Electronic circuits needing energy to go by (6)
I believe the answer is:
elapse
'go by' is the definition.
('elapse' can be a synonym of 'go by')
'electronic circuits needing energy' is the wordplay.
'electronic' becomes 'e' (as in e-mail or e-books).
'circuits' becomes 'laps' ('lap' can be a synonym of 'circuit').
'needing' means one lot of letters go next to another.
'energy' becomes 'e' (physics symbol as in E=mc2).
'e'+'laps'+'e'='ELAPSE'
'to' is the link.
(Other definitions for elapse that I've seen before include "'Pass by, as time (6)'" , "(Of time) go by" , "pass in silence" , "Tick by" , "Pass or expire - please" .)