I am designing a buck regulator LED power supply in LTspice. I'm trying to add an optocoupler on/off switch to it (which will be an option.) When the opto is ON, the output should be OFF (which is controlled by turning off the standby supply reducing consumption to a few microamps), and vice-versa. However, LTspice is giving me odd errors:

WARNING: Node N012 is floating.

WARNING: Less than two connections to node NC_01. This node is used by S:U4:1.

Singular matrix: Check node q5#collector
Iteration No. 2
Fatal Error: Singular matrix: check node q5#collector
Iteration No. 2

Does anyone know what's wrong?

 

Put a ground on V1.

 

That should do it.

Post your asc file, as well as any non-standard models.

It will make following along that much easier.

 

Put a ground on V1.

Okay, but doesn't that make it non-isolated? (I presume this is only a simulation bug/limitation?)

That should do it.

Post your asc file, as well as any non-standard models.

It will make following along that much easier.

See attached.

 

Spice requires a ground reference.

It checks to see if there is a ground in the schematic, but doesn't check to see if it is in the proper places.

 

I am not sure if you can tell spice to use to different grounds. In reality it will work with two isolated grounds but here it needs to have ground every where to work.

 

Tom66,
I can't load that .asc file; my LTSpice doesn't like it one bit.
Did you upload a shortcut to the .ASC file instead of the actual .asc file?

 

I couldn't get it to load either.

Ahh... You uploaded the plot setting file:

Title: * C:\Documents and Settings\Thomas\My Documents\LED driver-5.asc
Date: Sat Nov 20 15:01:43 2010
Plotname: Transient Analysis
Flags: real forward
No. Variables: 98
No. Points:            0
Offset:   0.0000000000000000e+000
Command: Linear Technology Corporation LTspice IV
Backannotation: u3 1 2 200 300 101
Backannotation: u2 1 2 200 300 101
Backannotation: u1 1 2 3 4 5 6 7 8
Backannotation: u4 1 2 3 4 5 6 7 8
Backannotation: u5 1 2 3 4 5
Variables:
	0	time	time
	1	V(n001)	voltage
	2	V(n005)	voltage
	3	V(n003)	voltage

etc....etc...

 

Ah, silly me. Try this file.