[sdiy] LTspice - exponential voltage curve

[Neil Johnson]

Which can be simplified to

V=0.15621*exp(3.466*time)

Neil

On 29 October 2013 16:31, Neil Johnson <neil.johnson71 at gmail.com> wrote:
> Justin,
>
> In future it would REALLY help if you ask what you actually want.  In
> this case it's an easy bit of mathematical manipulation to come up
> with the right exponent formula to plot what you want:
>
> V=5*exp(3.466*(time-1))
>
> Neil
>
> On 29 October 2013 16:15, Justin Owen <juzowen at gmail.com> wrote:
>> Still not having any luck with this.
>>
>> I've tried scaling the arb voltage based on a 5V ramp using V=exp(V(Ramp)/2.8)-1 where (Ramp) is a 5V Pulse that ramps up from 0V to 5V across 1 second.
>>
>> I've tried scaling exp() against time V=exp(1.7917*time)-1.0 and a variation on Neil's suggestion of V=exp(time/0.56)-1.
>>
>> These all give pretty much the same results - but none of them have the exact curve I'm looking for which is:
>>
>> 0s = 0V (OK 0V = 0.15625)
>> 0.2s = 0.3125V
>> 0.4s = 0.625V
>> 0.6s = 1.25V
>> 0.8s = 2.5V
>> 1s = 5V
>>
>> Any other suggestions? Thanks.
>>
>> -----Original Message-----
>> From: Neil Johnson [neil.johnson71 at gmail.com]
>> Received: 28.10.2013 15:19:41
>> To: Justin Owen
>> Cc: SDIY List
>> Subject: Re: [sdiy] LTspice - exponential voltage curve
>>
>> Use an arbitrary voltage source and set the equation to use "exp()"
>> with some time-based function.  E.g. "V=exp(time/100)".
>>
>> Neil
>>
>> On 25 October 2013 16:52, Justin Owen <juzowen at gmail.com> wrote:
>>> Hello,
>>>
>>> Taking my first few steps with LTspice. I'm simulating a simple Linear to Exponential converter running a VCA. I'm scoping/probing the sine wave output of the VCA.
>>>
>>> For the linear current source I could run a scope of the linear CV input as it ramped from 0V to 2.5V and graph that against the VCA output to check it's linearity - now I'd like to have a similar exponential voltage source to graph the VCA output against using the Lin/Exp converter.
>>>
>>> How would I do that in LTspice?
>>>
>>> Got sort of close with an arbitrary voltage source reading of a linear source.
>>>
>>> Thanks!
>>>
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>>
>>
>>
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>> http://www.njohnson.co.uk
>>
>>
>
>
>
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