I have a couple questions about boost and buck converters.
First, do they try to hold the output voltage constant, or do they alter the input voltage by a constant factor? For example, if I change the input voltage, will the output voltage change?
Secondly, what happens when you give a higher voltage than you're trying to achieve to the input of a boost converter (or a lower voltage to a buck converter)? For instance, let's say I was trying to use a buck converter to convert some voltage to five volts. What would happen if I gave it 3.3 volts on the input?
Best Answer
do they try to hold the output voltage constant
Yes they do, these converters are mostly used for supplying a circuit with a constant supply voltage. Although it would be possible to make a converter where \$V_{out} = n *Vin\$ there is not much use for such a circuit. Most circuits rely on/need a constant supply voltage.
Ideally you want the output voltage to be independent of changes in the input voltage.
Higher input voltage:
No problem for a buck/down converter as long as it is within the limits it can handle
For most boost converters, depending on how they're made, the output voltage would rise with the input voltage. So for a boost converter, increasing the input voltage too much is not desirable.
Too low input voltage:
A buck/down converter will output a voltage as high as it can, this will then often be the input voltage or a bit lower.
For a boost converter it will maintain the proper output voltage as long as it is capable.