Replacing inefficient 5V SMPS with more efficient module

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Replacing inefficient 5V SMPS with more efficient module

Postby AdrianM » May 19th, 2017, 5:03 am

In my topic regarding the repair of a Roomba 530 I ended up replacing the original 5V Buck regulator with an integrated module. I think it's an inexpensive and effective mod - not least because the original is not very efficient but also seems to fail people on occasion. The MC34063 quiescent and outboard FET driver currents sum to around 7mA which is the bulk of the 530's load in sleep mode. I used a commonly available module based on the MP1584 regulator which measures only 22mm x18mm and has a quiescent current draw of only 0.1mA
MP1584.jpg (22.11 KiB) Viewed 115 times

Searching for MP1584 in your favouite online store should get you one for around 5$ or less.

WARNING: This particular module has a trimmer potentiometer which is used to set the output voltage. Before connecting to Roomba it must be adjusted to output 5V. This requires an accurate method of measuring the voltage - ideally using a small load to keep the output capacitor in line with changes in voltage. Having set it, a dab of hotmelt glue or paint is advisable to keep it there! Only think of attempting this mod if you are comfortable with the techniques involved and the potential for severe damage that might result if you mess up.

First I removed all the components marked in red here:

L1 does not have to be removed as it is blocked by D55 - I just didn't like it! I do have a vacuum desolder pump though but if you don't it might be better to leave it alone.

(Without a pump, I find the simplest way to remove such parts is to use a fairly large soldering-iron bit to blob enough solder to bridge the component - or one side of the component (levering it up with a thin blade) and clean-up after with de-solder braid.)

Next I soldered three short flying leads to the IN+ OUT+ and IN- (connected on the module to OUT-) and heatshrink wrapped the entire module. The flying leads were soldered to the matching points labelled in the schematic. I made connections to the underside of the main PCB so the module could nestle beneath in the space behind the bumper.

The best place to make these connections depends on whether or not you remove L1. I used the vacated hole connected to C287 to attach OUT+ and solder bridged S & D on Q7 to get power to IN+ on the former other side of L1. The SYS_RET ends of leaded Diodes make a good place to attach the IN/OUT - Next time I have the case open I will take some photos.
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Re: Replacing inefficient 5V SMPS with more efficient module

Postby vic7767 » May 19th, 2017, 9:34 am

:thanks: :icon-lol: :cheers: Great info!
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