Real Dictionary

step up
to increase or raise by stages; accelerate
phrasal verb: If you say that someone should step up, you mean that they should start to take responsibility for something.
phrasal verb: If you step up something, you increase it or increase its intensity.

step-up in British English
an increase, as in amount, intensity, etc.
that steps up, or increases
to go or come near; approach
to raise or increase by degrees
adjective: (of a transformer) increasing a low voltage applied to the primary winding to a higher voltage on the secondary winding
adjective: effecting an increase
noun: an increase or rise in the rate or quantity of something
noun: an increment in quantity, size, etc

step-up in Electrical Engineering
adjective: A step-up transformer increases a low voltage applied to the primary winding to a higher voltage on the secondary winding.