I'm reviewing the datasheet for the LM1875.
Page 4, upper-left, has a Power Dissipation vs. Power Output graph for a 4-ohm load.
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
** 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 speaker load.
....... Phil
That is true.
No, efficiency in this case is 30W / (30W + 47W) or 39%.
- Don Klipstein ( snipped-for-privacy@misty.com)
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