Discussion in 'Electronic Basics' started by [email protected], Mar 24, 2008.

1. ### Guest

I'm reviewing the datasheet for the LM1875.

Page 4, upper-left, has a Power Dissipation vs. Power Output graph for

For +/-30V, to get 30W out, power dissipation is given as 47W.

What is meant by "power dissipation"?

Is this total heat generated, for heatsink load calcs?

Is this the total power consumed ( = the power delivered by the power
supply)? If so, then the chip is 30W / 47W = 64% efficient, right?

Michael

2. ### Phil AllisonGuest

** Yep.

** Nope.

** No.

The LM1875 is not usable at 4 ohms with more than a +/- 20 volt supply -
as it has in internal current limit of 4 amps.

30 watts into 4 ohms = 11 volts rms = 15.5 volts peak.

So with a +/- 30 volt supply, the IC is only able to use half the available
supply voltage with a 4 ohm load.

Makes it very INEFFICIENT !!

It will go into thermal shutdown and/or gross distortion with a 4 ohm

........ Phil

3. ### Don KlipsteinGuest

In <>,
That is true.
No, efficiency in this case is 30W / (30W + 47W) or 39%.

- Don Klipstein ()