Home brew SMPS PSU

"Science is a wonderful thing if one does not have to earn one's living at it."

Albert Einstein

Intro 

 For this Project I wanted to make a PSU. I had found a Brute force PSU Made for a CB. Its original specs were 13V @4 Amps. I opened her up and gutted it. I saved The transformer and plan on using the case. I was originally going to use a Linear Regulator, but then I got a job, and Bought the parts for a SMPS PSU.
 

Why SMPS? SMPS Stands for Switch mode Power Supply. SMPS's Are way more efficient than their Linear Counterparts, because there isnt much loss in the components. You can think of a linear Regulator as a variable Resistor. If there is a large input voltage, The regulator has to drop a Large Voltage and pass the same current as if it were running from a smaller voltage. This means there is a Large Power Loss if your Output is very Low or your input it very High. SMPS address's this by using switching regulation. Instead of acting like a resistor, SMPS's use switching to control an Inductor to buck, boost or invert the Output. Efficiency's are Now ranging from 80 to 95% Versus 40 to 50% for Linear Regulators.

However, Everything is not without cost. SMPS are a bit Bigger, but if you compare this with the physical size of the needed heatsink for the same linear counter part (along with the transformer) SMPS becomes a better option. Linear Maybe cheaper, But the Cost for this project is $16. I have the filter caps that I got from a friend sometime ago.

For this Project I am going to use the LM2679 Simple Switcher Buck Regulator. The Simple switcher family is meant to be simple, and not complex, Like the LM780X Family. Pretty much Plug and Play. I am also using Through hole, since SMD parts might be a bit hard to come by.


Technical Info:

  • Vin Max: 16.46 V
  • Vin Min: 11.45 V
  • Vout Min: 2V
  • Vout Max: 15V
  • Iout Max: 4A.
  • Expected Efficiency: 80 to 90% 

 

 

 


  The Only difference in my version is the fact I am using a Pot for R1 to adjust Voltage. I may Add in a pot at Radj to adjust current also.

Parts Chosen:

Flywheel Diode:

  • MBR1060G- 10A 60V Schottky Diode. 

Inductor:

  • 33uH- 
  • DC Resistance: 13mOhms
  • Max DC Current: 11.7A


C in: (not including Filter Caps)

  • 2,000 uF Cap @35V
  • ESR Per Cap: 30mOhms @25C
  • Total ESR: 15mOhms 
  • Number of Caps In Parallel: 2 (1,000 uF Each)
  • High Temperature Electrolytic Type


Cout:

  • 3,000 uF @ 35V
  • ESR Per Cap: 30mOhms @25C 
  • Total ESR: 10mOhms
  • Number of Caps In parallel: 3 (1,000 uF Each)
  • High temperature Electrolytic Type


Radj (limits Peak Current)

  • Value:6.2k Ohms 
  • Tolerance:+/- 1% 
  • Wattage: 1/4W


FB R1

  • Value: 1kOhm 
  • Tolerance: +/- 1 % 
  • Wattage: 1/4W


FB R2

  • Value: Variable 2k Pot 
  • 20% Tolerance
  • 300 Deg Rotation +/- 5 deg
  • *NEW* I found 10k Is too coarse, so 2k Is better. I wonder if 1k Would be better and allow me to get more voltage adjustment.


Cboost:

  • Value: 0.01uF Ceramic 
  • Voltage: 50V


And of course the IC cost $6.50 or So


Total Cost is $16. Not bad for a homemade Lab PSU.