
handling / unplugging of EDU from plastic Beacon connector to bare gate FET.

2. Our Beacon doesn't get turned off much
so depleats 800 mAHr batteries fast.

I was not suggesting using a variable unreg source.

Just suggesting ways to better use it based on assumption it was used.
Assumption was made using measuremnet of our EDU controller
(according to your reply is miswired - thanks for enlightenment)
having unreg battery power on the red lead.

Inspection reveals that the LED current was set at the lowest
Battery voltage equal to the FRC current at 5V regulated.

But I agree varying the IR intensity is undesirable but not likely a problem.
(is FRC using the LEDs distributed to Teams or the more powerful Sony?)

3. I agree that it is of little consequence
re: LEDs getting HOT when not pulsed

Was just presenting some enlightening duty cycle data.

The DUTY cycle thus LED heating goes WAY up if the switching stops...

Our EDU occassionally drops the programming (reason UNK).

4. Thanks for pointing out the correct 4 pin wiring. We'll correct it.

5. Post purpose was to suggest some tech options to solve our
and perhaps others battery life problem.

We use two series LED Strings, two resistors, and 5V regulated.
Two series strings same Ipk = 1/2 current switched by FET.

Thanks for taking time to reply,
appologies to your wife; I didn't know it wasn't broken,
was trying to assure Beacon lives long & prosperous life

Dave et al apparently has plans for IR for some time to come.
 


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