Energy for your hacks

Inexpensive eBay DC/DC Converter

First things first

For the first entry of the website, a review. Nothing exciting but a good starting point to warm up. It will also help me to discover how should I input things here and how to structure it.

About the DC/DC Converter then! This inexpensive board is an converter for breadboards, with selecteable output voltage for pratical use. This one was bought on eBay in the listing MB102 Breadboard Power Supply Module 3.3V/5V For Solderless Bread Board TE for under 1€ with transports included. They promise the following features:

Input voltage: 6.5-12 V (DC) or USB power supply;
Output voltage: 3.3V/5V;
Maximum output current: <700 ma;
On-board two groups of 3.3V, 5V DC output plug pins;
Breadboard power supply module, compatible with 5 V and 3.3 V.

The guts of the board

This board is mainly built around two simple voltage regulators from Advanced Monolithic Systems. The AMS1117 is one 1A low dropout voltage regulator. The datasheet claims they are protected against short circuit and thermal overloads. "Thermal protection circuitry will shut-down the regulator if the temperature exceed 165°C", but I didn´t tried it out because I only bought one board and don't want to toast it already. On the barrel connector you have a diode to protect against reverse polarity damage.

WARNING! The board circuitry doesn´t protect the input, which means that if you connect your PC USB and short circuit it, you may end with a burnt USB port or worse. I recommend either using the barrel connector with an external power supply or a proper USB hub.

The quality of the board is OK. I like the black pcb color, it gives the board a geeky nature which I think is appropriate for what we do with it. The connectors, both USB and the barrel connector have enough quality to make a good and firm connection. We also get a ON/OFF button, as well as an LED. The connectors for the breadboard are positioned just about right.

What to expect?

12V -> 5V No Load

I will be loading the voltage regulators with resistive loads only. Starting with the 12Vdc supply and 5V output. The tension without load is around 5.04V but with a ripple of 480mV.

12V -> 5V 18Ohm Load

Adding now a 18Ohm resistor we pull from it 278mA, and we see no change, but the chip heated immediately to around 60-70ºC.

12V -> 3.3V No Load

Going now for the 3.3V output, this means using the other voltage regulator. Again with no load the output is 3.36V with a ripple amplitude of 480mV.

12V -> 3.3V 18Ohm Load

Finishing the 12V input test, I´ll use again the 18Ohm load on the 3.3V output. We have a readout of 183mA@3.28V. The power consumption is lower but the voltage drop is higher and therefore the chip heated even more to around 70-80ºC.

5V -> 3.3V No Load

If we use the USB connector, only the 3.3V output is regulated. The 5V output will be directly powered from USB VCC. The voltage regulation with the USB connector is worse than with the 12V input.

5V -> 3.3V 3.3V 18Ohm Load

Adding the 18Ohm load doesn´t change from the previous obtained values.

Conclusion

And that's it. First post :)