Electronics - Simulation and Judgement

Created; 14/04/2016, Changed; 12/03/2024, 13/03/2024

Previous page; Electronics - Minimum design for Electromagnetic Compatibility and Electrostatic Discharge

I use spreadsheets and other tools provided by wound component and switch mode power supply IC makers, and they are very good.  This and linked pages show my evaluation of spice simulation tools for general circuit modelling.  I have been recommended simulation tools in places that I have worked, but I observe that they will mislead an engineer if he has not thought through the circuit, PCB layout parasitics and what is required.  In another case, a spice tool was recommended to me for power handing and therefore thermal modelling.  I agree that spice tools can be good but taking care with the result.  I have also been advised that simulation would do things that I have not seen so far, instead of using a calculator, spreadsheet or mental arithmetic and figuring out before I apply myself to putting any part in to a draft circuit.  Then I would most likely go straight to circuit and PCB design to figure layout parasitics and component package shape implications, these things being very important. 

The simulation tool I use is SiMetrix and also;

LTspice has a good support group; 

I have only come to using simulation at home, but not at work.  For work, I keep a design straightforward and so robust.  But at home I can test things without using a soldering iron, and that is adequate for this website.

Blog with design examples; http://blog.andrew-lohmann.me.uk/p/electronics.html

Peak detector worked through from my blog discussion; Electronics - Robust design methods - Theoretical example outdoor

Positive and negative Peak detector;


More features of simulation tools. (also see; Electronics - Control Loops)

The circuit above is a Class D amplifier (AL-0021-04A) there are other variants of this class D amplifier at; Electronics control loops Simulated using LTspice.  The Infineon gate driver adds a small delay so that both transistor are not turned on at the same time without requiring a Diode+Resistor+Capacitor network used in the previous version of this circuit.  The power output could be increased to 600W peak into 8R if the power supply were increased to 200V.

The power transistors are designed to be soldered to a PCB on top of a close matrix of small vias to conduct heat to the under side of the PCB, where the heat sink would be fitted.  The current probe is placed near the capacitor where the transitions are slower, so less noise is injected to the PCB, though functionally it is sensing the transistors current to the first inductor.

AL-0052-01A - Switch mode amplifier output protection CADSTAR 18.  There are a number of ancillary circuits and decoupling capacitors that need to be added.  It is usual to buy in a power supply rather than design one.  Similarly, it is better to buy in a transformer and wound parts that are required rather than design them, you will get a smaller more efficient part that way.  The red LED will flash briefly if the output is shorted and the green LED, indicates the power is connected.

AL-0052-01A 100KHz Oscillator 0.7C.R, and power indicator LED.

Time constant 2x 2/3 - 1/3

1/3 = e-t/c.r =  -1.1*c.r 

2/3 = e-t/c.r  = -0.4*c.r

Therefore, Time Constant is; 2x 0.7*C.R


AL-0052-01A Block diagram circuit revisions required to implement this.  The input and driver circuit needs to be changed for +-2.5V operation and the gate driver changed to a fully isolated drivers type. 

Features of the circuit;

Out standing design work;



Modelling tools allow an engineer to try more variations without damaging a PCB that traditional prototyping method would tolerate easily.  I have shown some cases where modelling looks useful, but in most cases a design would either be trivial or an engineer should not pursue such a marginal design anyway.  For example, there are refinements in the conventional peak detector that I have played with, but I would not be pursued though they were useful for play to evaluate simulation tools.

I probably would not use the novel peak detector circuits with either BJT or feedback steering, that I have not included but work.  In playing with those ideas, some useful features of some components are demonstrated.  Simulation tools are beneficial for calculating power dissipation in switch mode power output circuits, snubber networks for switch mode inductive part and gate series resistors to minimisation shoot through current in CMOS type drive.  The simulation gives an ideal case without circuit board parasitic capacitance and inductance.  But a circuit performance depends on good PCB design and tolerant circuit design.  Do break and simplify the circuit into small sections and simulate each sections that need simulation, or else the simulation time will be very long or impossible.

The simulation is not as good as doing the worse case design and if necessary prototyping.  Simulation looks useful in the Class-D amplifier's at Electronics control loops, but I made the original successfully some decades ago without simulation but using pen and paper modelling easily enough.  It is best to make the real circuit board and test that in practice, but not make a veroboard prototype unless you are unsure.

Theoretical design example with the circuits above; http://blog.andrew-lohmann.me.uk/p/electronics.html

Next page (blog); http://blog.andrew-lohmann.me.uk/2016/02/electronics-dicussion.html

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