# Help me with "Power Dissipation" topic....

#### mris786

Joined Feb 11, 2004
3
Currently i'm doing assignment which the title is
"Discuss the power dissipation and its protection"
(Don't discuss this topic on a certain produts only. It's a general discussion topic)

I want to use Internet as main resource for my assignment but it is very hard to find websites that contains information on given topic. Somebody please help me with giving the internet address or post information to my e-mail address
mris786@yahoo.com
I will really thankful the person who can help me.....

#### mris786

Joined Feb 11, 2004
3
I will also submit my assignments sub - questions here :

1. Discuss in detail what is power dissipation? [3 marks]
2. How it is happened in any type of circuits? [5marks]
3. What effects that cause by power dissipation [6 marks]
4. How to avoid and protect the power dissipation? [6marks]

#### Dave

Joined Nov 17, 2003
6,970
Here is a good page on the web that was posted by a forum member. Third block along on the top row (Electronic circuits), down that column is "Power control". You should be able to find what you want in there.

As a side note have you put "Power distipation" into the All About Circuits search engine on the opening page? This site has that much information that I'm sure you could find what you want in here.

Post back if you need any further assistance

#### Battousai

Joined Nov 14, 2003
141
I'm not going to do your homework for you, but I will add that power dissipation is very important.

Nowadays it is arguably the most important spec: think of new laptops and their 1 hour battery life.

Lots of power dissipation means lots of heat, which means circuits have to operate above their nominal operating temperatures. Cooling may be required which consumes even more power.

Also, if you dissipate too much power in certain circuit elements you can burn them out completley making them unusable.

#### mozikluv

Joined Jan 22, 2004
1,437
hi,

heat is the vain of all electronic components. it degrades and destroy the devise.

whenever i put a heatsink i make sure it does not go beyond 50 degrees C :unsure:

#### Dave

Joined Nov 17, 2003
6,970
heat is the vain of all electronic components. it degrades and destroy the devise.

Not to mention the fact that it changes the way devices operate. Think of thermal run away in Germanium BJT's, the excess current due to this problem has immense knock on effects to all parts of an electronic system.

#### mris786

Joined Feb 11, 2004
3
Hi everyone, thanks to your replies to my proble.

Dave sir - you asked to search for power dissipation in allaboutcircuits.com - I searched but only I can only use one site from e-book written by Tony sir.

In the website address you give i didn't found any that contains info about power dissipation. Dave sir and everyone, I need general information of what is power dissipation is all about. My lecturer don't want me to explain power dissipation concerning on certain objects . He wants me to explain general characteristics and effects that caused by power dissipation also how to avoid and protect from power dissipation.

I do search in Google and Yahoo but that only returns power dissipation topic concerning with other objects like power dissioation in MOSFET, power dissipation in IC and etc. Not only me have problems with this assignment topic but also my friends. So, here i want to seek help of you all where to find information and general notes on power dissipation topic on the internet. I will use it for myself and share it with my friends. My lecturer adds if it is too difficult to search general information on power dissipation , it is okay if we do assignment on Power Dissipation on Power Supplies (Switched mode power supplies) but he asks ask to try our level best to search for general information about power dissipation first.
Help me.....

#### Dave

Joined Nov 17, 2003
6,970
Ok, lets go back to basic on power.

Power is defined as the rate of doing work, or in our case the rate of change of energy with respect to time. The voltage across any two points is defined as the work done in moving unit positive charge from the point of lower potential to the point of higher potential. Thus mathematically:

W = qV

where q is the charge in coulombs

In incremental form, this is:

dw = dq.v

Power is given by:

p = dw/dt = dq.v/dt = iv

Which should be more familiar.

Now when you talk about power disapation you must look at the Conservation of Energy - energy cannot be created or destroyed, it can only be converted from one form to another. Mathematically speaking:

Energy in = Energy out

So dissipation of energy is looking at the convertion of energy from one form to another. In resistive elements the energy is lost through heat, vibration etc This is one of the primary function of a resistor in electronic circuits - to dissipate heat, protecting the circuit where there are high current loads. You could analyse this more thoroughly by looking at the p =vi equation above. More current means more power, which means that the rate of change of energy over a period of time has increased, i.e. more power dissipation.

Inductive and capactive elements store energy in the form of electromagnetic energy and charge respectively. You might think that they don't dissipate any energy, but this would only be the case in a perfect inductor or capacitor. In practice energy is dissipated as heat etc the same as the resistive elements.

The mathematics becomes increasingly more complex as you analyse AC circuits and inductive and capacitive elements, but the basic priciples are the same.

This should give you something to work with, I have tried to give you as must information so that you could go away and look at the questions and have a go. If you want to, have a go at them and post back you answers and I'll suggest further additions if I see fit. I'm not going to do all your holmework for you

Hope its helped a little. I am also moving this to the Homework Forum as I see it more suitable for in there.

#### chuckey

Joined Jun 4, 2007
75
If the efficiency of a device is N%, this is wanted Pout/ Pin, Pin - wanted Pout = loses = heat. With Processes, the losses are most critical for BIG Pouts(big\$), Mains generators, broadcast transmitters or for high heat densities( on edge of degradation), where Pout/ area is very high, i.e. area is small i.e. micro chips and transistor junctions.
So google on power alternator cooling (500MW!) and UHF power transistor cooling.
Frank

#### zero_crack87

Joined Sep 3, 2008
2
hi...

why the specified maximum power dissipation of a power transistor at an ambient temperature 0f 25 celcius is much less than maximum power dissipation at a case temperature of 25 celcius?

From moderator - this is a repeat of a post active unter the topic of "transistor dissipation" Please stop hijacking threads or reposting the same question.

Last edited by a moderator: