[Test-Equipment] Transistor Circuit Design Question

[Mike Manes]

Hi Barry,
Yeah, that'll work.  But you could get by with a single NPN in common 
emitter by putting 2 10k in series from the -5/0v sig to +5V, and put
the junction on the base of the NPN.  NPN E=gnd NPN C to +5V thru 1K.
73 de Mike W5VSI

On 5/25/15 18:33, Barry wrote:
> 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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