Jones Chopper

• The basic circuit of the Jones chopper is shown in the figure A. 
• The Class D commutation circuit is used in the Jones chopper. 
• The SCR T1 is main SCR whereas SCR T2, diode D1, capacitor C and auto – transformer T makes commutating circuit for SCR T1. 
• The inductor L1 and L2 are closely coupled and they provide sufficient energy to capacitor to turn off main SCR T1.

     

• The capacitor initially charges with upper plate positive and lower plate negative.  
• When the SCR T1 is turned on, the load current flows through path (+)V_dc  – T1 – L2 – MOTOR ARMATURE  – V_dc (–). 
• The capacitor discharges through path (+)C – T1 – L1 – D1 – C(–). Once capacitor discharges, it will again charges with reverse polarity with upper plate negative and lower plate positive.  
• The stored energy of load flows through freewheeling diode when SCR T1 is turned off. 
• The SCR T1 gets reverse voltage and turned off when SCR T2 is turned on. The load current flows through path (+)V_dc  – C – T2 – L2 – MOTOR ARMATURE – V_dc (–). 
• As the load current flows, the capacitor again charges with upper plate positive and lower plate negative. 
• When the voltage across capacitor is equal to supply voltage, the charging current of capacitor is less than the holding current therefore the SCR T2 is turned off. 

• When SCR T1 is turned on once again cycle will repeat. 
• The speed of the motor in the range of maximum to minimum can be achieved by switching of SCR T1 frequently or by adjusting its duty cycle. 

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