[Test-Equipment] Transistor Circuit Design Question

[Barry]

CORRECTION

The collector of Q2 is connected to +5V through a 1K resistor.

Thanks,
Barry - N4BUQ

----- Original Message -----
> From: "Barry" <n4buq at knology.net>
> To: "Test Equipment" <test-equipment at mailman.qth.net>
> Sent: Monday, May 25, 2015 7:33:35 PM
> Subject: [Test-Equipment] Transistor Circuit Design Question
> 
> I have a situation where I have strobe and data signals originating from a
> 3870 CMOS microprocessor (part of a Fluke 8050A) that I need to convert to
> make them compatible with the display/latch I'm using to retrofit a
> different display.
> 
> The strobe is currently a positive-going pulse from -5V to 0V (GND).  I wish
> to make this a negative-going pulse from +5V to 0V (GND).
> 
> To do this, I have an external +5V supply and have configured the following:
> 
> 1. A 2N3904 (Q1) with the base at GND, the collector connected to +5 through
> a 10K resistor, and the emitter is connected to the strobe line through a
> 10K resistor.  This is shifting the pulse from -5/GND to GND/+5.
> 
> 2. The base of a second 2N3904, Q2, is connected to the collector of Q1
> through a 10K resistor.  The collector of Q2 is connected to +5 and the
> emitter is connected to GND and I'm taking the output at the collector of
> Q2.  This is functioning as an inverter.
> 
> This configuration is creating a fairly decent-looking pulse as I wanted but
> what I was wondering is if the components I'm using are somewhat correct
> (e.g. I'm not pushing any of the components too "hard", etc.), and whether
> there might be some other components that really should be used here.  I
> guess I'm looking at this as a really simple circuit that might function a
> bit better with some tweaks.
> 
> I hope the schematic is clear (it is really pretty simple).  If not, I can
> draw and scan it and post it somewhere.
> 
> Thanks,
> Barry - N4BUQ
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