Buck Converter Issue

I am trying to step down a voltage ranging from 5v-12v down to 3.3v, using this buck converter http://www.ebay.com/itm/Mini-MP1584EN-DC-DC-BUCK-Adjustable-Step-Down-Module-Effect-Higher-Than-LM2596-/301668096806?hash=item463cd1db26:g:0wAAAOSwT6pVhnzf.

However, I seem to be seeing this issue:

Input voltage: 5.5-12v Output voltage: 3.3v -> OK
Input voltage: 4.5-5v Output voltage: 3.9v
Input voltage: 4-4.4v Output voltage: 3.1

Why does the output voltage jump to 3.9v with 5v input? I have a handful of the same buck converter, I tested them all and got the same result.

I also have these http://www.ebay.com/itm/mini-DC-DC-Converter-Step-Down-buck-Power-Supply-Module-for-Flight-Control-Car-/400985370863?hash=item5d5c9730ef:g:ufQAAOxy4t1ShMyT, which doesn't seem to have that issue. These converters appear to output 3.3v when the input voltage is 3.8v-12v.

Does anyone know the cause and reason of the voltage increase at 5v?

Did you have any load on the output? Sometimes a regulator can be a bit jumpy without.

Being lightly loaded sounds like the culprit. This is from the MPC data Sheet:

At no load or light load, the converter may operate in pulse skipping mode in order to maintain the output voltage in regulation. Thus there is less time to refresh the BS voltage. In order to have enough gate voltage under such operating conditions, the difference of VIN –VOUT should be greater than 3V. For example, if the VOUT is set to 3.3V, the VIN needs to be higher than 3.3V+3V=6.3V to maintain enough BS voltage at no load or light load. To meet this requirement, EN pin can be used to program the input UVLO voltage to Vout+3V.

The complete data sheet can be found here: MP1584EN data sheet

Thanks septillion, avr_fred. You were both right, I was testing it on no load. On very light load, it dropped from 3.9v to 3.5v. I appreciate the replies, now I know it requires a minimum load to run properly. :slight_smile:

Hi,

Yes, a lot of switchers are like that too not just this one. The boost circuit are sometimes even worse.

Well, even linear regulator sometime has a minimum load, eg. LM317 require at least 4 to 10 mA to mantein regulation.

Ciao, Ale.