21/08/2017

Pulse Transformer ( Isolation Transformer )

Main Function
  • The function of pulse transformer is to generate pulse for semi conductor device and provide electrical isolation.
pulse transformer

Structure
  • The figure A shows toroidal shaped pulse transformer. 
  • It consists of one primary winding and one secondary winding
  • Each winding consists of same number of turns therefore any winding works as primary or secondary winding
  • The pulse to SCR is given by 1:1 or 1:1:1 pulse transformer. 
  • The pulse to the back to back SCR is given by the three winding pulse transformer. 
  • The firing circuit of gate pulse by 1:1 pulse transformer is given in the figure B. 
  • The function of the series resistor R is to limit the holding current of the SCR
  • The function of diode D is to prevent reversing gate current. The 1:1:1 pulse transformer is used to generate pulse for back to back SCR.

three winding pulse transformer

The design of Pulse transformer is made such that
Effect of Frequency on Output Pulse
  • The frequency and shape of the output pulse and input pulse same for high pulse frequency.
  • The output is directly proportional to integration of input at low pulse frequency. 



input and output of the pulse transformer


Advantages
  • Small size
  • Low cost
  • It can operate at high frequency.
  • High isolation voltage
Disadvantages
  • The secondary waveform should be different from primary waveform at low frequency.
  • The DC current flows through primary winding in order to reduce saturation of the core.
Applications
  • Power electronics
  • Communication
  • Digital electronics
  • Radars
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