While a lot of manufacturers have “design” tools to help you choose their parts, there are also other useful tools out there. Some, like Appcad, were just tools without trying too hard to sell you anything. Appcad is still available www.hp.woodshot.com and the current version 4.0.0 is really version 3.0.2 with the branding changed. I still find it useful for calculating microstrip lines for example.
There are several filter design tools around that you can download such as FilterPro from Texas Instruments although you are more likely to come across the Webench online tool as the downloadable software is a bit hidden (you can find links to it in the TI E2E community). Webench is more than just a filter designer because it will also simulate the filter as well – handy if you don’t have a SPICE simulator, although it will only be designing with TI parts, of course. There are plenty of DC-DC converter online tools from the main manufacturers such as Texas Instruments, Linear Technology and Analog Devices.
There are other, less common tools out there worth knowing about such as Texas Instrument’s PCB coil designer. It is really intended for their inductive proximity sensors but it can be useful for other purposes.
If you need to calculate PCB track widths for a particular current carrying capability, there are dozens (or more likely thousands) of online calculators out there to choose from. You might want to compare results from more than one, just in case, as some are incorrect or based on old standards. Calculators that claim to work to IPC-2221A give a little more confidence that they are correct.
There are free online SPICE simulators around such as PartSim.com from Digikey. In fact Digikey have number of design tools although some are restricted and not free. For example the Mentor Graphics Designer Schematic/Layout costs $849 for a license restricted to 1500 connections. It isn’t an online tool. I wasn’t very keen on Partsim though from a quick look. Circuitlab.com is another online simulator and seemed better, but isn’t free – the cheapest access costs $79 a year. Personally I would rather buy something I can download and use for ever if it isn’t free.
EasyEda seemed a little easier to use than PartSim. It is free and covers schematic capture, simulation and PCB layout and will import Eagle, Kicad, Altium and LTSpice files. My attempts to import LTSpice files resulted in empty spaces for some of the parts but I guess that will be down to it not being able to find libraries for some reason. Like any new software, it takes time to find your way round it, particularly when it covers so many areas. It is free though and even has autorouting so might be worth a look.
If you don’t mind a step back in time, ngspice.com is free but has no schematic entry so it is back to SPICE netlists for entry e.g.
*CMOS Ring Oscillator example V1 vdd 0 3V V2 vss 0 0V .subckt inv vdd vss in out Mp1 vdd in out vdd pch l=0.35u w=20.0u Mn1 vss in out vss nch l=0.35u w=10.0u Cload out vss 100f .ends *5 stage ring x1 vdd vss 1 2 inv x2 vdd vss 2 3 inv x3 vdd vss 3 4 inv x4 vdd vss 4 5 inv x5 vdd vss 5 1 inv .MODEL nch NMOS .MODEL pch PMOS .TRAN 10p 4n .end
I am not sure I could step that far backwards though. Even before PSpice had schematic entry I used Orcad to generate the netlists to feed into PSpice.
If you don’t restrict yourself to online tools there are others to choose from such as LTSpice – probably the best free SPICE simulator. Eagle PCB CAD also integrates with LTSpice now.
Online electronic tools tend to be best for simpler calculations or well defined design tasks such as filter design rather than work requiring a complex interactive GUI and parts library such as general purpose SPICE simulation. EasyEda and PartSim are worth a look though if you are determined to use online tools and certainly the DC-DC converter and filter design tools from the main manufacturers are very usable. Online tools have the advantage of being cross platform provided they work with your chosen browser. You designs will be stored online as well so accessible from anywhere. However, if you lack an internet connection at the time your designs are accessible from nowhere.