Measurements of DC-DC Converters

Oscilloscope tests to check shape, ripple, accuracy

Update: for some more detailed tests, check this article.

I bought some DC-DC converters to make a custom car USB-charger for my phone, able to supply more than 1.5 A on each USB port, with a good filtering of the spikes from the ignition coils and with low noise. The idea came after reading Ken Shirriff's article and after noticing that my car has no cigarette connector for ready-made chargers.

Since my phone can be charged with up to 1.6 A and I wanted to provide two connectors, for a total 3.2 A current at 5 V, my choice for a DC-DC converter was Buck Constant voltage Constant Current Module - Blue (DC-DC / 5A). I report here the original photos and the specifications.

Non-isolated step-down module (Buck);
Input Voltage: 4.5~30V;
Output Voltage: 0.8~30V continuously adjustable (default output 5V); 0.8~30V fixed output;
Output Constant Current Range: 0.1~5A (default output current 3A);
Output LED jumping range: 0.1~5A (default LED-jumping current 0.3A);
Working Temperature: -40'C~+85'C;
Working Frequency: 300KHz;
PWM Controllable Frequency range: 100~300Hz

Dimensions: 2.44 in x 1.06 in x 0.94 in (6.2 cm x 2.7 cm x 2.4 cm)
Weight: 0.92 oz (26 g)

Then I performed the following tests with a Hamed-312-8 oscilloscope and a 60 MHz probe used at 1X:

12 V input, 5 V output, no load; 24 V input, 5 V output, no load
24 V input, 5 V output, no load

24 V input, 0.77 A resistive load
24 V input, 0.77 A resistive load; different scaling

24 V input, 3.95 V, 1.45 A resistive load
24 V input, 3.95 V, 1.45 A resistive load; different scaling

12 V input, 5.60 V, 0.77 A resistive load
12 V input, 5.60 V, 0.77 A resistive load with ferrites on the output

12 V input, 5.60 V, 2.00 A resistive load
12 V input, 5.60 V, 2.00 A resistive load; with ferrites on the output

12 V input, 5.60 V, 2.00 A resistive load, with ferrites and plastic film capacitor on the output
12 V input, 5.60 V, 2.00 A resistive load, with plastic film capacitor on the output

The following ones are similar tests performed on a step-up & step-down module from AliExpress: DC-DC Boost Buck Converter Step Up Step Down constant current adjustable output voltage. I report here the original photos and the specifications.

Module Properties: non-isolated step-down constant current, constant voltage module (CC CV) charging module
Input Voltage :4-35V
Output voltage: Continuously adjustable(1.25-25V unload adjust)
Output current:Max 3A(If more than 15W, please install the heat sink)
Revolving light current: CC value * (1%-100%), default is 0.1 times
Minimum voltage gap: 2V
Output power: natural cooling 15W
Conversion efficiency: 80% (the higher the output voltage, the higher the efficiency)
Operating Temperature: Industrial (-40 °C to +85 °C) (ambient temperature more than 40°C, lower power use, or add heat sink)
Full load temperature rise: 45 °C
Indicator: CC indicator is Red, charging indicator is Red, charging completed the indicator is Blue.
Output short circuit protection: Yes, constant current.
Module Size: 50 x 37 x 13mm

No load

Resistive load (the shape is about the same for both buck and boost modes)

Author: Olaf Marzocchi

First revision: 2015-01-20.
Last revision: 2018-01-06.