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AD8642 Production
The AD8641/AD8642/AD8643 are low power, precision JFET input amplifiers featuring extremely low input bias current and rail-to-rail output. The ability...
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AD8642 on Analog.com

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Boosting AD8642 output current

		
	
				

			

									
					    Damaso
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Jun 25, 2013 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
		    			
    
			    
    I'm testing a design in which I need to do a current to voltage conversion. The current ranges from picoamperes to 100mA (both positive and negative), so I use 4 different resistors and a switch to select each of them. I filter the corresponding signal (not shown in the image), use a variable gain (x1, x10, x100, x1000) amplifier and then adapt it and detect it.  
    
 
    Everything works perfectly fine till 20mA, the op amp output current limit. Can anyone please show me a simple power stage that can be used preferibly inside the feedback loop? The output voltage has to be between -5 and +5 volts and has to work for +-100mA. 
    
			
    
			
									
		                             
                        

    
    
                                            
                 Operational Amplifiers (Op Amps)
                
                                                    
                 amplifiers
                
                                                    
                 AD8642
                
                                                    
                 High Voltage Op Amps =12V
                
                                
            
    
    
    
		
    

							
    
				
				
			
    
					
				        
        		
    
			
						
									
												
			
			
                        
                                    
                        
                        
                        
            
			            
						
						
			
			
			
			
		
    

        
        
        
    
					
    
			
    


    
















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Jun 25, 2013 8:09 PM
            
            
						
			            		
      
		
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      Hi Damaso,
      
 
      Thanks for using ADI products on your application. If replacing the AD8642 with another opamp that has a higher output drive capability is not an option for you then you can try to implement the circuit below. 
      
 
      
 
      There are other power/current booster design circuits on the internet which you can also consider and implement. 
      
 
      Also, I noticed from your schematic that there is a short between the output pin of U2 and the negative supply. I would recommend that you avoid this in your actual circuit 
      
 
      I hope this helps!
      
 
      Best regards,
      
 
      Emman
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Jun 25, 2013 8:09 PM
            
            
						
			            		
      
		
										0
					
	
      

		
		
      
		
      
                                
                                                            
      
					
      Hi Damaso,
      
 
      Thanks for using ADI products on your application. If replacing the AD8642 with another opamp that has a higher output drive capability is not an option for you then you can try to implement the circuit below. 
      
 
      
 
      There are other power/current booster design circuits on the internet which you can also consider and implement. 
      
 
      Also, I noticed from your schematic that there is a short between the output pin of U2 and the negative supply. I would recommend that you avoid this in your actual circuit 
      
 
      I hope this helps!
      
 
      Best regards,
      
 
      Emman
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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