I soldered up a LM2678 for a 5V 1A output with a 12 volt input (Input voltage and current from (12v supply @2A) like shown here. http://www.ti.com/lit/ds/symlink/lm2678.pdf
It outputs a solid 5 volts under low < 50mA loads but experiences significant output voltage drop to ~3.6 volts under loads as small as 400mA. Any ideas what is causing this? It is soldered on perfboard with small distances between components. Mylar and Electrolytic capacitors are used for decoupling are are close to the input leads on the LM2678.