PASE CONTROL OF SCR USING R,RC,& UJT TRIGGERING
22:29:00
AIM:
a) To conduct R,RC triggering circuit for SCR and plot its output wave form for various register values,
b) To construct UJT triggering circuit for SCR and plot is output wave form for various values of register
APPARATUS :
1. AC phase control trainer kit
2. Oscilloscope 20Kz
3. Incandescent lamp : 36V, 100W
4. Patch chord.
SPECIFICATION:
Ac phase control using SCR for R,RC & UJT comprises of the following modules. AC source, Triggering circuit, R,RC & lamp load
1. AC source 24V
2. Trigger circuit
a) Diode D – IN5408
b) Potentio meter R – 5KΩ,1W
c) Resistors R - 100Ω & Rc - 220Ω/1W
3. RC Triggering circuit
a) Diode D1 D2 – IN 5408
b) Potentiometer 1KΩ/1W
c) Resister R – 50 Ω /5W, Rc – 220 Ω/1W
d) Capacitor - 10µF/100V
4. UJT Triggering circuit ,
a) UJT – 2N2646
b) Resisters - 200 Ω/5W
c) Resistance R3 – 11K Ω/0.25W
d) Potentiometer – 43K Ω/1W
e) Zener Diode - 12V /1W
f) Capacitor – 0.1µF/6.3V
g) Thyristor – 74N612
THEORY:
The most common method for controlling the conduction in an SCR is by means of gate voltage control. The gate control and circuit is called firing or triggering circuit. These gating circuit are low power electronics circuits. The basic requirement for firing the SCR are that the current supplied to the gate should be
1. Of adequate and sufficiently short rise time,
2. Of adequate duration,
3. Occurs at a time when the main circuit durations are favorable to the conduction.
R – triggering circuits :
This is the simple method of varying the trigger angle and there for the power in the load. They how even suffer from a linked range of firing angle control ( 0 to 90° )
RC - triggering circuits :
By the RC network a large variation in the value of the firing angle can be obtained by changing the firing can be controlled .
UJT – Triggering Circuit :
The UJT is often used as trigger device for SCR and TRIACS. Its switching time is in the range of nano seconds . the most common UJT circuit used today is the relaxation circuit. Oscillator R and RC triggering circuit cannot be used for automatic or feed back control system. This difficulty can be over come by the UJT triggering circuit. It gains pulse triggering and reduces power dissipation in the gate circuits.
PROCEDURE :
For R and RC triggering
1. Make connections as per the circuit diagram
2. Vary the DRB to get its maximum resistance position
3. Switch on the power supply
4. Note down the output wave form across the load and the voltage across the gate and cathode of SCR using CRO
5. Repeat the above step for various values of potentiometer.
UJT Triggering :
1. Make connections as per the circuit diagram
2. Switch on the power supply and set the biasing voltage to 18V
3. Note down the wave form voltage ( V0 and Vap ) using CRO
4. Repeat the procedure for various values of potentiometer
5. Switch off the power supply and remove the connection
RESULT :
The R , RC ,and UJT Triggering circuits for SCR were constructed and the output wave form were plotted.
AIM:
a) To conduct R,RC triggering circuit for SCR and plot its output wave form for various register values,
b) To construct UJT triggering circuit for SCR and plot is output wave form for various values of register
APPARATUS :
1. AC phase control trainer kit
2. Oscilloscope 20Kz
3. Incandescent lamp : 36V, 100W
4. Patch chord.
SPECIFICATION:
Ac phase control using SCR for R,RC & UJT comprises of the following modules. AC source, Triggering circuit, R,RC & lamp load
1. AC source 24V
2. Trigger circuit
a) Diode D – IN5408
b) Potentio meter R – 5KΩ,1W
c) Resistors R - 100Ω & Rc - 220Ω/1W
3. RC Triggering circuit
a) Diode D1 D2 – IN 5408
b) Potentiometer 1KΩ/1W
c) Resister R – 50 Ω /5W, Rc – 220 Ω/1W
d) Capacitor - 10µF/100V
4. UJT Triggering circuit ,
a) UJT – 2N2646
b) Resisters - 200 Ω/5W
c) Resistance R3 – 11K Ω/0.25W
d) Potentiometer – 43K Ω/1W
e) Zener Diode - 12V /1W
f) Capacitor – 0.1µF/6.3V
g) Thyristor – 74N612
THEORY:
The most common method for controlling the conduction in an SCR is by means of gate voltage control. The gate control and circuit is called firing or triggering circuit. These gating circuit are low power electronics circuits. The basic requirement for firing the SCR are that the current supplied to the gate should be
1. Of adequate and sufficiently short rise time,
2. Of adequate duration,
3. Occurs at a time when the main circuit durations are favorable to the conduction.
R – triggering circuits :
This is the simple method of varying the trigger angle and there for the power in the load. They how even suffer from a linked range of firing angle control ( 0 to 90° )
RC - triggering circuits :
By the RC network a large variation in the value of the firing angle can be obtained by changing the firing can be controlled .
UJT – Triggering Circuit :
The UJT is often used as trigger device for SCR and TRIACS. Its switching time is in the range of nano seconds . the most common UJT circuit used today is the relaxation circuit. Oscillator R and RC triggering circuit cannot be used for automatic or feed back control system. This difficulty can be over come by the UJT triggering circuit. It gains pulse triggering and reduces power dissipation in the gate circuits.
PROCEDURE :
For R and RC triggering
1. Make connections as per the circuit diagram
2. Vary the DRB to get its maximum resistance position
3. Switch on the power supply
4. Note down the output wave form across the load and the voltage across the gate and cathode of SCR using CRO
5. Repeat the above step for various values of potentiometer.
UJT Triggering :
1. Make connections as per the circuit diagram
2. Switch on the power supply and set the biasing voltage to 18V
3. Note down the wave form voltage ( V0 and Vap ) using CRO
4. Repeat the procedure for various values of potentiometer
5. Switch off the power supply and remove the connection
RESULT :
The R , RC ,and UJT Triggering circuits for SCR were constructed and the output wave form were plotted.
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