Switching voltage regulators
Buck-boost using XL6009
buck using LM2596
buck using MP1484 or MP2307

Switching Regulator Boards

Switching regulators can be grouped into a few basic flavors:

Buck

or down: Output voltage is lower than the input voltage.

Boost

or up: Output voltage is higher than the input voltage.

Buck-Boost

or up-down: Output voltage may be either higher or lower than the input voltage.

Inverting

Output voltage in negative, input voltage is positive.

Typically buck-boost converters are more complicated than straight buck or boost. They come in handy with batteries, where the voltage can vary widely depending on the state of charge.

For low power applications such as an Arduino, Raspberry Pi, or similar boards, suitable Chinese regulators typically consist of a single-chip switching regulator with the inductors and capacitors it requires. So comparing boards means finding the data sheet for the IC.

Selection Considerations

First step in selecting a regulator is to make sure it can deliver the output voltage and current needed, and that it can handle the input voltage.

Other significant parameters to consider are:

Switch frequency

a higher switching frequency means lower inductor and capacitor values can be used. In other words, higher frequency means the circuit can be smaller and cheaper.

Synchronous

the function of the diode is performed instead by circuitry inside the chip. In addition to saving one component, efficiency is usually higher.

Switch type

Chips using bipolar transistors are usually cheaper, but FET's tend to be more efficient.

My Buys

I have these:

Chip	Type	Khz	Switch	Vin	Iout	Synchronous
XL6009	up/dn	400	N-MOS	5-32	?	No
LM2596	dn	150	NPN	4.5-40	3A	No
MP1484 MP2307	dn	400	N-MOS	4.75-18 4.75-23	3A	Yes

For the third one, the Ebay listing said the board uses the MP1484 chip, but the ones I received are marked MP2307. Assuming the chip markings are accurate and not counterfits, it's a slightly better chip than what I ordered.

Testing

For a simple test, I connected the LM2596 and MP2307 to a 12-volt supply (measured 12.13 actual) with a resistor load measured at 63.0 ohms. Output voltage was set to approximately 5 Volts using the on-board potentiometers.

Chip	Input Current No Load	Input Current Loaded	Input Power	Output Voltage	Output Power	Efficiency
LM2596	7.54mA	47.1mA	0.571W	4.95V	.389	68.1%
MP2307	6.86mA	41.4mA	0.502W	5.08V	.410	78.8%

Output ripple waveform for LM2596

Output ripple waveform for MP2307

The data sheets for the two chips assume operation at higher currents (1 to 2 Amperes). The LM2596 output waveform is consistent with discontinuout mode (ie, lightly loaded), and the measured efficiencies are roughly consistent with the published curves (efficiencies should be in the 90 to 95% range at 1A output).

I didn't do measurements on the XL6009: I only have one, and I managed to damage it. Per a Discussion on Stack Exchange, this board appears to use a two-inductor circuit for up-down operation. That's said to be simpler, cheaper, and less efficient than the transformer-based circuit recommended in the data sheet.