triac firing angle control circuit




triac Firing angle control circuit is designed to control flow of AC power from input supply to load by changing the average voltage appearing across load. In this project triac firing angle is controlled to control amount of power flow to load. Firing angle control circuit is designed using analog electronics components like operational amplifier, resistor and capacitor. zero crossing detection, step down transformer , rectifier , comparator and ramp generator are the basic components of firing angle control circuit for triac. Triac have many applications in power electronics especially in AC voltage controller circuits.




Applications :

AC voltage controller have many applications in power electronics  devices. some of them are mentioned below :

Circuit description :

Basic components of Firing angle control circuit for triac is shown below in circuit diagram.




Zero crossing detection circuit :

It is used to detect zero crossing of sine wave, when AC sine wave cross zero reference voltage. Zero reference voltage is used to determine firing angle time duration for positive and negative cycle of sine wave. For zero reference detection circuit, step transformer of rating 220-12 volt is used to step down voltage and rectifier bridge is fully rectify this step down voltage. As shown in figure after full bridge, comparator is used. Full bridge output is connected with inverting input of comparator and diode is connected with non-inverting input of comparator. So when voltage at non inverting pin become grater than inverting output of comparator becomes high and pulse is produce at output of comparator for every zero crossing detection. Comparator output is shown below:

zero crossing detection
zero crossing detection
Ramp generator :

Output of comparator is connected with transistor and capacitor keep charging through 12 volt source. Transistor turn on only when zero crossing occur, because at zero crossing comparator produce pulse which turn on transistor and when transistor is on when across capacitor become immediately zero.In this way ramp is produce, when transistor is off capacitor keep charging and when transistor is on, voltage of capacitor become zero as shown in figure below :

ramp output
ramp output of ramp generator

Ramp voltage is again compared with a output voltage from variable resistor. If ramp voltage is greater than variable resistor output voltage, greater power will appear across load. Hence this variable resistor is used to control firing angle of triac. Optocoupler MOC3021 is used for isolation between high voltage side and low voltage control signals side.complete circuit diagram of firing angle control circuit for triac is shown below :

schematic of omplete circuit diagram of firing angle control circuit for triac
schematic of complete circuit diagram of firing angle control circuit for triac

Diagram below shows output of voltage appearing across lamp. I have used lamp in Proteus for simulation purpose. Simulation results of  firing angle control circuit for triac is shown below :

simulation schematic of firing angle control circuit for triac
simulation of firing angle control circuit for triac

When output of second compartor is on, triac is also on and voltage is also appearing across load. When output of second comparator is off triac is also off and zero voltage is appearing across load. Variable resistor can be used to adjust turn on or off time and in return voltage magnitude across load.

To understand working of  firing angle control circuit for triac watch following video :

PCB design of firing angle control circuit for TRIAC

 Top view :
top view of firing angle control circuit for triac
top view of PCB firing angle control circuit for triac
Front view :
Front view of PCB firing angle control circuit for triac
Front view of PCB firing angle control circuit for triac

I hope that you have gained some useful knowledge by reading this article and watching above video. If you have found it useful.kindly don’t forget to share it with others.More you share, more you gain. 🙂



14 thoughts on “triac firing angle control circuit”

  1. Dear Mr. Bilal Malek;
    Would you please specify more details about ICs used (their codes or names), and other components (like to what value the transformer should step the voltage down, resistors, capacitors…etc) since I am going to build this circuit and I can’t see specifications clearly.
    I would be very granted.
    Regards

  2. Hello, came across your site and it is what i have been looking for a while. I have a project on phase control of heating sytems. i am confused if i should use the microcontroller you used in your post for AC Power control or the one you used for your post on Triac Firing angle. Thank you for your earnest reply.

  3. So how are the pins set on an arduino uno ? And can the triac be set to fire at the peak? What is the software you have used for the oscilloscope and schematics ?

  4. a 100ohms load is connected to peak supply of 300V through a control half wave rectifier the load power is to varied from 25watt to 80watt. what is the angler firing control required? Neglect forward drop of the control please I need answers or formula to calculate it

  5. hello sir actually when i simulated this circuit on proteus first I used 50Hz alternator on the output it showed the firing angle of only one half of wave but when I set frequency of 25Hz it showed the required output kindly tell is it designed for 25Hz and how can I control the firing angle with 50Hz as well???

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