Alt-BEAM Archive
Message #05035
To: beam@sgiblab.sgi.com
From: Bob Shannon bshannon@tiac.net
Date: Mon, 05 Jul 1999 10:03:22 -0400
Subject: [alt-beam] Re: Something funny with the 1382 voltage triggers?
Sean Rigter wrote:
> Hell Bob,
>
> Almost certainly a problem with "holding" current. Your solar cell is
> putting out too much current(grin). The SE latch current must drop below
> some minimum level before it will "unlatch" and allow the cap to charge
> up again. The SMT devices or the solar cell may have a little more gain
> and this makes this version more sensitive to the holding current. Need
> some ideas to fix it? You could try to increase the resistor ie from
> 2.2K to 4.7K. That will also reduce the maximum load current above which
> the circuit will oscillate.
Very interesting. I've often found that going from 2.2K to 1.8K prevented the
oscillation problem. But you reccoment going the other way eh? Hmmmm.
What will this do to the power delivered to the motors once the latch fires?
Will it effect the degree of saturation of the NPN motor driver transistor?
What if I simply added some small additional load across the motor, say a micro
LED and 4.7K series resistor? That ought to drop the cap voltage a bit lower than
it is currently.
> Adding a 10uf cap in parallel with the
> resistor may help to overcome that problem by providing sufficient
> positive feedback to latch under the initial "motor inrush" current
> condition.
Now thats a good idea! It almost seems that that should be there anyway!
> I will experiment a bit to get the feel of this circuit
>
> wilf
I'm very supprised that the SMT version works so very differently than the same
circuit with conventional parts of the same values.
Clearly beam tech has a long was to go before its production worthy.
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