I am trying to make nixie clock and I use MC34063 for buck/boost converters. The nixie tubes require 180 V to operate and the microcontroller and LEDs need 5 V. I use external 20 V power supply as a source. Here are the circuits:
When the circuit is powered I can hear an annoying audible noise. The sound comes from all small SMD capacitors. It sounds something like 13 kHz sine wave. I power the raspberry pi from the 5V line and it's capacitors become noisy too.
I have tried to change 100 uH coils to 220 uH, but it didn't change anything. Please help.
Here is a link to full project and PCB design for more info
UPD1: The external power supply is not the issue. I tried to power the circuit from a different one and even from a 12V LiPo battery and the noise didn't change.
UPD2: I measured the frequency of the timing capacitor charge/discharge:
The 180 step-up converter is running at 47 kHz
The 5v step-down is running at 49 kHz
I also noticed a weird behavior of 5V's timing capacitor when the LEDs are on
UPD3: here I found that capacitors used in switching power supply should be low-ESR. I am not sure, that my capacitors fit this rule. Here are the datasheets of my capacitors:
220uF
: https://lcsc.com/product-detail/Aluminum-Electrolytic-Capacitors-SMD_220uF-35V_C3340.html
4.7uF
: https://lcsc.com/product-detail/Aluminum-Electrolytic-Capacitors-SMD_4-7uF-400V_C88703.html
100uF
: https://lcsc.com/product-detail/Aluminum-Electrolytic-Capacitors-SMD_100uF-35V_C88675.html
UPD4: I swapped all my electrolytic capacitors with low ESR ones, but the noise didn't change. I measured the voltage ripple of 5v line, it wiggles in 300mV window at approx 4kHz: