RC Triggering Circuit

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This blog post summarize RC Triggering Circuit

RC Triggering

It includes variable resistor, two diodes,SCR(Silicon Controlled Rectifier), Capacitor, Load resistor.

The circuit diagram of an RC Triggering is shown below (Figure 2).

Figure 2 shows an R-C-Diode circuit giving full half-cycle control (180 electrical degrees). On the positive half-cycle of SCR anode voltage the capacitor charges to the trigger point of the SCR in a time determined by the RC time constant and the rising anode voltage. The top plate of the capacitor charges to the peak of the negative voltage cycle through diode D2 on the negative half-cycle, resetting it for the next charging cycle.

RC Triggering Circuit

Working of Capacitor

During negative half cycle capacitor charges in reverse direction when the supply voltage increases towards positive side the capacitor voltage also recharges in opposite direction. When this capacitor voltage reaches threshold voltage SCR will turn on and capacitor discharges through diode D2 and its voltage become very small positive voltage. Firing angle can be varied from 0 to 180 degree.

Lab Experiment


To Study and verify RC Triggering circuit of SCR.

Apparatus required

RC Triggering circuit kit

☞Patch cards

☞Power card


☞60W Bulb

Circuit Diagram for RC Triggering Circuit

circuit-diagram-for-rc-triggering-circuit.jpg (472×222)

Procedure of RC Triggering Circuit

CRO Settings

☞Time (X) Axis: 5ms/div

☞Voltage (Y) Axis: 20V/div

☞Probe: 1:10 CRO Probe is suitable one.

Initial Settings

☞Ensure the 230V Power Supply is in proper with Tester.

☞Ensure the CRO is working properly with probe checking and proper ground line axis.

Mimic Diagram for RC Triggering


Experiment Steps

☞The connections are made as per the circuit diagram given above.

☞The R Load must be 60W bulb.

☞Turn ON SW1 and observe the waveform across the R load.

☞Measure the X-axis time interval of ON time of Load Voltage and OFF Time of Load Voltage.

☞Adjust the value of Firing angle and note down the load voltage

☞Repeat the step 4.

☞Repeat the experiment for different values of α and note down Vo.


Model Graph


Total Time Period


The Average Output Voltage


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