I really don't understand it. But as your sentence appears passive (English sounds better where its active, that is, SVO) it probably needs a preposition. Thus we have "Output voltage is controlled (by) three times of the voltage, which is applied to the terminal.
However, that still doesn't sound right to me. It could be, though, as it's a matter of physics, with whose jargon I am unfamiliar.
John
P.S. Are you sure the verb "control" suits you in this case?
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