R, RC & UJT FIRING MODULE(Model No : PEC14M12) User Manual Version 1.0 Technical Clarification /Suggestion : N/F Technical Support Division, Vi Microsystems Pvt. Ltd., Plot No :75, Electronics Estate, Perungudi, Chennai - 600 096, INDIA. Ph: 91- 44-2496 3142, 91-44-2496 1852 Mail : [email protected], Web : www.vimicrosystem R, RC & UJT FIRING MODULE PEC14M12 Chapter-1 Introduction Vi Microsystems Pvt. Ltd., [1] R, RC & UJT FIRING MODULE 1.1 PEC14M12 INTRODUCTION Power electronics deals with the application of solid-state electronics for the control and conversion of electric power. Conversion techniques require the switching ON/OFF of power semi conductor devices. Modern Power Electronics started with the invention of SCR commonly known as thyristor in 1956. At present, a number of power switching semiconductor devices are available namely BJT, MOSFET, IGBT and GTO etc. All these devices are turned ON/OFF through control terminal, 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 SCR can be switched from OFF state to ON state by means of triggering. Gate triggering is the most 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 are usually 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 pulses for 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. It is therefore common to feed the voltage pulses to a driver circuit and then to gate cathode circuit. A driver circuit consists of a pulse amplifier and a pulse transformer. Vi Microsystems Pvt. Ltd., [2] RC & UJT FIRING MODULE PEC14M12 Chapter-2 About Our Trainer Vi Microsystems Pvt.. Ltd.R. [3] . Zener Diode : 18V/1 W 8.. Ltd. Load Rheostat : 50E/4A 4. Fuse : 0. 50 Hz. SCR (TYN612) : 600V. UJT : 2N2646 7. 2.2 SPECIFICATION 1. Transformer : 230V/24V AC 3. 12A 6. Maximum Load Rheostat : 2 Amps 5.R. RC & UJT FIRING MODULE PEC14M12 2.5 Amps Vi Microsystems Pvt. Power Input : 230V AC. [4] . RC & UJT FIRING MODULE 2.R. [5] . Ltd.3 PEC14M12 FRONT PANEL VIEW Vi Microsystems Pvt.. Pulse output from each firing circuits are terminated at respective G and K terminals. [6] .. The input supply to the R. T12 -T13 and T1-T2 terminals respectively. Vi Microsystems Pvt. P & N terminals are provided to apply 24V AC input to the firing circuits. RC & UJT Firing module consists of i. AC ON/OFF switch is provided to control input AC voltage to the power circuit. 3. 4.T9. 6. 5.R. R Firing Circuit ii. 2. RC & UJT firing circuit are given through the T7. RC Firing Circuit iii. Ltd. RC & UJT FIRING MODULE 2. Test points are provided to view different signals in the power circuit. Power ON/OFF switch is provided to control the input AC mains supply to the module.4 PEC14M12 FRONT PANEL DESCRIPTION The front panel of R. UJT Firing Circuit 1. . - Test points to check the output trigger pulse. RC FIRING Vi Microsystems Pvt. T14 & T16 - Test points to check the capacitor voltage ii. RC & UJT FIRING MODULE PEC14M12 TEST POINT DESCRIPTION i. Ltd. T15 & T16 - Test points to check the output trigger pulse.R. R FIRING T10 & T11 iii. [7] . 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. 1 Block Diagram 230V AC 50 Hz Step Down Transformer Diode Bridge Rectifier UJT Firing circuit Pulse Transfomer G K To G & K of SCR 230/24V R Firing circuit RC Firing circuit The block diagram consists of i. vi. v. This dc voltage is given to UJT Firing circuit. The constant rectified DC voltage is obtained through the zener diode. iv. Diode Bridge Rectifier The diode bridge rectifier converts the input AC voltage into fixed dc voltage. UJT Firing Circuit The resistor. iii. Step Down Transformer The 230V AC input supply is step down to 24 V AC using step down transformer. charging circuit (RC) Zener diode (Z) & UJT (2N2646) forms the UJT firing circuit. This voltage is given as input to the firing circuit. The input is DC voltage. It is used to generate triggering signals to SCR.( This rectifier is only for the UJT Firing circuit). RC & UJT FIRING MODULE 2.5 PEC14M12 HARDWARE DESCRIPTION 2. [8] . iii..R. ii.5. Step down transformer Diode bridge rectifier UJT Firing circuit R Firing circuit RC Firing circuit Pulse Transformer 2. Ltd. Vi Microsystems Pvt. ii.5.2 Block Diagram Description i. SCR Device (TYN612) SCR Device along with RC Snubber protection circuit is provided in the module.R. v. The triggering of two or more devices from the same trigger source. Snubber circuit is provided to limit the switching losses of the device. This method also controls the gate current to the SCR. The isolation of low voltage gate circuits from high voltage anode circuit. Ltd. ii. PEC14M12 R Firing Circuit R Firing circuit is made up of variable resistance which controls the firing angle of SCR in the range of 0-90°. Pulse transformer The purpose of pulse transformer used in triggering circuit are i. [9] . vi. Vi Microsystems Pvt. On varying the resistance. the current through the gate varies and controls the firing angle in the range of 0-180°. vii. Using the device the study of SCR operation for different firing circuit can be done. RC Firing Circuit RC Firing circuit is made up of resistance and capacitance. RC & UJT FIRING MODULE iv. This circuit controls the gate current to the SCR.. 24V input AC to the SCR device should not be connected directly. 2. 3. Load Rheostat should be kept in maximum position. 3.8 Precautions 1. 2. [ 10 ] . 2. Before doing connections make all switches in OFF position. Do not view the AC input waveform and pulse waveform in CRO with dual mode.R. Vi Microsystems Pvt. Earthing is provided to protect the trainer module. RC & UJT FIRING MODULE PEC14M12 2. RC Snubber circuit is provided to protect the SCR. Ltd.7 Protection 1.. Fuse is provided to protect the trainer from over current faults. 4. R. RC & UJT FIRING MODULE PEC14M12 Chapter-3 Experiment Section Vi Microsystems Pvt. [ 11 ] .. Ltd. Ltd. [ 12 ] .. Accessories to be provided by the institution 1.01 Circuit Diagram 50E/4A A Load Rheostat 24V AC 50 Hz SCR D Rmin Rv (POT) Rb K Vi Microsystems Pvt. PEC14M12 Module Patch chords. 2. 2. RC & UJT FIRING MODULE Experiment 1: PEC14M12 Study of R-Firing Circuit Aim: To study the operation of resistance triggering circuit using R. RC & UJT Firing module. CRO 50E/4A Rheostat Digital Multimeter .R. 3. Apparatus Required: 1. R. [ 13 ] .. Ltd. RC & UJT FIRING MODULE PEC14M12 Connection Diagram Vi Microsystems Pvt. 9. 2V 1 cos 2 [ 14 ] . Measure the average DC voltage across the load & rms value of the ac input voltage using a Digital multimeter. 5. RC & UJT FIRING MODULE PEC14M12 Connection procedure: 1. 6. Use line trigger module. Connect the input supply to the module. 3. Switch ON the power on/off switch.R. plot the waveforms on a graph sheet to scale. 4. Vdc Vi Microsystems Pvt. 2. Verify the connection as per the connection diagram. Connect channel 1 probe to T7 & channel 2 probe to cathode of SCR. 10. Ltd. Switch ON the 24V AC S/W. Connect the CRO groung to Anode of SCR. 5. For a particular firing angle. 7. 3. Switch ON power supply to CRO & select suitable sensitivity and time settings. Switch ON the power supply. 7.. Connect the other end of the load rheostat to the P terminal of 24V AC supply. Observe the waveform for input AC voltage & the load voltage. 6. 8. Connect the cathode (K) of SCR to the N terminal of 24V AC supply. Connect the G & K terminals of firing circuit to G & K terminals of SCR. 4. Connect P & N terminals to T7 & T9. Connect one end of load rheostat to anode (A) of SCR. Experiment Procedure 1. Study the waveform for various firing angle by varying the POT in R firing circuit. Calculate the dc output voltage using the equation. 2. i L Vi Microsystems Pvt.R. Ltd.. Model Graph es t Vak t VL. RC & UJT FIRING MODULE PEC14M12 and compare the measured value. V - Firing angle delay RMS value of the ac input voltage. t [ 15 ] . Apparatus Required: 1. RC & UJT Firing module. CRO 50E/4A Rheostat Digital Multimeter .01 Circuit Diagram 50E/4A + A Load Rheostat 24V AC 50 Hz D2 SCR Rv (POT) D1 G C K Vi Microsystems Pvt. PEC14M12 Module Patch chords.. 2. Accessories to be provided by the institution 1. [ 16 ] .R. 3. RC & UJT FIRING MODULE Experiment 2: PEC14M12 Study of RC-Firing Circuit Aim: To study the operation of resistance capacitance triggering circuit using R. Ltd. 2. Ltd.. [ 17 ] .R. RC & UJT FIRING MODULE PEC14M12 Connection Diagram Vi Microsystems Pvt. 2. 6. 2. Switch ON the 24V AC S/W. Connect the other end of the load rheostat to the P terminal of 24V AC supply. Switch ON the power on/off switch. 3. Connect the cathode (K) of SCR to the N terminal of 24V AC supply. For a particular firing angle. Connect the G & K terminals of firing circuit to G & K terminals of SCR. Vdc Vi Microsystems Pvt. Connect P & N terminals to T12 & T13. 7. Study the waveform for various firing angle by varying the POT in R firing circuit.R. 4. 6. 4. Switch ON power supply to CRO & select suitable sensitivity and time settings. Observe the waveform for input AC voltage & the load voltage. RC & UJT FIRING MODULE PEC14M12 Connection procedure: 1. 3. plot the waveforms on a graph sheet to scale. 5. 5.. 8. Calculate the dc output voltage using the equation. Connect the CRO ground to Anode of SCR connect channel -1 probe to T12 & channel 2 probe to the cathode. Ltd. 7. Connect one end of load rheostat to anode (A) of SCR. Experiment Procedure 1. 2V 1 cos 2 [ 18 ] . Connect the input supply to the module. Switch ON the power supply. Use line trigger module. 10. Measure the average DC voltage across the load & rms value of the ac input voltage using a Digital multimeter. Verify the connection as per the connection diagram. 9. t [ 19 ] .i L Vi Microsystems Pvt. Model Graph es t Vak t VL. RC & UJT FIRING MODULE PEC14M12 and compare the measured value. Ltd.R. V - Firing angle delay RMS value of the ac input voltage.. RC & UJT Firing module.01 Circuit Diagram 50V/4A A Load Rheostat R1 D1 D3 R (POT) Z 24V AC E D4 D2 B2 B1 SCR G C K Vi Microsystems Pvt.R. PEC14M12 Module Patch chords. RC & UJT FIRING MODULE Experiment 3: PEC14M12 Study of UJT Firing Circuit Aim: To study the operation of UJT triggering circuit using R. CRO 50E/4A Rheostat Digital Multimeter . 2.. 3. 2. Ltd. Apparatus Required: 1. Accessories to be provided by the institution 1. [ 20 ] . [ 21 ] . RC & UJT FIRING MODULE PEC14M12 Connection Diagram Vi Microsystems Pvt..R. Ltd. 7. 5. 3. For a particular firing angle plot a waveform on a graph sheet to scale. 8. Ltd. Switch ON the power supply. Experiment Procedure 1. RC & UJT FIRING MODULE PEC14M12 Connection procedure: 1. Use line trigger module. 10. Connect channel 2 probe to terminal T5 and to observe the capacitor voltage. 3.. Observe the capacitor voltage is zero at the end of every half cycle. Connect the input supply to the module. Connect one end of load rheostat to anode (A) of SCR. Connect the other end of the load rheostat to the P terminal of 24V AC supply. Study the waveform for various firing angle. 6. Connect the G1 & K1 terminals of the UJT firing circuit to gate(G) and cathode (K) terminals of SCR. 4. [ 22 ] . 2. Switch ON the power on/off switch. Connect the CRO ground to ground terminal of UJT Firing circuit. 9. 4. Observe the waveform for input ac voltage & pulsating DC output. Verify the connection as per the connection diagram. 2. 11.R. Vi Microsystems Pvt. Connect channel 2 probe to terminal T4 and to observe the zener diode voltage. Switch ON the power supply to CRO & select suitable sensitivity and time settings. Ltd.. t [ 23 ] .R. RC & UJT FIRING MODULE PEC14M12 Model Graph Vac t Vdc 0 t Vz 0 t Vc 0 t Vg Vi Microsystems Pvt. R. Ltd. RC & UJT FIRING MODULE PEC14M12 Chapter-4 Theoretical Concept Vi Microsystems Pvt.. [ 24 ] . This can happen only when Rv is zero. 6. When a gate current Ig is equal to Ig(min). [ 25 ] . SCR turns OFF and the load voltage (eL) is zero during this period. 4. 2. 8.. RC & UJT FIRING MODULE PEC14M12 The following section is discussed about the various types of firing circuits. The purpose of the diode(D) in the gate circuit is to prevent the gate cathode reverse bias during the negative half cycle. 4. As es goes negative.R. here gate current is used to trigger the SCR. The circuit diagram is shown in fig 4.a. If Rv increases. 3. The stabilizing resistor Rb should have such a value that maximum voltage drop across it does not exceed maximum possible gate voltage Vgm.1. SCR turns ON while es goes positive and eL is approximately equal to es. 7. 5. By varying Rv. Vi Microsystems Pvt. the firing angle ’ will increase & vice versa. 1. R Firing Circuit: This is the simple method for varying the triggering angle upto 90º. The limiting resistor Rmin is used to limit the gate current to a safe value while varying Rv. Vo + Load A Rmin 24V AC 50 Hz SCR D Rv Rb K Fig 4. R Firing circuit The circuit operates as follows. The same sequence is repeated. Instead of using gate pulse. Ltd. the load voltage can be controlled. when eS again goes positive.a. b. [ 26 ] . The waveform for R firing circuit is shown in Fig 4. 4. RC & UJT FIRING MODULE PEC14M12 When the supply voltage has reached its peak. es t Vak t VL. es.R.b Waveform for R Firing circuit Vi Microsystems Pvt.i L t Fig. is where Ig(min) = Vd = Vg(min) = Minimum gate current to trigger the thyristor Voltage drop across the diode gate-voltage to trigger. Ltd. corresponding to Ig(min).. Emax From the voltage distribution The thyristor will trigger when the instantaneous anode voltage. 1. When es goes positive and the capacitor voltage Vc equals to gate trigger voltage Vgt(=Vg min + VD1). The diode D1 prevents the break down of the gate to cathode junction during negative half cycle.. Vi Microsystems Pvt. 4. The maximum value of Rv is given by. 5. 4.c. [ 27 ] . the capacitor holds to a small positive voltage as shown in the waveform. Vo + Load A D2 24V AC 50 Hz SCR Rv D1 G C K Fig. 3. The circuit diagram is shown in fig 4.R. In the range of power frequencies. Ltd.c RC Firing circuit The circuit operates as follows. After this. RC & UJT FIRING MODULE 4. PEC14M12 RC Firing Circuit: The RC firing circuit which is normally used for simple phase control gives variation of firing angle beyond 90.2. the RvC for zero output voltage is given by 137 . 2. capacitor c charges through D2 with lower plate positive to the supply voltage Emax. During negative half cycle. the SCR will turn ON. Rv C 2 Where T= 1/f = period of AC line frequency in seconds 6. Ltd. [ 28 ] .R.d Waveform for RC Firing circuit Vi Microsystems Pvt. Emax es Vg(min) t Vc -Emax e L t V AK t Fig.. RC & UJT FIRING MODULE PEC14M12 Where VD1 eS = Voltage drop across the diode D1 Supply voltage at which SCR turn ON = The waveform for RC firing circuit is shown in Fig 4.d. 4. V E Negative Resistance Region Cutoff region VP Saturation region Peak Point Valley Point IP IV IE Fig.R. UJT FIRING CIRCUIT: 4. 4.3. UNI JUNCTION TRANSISTOR: UJT is commonly used to generate triggering signals for SCR. [ 29 ] .7 to 9. Base one.. RC & UJT FIRING MODULE PEC14M12 4.1K.e. V-I Characteristics of UJT Vi Microsystems Pvt. Basic Structure of UJT Fig.g. 4. 4.3.1. The basic structure and circuit symbol of UJT is shown in Fig 4. Ltd. B2.e and 4.f.f. This is the interbase resistance RBB and has value in the range 4. Circuit Symbol for UJT Between B1 and B2 the unijunction has the characteristics of an ordinary resistance.g. B1 and Base two. The VI characteristics of UJT is shown in fig 4. B2 B2 R B2 P-type E E R B1 N-type B1 B1 Fig. UJT has three terminals called the Emitter E. [ 30 ] . Vdc Vc Vz Vdc Vz Vc Vc t Pulse Voltage t Fig.i Waveform for synchronized UJT triggering circuit Vi Microsystems Pvt..3.R. which remains constant except near the Vdc zero. R1 + D1 + i1 D3 R2 R Z 24V AC Vdc VZ E B2 G1 D4 + D2 C Vc - B1 - K1 G2 Pulse Transformer K2 Fig. The firing angle can be controlled up to 150.4. Varying R can control rate of rise of capacitor voltage. Ltd.h.i. The waveform for generation of output pulses for the given circuit is shown in fig 4. So capacitor C charges by current i1.h Synchronized UJT Triggering circuit The zener voltage Vz is applied to charging circuit RC. This method of control is called ramp control. RC & UJT FIRING MODULE PEC14M12 4. When the capacitor voltage reaches threshold voltage Vz. 4. the E-B1 junction of UJT breaks down and C charges through primary of pulse transformer sending a current i2.2 Synchronized UJT Triggering [or Ramp Triggering A synchronized UJT triggering circuit using an UJT is shown in fig 4. Zener diode Z is used to clip the rectified voltage to a standard level Vz. As the current i2 is in the form of pulse. Diodes D1-D4 rectifies the input AC to DC. SCR with positive anode voltage would turn ON. RC & UJT FIRING MODULE PEC14M12 The period of oscillation. Single phase controlled rectifier with center-tapped transformer (bi-phase half wave converter) 4. [ 31 ] . and is given by (5. Ltd. 1.1) The line synchronized UJT trigger circuit can be used for. Single phase half wave controlled converter 3. Single phase AC controller 2. T. Single phase half controlled bridge rectifier. Vi Microsystems Pvt.R.. is independent of the dc supply voltage Vs. .R. PEC14M12 DATA SHEETS SCR (TYN612) Vi Microsystems Pvt. [ 32 ] . Ltd.6 1. RC & UJT FIRING MODULE 2. RC & UJT FIRING MODULE 2. [ 33 ] .. Ltd. PEC14M12 UJT (2N2646) Vi Microsystems Pvt.R.