I'm planning on building a small constant current power supply for charging lithium-ion batteries on the go. While they normally use constant current AND constant voltage, I've elected not to include the latter for design concerns - it's not necessary since I won't need to fully charge the battery, and constant-current will suffice for about 70% capacity depending on charge rate.
Looking at normal CC-CV chargers (such as one for the LTC1541, seen here: http://cds.linear.com/docs/en/design-note/dn188f.pdf), it seems this may be achievable with a Schmitt trigger combined with a current-sense resistor and voltage reference, as well as an inductor for filtering and MOSFET for switching. I envisage a system whereby the current sense (resistance would be <0.1ohm) is connected as close to ground as possible, and the voltage drop across the current sense compared with a voltage reference; the hysteretic output should yield a small current ripple but hopefully should keep it relatively constant.
I imagine a voltage drop across the current sense of about 0.05V, driven by a current of 2A. Since the ripple needs to be fairly low - say, plus/minus 0.02A, which corresponds to a very low fluctuation in voltage - would the comparator-driven schmitt trigger be able to detect this change and switch the MOSFET effectively?
While I understand the circuit theory I'm afraid I don't have much experience building these sorts of circuits (I normally buy micro power supplies), so I'm not sure what sort of values to use, nor the feasibility of something like this. I'm aiming for high-efficiency of the circuit, so a linear regulator is out of the question.