Our great sponsors
-
WorkOS
The modern identity platform for B2B SaaS. The APIs are flexible and easy-to-use, supporting authentication, user identity, and complex enterprise features like SSO and SCIM provisioning.
It's extremely useful when used for its intended purpose - designing power supplies using Linear Technology components. Here's a design I did with it.[1] This is a little box for driving antique Teletype machines from a USB port. Those need a current loop running at 60mA constant current, up to 120VDC, driving an electromagnet with a 5H inductance. I wanted to generate that from the USB port's power, which required a moderately exotic switching power supply design.
The LTSpice simulation made it possible to get that right. Especially from a noise control perspective. Switching power supplies generate spikes, and so does turning off that electromagnet with its huge inductance. Those spikes have to be kept out of the USB port or its protection circuitry will shut it down. Spikes need to be suppressed in both the current and voltage dimensions. LTSpice lets you watch the switcher spikes, the elecromagnet spikes, and the inrush current. When you add a few surface mount capacitors and ferrite beads in the right places, the spikes can be almost totally suppressed. It just took a few cheap parts. The simulator lets you find values that work.
The SPICE models for Linear Technology components match reality well. That's what LTSpice is really about - a good model library.
[1] https://github.com/John-Nagle/ttyloopdriver/tree/master/circ...
Also see Qucs-S, which is a GUI for ngspice and a few other engines.