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$5.00 Buck/Boost Power Supply Module from China

Low-cost power supply module from China

A quick look at a power supply module I recently picked up from China via eBay.  Listed as: “DC-DC Step Up Down Boost buck Voltage Converter Module LM2577S LM2596S Power N2” at a price of $3.20+$1.85 shipping.  Input 4-35V, Output Adjustable from 1.25 to 25V. Current adjustable 0 to 2Amps.  There are three 10-turn adjustments for Voltage, Current, and “I don’t know”

The eBay listing includes the following specifications:

Input Voltage :4-35V
Output voltage: Continuously adjustable(1.25-25V unload adjust)
Output current: 3A Max(If more than 15W, please install the heat sink)
CC range :0-2A (adjustable)
Revolving light current: CC value * (1%-100%), default is 0.1 times
Minimum voltage difference: 2V
Output power: natural cooling 15W
Conversion efficiency: 80% (the higher the output voltage, the higher the efficiency)
Operating Temperature: Industrial (-40 ℃ to +85 ℃) (ambient temperature more than 40℃, lower power use, or add heat sink)
Full load temperature rise: 45 ℃
Indicator: CC indicator is Red, charging indicator is Red, charging completed the indicator is Blue.
Output short circuit protection: Yes, constant current.
Connect method: Can solder on the PCB with wire directly
Input: IN+ input Positive is, IN- input negative
Output: OUT+ output is positive, OUT- output negative
Module Size: 50 x 37 x 13mm
Some Applications:
High-power LED constant current driver.
Lithium batteries (including ferroelectric), 4V, 6V, 12V, 14V, 24V battery charging, nickel-cadmium nickel-metal hydride batteries (battery) charge.
Solar panels, wind generator voltage regulator circuit board power supply, such as automatic buck regulator circuit.

Some of the specifications don’t make a lot of sense to me.   What is “Revolving light current” for example?

Looking at the parts on the board I find

  • LM2577S 
    • TI Simple Switcher – Step-Up
    • Boost (Step-Up) the 4-35V input, making an internal supply of ?V
  • LM2596S
    • TI Simple Switcher – Step-Down
    • Bucks (Step-Down) the internal supply from the LM2577S to the desired output voltage or regulated current setting
  • 78L05
    • 5V Linear Regulator
    • Makes an onboard supply for reverence voltages and circuit operation.
    • Does this try to work on the input voltage or is it on the boosted supply rail?
  • SMD SS34
    • Schottky Barrier Rectifier
    • Input protection diode with 0.5V drop at 3A
  • Unmarked 8Pin SOIC
    • Probably an OPAMP used in the current limit feedback.

I played with the module a bit. The claimed efficiency is 80% but at idle with a 5V input and 15V output at no load, the module was drawing around 100mA.  There was a blue LED active on the board and my bench DVM on the output.

I may update this quick look review as I play more with the module.  When I find the time I plan to use the module to make a portable supply using a spare RC car battery I have sitting around.

What is the middle adjustment for?

I don’t know what they mean by “Revolving light current” which is apparently what the middle pot is for.  I’ve played a bit with the adjustment and might see a correlation to the output current setting.  Like maybe the light shows that some current is flowing at an adjustable level.

I’d love to see a schematic for this module.

Let us know if you know what the middle pot and the third LED does…

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