Admin Group
Joined: 31/12/2012
Location: New ZealandPosts: 10037
| Posted: 04:12am 09 May 2019 |
I've used lots of those LM2596 modules, and they work well, but are a buck-converter, and the input voltage has to be larger then the wanted output - pretty much like any standard linear regulator.
No, they cannot boost.
The 3608 module is really only good for boosting when the input voltage is 5v or less. It is because of the way the module has the trimpot arranged, which can easily allow for over-voltage on the FB pin.
Here is a schematic of the module:
As you can see, they have made the multi-turn trimmer R1, and the issue you have with this arrangement, is that if you apply - say - 12v to the input, and the trimmer is up near the positive output end of it's travel, when you switch on the juice, the supply voltage flows into the trimmer via the 22uH inductor and the Schottky diode. with the wiper of the trimmer up too far towards the positive end, this puts a potential of much more then 6v on the FB pin, and the device catastrophically fails due to breakdown of the FB pin input. The FB input is probably nothing much more then a gate junction internally, and just like any other MOSFET gate, if you exceed the maximum gate voltage.....Bang!
With a different schematic layout, this chip would work fine with higher input voltages, but the way they have designed the module, if your input voltage is more then 6v, and you turn the trimmer up too far, it is fatal for the device. The design needs refinement for use as an adjustable boost converter, as it is not very foolproof the way they have made them.
The datasheet gives the formula to calculate the output voltage from R1 and R2, but they are expecting you to use set resistors for R1 and R2, NOT an adjustable resistor for R1 - that is where the design falls over a little.
They are only for low-power use. Less then 1A, really. Although they are rated for 2A, I tend to de-rate things like this UNLESS you can guarantee the source of the parts that they have used, and as you can't.....
Smoke makes things work. When the smoke gets out, it stops!