Sunday, April 29, 2018

Distortion noise from USB power supply

Just for experimentation sake - because i use to power my circuit using the USB 5 Volt power supply as it is easily available in front of my table. The batteries always gone out of juice and i am tired of buying them again and again. So the USB power supply either from the PC or the from USB charger is a great power source for small electronic projects.

However if you don't look into the details you won't realize there is a great significant of distortion noise coming from the USB power supply. This is very important aspect to understand especially when building circuit like audio amplifiers and radio frequency amplifiers. The impact of the distorted noise could ruin the project without you knowing it where it comes from and how to fix it.

I believe the noise could be emanating from the step down transformers which generated by electro-magnetic fields. This could be detected if you place non-touching AC detector near the USB power supply. If you don't fix the noise from the USB power source an amplifier circuits will carry it inside the circuit and generate distorted output.

There are 2 solutions that i can think of how to solve the noise from the USB power:

One of to make a circuit using linear voltage regulator - the idea is to regulate the voltage / current flow and reduce the electromagnetic noise from the USB. 5 Volt voltage regulator is suitable to use in this case so that we can still have the 5 volt output.

Another way is perhaps to add capacitor or resistor - but this might reduce the current output of the USB power.

Toroid core could also reduce the electromagnetic noise within the USB cable. That's why most charger cables with with the bulge in it - that is the toroid core

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