Glancing through my feeds, I stumbled across a note on The Paleotechnologist describing a new replacement for the venerable LM7805 linear regulator IC. It turns up in a ton of devices, pretty much anything with a medium-current 5V rail including some stereos, computers, power supplies…mostly anything you can think of. And the old version isn’t that efficient:
Take the LM7805, for example. It does a good job of regulating voltage — from a minimum of about 7V or so, it will provide a steady 5VDC output. The only real problem is that it does this by basically adding a dynamic resistance to simply burn off the excess voltage at whatever current you’re using. If you were to power a 5V, 1A load through a LM7805 connected to 12V, it would need to dissipate 7W of power, since it would basically be acting as a resistor; that 7V voltage drop, combined with the 1A of current, means it would be putting out 7W of heat. Without a BIG heatsink, it would quickly get too hot to work. Also, you’d be wasting over half of the power for the device, even if the rest of your circuit was 100% efficient.
Looks like CUI came out with a new, drop-in 7805 replacement which implements a DC-DC switching converter for voltage regulation, rather than a linear regulator. Way less heat and lost power with this module! I’ll probably spec it in future projects if I end up needing to replace a 7805 in some old gear, looks very interesting!
The folks over at Hack-a-Day have already found a hobbyist who put this module through it’s paces. Daniel over at Daniel’s Electronics Blog does some bench testing the switching drop-in replacement for the 7805. to test it’s efficiency.
The graph of efficiency versus load is shown below, the peak efficiency is around 92%. Not bad for a 12V input.
Not bad for a 12V input indeed, the linear chip would be wasting a ton of power as scorching heat with the same conditions.
The Paleotechnologist: A Better Voltage Regulator
Hack-a-Day: BENCH TESTING A SWITCH MODE DROP IN REPLACEMENT FOR THE LM7805