![]() Or download different sizes from Instructables : You can use any other V or A modules without much modifications.Äownload high resolution PNG image of the schematic here. See the "Wiring" section to see the modifications to be made to the voltmeter module. A DSN DVM-368 (tutorial on my website) voltmeter module is connected to the variable output to display the voltage at front panel. I used a 5K potentiometer in series with a 1K pot to have coarse and fine adjustment of output voltage. The variable output is taken from U3 as shown in the schematic. So it's a series network of different regulators. One of the 5V output is connected to a AMS1117 regulator for 3.3V output. The auxiliary 12V output is connected to inputs of three LM2940 ultra-low dropout 5V 1A regulators of which two are used for USB outputs and the other is for front panel output. The 2W resistors R5, R7 and R9 will produce enough voltage to bias the pass transistors at low currents. But they exhibit some output stability issues which can be mitigated by adding capacitors at the output. PNP transistors are used as pass elements in low dropout and ultra-low dropout regulators. But the reason I chose PNP ones is because they do not alter the output voltage as NPN transistors would do (output will be +0.7V higher when NPN is used). You could use TIP3055 or 2N3055 as pass element on the negative side or the output side. Here I've used TIP2955 power transistor as pass element on the positive side. ![]() But in this case, with large difference in input and output voltages, LM317 will have to dissipate the excess power as heat so much heat. LM317 can provide output current in excess of 1.5A. U2 will output a constant 12V, U3 will output a variable voltage and U1 will produce an auxiliary 12V for other 5V and 3.3 regulators so as to reduce the heat dissipated by them. Each of those LM317s will reduce the 36V input to programmed voltages. ![]() There are three LM317s and three TIP2955 PNP pass transistors for each. You have to select proper packages if you want to create a PCB layout. So I didn't care about the component packages. But it was not designed to generate a PCB file as I usually perfboard for my one off designs. The schematic will give you an insight on my plan.
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