Switcher CAD 3

[LED_ASAP]

I installed this great and *FREE* software from LinearTechnologies, but I couldn't figure out how to get the efficiency report module to work (not even on the sample files /ubbthreads/images/graemlins/confused.gif). Could anybody walk me through the steps? Thanks in advance.

 

[CM]

I know what you mean. Sometimes you have to trick it into giving you efficiency. Or should I say, you have to calculate it yourself by calculating output vs. input power. By using a very small resistor in line with the load, you can calculate load power. I think input power is easily calculated without doing any tricks. Also beware that switcher cad does not always give you a correct answer. You have to use engineering judgement to determine if what it's telling you is correct.

 

[dat2zip]

The trick to that is to set the checkbox for steady state when you setup the simulation command for transient time.

There is a checkbox which says "Stop simulating when steady state is reached"

If it reaches steady state, it will then calculate the efficiency report.

Wayne

 

[LED_ASAP]

I tried that check box, but the software complained something like "don't know how to determine steady state", and refused to run the simulation. (Could it be that the output has too much ripple so that the simulator couldn't find out the average?) In the HELP file it says there is an interactive mode, but I just couldn't figure out how to enter that mode, nor do I see ways to enter the tolerance for the steady-state manually.

 

[dat2zip]

Ah yes. Well, that is a problem. I've seen many of my runs don't reach steady state. This can happen for many reasons, but, it's likely unstable or oscillating for some reason.

You need to tweek the circuit to get it more stable is the general observation I've seen. For DC/DC converters, to much output ripple can cause loop unstability which the program won't converge and go steady state.

Is your circuit complex? If you post it or email it to me I'll take a gander at it unless it is something confidential in nature and I'll understand if you don't want to.

Wayne