Chinese LM2596 step-down converter modules

R

Redwire

New member
I needed a high-current car USB charger 5V at 2.1A for my iPad, smartphone etc. Chinese LM2596 3A step-down converter modules are for sale on eBay and DX for $1.50 to $4.40 (which is cheaper than I can buy the IC for), so I picked some up. I bench tested them and here are the results and thermal-camera pics at 5V 2.4A output and 13.5VDC input (~81% efficiency). The LM2596 runs 105°C and the diode 112°C ! x-(
As you can see, they run way hot and the diode is only a 1A part. I thought, why run a $450 tablet off a crappy $2 converter, that has no overvoltage protection, no fuse, overheats... I'm building something better...

LM2596_module_c.jpgLM2596_module_back_c.jpgIR_0688.jpgLM2596_eBay schematic.jpg
 
T

Tahmid

New member
Hi,

I'm curious about the camera. Could you post some information about it?

As for the converter, you could build a simple switching regulator using one of many available converter chips. One chip that I used extensively that performed reliably was the L4960. For higher current, you may take a look at L4964.
 
R

Redwire

New member
That IR camera is a Flir E30, I use at work to identify hot spots on circuit boards for UL/CSA tests on my designs. IR cameras are expensive and low-resolution. Our budget was around $2,200 and that gets you 160x120 pixels IR with a 2MP visual camera. It's very uselful for electrical panels and building heat loss too.

I'm going ahead with a design for a high-current USB car charger using the TPS54360 for 6-60VDC in, 3.5A max. output, in a SOIC-8 with thermal pad. The newer IC's have a mosfet switch, instead of bipolar transistor, and are much more efficient = less heatsinking.

If anyone is interested I can post the draft schematic, I started PCB layout.
 
R

Redwire

New member
5.1V or 5.2V is nice to have - some USB chargers output 5.1V; USB's voltage spec is 5.0V +/- 5% (4.75V to 5.25V) so I think the extra 0.1V compensates for the voltage drop across the USB cable/connectors.
I also want to run a Raspberry Pi in the car and it has a lossy polyfuse and 5.0V is pretty slim
 
T

Tahmid

New member
Redwire said:
That IR camera is a Flir E30, I use at work to identify hot spots on circuit boards for UL/CSA tests on my designs. IR cameras are expensive and low-resolution. Our budget was around $2,200 and that gets you 160x120 pixels IR with a 2MP visual camera. It's very uselful for electrical panels and building heat loss too.
Click to expand...

Thanks for the information. Neat device! But so expensive! :eek: But I guess, if you dish out the cash and use it frequently, it's every bit worth it.
 
R

Redwire

New member
Just an update- I found part of the overheating is due to instability. At certain loads and input voltages, the freq. is all over the place.
I optimized for 11-16VDC in, and 5V out up to 2.5A output by increasing the input cap from 220uF to 330uF, and output cap from 220uF to 1000uF (although datasheet max. is 680uf).
Changed the pee-wee buck diode to B340 and this runs much coolerl.
 
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