Single phase half bridge converter working help

AI Thread Summary
In a single-phase half-bridge converter, using two diodes instead of two SCRs simplifies operation, especially in resistive loads. While SCRs can be used, they require simultaneous triggering with the other switches, which can lead to negative voltage output before activation. The presence of a freewheeling path when diodes are used prevents this issue, making the circuit more efficient. Concerns arise with highly reactive loads, where SCRs may face complications. Overall, the choice of diodes enhances reliability and performance in this configuration.
electricallov
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why are we using two diodes instead of two scrs in a single phase half bridge converter? What difference does it make? (say in my attachment s2 and s3 are diodes instead of scrs?)
Wont we get the same operation with two scrs itself (only thing you have to fire them together with s1 and s4). I am confused. Please help.
 
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electricallov said:
why are we using two diodes instead of two scrs in a single phase half bridge converter? What difference does it make? (say in my attachment s2 and s3 are diodes instead of scrs?)
electricallov, your attachment is missing.
 
Im sorry. Now I've resubmitted.
 

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  • RLload.gif
    RLload.gif
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Hi electricallov. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

Offhand, I can't see a reason for not using 2 SCRs and 2 diodes here, at least for resistive loads. (Highly reactive loads can pose problems for SCRs, so I'd need to examine this closely to see whether that may be a consideration, especially when the L element is shown so prominently in the schematic here. :wink:)
 
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In my humble opinion,
if you use all four SCRs then you would end up with negative voltage output for a short duration before s2 and s4 are triggered.
 
GingerLee, this negative voltage concept solves everything. I did not notice the freewheeling path created when the two scrs are replaced by two diodes. This solves my question. Thanks
 
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