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# Need Help: Phase Firing Angle

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#### Don_dody

##### Full Member level 1
In phase firing angle application, what is actually limited (power, current, or voltage)?

Let say it is used to control a lamp.The theory says, the shorter the firing delay, the brighter the lamp will be. My question, is there any formula or graph to show the relation between firing delay with the phase angle? and also the formula to show how much energy delivered into the lamp with a certain delay/angle.

Thank you.

hi,
a semiperiod is from 0 to pi , so you can control a triac or tiristor to switch on by a delay circuit between the limits 0 and pi. For example for no delay on the first semiperiod (the tiristor or triac is conducting from 0 to pi) you have the full energy on the lamp, with a delay of pi/2 you will have only the half of that energy on that semiperiod

zsolt

ps: regarding time & angle ... for 50 Hz ac mains a period is 1/50 = 20 ms, then a semiperiod pi is 10 ms, pi/2 is 5 ms and so on for any value between 0 and pi

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I understood that principle already, but my problems are clearly stated above. Can you tell me the formula or explanation related to my questions?

P = UIcos fi , since a lamp is not reactive element cos fi = 1 because curent is in phase with voltage, so P =UI (efective values) (t) , the energy on a semiperiod is w = ∫ from 0 to pi of P dt, and for any t period w = ∫ from 0 to t of P dt

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