#PI FILTER AUDIO POWER SUPPLY DESIGN HOW TO#

I don’t think your sensitive analogue components would thank you for connecting them to this supply. I’m sure you’ll agree the noise levels are pretty awful with spikes of +/- 100mV. The vertical resolution is 50mV/div in all the captures. Here’s a selection of screen grabs from the oscilloscope showing the noise on the supply from the two ports. Let’s get started by showing just how bad things are without any filtering. The cables from the back of these ports has to travel quite a long way across the case to the motherboard header for the USB 2 ports and across the board to the slots for the USB 3 ports. The remaining four ports connect back into the motherboard USB 2 headers.įor these tests I’ll be looking separately at VUSB on the USB 2 and 3 hubs on the left of the picture. The two blue ports on the left connect to a generic no-name PCIe USB 3 expansion card. I have a number of root hubs exposed through the front panel of my case. I should really be using a ground spring on the scope probe instead of a wire and clip but I haven’t got one those so I can’t.įirstly let’s establish the baseline by probing VUSB on a couple of USB ports. I’ll be using my trusty old HP 500MHz oscilloscope and I’ll be probing directly at the component legs so as not to introduce noise from jumper wires. I’l be using the hacked USB B connector pictured above and connected to a breadboard for testing. The result is a nice and stable VBUS line that you can use to feed your sensitive circuits.

#PI FILTER AUDIO POWER SUPPLY DESIGN HOW TO#

If you’re running a sensitive component such as an ADC or DAC then you need a clean power supply and all this noise will really ruin your day.Īnyway I thought I’d provide a practical example of how to clean up the power supply and eliminate all that noise. There’s persistent ripple and some mightily impressive spikes that sail through at seemingly random time intervals. There’s random noise at high and low frequencies. In fact I was surprised at just how noisy it is. I’m currently working on a new project that contains sensitive analogue components and have rediscovered what many before me already know, that is that the VUSB 5V line that comes out from your computer’s USB hub is noisy.

Pi filter audio power supply design