When I run “UC1846 - push-pull-current-mode-open-loop.qsch” from J Marcos Alonso, there are some errors as follows indications in the “output window”，how to troubleshoot these errors?
Ignoring shorted resistor: “R23昘1”
E:\Studying\Qspice studying\file and lib from J Marcos Alonso\Qspice-6-main\Qspice-6-main\1.- UC1846 - push-pull-current-mode-open-loop.qsch
Starting Gmin stepping.
Warning: Gmin stepping failed.
Starting source stepping.
Warning: Source stepping failed at 0.853053(8.31633e-16)
Starting pseudo transient analysis.
Warning: Singular matrix. Check node D2
Pseudo transient analysis failed.
Warning: Using skipbp
Warning: Singular matrix. Check node D1
Fatal error: Timestep too small(1.25003e-19) at t=2.62693e-11
1.- UC1846 - push-pull-current-mode-open-loop.qsch (23.9 KB)
UC1846.qsym (3.6 KB)
I try to change the voltage source V1 from 15V to PWL source by “PWL 0 0 1n 15V”, let V1 start up from 0V, now everyting works well, but I don’t know why? Could anybody help me understand better? Thanks in advance!
.tran (transient analysis) separates a simulation into two parts: first, it solves for the DC solution, and then, based on that DC solution, it starts the time-domain simulation.
The errors you received are all related to being unable to solve the DC solution (refer to this post):
Pseudo transient analysis? - QSPICE - Qorvo Tech Forum
Convergence issues are particularly common when solving the DC solution for switching circuits (as switching circuit is bistable); therefore, you normally need to force initial conditions (i.e., what all currents and voltages should be at t=0s).
There are multiple ways in SPICE to force an initial condition—for example, using UIC in .tran (not recommended, but very commonly used.), adding startup to the DC input (the method you used), or using .ic to force initial conditions.
One missing point: the UC1846 subcircuit is from Texas Instruments. If you refer to the TI examples in PSpice or TINA-TI, they both require a PWL source for its supply startup. So, it looks like this was a simulation requirement established when TI developed this model.
This is a screenshot from Tina-TI.
KSKelvin, now I undersand deeply, thank you very much for detailed explanation.
