Thursday, October 22, 2015

Modifying YDS-812 buck converters

These buck converters are great; readily available on Ebay for about $4 a pop.
YDS-812DC 20V-45V to DC 12V 8A Synchronous Adjustable Step-down Power Modulebuck DC-DC 20-45V to 12V 0.7V-23V 8A Step-down Power Supply Module YDS-812 Japan

Wins:

  • Well heatsinked, well made
  • Synchronous  for higher efficiency
  • Easily modified in useful ways
Official datasheet is here - however practical experience actually you can ignore quite a lot of it :-)
The over-current shutdown doesn't seem to work very well (I pulled 13A @ 5v out of one) and the minimum voltage spec is also pessimistic - when modded you can run them on lower voltage inputs. YMMV of course.

The main control chip is the Texas Instruments LM2727
The fets are 52N06 fets

Firstly; you MUST add electrolytic capacitors on the input and outputs or they just don't work; I put e.g. 1000uf (e.g. 35v) on the input and 2500uf on the output. You should use low-ESR caps.

Adjusting output voltage

On the PCB, VR1 is 1k,  VR2 is composed of an 18k (on the left) and a 1k (right) in series = 19k.
The controller wants to see 0.6v on the FB input, so the default divider values of 1k & 19k gives you 
12v 'input' (buck output) = 0.6v output (feedback to chip). 

The resistor divider calc is of course (19k+1k)/1k * 0.6v =12v at Vout  

When modding this board for lower voltage output I find it easiest to piggyback an extra 0402 resistor on top of the 18k one 

Here's the datasheet sample schematic that roughly matches what we have on the board (minus the 5v regulator, FET driver and other bits and pieces)...

Soft on/off

The transistor just above VR1 on the board is an internal on/off switch (not sure when it's used), but if you solder a wire onto the right hand side pin of it (according to the above pic) you get access to /SD; pull this low and the buck switches off.  Note it has an extremely weak (microamps) 5v pullup on-chip.



Saturday, January 3, 2015

How to fix Crucial V4 SSD I/O errors

I use a 32GB Crucial V4 SSD for the OS drive of my home theater PC; it's not a great drive but it works.. well, up until today, when an unexpected powerdown corrupted it. I tried to reimage the drive (I use "DD" under linux) but I got a bunch of IO errors writing to the SSD. DOH!  Normally I'd bin the drive and buy another one (hint; not a Crucial drive) but this time I found a fix...

If you re-flash the drive's firmware (using the bootable usb stick image found here ) it cautions in the docs here "!ALL DATA WILL BE LOST!"   ...well, y'know actually that sounds ideal...

And lo! Even though my drive was already running the latest firmware, the tool allows you to reflash it anyway, and bingo - twenty seconds later a completely blank SSD with no hard errors.

Happy new year!