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Current Source simulation in Pspice Orcad.

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denesio

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Hello to All.
i need to simulate current source according to timing diagram.
how can i do it in pspice modeling in Orcad???
how do i built this model??
need i two current sources??
thanx.
photodiode00.jpg

timing diagram:
photodiode01.jpg
 

keith1200rs

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One way would be to add a switch driven by a waveform for the on/off timing of the current pulse.

Keith
 

LvW

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The parts library contains a current source called "ipulse" that exactly meets your needs, that means you can specify all the mentioned properties.
 

denesio

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Keith said:
add a switch driven by a waveform for the on/off timing of the current pulse

thnx... i thought about this... but it is not working.... see figure:

photodiode02.jpg


LvW said:
library contains a current source called "ipulse"

but i need every 40 mS pulse including about 13000 10nS pulses. see timing diagramm in my first post.... thanks.
 

keith1200rs

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Don't put the switch in series with the current source - put it in parallel.

Keith
 

denesio

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ideal switch is working... i check this. figure:

photodiode03_switch.jpg


Keith said:
Don't put the switch in series with the current source - put it in parallel.

aaaaaaaaaa........ THANKS!!!!!!!!....
current source is floating in switch OFF case...

do i think correct?????????????
 

keith1200rs

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Yes. You can put a switch in series to break a voltage but if you put it in series with an ideal current source, the current will still manage to get through the switch even if it is 1G ohm. You just need to dump the current somewhere i.e. Short it out.

Keith
 

denesio

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Keith said:
Short it out

thanks........!!!!...........

but i am confused from other....
i did a simulation two circuits without second pulses (10nS)....
it is not seems sames things...

where i see V-offset in second circuit from????

i thought, these circuites are identical!!!!!!!!.... :-(

figure of two circuites:
photodiode04.jpg


simulations:
photodiode04_simulation.JPG
 

keith1200rs

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I cannot see all the switch parameters. There is usually an on and off resistance. The defaults might be 1 ohm and 1 meg ohm. You need to change those, particularly the 1Meg.

Keith
 

denesio

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yes.... ROFF=1e6, RON=1........ it is correct..... i checked it in the "proprtires of switch".....

where i see V-offset in second circuit from? :-(

if i chancged RON=1e6, Orcad Pspice is in error....
if i chancged RON=1e7, V-offset is not chancged, but amplitude decreased down to 8V....
 
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keith1200rs

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I cannot see the simulation very well on my phone but you need to consider the effect of some current going through the switch resistance. That is why you need to increase the off resistance - a lot more than 1Meg.

Keith
 

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