# Circuit fail to converge

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#### chw82

##### Newbie level 4
I have try out a few option provide from the forum eg. STEPGMIN, increase ITL1=400, changing OP-AMP open loop to 1e-5. Attached is the schematic and hope someone will help.

Appreciate any help given.View attachment Power_Supply.zip

#### muthukumar_ece2004

##### Member level 4
Can you post the schematic in pdf? For most of us hard to see the .dsn file due to lack of software!

#### keith1200rs

##### Super Moderator
Staff member
Are you sure you have power connected to the opamps? - I cannot see any connections, nor any node names that might match the default power supply pin names.

Keith.

---------- Post added at 09:57 ---------- Previous post was at 09:45 ----------

You don't seem to be using opamps. Looking at the netlist you are using

Code:
E_U1         N04831 0 VALUE {LIMIT(V(N03028,N04557)*1E5,-15V,+15V)} _U1 N03028
+  N04557 1G
as an opamp. I think that is the source of your problem.

You would probably do better with an opamp model, even an "ideal" one.

Keith.

#### chw82

##### Newbie level 4
those opamp do not have supply pin out. We need to double click inside the properties and set out supply there. The text file do display the supply value (+/- 15V).

#### keith1200rs

##### Super Moderator
Staff member
As I said above - try a "real" opamp model. What you are using is something with infinite bandwidth and a gain of 180dB which is a bit extreme.

Keith.

#### chw82

##### Newbie level 4
i have used a real opamp (TL071) and it work.
BTW, im curious why it not able to work even i have change the open loop gain to 80dB?

#### keith1200rs

##### Super Moderator
Staff member
It may not be just the gain that is causing the problem. You also have infinite bandwidth and an abrupt limit when the output reaches the supply voltage.

Keith

#### chw82

##### Newbie level 4
thanks a lot.
May be i need to take a look on the opamp spice model text file and play around with the number.

#### keith1200rs

##### Super Moderator
Staff member
If I want an 'ideal' opamp for some quick simulations I usually use an E source with a gain of 60 or 80dB and add a single pole filter to the output - simple RC with a low R. No voltage limits.

Keith

#### LvW

It may not be just the gain that is causing the problem. You also have infinite bandwidth and an abrupt limit when the output reaches the supply voltage.

Keith
Yes, I agree with Keith. Sometimes I've made the same experience using the "OPAMP" model in PSpice that provides hard output limiting. Mostly for transient simulations with output amplitudes that reach these limits I have observed such convergence problems.

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