The Designer's Guide Community
Forum
Welcome, Guest. Please Login or Register. Please follow the Forum guidelines.
Mar 28th, 2024, 8:02am
Pages: 1
Send Topic Print
Switching power in cap (Read 962 times)
dnw
Junior Member
**
Offline



Posts: 26

Switching power in cap
Mar 09th, 2020, 8:16pm
 
If I have a step from 0 to V volts across a cap there is power dissipation of 0.5*CV^2.
Is it true that if I go from 0 to V/2 and then V/2 to V then the power dissipation would be 0.5*C(V/2)^2 + 0.5*C(V - V/2)^2  i.e. .5*CV^2/2

Which is half of the earlier case? I am not able to figure out where I am getting this wrong as the final charge on the cap is the same in both cases.

It will be great help if someone could help me understand this
Thanks
Back to top
 
 
View Profile   IP Logged
rajasekhar
New Member
*
Offline



Posts: 7

Re: Switching power in cap
Reply #1 - Mar 10th, 2020, 7:32am
 
Your calculations are correct. The smaller the voltage charged to the cap, the lesser the energy lost in the resistor. You can consider each step charging voltage is V/N, replete this N time. When N-->inf, you would see no energy loss. Another simple way is to check the current waveform. In your example-charging directly to V, would result in impulse current of VC. If you do the two steps charging you would see CV/2 impulses two times. I hope it is helpful.

Thanks,
Raj.
Back to top
 
 
View Profile   IP Logged
dnw
Junior Member
**
Offline



Posts: 26

Re: Switching power in cap
Reply #2 - Mar 10th, 2020, 8:17am
 
Hi Raj,
Thanks for the clarification.
With infinite steps, if I have something like sine wave you meant I will have negligible consumption?
Thanks
Back to top
 
 
View Profile   IP Logged
rajasekhar
New Member
*
Offline



Posts: 7

Re: Switching power in cap
Reply #3 - Mar 12th, 2020, 4:51am
 
I mean to say-first time V/n voltage, next 2V/n and so on until V..in, In this case, the Energy waste in the resistor is Zero when N tends to infinite. its good exercise..Let me know if you can't.. I will post the answer...

Thanks,
Raj.
Back to top
 
 
View Profile   IP Logged
Pages: 1
Send Topic Print
Copyright 2002-2024 Designer’s Guide Consulting, Inc. Designer’s Guide® is a registered trademark of Designer’s Guide Consulting, Inc. All rights reserved. Send comments or questions to editor@designers-guide.org. Consider submitting a paper or model.