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Old 18th November 2005, 01:43 AM   #1
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Default Waveforms for maximum power dissipation

I have simulated an amp circuit to look at the power dissipation in all devices. My original input source is a low frequency (100Hz) sine wave generator, designed to put the amplifier a smidgeon below clipping.

Here's my question: What kind of source will cause maximum power dissipation in transistors (amplitudes being equal):
sine, square, or triangle?
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Old 18th November 2005, 03:16 AM   #2
mzzj is offline mzzj  Finland
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Depends on output amplitude. With max amplitude (clipping) square wave results lovest losses.

And for absolutely highest losses choice is square-wave, at output voltage half of your supply rails. For sine-wave highest losses result when output voltage is around 70% of rail voltage.
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Old 18th November 2005, 03:48 AM   #3
jcx is offline jcx  United States
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for even more fun you can use a 2 channel source (cheap soundcard)

tie the load between the 2 pwr amp outputs and by adjusting the relative phase of the 2 channel drive you can simulate any reactive impedance you want with a single resistive load

by using different frequencies in the 2 channels you can exercise the amps over a wide range of the I-V output plane
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Old 18th November 2005, 06:58 PM   #4
AndrewT is offline AndrewT  Scotland
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Hi Jcx,
I knew I was here for a reason.
Quote:
load between the 2 pwr amp outputs and by adjusting the relative phase of the 2 channel drive you can simulate any reactive impedance
That's something else I have learned.
Now can you elaborate on how to achieve the phase difference.
Does that phase difference equal the reactive load that loads the output with a phase angle?
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Old 19th November 2005, 03:07 AM   #5
jcx is offline jcx  United States
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linear technology SwCad III free spice simulator has a .wav output option - just use the independent sources to define any wave/relationship you want

of course you have to decide on phase angle to simulate L or C and magnitude depending on your load R and amp gain

strictly speaking this gives equivalent output I-V relation to an arbitary complex load but since the load isn't really "reactive" you won't see possible instabilities that an actual reactive load could cause

http://www.linear.com/company/software.jsp

(rename attachment, deleting .txt extension to get LtSpice circuit file)

plays fine thru winamp for me, i assume any soundcard driver can play 2 ch 16/48K
Attached Files
File Type: txt wavout2ch.asc.txt (1.1 KB, 2 views)
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Old 19th November 2005, 08:54 AM   #6
AndrewT is offline AndrewT  Scotland
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Thanks Jcx
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