1.R,RC,UJT firing
description
Transcript of 1.R,RC,UJT firing
R, RC & UJT FIRING MODULE(Model No : PEC14M12)
User Manual
Technical Clarification /Suggestion :NNNN / FFFFTechnical Support Division,Vi Microsystems Pvt. Ltd.,Vi Microsystems Pvt. Ltd.,Vi Microsystems Pvt. Ltd.,Vi Microsystems Pvt. Ltd.,
Plot No :75, Electronics Estate,Perungudi, Chennai - 600 096, INDIA.Ph: 91- 44-2496 3142, 91-44-2496 1852Mail : [email protected],Web : www.vimicrosystem
Version 1.0
R, RC & UJT FIRING MODULE PEC14M12
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Chapter-1
Introduction
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1.1 INTRODUCTION
Power electronics deals with the application of solid-state electronics for the control andconversion of electric power. Conversion techniques require the switching ON/OFF of powersemi conductor devices.
Modern Power Electronics started with the invention of SCR commonly known as thyristor in1956. At present, a number of power switching semiconductor devices are available namelyBJT, MOSFET, IGBT and GTO etc. All these devices are turned ON/OFF through controlterminal, either base or gate as the case may be. This makes simple power circuit.
This manual is intended to give you description of R, RC & UJT Firing Circuits. An SCRcan be switched from OFF state to ON state by means of triggering. Gate triggering is themost common method of turning ON the SCRs, because it is an efficient and reliable method.
The gate control circuit is also called firing or triggering circuit. These gating circuits areusually low power electronic circuits. A firing circuit should fulfil the following two functions.
(i). If power circuit has more than one SCR, the firing circuit should produce gating pulsesfor each SCR at the desired instant for proper operation of power circuit.
(ii). The control signal generated by a firing circuit may not be able to turn-on an SCR. Itis therefore common to feed the voltage pulses to a driver circuit and then to gatecathode circuit. A driver circuit consists of a pulse amplifier and a pulse transformer.
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Chapter-2
About Our Trainer
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2.2 SPECIFICATION
1. Power Input : 230V AC, 50 Hz.
2. Transformer : 230V/24V AC
3. Load Rheostat : 50E/4A
4. Maximum Load Rheostat : 2 Amps
5. SCR (TYN612) : 600V, 12A
6. UJT : 2N2646
7. Zener Diode : 18V/1 W
8. Fuse : 0.5 Amps
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2.3 FRONT PANEL VIEW
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2.4 FRONT PANEL DESCRIPTION
The front panel of R, RC & UJT Firing module consists of
i. R Firing Circuit
ii. RC Firing Circuit
iii. UJT Firing Circuit
1. Power ON/OFF switch is provided to control the input AC mains supply to themodule.
2. AC ON/OFF switch is provided to control input AC voltage to the power circuit.
3. The input supply to the R, RC & UJT firing circuit are given through the T7- T9, T12-T13 and T1-T2 terminals respectively.
4. Test points are provided to view different signals in the power circuit.
5. P & N terminals are provided to apply 24V AC input to the firing circuits.
6. Pulse output from each firing circuits are terminated at respective G and K terminals.
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TEST POINT DESCRIPTION
i. UJT FIRING
T3 & T4 - Test points to check the input DC current
T3 & T7 - Test points to check the input DC voltage
T4 & T7 - Test points to check the Zener diode voltage
T5 & T7 - Test points to check the capacitor voltage
T6 & T7 - Test points to check the output pulses.
ii. R FIRING
T10 & T11 - Test points to check the output trigger pulse.
iii. RC FIRING
T15 & T16 - Test points to check the output trigger pulse.
T14 & T16 - Test points to check the capacitor voltage
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2.5 HARDWARE DESCRIPTION
2.5.1 Block Diagram
The block diagram consists of
i. Step down transformerii. Diode bridge rectifieriii. UJT Firing circuitiv. R Firing circuitv. RC Firing circuit vi. Pulse Transformer
2.5.2 Block Diagram Description
i. Step Down Transformer
The 230V AC input supply is step down to 24 V AC using step down transformer. Thisvoltage is given as input to the firing circuit.
ii. Diode Bridge Rectifier
The diode bridge rectifier converts the input AC voltage into fixed dc voltage. The constantrectified DC voltage is obtained through the zener diode. This dc voltage is given to UJTFiring circuit.( This rectifier is only for the UJT Firing circuit).
iii. UJT Firing Circuit
The resistor, charging circuit (RC) Zener diode (Z) & UJT (2N2646) forms the UJT firingcircuit. The input is DC voltage. It is used to generate triggering signals to SCR.
Step DownTransformer
Diode Bridge UJT Firing Pulse Transfomer
RC Firingcircuit
Rectifier
circuitR Firing
230V AC50 Hz
230/24V
G
KcircuitTo G & Kof SCR
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iv. R Firing Circuit
R Firing circuit is made up of variable resistance which controls the firing angle of SCR in therange of 0-90°. This circuit controls the gate current to the SCR.
v. RC Firing Circuit
RC Firing circuit is made up of resistance and capacitance. On varying the resistance, thecurrent through the gate varies and controls the firing angle in the range of 0-180°. Thismethod also controls the gate current to the SCR.
vi. Pulse transformer
The purpose of pulse transformer used in triggering circuit are
i. The isolation of low voltage gate circuits from high voltage anode circuit.
ii. The triggering of two or more devices from the same trigger source.
vii. SCR Device (TYN612)
SCR Device along with RC Snubber protection circuit is provided in the module. Using thedevice the study of SCR operation for different firing circuit can be done. Snubber circuit isprovided to limit the switching losses of the device.
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2.7 Protection
1. Fuse is provided to protect the trainer from over current faults.
2. Earthing is provided to protect the trainer module.
3. RC Snubber circuit is provided to protect the SCR.
2.8 Precautions
1. Before doing connections make all switches in OFF position.
2. Load Rheostat should be kept in maximum position.
3. Do not view the AC input waveform and pulse waveform in CRO with dual mode.
4. 24V input AC to the SCR device should not be connected directly.
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Chapter-3
Experiment Section
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Experiment 1: Study of R-Firing Circuit
Aim:
To study the operation of resistance triggering circuit using R, RC & UJT Firing module.
Apparatus Required:
1. PEC14M12 Module2. Patch chords.
Accessories to be provided by the institution
1. CRO2. 50E/4A Rheostat3. Digital Multimeter - 01
Circuit Diagram
minR
50 Hz24V AC
K
50E/4A
RDSCR
A
v
bR
LoadRheostat
(POT)
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Connection Diagram
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Connection procedure:
1. Connect the input supply to the module.
2. Connect P & N terminals to T7 & T9.
3. Connect one end of load rheostat to anode (A) of SCR.
4. Connect the other end of the load rheostat to the P terminal of 24V AC supply.
5. Connect the cathode (K) of SCR to the N terminal of 24V AC supply.
6. Connect the G & K terminals of firing circuit to G & K terminals of SCR.
7. Connect the CRO groung to Anode of SCR. Connect channel 1 probe to T7 & channel2 probe to cathode of SCR.
Experiment Procedure
1. Verify the connection as per the connection diagram.
2. Switch ON the power supply.
3. Switch ON the power on/off switch.
4. Switch ON the 24V AC S/W.
5. Switch ON power supply to CRO & select suitable sensitivity and time settings. Useline trigger module.
6. Observe the waveform for input AC voltage & the load voltage.
7. Study the waveform for various firing angle by varying the POT in R firing circuit.
8. For a particular firing angle, plot the waveforms on a graph sheet to scale.
9. Measure the average DC voltage across the load & rms value of the ac input voltageusing a Digital multimeter.
10. Calculate the dc output voltage using the equation.
VV
dc 2
21
cos
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and compare the measured value.
- Firing angle delayV - RMS value of the ac input voltage.
Model Graph
L,i
LV
V
e
t
t
t
s
ak
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Experiment 2: Study of RC-Firing Circuit
Aim:
To study the operation of resistance capacitance triggering circuit using R, RC & UJT Firingmodule.
Apparatus Required:
1. PEC14M12 Module2. Patch chords.
Accessories to be provided by the institution
1. CRO2. 50E/4A Rheostat3. Digital Multimeter - 01
Circuit Diagram
G
D2
A+ -
SCR
C
D1R
50E/4A
K
24V AC50 Hz
v
LoadRheostat
(POT)
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Connection Diagram
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Connection procedure:
1. Connect the input supply to the module.
2. Connect P & N terminals to T12 & T13.
3. Connect one end of load rheostat to anode (A) of SCR.
4. Connect the other end of the load rheostat to the P terminal of 24V AC supply.
5. Connect the cathode (K) of SCR to the N terminal of 24V AC supply.
6. Connect the G & K terminals of firing circuit to G & K terminals of SCR.
7. Connect the CRO ground to Anode of SCR connect channel -1 probe to T12 &channel 2 probe to the cathode.
Experiment Procedure
1. Verify the connection as per the connection diagram.
2. Switch ON the power supply.
3. Switch ON the power on/off switch.
4. Switch ON the 24V AC S/W.
5. Switch ON power supply to CRO & select suitable sensitivity and time settings. Useline trigger module.
6. Observe the waveform for input AC voltage & the load voltage.
7. Study the waveform for various firing angle by varying the POT in R firing circuit.
8. For a particular firing angle, plot the waveforms on a graph sheet to scale.
9. Measure the average DC voltage across the load & rms value of the ac input voltageusing a Digital multimeter.
10. Calculate the dc output voltage using the equation.
VV
dc 2
21
cos
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and compare the measured value.
- Firing angle delayV - RMS value of the ac input voltage.
Model Graph
L,i
LV
V
e
t
t
t
s
ak
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Experiment 3: Study of UJT Firing Circuit
Aim:
To study the operation of UJT triggering circuit using R, RC & UJT Firing module.
Apparatus Required:
1. PEC14M12 Module2. Patch chords.
Accessories to be provided by the institution
1. CRO2. 50E/4A Rheostat3. Digital Multimeter - 01
Circuit Diagram
D1
C
50V/4A
SCR
G
E
R1
B2
B1
D3
D4 D2
Z
R
24V AC
ALoad
Rheostat
(POT)
K
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Connection Diagram
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Connection procedure:
1. Connect the input supply to the module.
2. Connect one end of load rheostat to anode (A) of SCR.
3. Connect the other end of the load rheostat to the P terminal of 24V AC supply.
4. Connect the G1 & K1 terminals of the UJT firing circuit to gate(G) and cathode (K)terminals of SCR.
Experiment Procedure
1. Verify the connection as per the connection diagram.
2. Switch ON the power supply.
3. Switch ON the power on/off switch.
4. Connect the CRO ground to ground terminal of UJT Firing circuit.
5. Switch ON the power supply to CRO & select suitable sensitivity and time settings.Use line trigger module.
6. Observe the waveform for input ac voltage & pulsating DC output.
7. Connect channel 2 probe to terminal T4 and to observe the zener diode voltage.
8. Connect channel 2 probe to terminal T5 and to observe the capacitor voltage.
9. Study the waveform for various firing angle.
10. For a particular firing angle plot a waveform on a graph sheet to scale.
11. Observe the capacitor voltage is zero at the end of every half cycle.
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Model Graph
V
0
0
0
dc
zV
Vc
gV
acV
t
t
t
t
t
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Chapter-4
Theoretical Concept
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The following section is discussed about the various types of firing circuits.
4.1. R Firing Circuit:
This is the simple method for varying the triggering angle upto 90º. Instead of using gatepulse, here gate current is used to trigger the SCR. The circuit diagram is shown in fig 4.a.
Fig 4.a. R Firing circuit
The circuit operates as follows,
1. When a gate current Ig is equal to Ig(min), SCR turns ON while es goes positive and eLis approximately equal to es.
2. As es goes negative, SCR turns OFF and the load voltage (eL) is zero during thisperiod.
3. The purpose of the diode(D) in the gate circuit is to prevent the gate cathode reversebias during the negative half cycle.
4. The same sequence is repeated, when eS again goes positive.
5. By varying Rv, the load voltage can be controlled.
6. If Rv increases, the firing angle ’ will increase & vice versa.
7. The limiting resistor Rmin is used to limit the gate current to a safe value while varyingRv.
8. The stabilizing resistor Rb should have such a value that maximum voltage drop acrossit does not exceed maximum possible gate voltage Vgm. This can happen only when Rvis zero.
b
v
oV
-+Load
minR
50 Hz24V AC
K
RD
R
SCR
A
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When the supply voltage has reached its peak, Emax
From the voltage distribution
The thyristor will trigger when the instantaneous anode voltage, es, is
where Ig(min) = Minimum gate current to trigger the thyristorVd = Voltage drop across the diodeVg(min) = gate-voltage to trigger, corresponding to Ig(min).
The waveform for R firing circuit is shown in Fig 4.b.
Fig. 4.b Waveform for R Firing circuit
L,i
LV
V
e
t
t
t
s
ak
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4.2. RC Firing Circuit:
The RC firing circuit which is normally used for simple phase control gives variation of firingangle beyond 90. The circuit diagram is shown in fig 4.c.
Fig. 4.c RC Firing circuitThe circuit operates as follows,
1. When es goes positive and the capacitor voltage Vc equals to gate trigger voltageVgt(=Vg min + VD1), the SCR will turn ON.
2. After this, the capacitor holds to a small positive voltage as shown in the waveform.
3. During negative half cycle, capacitor c charges through D2 with lower plate positive tothe supply voltage Emax.
4. The diode D1 prevents the break down of the gate to cathode junction during negativehalf cycle.
5. In the range of power frequencies, the RvC for zero output voltage is given by
R Cv 137
2.
Where T= 1/f = period of AC line frequency in seconds
6. The maximum value of Rv is given by,
oV
Load
G
D2
A+ -
SCR
C
D1R
K
24V AC50 Hz
v
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Where VD1 = Voltage drop across the diode D1 eS = Supply voltage at which SCR turn ON
The waveform for RC firing circuit is shown in Fig 4.d.
Fig. 4.d Waveform for RC Firing circuit
Emaxes
t
L
g(min)
t
V
e
-Emax
t
VAK
cV
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4.3. UJT FIRING CIRCUIT:
4.3.1. UNI JUNCTION TRANSISTOR:
UJT is commonly used to generate triggering signals for SCR. UJT has three terminals calledthe Emitter E, Base one, B1 and Base two, B2. The basic structure and circuit symbol of UJTis shown in Fig 4.e and 4.f.
Fig. 4.e. Basic Structure of UJT Fig. 4.f. Circuit Symbol for UJT
Between B1 and B2 the unijunction has the characteristics of an ordinary resistance. This isthe interbase resistance RBB and has value in the range 4.7 to 9.1K. The VI characteristicsof UJT is shown in fig 4.g.
Fig. 4.g. V-I Characteristics of UJT
RB1
B2R
N-type
P-type
E
B1
B2
B1
B2
E
PI
VP
I VEI
EV
Peak Point
Cutoffregion
Valley Point
regionSaturation
RegionResistanceNegative
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4.3.2 Synchronized UJT Triggering [or Ramp Triggering
A synchronized UJT triggering circuit using an UJT is shown in fig 4.h. Diodes D1-D4rectifies the input AC to DC. Zener diode Z is used to clip the rectified voltage to a standardlevel Vz, which remains constant except near the Vdc zero.
Fig. 4.h Synchronized UJT Triggering circuit
The zener voltage Vz is applied to charging circuit RC. So capacitor C charges by current i1.When the capacitor voltage reaches threshold voltage Vz, the E-B1 junction of UJT breaksdown and C charges through primary of pulse transformer sending a current i2.
As the current i2 is in the form of pulse, SCR with positive anode voltage would turn ON.Varying R can control rate of rise of capacitor voltage. This method of control is called rampcontrol. The firing angle can be controlled up to 150. The waveform for generation of outputpulses for the given circuit is shown in fig 4.i.
Fig.4.i Waveform for synchronized UJT triggering circuit
24V AC
R
Z
D2D4
D3
B1
B2
R1
E
G1
C
D1
K1G2
K2
ZV
R2
Vc
+
-
PulseTransformer
i1
Vdc
+
-
+
-
Vc
dcV
cV Vc
dcV
Vz
Pulse Voltage
zV t
t
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(5.1)
The period of oscillation, T, is independent of the dc supply voltage Vs, and is given by
The line synchronized UJT trigger circuit can be used for,
1. Single phase AC controller
2. Single phase half wave controlled converter
3. Single phase controlled rectifier with center-tapped transformer (bi-phase half waveconverter)
4. Single phase half controlled bridge rectifier.
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2.6 DATA SHEETS
1. SCR (TYN612)
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2. UJT (2N2646)