Designing a binary output current sensor

[tmd63]

I had a design from years ago that had reed switches with a wire wrapped around them. If current was flowing (depending on the wire gauge and number of turns) then the magnetic field would cause the reed to switch on and cold be used to indicate current flowing.
This was great but in a high vibration environment, The reeds could still bounce and doesn't help with todays low current LED devices.
Is there a simulator that can be used to work out which diodes could provide a 1V Vf for a very wide range of currents If? (Typically 20mA to 2.5A or more)2.5A on a 12V system gives a power of 30W, but it is the very low Vf at If=20mA that is an issue for a single diode.
I need to reliably trigger a transistor with a Vf> 0.6V but I don't want a high Vf at higher currents (1V is good enough but 2V is too much)

[xvr]

> Is there a simulator that can be used to work out which diodes could provide a 1V Vf for a very wide range of currents If?

LTSpice, but you need accurate diodes models.

> Typically 20mA to 2.5A or more

This is a very wide range for a single diode. Voltage drop will vary.

[tmd63]

I tend to use the falstad visual circuit simulator. I had tried different diodes wired in parallel so the lower currents would give a higher voltage but they failed in simulation the currents didn't flow where I thought they would.

[xvr]

> I had tried different diodes wired in parallel so the lower currents would give a higher voltage

For larger voltage drop diodes should be connected in series, not in parallel

[Marco]

You seem to have power on the other side, so why not a hall effect current sensor? (You can make a few loops of PCB tracks to increase sensitivity.)

[DavidAlfa]

How about a shunt resistor for small power loss + opamp?

A 10mOhm shunt will only drop 100mV at 10A, seems way more than your application requirement, so actual drop will be even lower.
A dual 8-pin package op-amp will do the job, 1st stage amplifies the voltage by x100 (For example) as it's hard to compare against millivolts, the second one compares the high level output against a reference (Like 2.5V or whatever), toggling the output when surpassing it.
Add a small hysteresis so it doesn't toggle like crazy (For example, switching at 1A, releasing at 900mA).