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#71 |
diyAudio Moderator
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Testing under load. Here is a quick and easy way. We can use a FET to switch the load across the supply to check how well the regulator functions. We can also modulate that switching function to test the dynamics of the regulator.
You will need to zoom out the circuit slightly to make room for the extra part... yes we only need one. Go to the component library and add an NMOS transistor. Now connect a second voltage source between gate and source as shown. Use the scissors and the "hand" to cut the load resistor and re attach it as shown. Right click the transistor and select a suitable device. I'm using the IRF2807Z as a typical low Rds device. Now make the voltage source you just added into a pulse. Lets set it for a 2 second period. Now alter the <edit simulation> to give a longer run time of 10 seconds so that we can see more of what is going on. We can see that the regulator isn't brilliant... and that is one for you to work on and improve ![]() Now change the voltage source to a 1ms pulse (Ton = 0.5ms and TPeriod = 1ms) Change the stop time to just 200ms now, otherwise you will be waiting all day for it. For the amplitude... well as its a FET we are controlling a 0 to 10 volts setting shouldbe ideal. Run the sim again. Now zoom in on the last few millisconds and look at the detail. You can see the hf ripple (our FET modulating the output) combined with the ripple we had before. The file up to this point is attached.
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Installing and using LTspice IV. From beginner to advanced. |
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#72 | |
diyAudio Moderator
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Quote:
Circuit. Ripple. Detail of Ripple. Note the output still climbing toward its final value (the effect of the 470uf and 4k7 time constant)
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Installing and using LTspice IV. From beginner to advanced. |
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#73 |
diyAudio Member
Join Date: Jul 2011
Location: Columbia, MD
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Mooly,
Thanks for putting this together! LTspice was dormant on my system for many months because I couldn't get it to do what I wanted. In my opinion good software should be self explanatory but that is unfortunately not the case here. This weekend, I decided to take some time and follow your instructions, and voila, I obtained the results I was looking for! ![]() |
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#74 |
diyAudio Moderator
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Excellent, I'm pleased you are finding it helpful and of use. When I first attempted to use LT and started asking questions I found that a lot of knowledge was assumed... which I didn't have.
You will find that the more you learn, the "easier" it becomes and you will start figuring out the twists and turns your self.
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Installing and using LTspice IV. From beginner to advanced. |
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#75 |
Banned
Join Date: Jun 2012
Location: NSW, Australia
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The point being that LTspice was intended for internal use in the company, to get the job done - impressing unfamiliar users straight off was not part of the design brief ...
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#76 |
diyAudio Moderator
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Actually it is a marketing tool for use by Linear Tech's customers and prospective customers. It's free and not hobbled like most of the versions offered by competitors, and with experience can produce excellent results - this is its great strength.
It has an extensive library of LT parts (not spice models) as well as the ability to add an extensive custom spice parts library. I use it to simulate tube circuitry as well as other things.
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"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine |
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#77 |
Banned
Join Date: Jun 2012
Location: NSW, Australia
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Not quite - there are numerous undocumented features, which only those in the know can properly access ... here's a bit of a rundown - LTspice Genealogy - The Heritage of Simulation Ubiquity - LTwiki-Wiki for LTspice
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#78 |
diyAudio Member
Join Date: Aug 2006
Location: Texas
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Nice thread Mooly.
To me, "advanced" would be setting up schematic hierarchies to do batch testing to compare many different amplifier simulations using the same set of tests. I haven't tried stuff like this yet but it seems possible.
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#79 |
diyAudio Member
Join Date: Jan 2011
Location: Hyderabad
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Thank you, Mooly!
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www.samritatrust.org Teach me the glorious lesson that occasionally, I might be mistaken. Keep me reasonably sweet. |
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#80 |
diyAudio Moderator
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Thanks Kean, I've still a few ideas up my sleeve on what to add next to this thread.
Nothing as advanced as your proposals though ![]()
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Installing and using LTspice IV. From beginner to advanced. |
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