3 4 Freewheeling diode The inductor has property
- Slides: 11
3. 4 Freewheeling diode �The inductor has property to store energy �In ac current, during positive high cycle the inductor stores energy.
Freewheeling diode �At negative half cycle the inductor deenergies , so there must be reverse current which will make SCR on. �This may cause reverse damage to circuit �To avoid energy dissipation freewheeling diode is used.
Effect of Freewheeling diode �In negative half cycle , the freewheeling diode becomes forward biased so that the current will flow through diode �Therefore it deenergies inductor without making SCR forward biased. �To cut off the negative portion of the instantaneous output voltage & smooth the output current ripple free, a freewheeling diode is used.
Effect of freewheeling diode on o/p waveforms � O/P WAVEFORMS OF HWR with FWD
3. 5 Circuit dig. Of single phase fullwave rectifier with freewheeling diode
Circuit description �In single phase rectifier , freewheeling diode is connected across the RL load. �Due to freewheeling diode we overcome the problem of FWR with RL load
Operation of FWCR with FWD �During positive half cycle �Upto point α the SCR 1 is in forward blocking state so it will be in off state. �After the point α the SCR 1 will be turn on & starts conducting. �It continuous in conduction state until it reaches to π
Operation of FWCR with FWD �During negative half cycle �As the load current tend to go to negative the FWD becomes forward biased & it starts conducting �Therefore SCR 1 becomes revered biased & it will be off.
Operation of FWCR with FWD � Now the SCR 2 becomes forward biased due to negative half cycle. �Upto pt α it will be in forward blocking state so it is in off state.
Operation of FWCR with FWD �When i/p voltage becomes more than α , SCR 2 will be turn on & starts conducting we get o/p voltage. & constant dc current as output. �Due to FWD we get the ripple free output voltage (where the inductive load effect is avoided by FWR)We get constant DC output current
w/f of single phase fullwave rectifier with freewheeling diode