A previous circuit used a ULN2003 Darlington pair as a single-ended (N-side) solid-state switch with a maximum current capacity of about 500mA.
However, it has no over-current protection, so I'm researching either a replacement or a surrounding circuit to do so. Protection would ideally apply to the channels individually, but a simple solution for the entire circuit would also do. I've found these options:
- Add a PPTC self-resetting fuse on the output of each of the channels. Cheap, simple, but I'm not thrilled with the prospect of waiting >2s for it to trip. The switch can easily be destroyed in that time - especially since the ULN200x datasheet does not specify a max time for the peak current, only a duty cycle, and the duty cycle in this application will be 100%.
- Add a 1R res to the output channels, and then either an ADC or a comparator with further shut-off circuitry. More complex and expensive, but faster and more precise.
- Rely on the
Vcesatparameter of the ULN2003. If
Vceexceeds about 1.4 V, infer that the current exceeds 500mA and then add the same circuitry as #2.
- Replace with a switch that has current protection built-in. Haven't been able to find something nearly as affordable as the ULN200x.
I'm leaning toward #3. Something like:
- Is the above circuit safe, stable, and an appropriate way to implement current protection?
- Among my other listed alternatives (or not), is there a better way? I usually lean toward simplicity.