I'm wondering the possibility of a circuit where there is a varying input voltage to a DC buck converter, that would output a constant current with varying voltages?
Let me explain via this diagram:
A simple buck convert circuit:
simulate this circuit – Schematic created using CircuitLab
The output voltage \$\ V_o\$ is now less than \$\ V_p\$(or \$\ V_i\$), however, the output current is now higher than the input current as that is the functionality of the buck converter. What if I introduced \$\ V_1\$ in series with\$\ V_p\$ after some time \$\ t\$, is there a way to output the same current with the following: \$\ V_o + V_1\$? With \$\ V_1\$ as one of the input voltages(meaning can't have it in series with the output).
Best Answer
Basically what you're asking is, do current controlled switching convertes exist. The answer is yes, as you can see here:
Yes, that looks complicated ! But it's not (for me at least). The MAX649 is a DCDC Buck converter controller IC, it does not have a build in switch, PMOS Q1 is the switch. If you would want a constant output VOLTAGE, you would need a voltage divider (2 resistors) and feed a divided value of the output voltage back to the FB (feedback) pin.
But in this circuit, has a constant output CURRENT, to charge a battery ! Instead of sensing the output voltage, now the output current is sensed by taking the voltage across R10, amplifying this voltage (the opamp does this, with a feedback network to set the gain) and where does ths feedback signal go ? Straight back in to the FB pin !
The simple buck converter in your schematic is too simple to be considered having a voltage or a current output. If you change the load then voltage and current change, it is not regulated in any way. Yes you can change the PWM of the switch signal but that PWM signal needs te be determined somehow. This is done with voltage or current feedback.