Welcome to electrical and electronics engineering discussion website, Please login or register to continue.

Welcome to electrical and electronics engineering Q&A site...

Join our WhatsApp group

267 views
in Unit 1 by
What is holding current and latching current in SCR? Draw the gate characteristics of an SCR and explain the characteristics. What are the different signals which can be used for turning on SCR by gate control? compare them.
Join me on Google Pay, a secure app for money transfers, bills and recharges. Enter my code 908dq to earn ₹51 back on your first payment!

Please log in or register to answer this question.

1 Answer

0 votes
by
 
Best answer

Holding current:

Holding current is the minimum current flow in SCR to hold SCR in on state. If the anode current fall below holding current SCR will turn off. And that voltage is known as holding voltage. Holding current is less than latching current. The holding current is in the range of 8 to 10 milliamperes.

image

Latching current:

Latching current is for turning on the SCR. Latching current is the current which is required to turn on the SCR and latch the SCR in conduction mode. Latching current is in the range of 10 to 15 milliamperes.

Gate characteristics of SCR:

image

Ig (min) and Vg (min) is the minimum current and voltage below which the SCR will not turn on. Ig (max) and Vg (max) is the maximum current and voltage above which SCR will damage. Means the shaded area is the safe operating area for SCR. For turning on SCR the gate current should be greater than Ig (min) but less than Ig (max) similarly, the gate voltage should be greater than Vg (min) but less than Vg (max).

Turning on SCR by gate control:

The turning on of SCR using gate control is the most commonly used method. The current is applied between gate and cathode of SCR. That current may be AC, DC or pulsating. Once the SCR start conducting because of positive gate current, the gate current is no longer needed to keep the SCR in conduction mode. The gate signal should not be applied if the SCR is in reverse bias condition. The gate terminal should be more positive with respect to a cathode for turning on of SCR.

The three different types of gate control signals are:

1. DC gate signal

2. AC gate signal

3. Pulsed gate signal

1.DC gate signal: In DC gate signal triggering the DC voltage of proper magnitude and polarity is applied between gate and cathode. In DC gate signal triggering the gate, power losses are more.

2.AC gate signal: In AC gate signal triggering the AC voltage is applied between gate and cathode. This method is used for fast turning on of SCR. Due to the positive half cycle of AC at a particular point of that positive half cycle, the SCR will be turn on.

3.Pulsed gate signal: In pulsed gate signal triggering the pulse signal waveform is applied to the gate of SCR. In pulsed gate signal triggering the gate, power losses are less. In this type of triggering the pulse transformer is used. 

Amazon Shopping

Welcome to Q&A site for electrical and electronics engineering discussion for diploma, B.E./B.Tech, M.E./M.Tech, & PhD study.
If you have a new question please ask in English.
If you want to help this community answer these questions.

Categories

Most popular tags

power motor dc circuit transformer voltage current used system phase factor resistance load synchronous ac energy induction generator electric frequency series use speed between capacitor meter line electrical type mosfet control transmission difference magnetic plant high single instrument bjt source advantages function diode machine unit winding torque amplifier define supply thyristor motors arduino field shunt relay armature electricity maximum time problem parallel transformers types coil diagram state flow value material on three starting direction method emf operating theorem digital microprocessor test instruments efficiency ratio loss measure operation connected low applications wave effect and single-phase working losses different network wattmeter temperature measuring constant signal controlled breaker device full compare drive wire materials machines inductance switch flux resistivity disadvantages logic converter transistor gain protection scr angle force core measurement number free principle rc generators law negative bridge friction open pole conductor conservation steam iron loop resistors hysteresis short computer lines secondary station battery rectifier inverter linear relays nuclear regulation design using analog work rotor electronics gate forces diesel damping rlc connection factors capacitors minimum insulation basic moving running reactance systems circuits air fault range direct main stability quality starter igbt eddy ideal ammeter rl 3-phase plants arc induced thermal error fuzzy biasing dielectric pressure balanced errors rotation characteristics feedback measured electronic start alternator off back curve over solar three-phase tariff locomotive peak bias zener capacitance commutator surge rating universal potentiometer superposition permanent mechanical copper self transducer capacity electrons memory adc excitation inductive explain fuse pure harmonics application internal pmmc average reaction welding resonance traction breakers designed electromagnetic si generation brushes density switching shaded rate impedance distribution transfer methods star oscillator reluctance semiconductor inductor 8085 weston dynamometer insulating strength installation permeability definition fuel heating earth units neutral rms rated engineering conductors coefficient controller usually reverse excited change body components form made response terminals
...