DC-DC with lm2576

I've just wanted to experiment with DC-DC stepdown power sources but I'm just not skilled enough to start from scratch, so I've decided to use lm2576.

 

Parameters

The board is designed for one of following:
  • lm2576T-05 stepdown 3A 5V
  • lm2575T-05 stepdown 1A 5V
  • lm2576T-ADJ stepdown 3A adjustable
  • lm2575T-ADJ stepdown 1A adjustable
But should work with any of lm2575 or lm2576 stepdowns.

 

The stepdown needs at least 2V more on input compared to output (not counting additional 1.2V drop on rectifiers) otherwise output oscillates on the stepdown frequency.

Measured efficiency for lm2576T-05 module with 20V input was somewhere near 80%.

 

Schematics

The schematics is stepdown derivated from datasheet with additional rectifier on input and additional 52Khz filter on output.
lm2576 schematics

 

PCB

It's desgined to fit on 50mm x 100mm PCB.
lm2576 PCB layout

 

Parts


Common Parts

  • TO220 heatsink (V7142A in www.gme.cz)
  • CONN1, CONN2 connectors
  • Pins for jumper J1

Input rectifier 1A

  • D2, D3, D4, D5 - 1N4007
  • C1 1000uF 50V instead of 100uF 50V

Input rectifier 3A

  • D2, D3, D4, D5 - 1N5402
  • C2 2200uF 50V instead of C1

Additional filter

  • L3 22uH 3A
  • C4 100uF 50V

lm2576T-05

  • U1 lm2576T-05
  • L1 100uH 3A talema coil
  • C1 100uF 50V
  • C3 1000uF 10V
  • D1 1N5822

lm2575T-05

  • U1 lm2575T-05
  • L1 330uH 1A talema coil
  • C1 100uF 50V
  • C3 330uF 10V
  • D1 1N5819

lm2576T-ADJ

  • U1 lm2576T-ADJ
  • L1 150uH 3A talema coil
  • C1 100uF 50V
  • C2 2200uF 50V
  • D1 1N5822
  • R1 1k2
  • R2 50K pot

lm2575T-ADJ

  • U1 lm2575T-ADJ
  • L1 150uH 1A talema coil
  • C1 100uF 50V
  • C2 2200uF 50V
  • D1 1N5822
  • R1 1k1
  • R2 50K pot

 

Download

 

Galery

5V version with rectifier and output filter

stepdown I stepdown II stepdown III

Adjustable prototype

stepdown prototype I stepdown prototype II stepdown prototype III