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LTSpice 26 minor bug current source with a short circuit

		
	
				

			

									
					    Kapiti7
					
							

            
            			
				
									
											
			
			
				
			
			
			    	
			                    
                
				                on Jun 28, 2026 
				
			
			
		

		
		                    	    

        	    
Thread Summary

                The user reported a minor bug in LTSpice 26 where a current source is automatically set to zero current when short-circuited with a wire, unlike a voltage source which can still deliver expected current with a non-zero series resistance. The support engineer confirmed this as a bug and noted it will be fixed. The user suggested adding a tiny series resistance or an error message to handle such situations.
                        	    

                
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Category: Software

    		        		            		    
Product Number:  LTSpice 26 

    		        		        		        
Software Version: LTSpice 26

    		    		    

		    		    
		    			

			    
Sorry! 


This could be related to a previous post "LTSpice 26 minor bug when .NOISE points to wrong current source".  It seems that when any non-zero impedance (regardless of how small a value) is placed across a current or voltage source (both with .tran and .ac), the source delivers the expected current.  (The voltage source may add automatically a tiny series resistance to get DC convergence). 


However if the source has a short circuit drawn with a line, the two nodes of the source are recognised as identical, and the voltage/current value gets jammed automatically to zero.


This is logical when parsing a netlist, but not expected for a current source when looking at a schematic.  For the future, maybe LTSpice could recognise this situation with a current source in the netlist and automatically introduce another series node with a tiny series resistance.?  Or clearer, give an error message that shorted sources are not allowed?




Many thanks


Possible Bug Current source short circuited.asc 





			

			
									
		                             
                        

    

                                            
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    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Jun 29, 2026 11:29 AM
            
            
						
			            		
    
		
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    Hi  ,
    

    Kapiti7 said:
    For the future, maybe LTSpice could recognise this situation with a current source in the netlist and automatically introduce another series node with a tiny series resistance.?  Or clearer, give an error message that shorted sources are not allowed?
    

    This might be a case of is it helpful? The schematic is merely a way to produce a netlist. By shorting a source, the user is eliminating the component. I do know this is a way of commenting out components. That said, would it be useful to have note of this in the log?
    

    mike
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

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                on Jun 29, 2026 12:33 PM
            
            
						
			            		
    
		
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    Thank you for your patience Mike.  This is a very minor detail and I am OK if you drop it without commentary.
    

    Best regards
    

    

    These two details were confusing me:
    

    1. In circuit theory it is OK to leave a voltage source open circuit since the current doesn't go to infinity, and a current source short circuited so that its voltage doesn't go to infinity.
    

    

    2. In LTSpice the behaviour with the short circuit using a wire connection is a little different with voltage and current sources.:
    

    voltage source with non-zero internal series resistance still manages to give the expected current; with zero internal resistance the voltage gets jammed to zero, with no comment.
    

    current source gets the current jammed to zero and comments this as a possible error in the netlist (which may not be read so often).
    

    

    

     
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

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    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Jul 1, 2026 2:15 PM
            
            
												
						in reply to Kapiti7
					
										
			            		
    
		
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    Hi  ,
    

    Kapiti7 said:
    Thank you for your patience Mike.  This is a very minor detail and I am OK if you drop it without commentary.
    

    Turns out this is a bit of a bug; and it appears to be an old one. You are correct, these constructs should be supported, and not removed from the circuit or assigned zero current.
    

    Thank you for catching this and bringing it to our attention. It is admittedly a low priority fix, but will be fixed.
    

    mike
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
				
						
						
				
				
		
		
    
			
		
    
	
    

    

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