Division by zero in Pspice

[Animesh Maurya]

Iam simulating the circuit for maximum power transfer, which takes
place when internal resistance (RI) of the voltage source is equal to
the external load resistance (RL). For this Iam sweeping the value of
RL form 0 to 50 Ohms. When I simulate this circuit I get two errors

ERROR -- Resistor R_RL has zero value & INTERNAL ERROR -- Divide by
Zero in device R_RL, Divide(0)

Although simulation runs fine if value of RL is changed to 1 or so. If
I were to solve the circuit for RL = 0. I will do like this PL =
[V1/(RI + RL)]^2*RL = 0. Therefore power dissipated by load resistance
when RL = 0 is zero, so why no Pspice. Where is division by zero
taking place ? So I want to know which method is used by Pspice to
solve this circuit.

Thanks

 

[Malcolm Reeves]

Well, of course you get this error. You are setting R=0. That is not
possible. Pspice looks at the voltage across it, divides by the
resistance to get current and uh-oh divide by zero.

A spice simulator use successive approximation to get all circuit
values, voltages and currents. It does not just solve the equations.
When the answers are close enough, set by reltol, it goes to the next
point.



On 17 Aug 2003 00:40:14 -0700, animesh_m@yahoo.com (Animesh Maurya)
wrote:

Iam simulating the circuit for maximum power transfer, which takes
place when internal resistance (RI) of the voltage source is equal to
the external load resistance (RL). For this Iam sweeping the value of
RL form 0 to 50 Ohms. When I simulate this circuit I get two errors

ERROR -- Resistor R_RL has zero value & INTERNAL ERROR -- Divide by
Zero in device R_RL, Divide(0)

Although simulation runs fine if value of RL is changed to 1 or so. If
I were to solve the circuit for RL = 0. I will do like this PL =
[V1/(RI + RL)]^2*RL = 0. Therefore power dissipated by load resistance
when RL = 0 is zero, so why no Pspice. Where is division by zero
taking place ? So I want to know which method is used by Pspice to
solve this circuit.

Thanks

--

....malcolm

Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK
(mreeves@fullcircuit.com, mreeves@fullcircuit.co.uk or mreeves@iee.org).
Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power
electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see:

http://www.fullcircuit.com or http://www.fullcircuit.co.uk

NEW - Desktop ToDo/Reminder program (free)

 

[John Fortier]

[V1/(RI + RL)]^2*RL = 0 can, by substitution, become a divide by zero. For
example [V1/(RI+RL)/0 = 1/RL. Generally, spice will not run any formula
with a zero which can become a divider. However, there's nothing to stop
you using a number such as .00001 instead of zero. Since your circuit will
eventually, I assume, be used in the real world, where zero resistances do
not exist at room temperature, this seems a logical step to take.

Another question; if you are looking for maximum power transfer, it seems
fairly obvious that it won't take place anywhere near I^2*RL=0, which is
zero power, either one or both resistance or current at zero, so I'm afraid
I don't really understand why you are looking at this extreme.

Regards

John



"Animesh Maurya" <animesh_m@yahoo.com> wrote in message
news:58eab14a.0308162340.4610ae63@posting.google.com...

Iam simulating the circuit for maximum power transfer, which takes
place when internal resistance (RI) of the voltage source is equal to
the external load resistance (RL). For this Iam sweeping the value of
RL form 0 to 50 Ohms. When I simulate this circuit I get two errors

ERROR -- Resistor R_RL has zero value & INTERNAL ERROR -- Divide by
Zero in device R_RL, Divide(0)

Although simulation runs fine if value of RL is changed to 1 or so. If
I were to solve the circuit for RL = 0. I will do like this PL =
[V1/(RI + RL)]^2*RL = 0. Therefore power dissipated by load resistance
when RL = 0 is zero, so why no Pspice. Where is division by zero
taking place ? So I want to know which method is used by Pspice to
solve this circuit.

Thanks