Hey I just got pspice and I'm just trying to figure out how to use it. I want to start out simple and make a circuit where I know the currents flowing through resistors, and I know some voltages, and I want the program to tell me what the required resistor values are. I can't seem to get the program to let me make a netlist without specifying resistor values, and I don't know how to specify currents flowing through various resistors. Can anyone help me? Thanks
Dont we all brother. Resistor use is dependent on supply voltage and the rating and desired effect of each particular component. For instance, you add resistors to a 555 IC to tell the 555 how long you want to run the timer for. And for OPamps, the resistors in the feedback loop 'tell' the opamp the gain you want it to produce. LEDs use resistors so too much current doesn't flow through them in order to change brightness and extend life. The datasheets of each component will tell you how resistance, capacitance, etc.. will affect them. HOWEVER, Ohms Law will TELL you what resistance you need to meet a certain current. For instance, If you have a 5v battery and want to limit a LED with a 2.2Vf to a particular current, you would use Ohms law to figure out which resistor values would work. a 330 ohm resistor. Here is a post I did earlier showing Ohms law as a diagram. You should save this, print it out, book mark it, and memorize it. You WILL use this law every time you design or adapt or try to understand a circuit. http://forum.allaboutcircuits.com/showpost.php?p=240719&postcount=3
Suppose all I have is a bunch of resistors in parallel. If I know the voltages on either side, and I know the currents flowing through each resistor, can I get pspice to tell me the resistor values? I can do it by hand, I just want to see if the program can do it too, because eventually I want to do this for complicated circuits with series and parallel combinations of resistors. Thanks
You can measure the amperage and the voltage. Then using ohms law get the resistance If the amperage is 22mA and the voltage is 14.8v Using E / I = R where 'E' is Volts, 'I' is Amps, and 'R' is resistance in Ohms. So 14.8v / .022A = 672.72 Ohms You should have a list of standard resistors, if not, here is one: http://www.logwell.com/tech/components/resistor_values.html E12 and E24 are the standard used resitors used these days. More accurate the component, the more expensive.
If you use a passive component (R, L, C) it must be assigned a value that is 0 < <value> < ∞ It's more restrictive than that - it must be within the limits of the simulation settings. If you exceed the limits, you may receive helpful messages like "Timestep too small"