Is a $1 Power Supply Any Good? + Wave Winners

3 quick & easy power tests you can run with an oscilloscope: ripple, turn-on, and turn-off Sign up now for the Wave giveaway: http://bit.ly/YTWave2020 Click to subscribe! ► http://bit.ly/KLabs_sub ◄

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I recently came across some cheap boost converters on Amazon, these claim to take 5V in and boost it up from Vin to 25V. I’m a little skeptical, but I was curious how well they actually worked, so join me for a couple quick tests that I like to use to do a quick check of a supply, and we’ll put this thing through its paces. First off, let’s measure the output ripple. You can do this manually, but I prefer to use the power app on the scope. To set it up, we probe the output and setup our measurement. We can get a better measurement with a better probe, but this standard passive probe will work fine. To set this up manually put your channel into AC coupling mode, zoom in, and make your measurements. We have a micro USB input, so naturally we’ll use 5V as our input voltage, and our output voltage is clocking in around 20 V. So, when we make the ripple measurement we see our peak-to-peak and RMS values on our 20V output. I’m pretty happy with that, it’s just a couple percent. Ripple on a supply rail translates to noise, though, so for audio work or jitter sensitive designs this is probably not a good supply to use. With my cursors I can see this is about an 350 kHz signal, but to double check it won’t hurt to turn on an FFT. I’ll do FFT, set my start and stop frequencies, and I like to use “max hold” to make things easier to see. Only use this for consistent signals – it’s not a good option for 1-off measurements. I can see my peak, and a couple harmonics. I also see some 1/f action here, but my gut says this is also likely an artifact of this sawtooth shape. Notice how much this varies from cycle to cycle? That’s going to smear out the power over a range of frequencies, which is what we’re seeing here. Let’s also take a closer look at the signal – do you see these little spikes here? If I measure the frequency of them with my cursors, I would bet this scope that it’s caused by the boost converter’s switching frequency. It looks like 1 MHz, but don’t be fooled. Let’s grab a few single captures and see what we get. It looks like these spikes happen every 350 kHz. Let’s see what we find if we pull the part number. It looks like there’s a 35 ... https://www.youtube.com/watch?v=QYmR1rcznH8