IR Emitter Circuit, PSpice Error  - Page 1
Forum section: electronics / beginners

author: Mattjd
author_rank: Regular Contributor
timestamp: April 14, 2018, 04:25:46 pm
content: I'm working simulating a circuit for a project and am having difficulty running the PSpice simulation.The circuit in question is driving an IR LED using a power mosfet, and driving the mosfet with gate driver receiving a 38Khz signal from a microcontroller.(Apologize for the plain blocks, model import wizard wasn't changing those for some reason).What I have done is find the pspice models library files forSFH_4715A (IR Emitting Diode)PSMN1R0-30YLC (N channel power mosefet)ZXGD3005 (Gate Driver)I opened Pspice Model Editor Lite->File->Model Import Wizard->Found Model and Hit Next->Finish (Repeat for all 3 models). This created the .olb filesI then created the circuit shown above using the .olb files and performed in Capture CISPSpice -> New Simulation -> "enter name" -> Inherit From: "None" -> CreateI created a transient simulation to run for 1000ms, in steps of 1ms, and save data immediately. Then, from within Simulation Settings went toConfiguration Files -> Library -> "added each Pspice Model Library to the design" -> Apply -> OKI then ran the simulation.I am getting this output filehttps://hastebin.com/oxijiyoquq.mdWith the main error being line 178 and 180ERROR(ORPSIM-16550): Floating point computation failed during matrix solution. Possible solutions: 1)Ensure that all device parameters are in valid range. 2)Try using .options LIMITINTERNAL ERROR -- Overflow, Multiplyedit: I just noticed in the picture I have Fall time to be 1E-90, I fixed that but Im still having the same issue.

author: Mattjd
author_rank: Regular Contributor
timestamp: April 16, 2018, 01:42:50 am
content: Does my circuit atleast seem correct?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 16, 2018, 07:12:05 am
content: Assuming you found the correct models, and hooked them up properly... no.You didn't note that the ZXGD is a poorly disguised complementary BJT follower, so has no voltage gain -- you'll get about 2.6V Vgs(on) here -- and there's no current limiting resistor in series with the LED, unless you intended it to limit at whatever RS (check the model) plus Rds(on) (1mR I guess from the part number?) runs it at.Note that SPICE sources are ideal, i.e., your VPULSE can deliver 100kA+ into a low enough resistance, so a gate driver is quite superfluous for simulation purposes; but you won't get the 10V Vgs(on) you presumably wired up, anyway.Ed: also, you have the PULSE set for 1 nanosecond rise time, 10^-90 (!??) s fall time, 1s pulse width, and 40kHz repeat rate I think?? That seems a little bit odd, too...You certainly won't get a useful approximation of 1ns rise time, with a 1ms simulation step. It may slow down to evaluate it better, but that huge of a ratio may simply fault out instead (timestep too small).I don't know what PSPICE errors mean, if they're more verbose than most (sadly, most simulations are literally two kinds of fault: timestep too small, or singular matrix; absolutely no help whatsoever).The latter is the linear-algebra equivalent of divide-by-zero, a process which involves very unstable numbers, and could explain the reported overflow. But I think that's a little unlikely, because (again, assuming the models are connected up right) I don't think you've committed the error that usually results in a singular matrix. (So, at least there's that.)Tim

author: Mattjd
author_rank: Regular Contributor
timestamp: April 16, 2018, 02:16:48 pm
content: Where do you see in the datasheet that the output voltage of driver is only going to be 2.6 given vcc and Vin? I mean that's what spice was showing but it says typical vout is vcc-0.8

author: mikerj
author_rank: Super Contributor
timestamp: April 16, 2018, 02:25:48 pm
content: Quote from: Mattjd on April 16, 2018, 02:16:48 pmLook closely at the test conditions! Vout ~ Vcc-0.8 only when Vin=Vcc. You are only applying 3.3v to Vin.

author: Mattjd
author_rank: Regular Contributor
timestamp: April 16, 2018, 03:48:56 pm
content: So I need to amplify the pwm signal from micro with a mosfet then, it's a real same we already made the pcb for this.

author: Mattjd
author_rank: Regular Contributor
timestamp: April 16, 2018, 08:27:21 pm
content: So, I'm used to a circuit that amplifies the PWM signal, and inverts. That voltage coming out of NMOS M1 should be greater than 3.3v, but its not?http://

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 16, 2018, 10:38:34 pm
content: Are those the DC averages?Also, this is a transient analysis, right? Viewing the waveforms may be more informative.Tim

author: Mattjd
author_rank: Regular Contributor
timestamp: April 17, 2018, 12:19:30 am
content: 2.5v for the entire 500ms of the transient analysis