Just a Q about LM78XX

Lycurgus · Post by **Lycurgus** » Mon May 19, 2008 7:14 pm

My question is in regards to powering a slim ps2 or something else that requires enough amps to power, to my understanding, people have asked what regulator to use when they have a 12v battery and want to drop down to power screen/ps2

Now I know people have said in these threads "Use 7808" or other regs

But dont most regular regultors (especially in LM series) output current of 1 - 1.5amps, and the excess amps turn into heat? Just curious, Ive heard of a transistor to boost output amps from a regulator. But just checking here

Post by **marshallh** » Mon May 19, 2008 11:54 pm

The 78xx series regulators are linear regulators. All extra energy is wasted as heat.

What you need is a switching regulator. By using PWM it pulses the input voltage on and off very quickly, and the duty cycle determines the output voltage which is filtered. More complicated, but much more efficient and a necessity for portables.

See if you can find some TI PowerTrends integrated switching regulators (ISR).

Electric Rain · Post by **Electric Rain** » Wed May 21, 2008 10:11 pm

What Marshall said is, as usual, 100% accurate. For example, if you had a 7805, and you were giving it 12 volts, nearly 60% of that energy is wasted. So yes, you definitely want a switching regulator if efficiency is at all important to you.