# Simple Circuit: Why is one reporting High and one Low?

Discussion in 'General Electronics Chat' started by Mercfh, Feb 13, 2013.

1. ### Mercfh Thread Starter New Member

Apr 24, 2012
11
0
Still learning the basics, but after a bit it took me to realize that Voltage is measured for most logic outputs NOT current (I didn't realize you could Have a Logic HIGH without current).

Anyways that leads me to my next question.

Look at these 2 VERY simple circuits Why is one High? and One Low....when the voltage would be the same, and thats only a 100ohm resistor....so that shouldn't make a difference? Would it be different if the resistor wasn't there.

Also slightly more complex question:
tinyurl.com/b9lu8rj

How come current cannot flow out the the arrow marked in Red? Current is LITERALLY flowing right next to it? Why can't it flow out of it? especially when current is flowing right next to it?

Since OUTPUT complement is getting current, and current is flowing directly next to both outputs...I don't understand why the other output isn't receiving current (and therefore Low)...or is it because it's not receiving VOLTAGE...and if so why not?

Im still kinda understand the difference between voltage and pressure...so using the water analogy has really helped me.

2. ### crutschow Expert

Mar 14, 2008
20,223
5,718
Current (flow) is proportional to voltage (pressure) divided by the resistance in series.

Current could flow out of the arrow marked in Red if there was a path for it. The current value would depend upon the resistance of whatever would be connected to the Red output L and the voltage drop (typically a couple tenths of a volt) across Q2 when it is on.

If you have voltage connected to ground with no resistance than the current is theoretically unlimited.

3. ### Mercfh Thread Starter New Member

Apr 24, 2012
11
0
Ok., but it seems like there IS a path for it? current is flowing right next to it which is what confuses me?

4. ### crutschow Expert

Mar 14, 2008
20,223
5,718
What path? Current has to have someplace to flow. The connection you show doesn't go anywhere. The current can't go into thin air (unless it's a really high voltage).

I'm confused about your confusion. Do you understand Ohm's law and the difference between voltage and current?