d4rkzone Posted January 3, 2010 Report Share Posted January 3, 2010 Hi,I want to add to my power supply which is 0 - 20 V+/- @ 1 A and +5V @ 3A a LCD DMM. I want to use a 9V battery due the load of the LCD will be independent of the circuit.So I made a search. I want to make the following circuit: It is capable of switch between each output and to measure the output current. The problem is that I am having difficulties understanding the circuit shown. I don't understand what is the I-Sense resistor, and the "To +Vout Via Main board" outputs. Do I need to connect this directly to the cable that goes out from the PCB right?In addition he was talking about: "There are no RF decoupling capacitors in the circuit". Then he added some capacitors, for what this is benefit?Source: http://www.io.com/~n5fc/xp720.htm Quote Link to comment Share on other sites More sharing options...
Hero999 Posted January 3, 2010 Report Share Posted January 3, 2010 It's difficult to show you without a copy of the original power supply.The 'To +' and 'To -' inputs jusst go to the positive and negative supply outputs respectively.The current sense resistors go in series with the outputs but still enclosed in the feedback loop.I have a feeling that the current sensing has been incorrectly implemented. If this is a simple LM317 circuit connecting a resistor between the output and potential divider ruins the regulation. It's difficult to know because it's a 0-20V power supply, not a 1.25V to 20V supply, so there's probably more so it than a simple LM317 supply. Quote Link to comment Share on other sites More sharing options...
Alex Tsekenis Posted January 3, 2010 Report Share Posted January 3, 2010 Hero is right, we need the schematic of the XP-720 power supply. Also I dont know if you have noticed Hero but the current sensing resistor is connected to an LM337, not an LM317, which makes this a very weird circuit.I bet S1 and S3 cost nearly as much as a second DK203. Quote Link to comment Share on other sites More sharing options...
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