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Spice mosfet dissipation

Is there an easy way to get a graph of mosfet power dissipation vs time, or, alternately, to compute the dissipation within some time window on the transient analysis?

I guess I could do a behavioral voltage source whose output is the product of Id * Vds, and then lowpass filter that. Seems klunky.

I'm designing a dumb pure-hysteretic constant-current switcher and applying various step loads. I'd like to see the mosfet Pdiss at the various loads. The LT Spice efficiency report doesn't do quite what I'd like to see.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin
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Trivial to do. Just place it off in the corner somewhere and compute VDS(MN3)*ID(MN3). Of course that's instantaneous power, requiring interval integration or filtering to get average.

In PSpice you can do that multiplication (and integration) in the post processor (PROBE) without needing a behavioral device in the schematic. There's also W(MN3) in PSpice. I suspect there are similar methods in LTspice.

...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

Can't you just do waveform math in the graph window?

Just label a waveform as V(vds)*I(Id)

You may have to negate the equation to show positive power.

Reply to
Tom Swift

In PSpice you sure can.

...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

Den onsdag den 22. oktober 2014 01.37.58 UTC+2 skrev John Larkin:

hold down ALT and you get a thermometer mouse pointer, click on the FET ?

-Lasse

Reply to
Lasse Langwadt Christensen

Yes, that gives me a power graph, which I can integrate in any zoomed area to get average power.

Thanks.

The LT Spice "help" didn't.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

In SuperSpice, you don't have to do anything at all. It all automatic. Place a test point on the component (instead of a pin or wire) and instantaneous transient power will be plotted. Move the mouse cursor over the component and the data display window at the bottom right of the main widow will display DC and Average transient powers. Cursor over wire or pin displays DC voltage and current.

:-)

Kevin Aylward

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- SuperSpice

Reply to
Kevin Aylward

Is that symbol based (whether there's a MODEL or SUBCKT within), or only for MODELs?

Personally, I made my own EMETER, PMETER, SMETER, etc. components to deal with it. And a sampled filter component so I don't have to wait for RC filters to settle, or something like that. :)

Tim

--
Seven Transistor Labs 
Electrical Engineering Consultation 
Website: http://seventransistorlabs.com
Reply to
Tim Williams

Yes. It works the same whether a .model or .subckt.

It defaults with an available setup dialog with fields of integration start time and end time both equal to zero. End time at zero means integrate for the all of the data range.

There are other auto calculations as well :-)

Kevin Aylward

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- SuperSpice

Reply to
Kevin Aylward

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