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Simulators >> Circuit Simulators >> Capacitive DC-DC: Simulation problem
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Message started by melbadry on Jun 14^th, 2011, 7:22am

Title: Capacitive DC-DC: Simulation problem
Post by melbadry on Jun 14^th, 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

Title: Re: Capacitive DC-DC: Simulation problem
Post by Geoffrey_Coram on Jun 14^th, 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.

Title: Re: Capacitive DC-DC: Simulation problem
Post by melbadry on Jun 14^th, 2011, 1:54pm

Yes, exactly. That's why I am confused. The output power is higher than the input power!

Title: Re: Capacitive DC-DC: Simulation problem
Post by boe on Jun 15^th, 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

Title: Re: Capacitive DC-DC: Simulation problem
Post by JulianT on Jun 15^th, 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... :)

Title: Re: Capacitive DC-DC: Simulation problem
Post by melbadry on Jun 15^th, 2011, 2:16pm

Thanks