Adding a Digital Multimeter LCD to XP-720

[d4rkzone]

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

 

[Hero999]

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.

 

[Alex Tsekenis]

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.