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1. 01:04 PM - Re: Re: IVO Prop current limiter (Robert L. Nuckolls, III)
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Subject: | Re: IVO Prop current limiter |
At 11:16 AM 7/6/2017, you wrote:
>
>
> > This might be another opportunity for an open source
> > project. Once you've finely tuned the code, we can
> > poke it into chips for mounting on a dedicated
> > ecb . . . have you considered solid-state
> > switching as opposed to relay?
>
>
>Bob,
>
>I'm open to any of your great ideas.
>I had not considered a solid-state switch instead of a relay,
>but that does sound like a good way to go.
>
>It would be nice to have this in a small package.
>Right now, I have the Arduino (clone) board in an enclosure,
>and the other components in the separate enclosure I had
>been using for your original circuit.
Yup . . . make it work on the bench then
'distill' it . . .
Do I recall correctly that once you have
'golden code' in the silicon, the chip
can be lifted out and dropped into an
embedded controller with minimized
peripherals?
If I were stuffing this functionality into an
8-pin PIC chip, I would explore something
like this . . .
Emacs!
Set up Q1/R2/Q3 as a classic, ultra-fast current
limiter. Select R2 to target stall motor current
limit. Current limit is approximately
I(limit) = Vbe(Q3)/R1
Vbe(Q3) is about 0.6 volts. Hence, setting
R1 at 0.1 ohms would get you a 6A current
limit. I think we were shooting for 9A so
R1 = 0.066 ohms. I would parallel a number
of resistors on an ECB to achieve 66 milliohms.
Q1 doubles as a motor controller turned OFF
by clamping gate to ground with Q4.
D8/D9/R10/C11/Z12 conditions the COMMAND SENSE
signal to a discrete input.
R5/C6 conditions a CURRENT LIMIT SENSE input
to an analog input.
Q4 is a software driven clamp to remove drive
from Q1 during a LIMIT CURRENT shut down.
The +12 source in schematic above can be
BUS, a precision 5v source ie easily acquired for
small uC chips with a circuit like this:
Emacs!
Smartware would read something like this:
Power-up routine SETS a LIMIT LATCH which
drives gate of Q4 HI.
A rising edge on COMMAND SENSE clears the
LIMIT LATCH which removes drive from gate of Q4.
LIMIT SENSE is monitored for input greater
than 0.5 volts for greater than 0.5 second.
Any excursion below 0.5 volts resets the
limit timer.
If limit times out, then the LIMIT LATCH
is SET, gate of Q4 goes HI and motor power
is removed.
This condition is sustained until next
rising edge on COMMAND SENSE.
It looks like the tiny Arduino products
could piggy-back onto a board that hosts
the peripheral components . . . but as
long as you're making a board, you might
explore the option of programming a chip
in an Arduino development system for
dropping into your target ECB.
To the extend that any of this is useful, feel
free to adopt or adapt as you see fit.
Bob . . .
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