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Sequential Machines in LTSpice

I want to make a behavioral model of a power supply controller (a vastly simplified UCC28060). I want to do things like trigger a one-shot whenever a voltage drops below zero.

Does anyone have a favorite way to do this?

I'm thinking voltage -> comparator 1 -> 'S' on SR flip-flop -> Q* to gate of FET -> that shorts a current source -> that charges a cap -> comparator 2 -> reset the SR.

This has weaknesses -- not least of which is that the original triggering voltage will be zero as a consequence of the timer being active, which means I need to cook up an edge triggered flip flop (maybe they have a clocked D flip flop I can use).

At any rate, I don't often get to this depth with LTSpice, so if anyone has cleverness to share I'll listen.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
Reply to
Tim Wescott
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On Fri, 12 Mar 2010 10:49:45 -0800, Tim Wescott wrote:

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JF

Reply to
John Fields

Linear does provide a D-flip-flop. You can take advantage of the fact that the logic all uses a 0 to 1.0 output and a 0.5 threshold to make oneshots etc. You need to make the parts a little slower than they naturally are using something like a "tau=3D20n". If not they try to be infinitely fast. This can lead to troubles.

Hidden deep in the working of LTSpice is the ability to make a gated oscillator. They use it for their switcher chips. Unfortunately I don't think mere mortals can get to it.

Reply to
MooseFET

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