Power supply PCB problem

Thread Starter

Servinas Hassan

Joined Jun 23, 2022
2
IMG_20220623_210815.jpgScreenshot (238).png
I made a PCB Design for adjustable power supply circuit.
But I face some problems ... My real design doesn't work although it was work on simulation and testboard...but for pcb it doesn't...I checked the connection, soldering and made sure that all component work ...but in pcb I find that one of two diodes made short circuit from both side and I tried to change it but after remove it I found that diode is still working ...making this with two another diodes I think that the problem my by in my design, and the same thing happened with LED, and my instructor didn't find out the problem
Can anyone tell my where is the problem here and if I will face another problem?... I post also picture of my design on PCB and simulation
 

Jon Chandler

Joined Jun 12, 2008
260
R2 should be 120 ohms to maintain the minimum current required for regulation under all operating conditions.

Data sheets typically show this resistor as 240 ohms, but that's for the LM117, which has half the minimum operating current as the LM317. This has caught a lot of people over the years. Data sheets are usually for LM117 & LM317, but the latest TI data sheet is only for LM317, yet they still show the 240 ohm resistor.
 

bassbindevil

Joined Jan 23, 2014
461
C1 should be right next to the bridge rectifier. Capacitor charging current spikes through long traces could cause ripple in the output. For a layout like that, I'd start by drawing on paper, figure out the best orientations, and then go to CAD.
 

Jon Chandler

Joined Jun 12, 2008
260
Good call on C1, a 2200 uF electrolytic cap. The pattern on the board is for a small disk cap, not a relatively large electrolytic.

What type of cap is being used for C1?
 

dendad

Joined Feb 20, 2016
4,168
Well done on an early attempt for a PCB design.
When I draw power supply PBCs, I use large tracks, not thin like you have. After all, this is designed to supply current so you want to minimize the losses.
Also, as @dl324 asked, why such a lot of wasted space? Here is just the first PCB picture I found. Note the large areas of copper. And the compact layout.
1656037083007.png
This was a Google find from https://xtronic.org/circuit/regulated-power-supply-lm317/
 

dl324

Joined Mar 30, 2015
14,700
This board has 3 power supplies. A fixed 5V and 2 other supplies, each with 2 switch selectable voltages and 1 variable:
1656039151984.png1656039166591.png
The board is 2.5" x 1.7". One of the adjustable supplies has remote sensing.
 
Last edited:
Top