DC-DC dual output Switch Mode Power Supply (SMPS)

Dual_SMPS_assembled

This is a dual output 5V and 3.3V power supply, that operates from a 12 – 24VDC input. The intended use is for powering a special networking switch from a batterybacked supply. The device will need to operate in amient outdoor temperatures in the the central plains.
Requirements:

  • Input:  10.8 –  26 VDC, with +/–  2V fluctuation
  • Output 1: 5VDC at 1.5 amps
  • Output 2: 3.3VDC at 5.0 amps
  • Output ripple < 40mv p-p
  • Temperature operating range (-40 to +60 degrees C.)
  • High efficiency

Design is based upon the LM2673 5 volt and LM22679 3.3 Volt SMPS chips.  These simplify the circuit and cut the number of external components required.

The circuit is very sensitive to layout.  You can breadboard this, and it might run, but the output will be very noisy and may not deliver much current.  This really does need careful layout on the PC board, with care to keep the boost capacitor close to the chip, and the diode close to the inductor.

Dual_regulator_v1In the initial build, the 3.3V output has high noise (50mV p-p) and poor efficiency.  Redesigned the layout and changed to a better diode:  MBR745 from Vishay.  The new layout only has 30mV peak-to-peak noise.

Dual_regulator_layout

Shown here with out the copper pours, etc. The ICs and diodes are positioned with room to fit the heatsinks.  This version runs the network switch quite well.  The heatsinks do get warm, we’ll see how it performs outside on a hot day.

 

 

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s