ruffrecords
Well-known member
delphi said:Just read this thread and it looks like I am too late. Count me in for 4/6 if you do a second run please.
Probably a stupid question, but I recollect the regulation requires a minimum load of 15ma - so I assume this is taken into account with your output loading ??
The data sheet does indeed recommend 15mA minimum and sets the value of the resistor across the 1.25V reference to ensure this. It does however mean over 700mW of heat dissipated in the lower leg of the pot divider (which is why the layout allows space for a 2 watt resistor). To help even more I usually tweak this resistor to set the correct output voltage and I do this by using a pair off 2watt similar valued resistors in series which further reduces the dissipation in each one.
That said, the TL783 data sheet shows you only need 8 mA standing current to maintain regulation at an input voltage of 70V so I usually set the resistor across the 1.25V reference to 120 ohms (see PCB) which ensures a 10mA minimum.
Cheers
Ian