I’ve been having a hard time finding oscilloscopes and adjustable power supplies in the “hobbyist” price range, but I think I have cobbled together a solution.
A few key components:
- Power supply from old PC
- Make sure to short the correct pins to trick the power supply into turning on. This is usually green to black.
- yellow-black is 12 V
- red-black is 5 V
- orange-black is 3.3 V
- If you want other voltages, well.. time to built a buck-boost circuit!
- Gabotronics Xprotolab mini oscilloscope
- 2MHz sampling
- 8 bits resolution
- $50 (the best part)
Here is a recent test that is perfect for the components listed above: characterization of the DC buck converters for car USB chargers. In this test, I am measuring the operating frequency and ripple of an Adreama 1A USB charger. The charger is hooked up to the 12 V rail of the power supply, and the 5V output is applied to a power resistor as the load.
As expected, the performance of the charger is a strong function of the load. In this case, a 5 ohm power resistor is drawing 1 A from the charger. The buck circuit is operating at 50 kHz, but with 0.4 V of ripple. Ouch!