Re: Driving tri-state LED matrix


"Tomás Ó hÉilidhe" <toe@xxxxxxxxxxx> wrote in message
news:b0519651-362b-48ae-ac6d-fa93f7a3b3b8@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On May 30, 3:06 pm, Andrew Smallshaw <andr...@xxxxxxxxxxxxxxxx> wrote:

Try redrawing this in a conventional manner, with Vcc at the top.
I started looking at this diagram but I lost interest the minute
I saw that I was going to have to unravel the circuit before
considering it. There's only so much time people are willing to
invest in considering a news post.


Are you talking about the way the emitter on the PNP is the bottom pin
rather than the top pin? If so:

http://users.imagine.ie/toe/disp2.jpg


Tomas -

There is a reason for transistor symbols looking a bit like a diode between
the base and emitter. In your circuit a big current will flow from VCC
through the emitter and out of the base of the first (leftmost) PNP
transistor, into the base and out of the emitter of the NPN transistor. The
second PNP transistor will turn on, the first two transistors will be
destroyed.

Why not download SwitcheCAD from www.linear.com and simulate your ciruits.

Michael Kellett

www.mkesc.co.uk





.

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