Forums » CircuitLab Feature Requests

It would be nice to have a real comparator that modeled input bias currents, offsets and the input region voltage overdrive required along with the positive feedback the devices have. Also, it'd be nice to have the output open collector built in so you could pull it up to something other than 5V. Also the negative output terminal so you could have the output be pulled down to something besides signal common. An LM111 or equivalent with variable parameters like on the Opamp models (v/v gain, bias currents etc).

Thanks

Yes. Something along those lines. The real comparators usually have some positive feedback to get them going. Depending on the AVOL of the amps in them, some of them require a certain number of mV of overdrive above the input offset voltage to change state. There are surely some pretty complex SPICE models of some bread and butter comparators from manufacturers to borrow from. It's kind of a pain to model discretely as it is now every time I want to include a comparator in a design.

Also, in devices like LM111 and 119 (319) the pins labeled gnd don't have to be tied to signal common or power supply ground. It can be tied through a resistor to the negative supply rail. When you do that, you can set the logic low value to a negative voltage, which in some cases is preferred.

Thanks for all the good comments. This is a very good tool for the money.

Like you said, you can model the hysteresis with the external components. And you can model the open collector and pulldown terminal with external components, and use a customized opamp model for the amplifier section. So it can be done with what's already here.