SPICE (LT): determining dissipation by resistors, etc.?

  • Thread starter Mike Rocket J. Squirrel E
  • Start date
Mike Engelhardt wrote:

Mike,


What's the quick and easy way of finding the steady-state power
dissipation of resistors and other components in a circuit with SPICE?


There's a new feature in version 2.07a. From a schematic,
you can now plot the instantaneous power dissipation in a
device. This is accessed by Alt-Left clicking on a symbol.
It's computed as an expression of voltages and currents
that are already in the data set. For example, if you
Alt-click on a transistor, the trace you add might look
like "V(N001,N003)*Ic(Q1)+V(N002,N003)*Ib(Q1)" Average
power dissipation can be found by control clicking
on this trace label to integrate.
Click to expand...
Awwww -- and it even comes with a cute little bulb thermometer symbol!

Extremely handy addition, Mike. Many thanks!

--
Mike "Rocket J Squirrel" Elliott
 
On Tue, 18 Nov 2003 19:12:20 GMT, "Mike Rocket J. Squirrel Elliott"
<j.michael.elliottAT@REMOVETHEOBVIOUSadelphiaDOT.net> wrote:

Mike Engelhardt wrote:

Mike,


What's the quick and easy way of finding the steady-state power
dissipation of resistors and other components in a circuit with SPICE?

There's a new feature in version 2.07a. From a schematic,
you can now plot the instantaneous power dissipation in a
device. This is accessed by Alt-Left clicking on a symbol.
It's computed as an expression of voltages and currents
that are already in the data set. For example, if you
Alt-click on a transistor, the trace you add might look
like "V(N001,N003)*Ic(Q1)+V(N002,N003)*Ib(Q1)" Average
power dissipation can be found by control clicking
on this trace label to integrate.

Awwww -- and it even comes with a cute little bulb thermometer symbol!

Extremely handy addition, Mike. Many thanks!
Click to expand...
Reminds me of a simulation program from way back - Analog Artistry,
I think.
When the simulated component dissipation exceeded the part rating,
a curl of smoke was displayed on the screen next to the part.
 
On Tue, 18 Nov 2003 12:45:46 -0800, pat dot lawler att verizon dott
nneett wrote:

Reminds me of a simulation program from way back - Analog Artistry,
I think.
When the simulated component dissipation exceeded the part rating,
a curl of smoke was displayed on the screen next to the part.
Click to expand...
What an amusing and innovative idea!

--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill
 
Paul Burridge wrote:
On Tue, 18 Nov 2003 12:45:46 -0800, pat dot lawler att verizon dott
nneett wrote:

Reminds me of a simulation program from way back - Analog Artistry,
I think.
When the simulated component dissipation exceeded the part rating,
a curl of smoke was displayed on the screen next to the part.

What an amusing and innovative idea!
Click to expand...
Amusing yes, innovative no. Innovative is a term to describe things that
are reasonably new or unexpected. Since real components do smoke, the
idea to have them do this on a schematic is trivially obvious. It was
one I rejected a long time a go as a silly gimmick.

Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

http://www.anasoft.co.uk/replicators/index.html

Understanding, is itself an emotion, i.e. a feeling.
Emotions or feelings can only be "understood" by
consciousness. "Understanding" consciousness can
therefore only be understood by consciousness itself,
therefore the "hard problem" of consciousness, is
intrinsically unsolvable.

Physics is proven incomplete, that is, no
understanding of the parts of a system can
explain all aspects of the whole of such system.
 
On Wed, 19 Nov 2003 07:13:08 -0000, "Kevin Aylward"
<kevindotaylwardEXTRACT@anasoft.co.uk> wrote:

Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

http://www.anasoft.co.uk/replicators/index.html

Understanding, is itself an emotion, i.e. a feeling.
Emotions or feelings can only be "understood" by
consciousness. "Understanding" consciousness can
therefore only be understood by consciousness itself,
therefore the "hard problem" of consciousness, is
intrinsically unsolvable.

Physics is proven incomplete, that is, no
understanding of the parts of a system can
explain all aspects of the whole of such system.
Click to expand...

Kev, your sig appears to be a tad over the 4-line limit. Any chance of
trimming it in the interests of saving B/W? Thanks.

--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill
 
Mike Engelhardt <pmte@concentric.net> wrote:
: Mike,

: > What's the quick and easy way of finding the steady-state power
: > dissipation of resistors and other components in a circuit with SPICE?

: There's a new feature in version 2.07a. From a schematic,
: you can now plot the instantaneous power dissipation in a
: device. This is accessed by Alt-Left clicking on a symbol.
: It's computed as an expression of voltages and currents
: that are already in the data set. For example, if you
: Alt-click on a transistor, the trace you add might look
: like "V(N001,N003)*Ic(Q1)+V(N002,N003)*Ib(Q1)" Average
: power dissipation can be found by control clicking
: on this trace label to integrate.

An axix labels with "Watts" would be usefull.

Thanks for the feature!


--
Uwe Bonnes bon@elektron.ikp.physik.tu-darmstadt.de

=======================================================

Free software means: Contribute nothing, expect nothing

=======================================================
 
kensmith@violet.rahul.net (Ken Smith) wrote:

In article <zyyob.438$Bf7.374091@news1.news.adelphia.net>,
Mike Rocket J. Squirrel Elliott <j.michael.elliottAT@REMOVETHEOBVIOUSadelphiaDOT.net> wrote:
Newbie question:

What's the quick and easy way of finding the steady-state power
dissipation of resistors and other components in a circuit with SPICE?

Here's a handy little trick I've used a couple of times. Use the arb.
voltage source to multiply I*V then feed that into an RC model of the
thermal characteristics of the heatsinking. The result is a nice plot of
the temperature rise vs time when the circuit pulses on.
Click to expand...
In CircuitMaker you just move the probe to the component until a P
pops up (instead of V or I), and the power is shown automatically.

--
Terry Pinnell
Hobbyist, West Sussex, UK
 
In article <zyyob.438$Bf7.374091@news1.news.adelphia.net>,
Mike Rocket J. Squirrel Elliott <j.michael.elliottAT@REMOVETHEOBVIOUSadelphiaDOT.net> wrote:
Newbie question:

What's the quick and easy way of finding the steady-state power
dissipation of resistors and other components in a circuit with SPICE?
Click to expand...
Here's a handy little trick I've used a couple of times. Use the arb.
voltage source to multiply I*V then feed that into an RC model of the
thermal characteristics of the heatsinking. The result is a nice plot of
the temperature rise vs time when the circuit pulses on.

--
--
kensmith@rahul.net forging knowledge
 
Ken Smith wrote:
In article <zyyob.438$Bf7.374091@news1.news.adelphia.net>,
Mike Rocket J. Squirrel Elliott
j.michael.elliottAT@REMOVETHEOBVIOUSadelphiaDOT.net> wrote:
Newbie question:

What's the quick and easy way of finding the steady-state power
dissipation of resistors and other components in a circuit with
SPICE?
Click to expand...
In SuperSpice, simply move the mouse pointer over the component and
power will be immediately displayed in a text field in the docked
window, bottom right. Both bias power and transient power is displayed.

Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

http://www.anasoft.co.uk/NewBeginning.mp3

"quotes with no meaning, are meaningless" - Kevin Aylward.
 
On Mon, 1 Mar 2004 07:41:47 -0000, "Kevin Aylward"
<kevindotaylwardEXTRACT@anasoft.co.uk> wrote:

Ken Smith wrote:
In article <zyyob.438$Bf7.374091@news1.news.adelphia.net>,
Mike Rocket J. Squirrel Elliott
j.michael.elliottAT@REMOVETHEOBVIOUSadelphiaDOT.net> wrote:
Newbie question:

What's the quick and easy way of finding the steady-state power
dissipation of resistors and other components in a circuit with
SPICE?


In SuperSpice, simply move the mouse pointer over the component and
power will be immediately displayed in a text field in the docked
window, bottom right. Both bias power and transient power is displayed.
Click to expand...
In LT., simply multiply the voltage across the resistor by the current
flowing through it. :)
--

The BBC: Licensed at public expense to spread lies.
 
What's the quick and easy way of finding the steady-state power
dissipation of resistors and other components in a circuit with
SPICE?

Here's a handy little trick I've used a couple of times. Use the
arb. voltage source to multiply I*V then feed that into an RC
model of the thermal characteristics of the heatsinking. The
result is a nice plot of the temperature rise vs time when the
circuit pulses on.

In SuperSpice, simply move the mouse pointer over the component and
power will be immediately displayed in a text field in the docked
window, bottom right. Both bias power and transient power is displayed.

In LT., simply multiply the voltage across the resistor by the current
flowing through it. :)
Click to expand...
I think Ken's point of his late post to the thread was that he got
temperature vs time. But if you just want component dissipation
in LTspice, you can Alt-Left click on a component to plot instantaneous
dissipation of the component(The mouse cursor icon will turn into
a thermometer when you're pointing at a plotable power dissipation).
Then the waveform integrator can be used get the average dissipation
over a period of the simulation.

--Mike
 
Ken Smith wrote:

In article <zyyob.438$Bf7.374091@news1.news.adelphia.net>,
Mike Rocket J. Squirrel Elliott <j.michael.elliottAT@REMOVETHEOBVIOUSadelphiaDOT.net> wrote:

Newbie question:

What's the quick and easy way of finding the steady-state power
dissipation of resistors and other components in a circuit with SPICE?


Here's a handy little trick I've used a couple of times. Use the arb.
voltage source to multiply I*V then feed that into an RC model of the
thermal characteristics of the heatsinking. The result is a nice plot of
the temperature rise vs time when the circuit pulses on.
Click to expand...
But how to convert a device + heatsink's thermal specs into an
appropriate RC circuit? (Puzzle 1 for me.) And how to translate the
simulation data into the device's junction temperature? (Puzzle 2 for
me.) I'm lazy and hate doing thermal calcs by hand.

--
Mike "Rocket J Squirrel" Elliott
71 VW Type 2 -- the Wonderbus (AKA the Saunabus in summer)
 
On Mon, 01 Mar 2004 14:12:03 -0800, "Mike Rocket J. Squirrel Elliott"
<j.michael.elliottAT@REMOVETHEOBVIOUSadelphiaDOT.net> wrote:

But how to convert a device + heatsink's thermal specs into an
appropriate RC circuit? (Puzzle 1 for me.) And how to translate the
simulation data into the device's junction temperature? (Puzzle 2 for
me.) I'm lazy and hate doing thermal calcs by hand.
Click to expand...
Mike, what's your favourite Pizza topping?

--

The BBC: Licensed at public expense to spread lies.
 
In article <r8a440purv9dc7s5o1rhadmqc94529lqqj@4ax.com>,
Terry Pinnell <terrypinDELETE@dial.pipexTHIS.com> wrote:
kensmith@violet.rahul.net (Ken Smith) wrote:

In article <zyyob.438$Bf7.374091@news1.news.adelphia.net>,
Mike Rocket J. Squirrel Elliott
[...]
Here's a handy little trick I've used a couple of times. Use the arb.
voltage source to multiply I*V then feed that into an RC model of the
thermal characteristics of the heatsinking. The result is a nice plot of
the temperature rise vs time when the circuit pulses on.

In CircuitMaker you just move the probe to the component until a P
pops up (instead of V or I), and the power is shown automatically.
Click to expand...
Yes but it doesn't plot the temperature rise.

--
--
kensmith@rahul.net forging knowledge
 
Paul Burridge wrote:
On Mon, 01 Mar 2004 14:12:03 -0800, "Mike Rocket J. Squirrel Elliott"
j.michael.elliottAT@REMOVETHEOBVIOUSadelphiaDOT.net> wrote:


But how to convert a device + heatsink's thermal specs into an
appropriate RC circuit? (Puzzle 1 for me.) And how to translate the
simulation data into the device's junction temperature? (Puzzle 2 for
me.) I'm lazy and hate doing thermal calcs by hand.


Mike, what's your favourite Pizza topping?
Click to expand...
I'm pretty much a cheese guy. Cheese, tomato sauce, basil --
"Margherita" pizza just about does all I need. But artichoke hearts are
good, too.

--
Mike "Rocket J Squirrel" Elliott
71 VW Type 2 -- the Wonderbus (AKA the Saunabus in summer)
 
In article <c1vmvh$kki@dispatch.concentric.net>,
Mike Engelhardt <pmte@concentric.net> wrote:
[...]
I think Ken's point of his late post to the thread was that he got
temperature vs time.
Click to expand...
Yes, exactly, that was the whole point. Using this trick you can model
the temperature of a heatsink when there is a pulsed load. Often in a
switcher, there is a part of the circuit that only needs to provide power
for a short time when the circuit is switched on. Once the main section
is up and going, a secondary takes over the load.





--
--
kensmith@rahul.net forging knowledge
 
In article <asCdnZZbwZepKN7d4p2dnA@adelphia.com>,
Mike Rocket J. Squirrel Elliott <j.michael.elliottAT@REMOVETHEOBVIOUSadelphiaDOT.net> wrote:
[.. modeling heat sinking ..]
But how to convert a device + heatsink's thermal specs into an
appropriate RC circuit? (Puzzle 1 for me.) And how to translate the
simulation data into the device's junction temperature? (Puzzle 2 for
me.) I'm lazy and hate doing thermal calcs by hand.
Click to expand...
The thermal resistance is in Watts per degree C. These you just call
Ohms. The thermal mass looks like a capacitor with C = degree/J.

Heat into the sink is just a current equal to I*V in the component. The
outdoor temperature is just a voltage source at the far end of the
circuit.


--
--
kensmith@rahul.net forging knowledge
 
Ken Smith wrote:

In article <asCdnZZbwZepKN7d4p2dnA@adelphia.com>,
Mike Rocket J. Squirrel Elliott <j.michael.elliottAT@REMOVETHEOBVIOUSadelphiaDOT.net> wrote:
[.. modeling heat sinking ..]

But how to convert a device + heatsink's thermal specs into an
appropriate RC circuit? (Puzzle 1 for me.) And how to translate the
simulation data into the device's junction temperature? (Puzzle 2 for
me.) I'm lazy and hate doing thermal calcs by hand.
Click to expand...
Okay, looking at a standard part, like Aavid's 533522b02552
( http://www.aavidthermalloy.com/bin/stdisp.pl?Pnum=533522b02552 )
It's spec'ced thermal resistance is 2.7 degree C / Watt.

The thermal resistance is in Watts per degree C. These you just call
Ohms.
Click to expand...
So R = the inverse of thermal resistance? With thermal resistance of 2.7
C/W, then R = 1/2.7 ohm: 0.37 ohm, yes?

The thermal mass looks like a capacitor with C = degree/J.
Click to expand...
Degree /Joule? I'm a bit simple -- this one I don't get. Does a heatsink
data sheet provide sufficient information to calculate this number?

Heat into the sink is just a current equal to I*V in the component. The
outdoor temperature is just a voltage source at the far end of the
circuit.
Click to expand...
25 degrees C ambient would be . . . 25 volts?

--
Mike "Rocket J Squirrel" Elliott
71 VW Type 2 -- the Wonderbus (AKA the Saunabus in summer)
 
In article <6ImdnVpzjvBKjNndRVn-sA@adelphia.com>,
Mike Rocket J. Squirrel Elliott <j.michael.elliottAT@REMOVETHEOBVIOUSadelphiaDOT.net> wrote:
The thermal resistance is in Watts per degree C. These you just call
Ohms.

So R = the inverse of thermal resistance? With thermal resistance of 2.7
C/W, then R = 1/2.7 ohm: 0.37 ohm, yes?
Click to expand...
Sorry I either (A) had brain lock or (B) had beer. I should have said
that the heat sink makers usually give you Watts per degree. From that
you calculate the resistance in Degrees per Watt.


The thermal mass looks like a capacitor with C = degree/J.

Degree /Joule? I'm a bit simple -- this one I don't get. Does a heatsink
data sheet provide sufficient information to calculate this number?
Click to expand...
Brain trouble here too. If you use an alluminum heat sink each gram of
metal is good for 0.9uF For copper or brass, a gram is about 0.38uF.

25 degrees C ambient would be . . . 25 volts?
Click to expand...
This one I got right.
--
--
kensmith@rahul.net forging knowledge
 
I obviously am having an advanced case of brain lock or too much beer.
After checking my notes here's the right answers (I hope):

In article <6ImdnVpzjvBKjNndRVn-sA@adelphia.com>,
Mike Rocket J. Squirrel Elliott <j.michael.elliottAT@REMOVETHEOBVIOUSadelphiaDOT.net> wrote:
[.. I wrote ..]
The thermal resistance is in Watts per degree C. These you just call
Ohms.

So R = the inverse of thermal resistance? With thermal resistance of 2.7
C/W, then R = 1/2.7 ohm: 0.37 ohm, yes?
Click to expand...
No I meant to say that the data sheet I'd looked at gave you Watts per
degree. The Degrees per Watt is the right form to do resistance.

The thermal mass looks like a capacitor with C = degree/J.

Degree /Joule? I'm a bit simple -- this one I don't get. Does a heatsink
data sheet provide sufficient information to calculate this number?
Click to expand...
Another mistake, it is C=J/degree. I measured degree/J because that is
the easy way to make the measurement and then inverted. The capacitor
looks like 0.9F per gram if it is alluminum. Copper and brass are more
like 0.38F per gram.

25 degrees C ambient would be . . . 25 volts?
Click to expand...
Yes.

--
--
kensmith@rahul.net forging knowledge
 
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