# LTspice: plot of basic L circuit

Discussion in 'Homework Help' started by mikewax, Nov 6, 2016.

1. ### mikewaxMember

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i appreciate that. all i'm doing though is a simple PWM signal to drive my buck circuit.

2. ### ronsimpsonWell-Known MemberMost Helpful Member

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Here is a IC buck PWM. The circuit bucks 24V down to 5V at 1A.
Green=out put voltage. Blue is inductor current.

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3. ### mikewaxMember

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well the real problem was that i went through several tutorials and was frustrated because none of them included the very basic details that you guys have told me. i just wanted to see an L or a C acting roughly like an L and a C, without regard to tangible limitations of wire and such, so that i could proceed with my circuit and know what i'm lookin at.
i really appreciate everybody's patience in helping me with a really basic question. maybe this thread should be promoted to "sticky" status.
after i read your responses, i was able to make my circuit and what i now have is this:

the red trace is the current coming out of V2, the 5v source in my buck. After plotting that out, then i needed to plot the average of i(V2), like a mathematical "capacitor" to show the smoothed out version of i(V2). someone over on stackexchange illustrated the circuit on the right (B1 & R1) with an equation for V(B1) that's supposed to correspond with the value of that average.
The equation seems to express, as a voltage, the integral of i(V2) over a Δt of 1ms. therefore the green trace, the current through R1(1 ohm), = the average of i(V2), the red trace.
the PULSE coming outa V1 is actually a PWM signal from an arduino. The 5v coming from V2 is actually the usb connection off my laptop. And the point of all this is to charge of the capacitor underneath Vout (10mF) from the usb as quickly as possible without exceeding the 500mA current limit imposed by the usb protocol. so all i gotta do is get a current sense resistor (not shown) on the Vin line. The weenie will check the current i(V2) and increment/decrement the PWM duty cycle and hold the current at around 450 mA until the 10m cap reaches a voltage of 2.5v.
so the whole thing is pretty simple. thanx for the info

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5. ### mikewaxMember

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yeah we're crossing messages. that's very similar to what i originally planned to do, except i chose an LTC 3127. i'm still undecided on wether to use the LTC chip like in your picture or proceed with my own home brew buck circuit.

6. ### mikewaxMember

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THANKS that's exactly what i wasn't clear about. i ended up doing the 3a1 way and it finally worked.