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Installing and using LTspice IV (now including LTXVII). From beginner to advanced.
Installing and using LTspice IV (now including LTXVII). From beginner to advanced.
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Old 25th August 2014, 12:02 PM   #71
Mooly is offline Mooly  United Kingdom
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Installing and using LTspice IV (now including LTXVII). From beginner to advanced.
Default Testing under load and dynamically.

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.

Click the image to open in full size.

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.

Click the image to open in full size.

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.

Click the image to open in full size.

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.
Attached Thumbnails
Installing and using LTspice IV (now including LTXVII). From beginner to advanced.-nmos-png   Installing and using LTspice IV (now including LTXVII). From beginner to advanced.-regulation-png   Installing and using LTspice IV (now including LTXVII). From beginner to advanced.-dynamic-regulation-png   Installing and using LTspice IV (now including LTXVII). From beginner to advanced.-dynamic-zoom-png  
Attached Files
File Type: asc Voltage doubler Simulation Dynamic.asc (4.1 KB, 71 views)
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Old 25th August 2014, 12:35 PM   #72
Mooly is offline Mooly  United Kingdom
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Installing and using LTspice IV (now including LTXVII). From beginner to advanced.
Quote:
Originally Posted by AndrewT View Post
Looks like you are confirming that the remaining ripple is just as good as this version of the regulator can achieve with this level of ripple on the input.
Not a glitch due to drop out.

I think this does show that voltage doubling and even more so with tripling and quadrupling, creates a very ripply supply. Here with rCRC on the input, ripple still comes through on the output.

Use the sim to model and compare non doubled to doubled and tripled and quadrupled rectifiers.
By changing just the caps and series CRC resistor we can improve things a little.

Circuit.
Click the image to open in full size.

Ripple.

Click the image to open in full size.

Detail of Ripple. Note the output still climbing toward its final value (the effect of the 470uf and 4k7 time constant)

Click the image to open in full size.
Attached Thumbnails
Installing and using LTspice IV (now including LTXVII). From beginner to advanced.-ripple2-png   Installing and using LTspice IV (now including LTXVII). From beginner to advanced.-ripple-3-png   Installing and using LTspice IV (now including LTXVII). From beginner to advanced.-ripple4-png  
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Old 25th August 2014, 03:49 PM   #73
goodlionaudio is offline goodlionaudio  United States
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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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Old 25th August 2014, 07:19 PM   #74
Mooly is offline Mooly  United Kingdom
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Installing and using LTspice IV (now including LTXVII). From beginner to advanced.
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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Old 26th August 2014, 01:46 AM   #75
fas42 is offline fas42  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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Old 26th August 2014, 01:49 AM   #76
kevinkr is offline kevinkr  United States
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Installing and using LTspice IV (now including LTXVII). From beginner to advanced.
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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Old 26th August 2014, 02:12 AM   #77
fas42 is offline fas42  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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Old 26th August 2014, 02:58 AM   #78
keantoken is offline keantoken  United States
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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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Old 26th August 2014, 03:05 AM   #79
gannaji is offline gannaji  India
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Thank you, Mooly!
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Old 26th August 2014, 07:50 AM   #80
Mooly is offline Mooly  United Kingdom
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Installing and using LTspice IV (now including LTXVII). From beginner to advanced.
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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