Inst ToolsInst ToolsInst Tools
  • Courses
  • Automation
    • PLC
    • Control System
    • Safety System
    • Communication
    • Fire & Gas System
  • Instrumentation
    • Design
    • Pressure
    • Temperature
    • Flow
    • Level
    • Vibration
    • Analyzer
    • Control Valve
    • Switch
    • Calibration
    • Standards
    • Basics
    • Formula
    • Erection & Commissioning
    • Process Fundamentals
    • Root Cause Analysis
  • Interview
    • Instrumentation
    • Electrical
    • Electronics
    • Practical
  • Q&A
    • Instrumentation
    • Control System
    • Electrical
    • Electronics
    • Analog Electronics
    • Digital Electronics
    • Power Electronics
    • Microprocessor
Search
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Reading: Crowbar fault protection circuit
Share
Notification Show More
Font ResizerAa
Inst ToolsInst Tools
Font ResizerAa
  • Courses
  • PLC
  • Control Systems
Search
  • Courses
  • Automation
    • PLC
    • Control System
    • Safety System
    • Communication
    • Fire & Gas System
  • Instrumentation
    • Design
    • Pressure
    • Temperature
    • Flow
    • Level
    • Vibration
    • Analyzer
    • Control Valve
    • Switch
    • Calibration
    • Standards
    • Basics
    • Formula
    • Erection & Commissioning
    • Process Fundamentals
    • Root Cause Analysis
  • Interview
    • Instrumentation
    • Electrical
    • Electronics
    • Practical
  • Q&A
    • Instrumentation
    • Control System
    • Electrical
    • Electronics
    • Analog Electronics
    • Digital Electronics
    • Power Electronics
    • Microprocessor
Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Inst Tools > Blog > Power Electronics > Crowbar fault protection circuit

Crowbar fault protection circuit

Last updated: September 19, 2016 3:03 am
Editorial Staff
Power Electronics
No Comments
Share
5 Min Read
SHARE

Crowbar circuit is used to protect circuit or equipment under fault condition

Over Current Causes:

  1. Over current flow through thyristors in a circuit due to:
  2. Flow of short circuit current on the load
  3. Simultaneous triggering two thyristors in series in a circuit
  4. Sustained over load
  5. Stalling of an electrical motor

A Conventional fuse will take quite some time to clear the fault an is not suitable for protection of the device. Fast acting semiconductor fuses are connected in series with each thyristor.

Crowbar Circuit:

A Crowbar circuit is used to protect circuit or equipment under the fault condition. It consists of thyristor of a rating well in higher than the rating of the devices that are to be protected. On detection of the fault, crowbar thyristor is fired consequently fuse blows. Thus the devices are protected against over current. Crowbar protection is recommended for MOSFET circuits.

A crowbar circuit is a method of protecting a circuit against high voltages (overvoltage) in the event of a power supply malfunction or power surge. This is especially useful in a device using TTL components as these are very sensitive to overvoltage. However, there are many other devices which can be damaged by overvoltage.

A crowbar circuit works by sensing a voltage that is above a certain threshold and shorting out the power supply. This causes a voltage drop in the rest of the circuit and current surge through the power supply that will trip a circuit-breaker or blow a fuse. The circuit must have a fuse or circuit-breaker, as without it the power supply or the crowbar circuit will be damaged. Crowbar circuits are so named because their activation is similar in effect to dropping a crowbar across bus bars (heavy duty power supply lines).

A typical crowbar circuit is as follows:

Crowbar fault protection circuit
Crowbar fault protection circuit

This crowbar circuit has an power supply, and triggers at 9.1V. To change the power supply rating, the zener diode, ZD1, needs to be changed to reflect the new trigger voltage. It should be about 1V higher than the nominal supply voltage.

  • Fuse F1 is the fuse that blows if the current drawn by the circuit exceeds 250mA. This can be increased as needed, but make sure the thyristor Q1 has a higher current rating than the fuse. Typically this fuse is a resettable fuse.
  • Capacitor C1’s purpose is to reduce small, harmless, voltage spikes or noise which may trigger the circuit.
  • ZD1 is the Zener diode which detects the overvoltage condition. At the trigger voltage (here 9.1V), its resisitance decreases suddenly, bringing the junction with R1 and the gate of Q1 high.
  • R1 is a pull-down resistor which holds the gate of thyristor Q1 low when ZD1 is not triggered. Its other function is to provide a voltage difference for capacitor C2 to “snub” Q1 with. Without this, the capacitor would be shorted out and useless.
  • C2 is a snubber capacitor to prevent the thyristor being triggered by accident on being powered up. It must have a value high enough to snub Q1, but low enough so that the residual charge does not cause a transient “high” state at the gate of Q1 when powered up.
  • Q1 is the thyristor which is turned on by ZD1’s breakdown. This provides a short-circuit between the power rails, blowing the fuse.
  • SD1 is a Schottky diode to prevent capacitances in the main circuit triggering the crowbar circuit. Normal diodes can be used, but they have a larger voltage drop than Schottky diodes.
Don't Miss Our Updates
Be the first to get exclusive content straight to your email.
We promise not to spam you. You can unsubscribe at any time.
Invalid email address
You've successfully subscribed !

Continue Reading

Phase Controlled Rectifier – Half Controlled Rectifier with R Load
SCR Triggering Methods
Power Transistor – Structure, Biasing, Characteristics, Advantages
SCR Switching Characteristics
Power Electronic Devices Specification and Classification
Power Electronics – Phase Controlled Half Wave Rectifier RL Load
Share This Article
Facebook Whatsapp Whatsapp LinkedIn Copy Link
Share
Leave a Comment

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Stay Connected

128.3kFollowersLike
69.1kFollowersFollow
208kSubscribersSubscribe
38kFollowersFollow

Categories

Explore More

How to test SCR using Multimeter
R R-C Firing Circuits Disadvantages
What is Power Electronics? Evolution, Block Diagram, Advantages
How Snubber Circuit works ?
How to Test TRIAC with Multimeter
Thyristor Protection Circuits (SCR) – Types, Principle, Explanation
Top 100 Power Electronics Projects for Engineering Students
Single-Phase Mid-Point Converter – Bridge Rectifier with Center Tap

Keep Learning

triac

Turning Off SCR – Commutation

Basics of Thyristor

Basics of Thyristor

IGBT Switching Characteristics

IGBT – Symbol, Construction, Working, Characteristics, Advantages

igbt-symbol

Types of IGBT

SCR Full Bridge Converter

Power Electronics – Full-wave Rectifier With R and RL Load

Static VI Characteristics of Thyristor

Thyristors – Working, VI Characteristics, Turn ON Methods

SCR Class B Resonant-Pulse Commutation

Thyristor Commutation Techniques – Types, Working Principles

Two Transistor Model of Thyristor

Thyristors – Switching, Two Transistor Model, Advantage, Applications

Learn More

What is VLAN?

Difference Between Subnet and VLAN

Online Analyzers Questions & Answers

Online Analyzers Questions & Answers

PID Controller

Proportional Integral Derivative Controllers – PID MCQ

direct and reverse acting PID controller Tuning

Recognizing an Over-Tuned PID Controller by Phase Shift

Difference between Butterfly Valves and Ball Valves

Difference between Butterfly Valves and Ball Valves

factorytalk view studio hmi

How to Create Templates in FactoryTalk View Studio?

Advantages of Valve Regulated Lead Acid (VRLA) Batteries

Advantages of Valve Regulated Lead Acid (VRLA) Batteries

Strain Gauge Pressure Transducer

Resistance Type Pressure Transducers Principle

Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Welcome Back!

Sign in to your account

Username or Email Address
Password

Lost your password?