The Designer's Guide Community
Forum
Welcome, Guest. Please Login or Register. Please follow the Forum guidelines.
Mar 29th, 2024, 3:34am
Pages: 1
Send Topic Print
Capacitive DC-DC: Simulation problem (Read 5467 times)
melbadry
New Member
*
Offline



Posts: 4

Capacitive DC-DC: Simulation problem
Jun 14th, 2011, 7:22am
 
I am trying to simulate the efficiency of an ideal step-up capacitive DC-DC converter (Step-up charge pump). The problem is I get the output power is greater than the input power (The output current = Input current and output voltage > input voltage)

I use ideal switches and caps in my test-bench, and my load is a simple current source (I switch it in after the circuit starts-up and settle to its no-load value)

What is this problem caused by? What the right way to simulate efficiency?

Thanks
Back to top
 
 
View Profile   IP Logged
Geoffrey_Coram
Senior Fellow
******
Offline



Posts: 1998
Massachusetts, USA
Re: Capacitive DC-DC: Simulation problem
Reply #1 - Jun 14th, 2011, 1:49pm
 
Shouldn't the input current be greater than the output?  Otherwise it seems like your circuit is creating power.

It also seems, if you only have caps and ideal switches, then you have nothing that will dissipate power.
Back to top
 
 

If at first you do succeed, STOP, raise your standards, and stop wasting your time.
View Profile WWW   IP Logged
melbadry
New Member
*
Offline



Posts: 4

Re: Capacitive DC-DC: Simulation problem
Reply #2 - Jun 14th, 2011, 1:54pm
 
Yes, exactly. That's why I am confused. The output power is higher than the input power!
Back to top
 
 
View Profile   IP Logged
boe
Community Fellow
*****
Offline



Posts: 615

Re: Capacitive DC-DC: Simulation problem
Reply #3 - Jun 15th, 2011, 1:25am
 
melbadry,
you give very little information, so we have to guess: Did you perhaps use the wrong sign for your load current?
B O E
Back to top
 
 
View Profile   IP Logged
JulianT
New Member
*
Offline



Posts: 2
Swindon, UK
Re: Capacitive DC-DC: Simulation problem
Reply #4 - Jun 15th, 2011, 3:58am
 
I have found the same problems in simulating capacitive DC-DC charge pumps - that is the input power is less than the output power. But changing the simulator from Spectre to BDAsim gave me a different answer - with the Pin > Pout.

Make sure that the pulse generation does not contribute to the output power - the phase1/phase2 'vpulse' should have high-impeance loads!

If you use ideal switches and change the on-resistance of the switch you'll find that the simulator will give other answers - sometimes wrong, somtimes appearing correct. Ideally you should get near 100% efficiency with ideal components.

I looked at the averaging of the input current and output voltage - no errors from the waveform post-processing. So I can anly assume that its due to the simulator solver not getting the solution accurate - trying different tolerance settings and/or timestep controls may help.

Good luck... Smiley
Back to top
 
 
View Profile   IP Logged
melbadry
New Member
*
Offline



Posts: 4

Re: Capacitive DC-DC: Simulation problem
Reply #5 - Jun 15th, 2011, 2:16pm
 
Thanks
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.