reading Power Dissipation graphs

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

 

[Phil Allison]

<mrdarrett@gmail.com>

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?

** Yep.

Is this the total power consumed ( = the power delivered by the power
supply)?

** Nope.

If so, then the chip is 30W / 47W = 64% efficient, right?

** 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

 

[Don Klipstein]

In <d2045ee0-1028-40a6-b64e-11dfc97424a0@e6g2000prf.googlegroups.com>,
mrdarrett@gmail.com wrote:

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?

That is true.

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

No, efficiency in this case is 30W / (30W + 47W) or 39%.

- Don Klipstein (don@misty.com)

 

On 3ÔÂ25ČŐ, ÉĎÎç6Ęą04ˇÖ, mrdarr...@gmail.com wrote:

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

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On 3ÔÂ25ČŐ, ÉĎÎç6Ęą04ˇÖ, mrdarr...@gmail.com wrote:

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

Do you want access to China's massive pool of electronic
manufacturers... but lack the time to contact suppliers, negotiate
contracts, arrange shipping or monitor product quality? Don't worry -
Let seriouswholesale deal with all that for you.

*Check out the huge range of Gadgets, MP3 / MP4 Players, Car DVD /
Audio, and Computer Accessories now by visiting the online wholesale
catalog at seriouswholesale. com You'll have peace of mind thanks to
the seriouswholesale Quality Control, 12-month Warranty on all
products, and easy secure payment by credit card through Paypal.

Selling on eBay or your own online store? Send products direct from
our warehouse to your customers using our unique drop-shipping
service. You can profit by selling hundreds of different products,
without holding any of your own inventory! Any questions you have will
be answered by the seriouswholesale English-speaking customer support
team... Their aim is to make your China electronics importing business
easier to run than ever before.

Welcome to http://www.seriouswholesale.com.

seriouswholesale - Buy from the source, profit without the hassle.

- 12 Months Warranty - No minimum order restrictions - Drop-shipping
with no additional fee - Pay by safely by PayPal seriouswholesale
Wholesale Co., Ltd.: Chinas original and best online electronics
wholesaler & drop-shipper: seriouswholesale. com