# SCR stuff

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#### conchord

##### New Member
Sup peeps,
I'm having trouble finding a formula for a question.

I need to find the power delivered to the load if phase control is used when the trigger angle is 60 degrees

#### Leftyretro

##### New Member
Sup peeps,
I'm having trouble finding a formula for a question.

I need to find the power delivered to the load if phase control is used when the trigger angle is 60 degrees

Well considering that a single SCR can only work on 180 degrees of a sinewave (triacs can work on full 360 degrees) I would say (180-60) / 360 = 33.33% power delivered.

Lefty

Last edited:

#### on1aag

##### New Member
Hi Conchord,

First you calculate the power from 0 to pi, that's 50 %.
Then you calculate the power from 0 to pi/3 and subtract
this value from the previous one. You will find 46,875 %.
But the SCR only conducts from 0 to pi therefore the
power supplied to the load is 46,875 %.

on1aag.

#### crutschow

##### Well-Known Member
Since power is function of the voltage squared, the power delivered to the load is not a linear function of phase angle. (See Dimmer Phase Angle Test for a simulated example at selected phase angles.)

To determine the power requires the calculation of the rms value of the truncated sine wave, which is not a simple function.

It also depends upon whether the load is constant resistive or incandescent lamp whose resistance varies with brightness..

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