Power Sourcing Issue with PIC18F4550

[Hollowaykeanho]

Hi all,

I'm currently developing a mobile robot for my assignment and I wanted to design the PIC18F4550 PCB board powered using LiPo Battery 12V, while doing the output.

Problem: 1) When the battery power source is connected, everything is not working especially UART but there is a steady 5V voltage come out after L7805CV voltage regulator.

Complexity: 2) When reverted to PC USB power source, which is connected within PIC circuit, everything works out pretty fine even my UART, clock etc etc. This complicates the circuit as the circuit design is working.


The power circuit flow below:

Power 12V --> High Power Diode (1-2Amp) + (without Resistor) Filter Capacitor 30pF connected to ground ---> L7805CV ---> (without resistor) Filter Capcitor at 30pF connected to ground + PIC Circuit


USB Power ---> Directly into PIC Circuit within (Circuit secondary power source for debugging purposes)


More Information:
My Master Reset is set high for both (as pressing the button with short to GND). Works well for both.

Clock Capacitor: 33 pF
Crystal: 20MHz


I'm aware of the problem came from the power source itself but I couldn't find what's the cause of the issue. Could anyone help me spot the root cause of the problem? Please let me know if you need more information.

Thanks you in advance.

[ABSF]

Power 12V --> High Power Diode (1-2Amp) + (without Resistor) Filter Capacitor 30pF connected to ground ---> L7805CV ---> (without resistor) Filter Capcitor at 30pF connected to ground + PIC Circuit

Are there any electrolytic capacitors (47uF to 330uF before and after the 7805)? I think 30pF is too low for filtering power noise. Try 100nF to see if it works.

Allen

[Hollowaykeanho]

Are there any electrolytic capacitors (47uF to 330uF before and after the 7805)?

Yeap. Cap in and out are 30pF for each.

I think 30pF is too low for filtering power noise. Try 100nF to see if it works.

Changed to 100nF. Worked now. =)

Thanks ABSF.