# Direction of current flow in LTSpice

Discussion in 'Analog & Mixed-Signal Design' started by rds01, Dec 5, 2018.

1. ### rds01 Thread Starter New Member

Dec 5, 2018
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0
I am trying to simulate a simple circuit in LTSpice -- with resistors and a DC voltage source. I am noticing some of the currents appearing as negative and others as positive. Is there a way to display the direction of current flow in a circuit? I tried to look online but am unable to find any relevant posts. Would very much appreciate if you can share if this is possible or not. Thank you!

2. ### ericgibbs Moderator

Jan 29, 2010
7,094
1,403
hi rds,
Welcome to AAC.
One method to set the plot current direction thru a component, is to rotate the component 180deg', Cntrl + R

As the circuit creator you need to know the expected direction of the current flow.

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• ###### Direction2.asc
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Last edited: Dec 6, 2018
3. ### Alec_t AAC Fanatic!

Sep 17, 2013
9,377
2,251
In Spice-land even resistors are polarised! Flip one over and the current direction reverses. Hover the cursor over the resistor in the schematic to see Spice-current direction.

4. ### Bordodynov Well-Known Member

May 20, 2015
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You can make new symbols for the resistor (for example, marked with a positive pole). Then if a current flows into this pin, then the quantity is positive, and if it flows out, then the quantity is negative.

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5. ### rds01 Thread Starter New Member

Dec 5, 2018
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Thank you so much for your time and help -- much appreciate it. I was trying to see if there was a way to get LTSpice to post arrows indicating the current flow. If I hover the mouse over the resistor, I only see the 'Hand' symbol. Should I be doing something else to see the current direction? Thank you again.

6. ### ericgibbs Moderator

Jan 29, 2010
7,094
1,403
hi rds,
Post your asc file so that we can run it.
You must run the sim first to get a voltage or current value.
E

7. ### rds01 Thread Starter New Member

Dec 5, 2018
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Yes, I did run the sim. The -12.5 A is the current value post-calculation. I will attach the .asc file shortly. Thanks.

8. ### rds01 Thread Starter New Member

Dec 5, 2018
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Attached my .asc file. As you see, it is very simple -- just a DC source and a resistor for now. Thanks again!

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9. ### ericgibbs Moderator

Jan 29, 2010
7,094
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hi,
Try this.
You were using an .op , this has a .tran.
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10. ### rds01 Thread Starter New Member

Dec 5, 2018
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Thank you, I ran the try2.asc with the .tran. I didn't see any difference in the output. Are you able to see a current direction in the output? Can I request you to post an image of that?

11. ### ericgibbs Moderator

Jan 29, 2010
7,094
1,403
hi,
This what I see.
E

EDIT:
You know that you have to Hover the cursor over the component.???

12. ### rds01 Thread Starter New Member

Dec 5, 2018
9
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Wow! That would be so nice... Does that appear just by hovering the mouse or as part of the output itself.

Or, should I be turning some switch On for this to appear... I am guessing there is something I am likely overlooking.

Thanks again.

13. ### ericgibbs Moderator

Jan 29, 2010
7,094
1,403
hi,
You know that you have to Hover the cursor over the component to show the meter symbol, and keep it hovered, else it disappears.

It has been on every version I have used for the past few years.

14. ### crutschow Expert

Mar 14, 2008
21,141
6,013
Post an image of what your cursor looks like when hovering over the resistor after you've run the transient analysis as you did in post #5.

15. ### rds01 Thread Starter New Member

Dec 5, 2018
9
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Wanted to reply earlier but looks like there is a limit of 5 posts per hour and so had to wait this long to submit my Post.

My apologies... Yes, it does appear when I hover the mouse over in the .tran version.

Thank you again.

16. ### ebp Well-Known Member

Feb 8, 2018
2,332
808
I used to add a tiny dot next to pin 1 of all symmetric (non-polar) passive components like resistors, caps and inductors in my schematic libraries. It allows orientation to be seen easily without littering the screen and hard copy with pin numbers that aren't of any general use whatever or symbols like + and - that imply some sort of polar nature that doesn't exist.

17. ### WBahn Moderator

Mar 31, 2012
23,741
7,300
In virtually all (I know of know exceptions) SPICE simulators, current AT a component pin is defined as conventional current ENTERING the pin. This was the convention used by most datasheet writers at the time (and is still the case for many/most today). For a two-terminal device, current THROUGH the component is defined as the current at pin #1.

18. ### rds01 Thread Starter New Member

Dec 5, 2018
9
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Folks, thanks again for all your time and responses. Much appreciate them!

19. ### ericgibbs Moderator

Jan 29, 2010
7,094
1,403
hi rds,
I guess you noticed the current is flowing he 'wrong' way thru the resistor, in post #11, using Conventional current direction.?
Flip the resistor 180deg.
E

20. ### rds01 Thread Starter New Member

Dec 5, 2018
9
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Yes, I noticed that and I had to change the orientation... Thank you.