Power Electronics & Drives Lab

Study of Thyristor Firing Angle Controller Trainer (8085 based), Model: TFC – 901

The single phase thyristors full bridge  firing angle  control  unit  consists  of  power  circuit  and  a  micro-processor controlled  circuits.  The  firing angle  controller  rectifies  using four thyristors  are  used  to  obtained  controlled  D.C.  circuit.  D.C.  output  voltage  from  the  A.C.  mains  input  voltage.  The  output  voltage  is  varied  by  controlling  the  firing  angle  of  thyristors.

The single phase firing angle control unit is a fed from a single phase two windings transformer for isolation  as  well  as  to  get  the  maximum  desired  output  voltage  when a – 00. Since the maximum output of the unit is due  to input AC voltage. (Calculate the output voltage by formula F1). (The circuit makes use of input voltage using step down transformer for synchronization purpose and generates firing pulses or the thyristors at an angle a. The firing angle can be controlled using a controllable DC voltage and it varies in the rate 100<a<1700. The amplified firing pulses are given to thyristors with proper isolation and gate protection circuit.)

Four thyristors are connected in a bridge form with suitable heat sinks & snubber circuits for protection.


The  set – up  consists  of  :

  1. Microprocessor  (8085  based).
  2. Power  circuit  based  on  Thyristor  configuration  as  half  way.
  3. Test  Point  for  measure the waveform.
  4. Isolation  circuit.
  5. D.C.  Speed  Motor.  Capacity : 1 HP.  (Optional)
  6. Weight : 6.5Kg Approximately
  7. Dimension : 250mm × 350mm × 150mm


  1. To  study  the   thyristor  firing  angle  control  by  Microprocessor  (8085  base).


  1. A  general  purpose  C.R.O.
  2. Digital  Multimeter
  3. D. C.  Speed  Motor.  Capacity : 1 HP.   

Note : There may be any change in specification due to continuous R & D without notice.



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