Re: TI-H: LED Backlight

To: ti-hardware@lists.ticalc.org
Subject: Re: TI-H: LED Backlight
From: Grant Stockly <gussie@alaska.net>
Date: Thu, 28 Jan 1999 16:10:09 -0900
Delivered-To: ti-hardware-outgoing@towerguard.unix.edu.sollentuna.se
Delivered-To: ti-hardware@lists.ticalc.org
In-Reply-To: <00f901be4b1a$3fa58e80$c9648ed1@vizzini.rdtech.>
Reply-To: ti-hardware@lists.ticalc.org


>From: Grant Stockly <gussie@alaska.net>
>>>>A 2N2222 will work fine.  It shouldn't use over 100ma.
>>>
>>>
>>>It would work fine if transistors came with less variation in the
>>>beta, however, that circuit is very sensitive to transistor beta,
>>>not all transistors will work well, I'm estimating about 20% or
>>>so (based on a sample of about 25) have high enough beta to
>>>work in that circuit.  A darlington will work better, and the price
>>>difference is negligible.
>>
>>The calc isn't going to switch the line any faster than 10MHz.
>
>
>Huh?  Perhaps you misunderstand me.  The problem is not
>the switching speed, it is the gain.  In the circuit as it appears
>on my web page the gain of the transistor must be fairly high,
>something more than 200 for the NPN's I was using, otherwise
>the final output transistor will not allow enough current for the
>inverter to turn on (typically around 5-12mA, minimum acceptable
>is about 20mA).

Worket for me.

References:

Re: TI-H: LED Backlight

From: "David Knaack" <dknaack@geocities.com>