Whats the purpose of this circuit on this UPS

[neonwarrior]

Whats the purpose of winding 9-2 and its associated circuit (Q14 and Q28) ?
The schematic it's from an APC UPS.
Thanks in advance

 

[emresel]

might it be a feedback winding?
Just an estimation...

 

[RCinFLA]

This circuit is likely a modified sinewave inverter (three step AC output) using only a push-pull transformer. When output is suppose to be zero both (Q14,Q28) MOSFET's turn on to short the transformer at winding 9-2 to ensure output remains at zero volts. It can also act as an active snubber. The two diodes, along with MOSFET inherent D-S diodes, form a full wave rectifier that provides input to mcu for overshoots to trigger both MOSFET's on.

Somewhat more complicated then just using a H-Bridge output driver but transformer eliminates separate DC-DC converter. Reduces overall inverter major parts by two MOSFET's. It requires a large low frequency transformer. There are UPS supplies that use H-bridge drivers on battery side of low frequency transformer.

 

[vimalkhanna]

There is a retention of magnetization of the transformer as the BH loop changes across zero.The same needs to be neutralized for phase delay correction.The same happens for the reverse swings too. The winding caters to the pos. and neg swings of the sinewave.The Cgs of the Mosfets generate a delay in switchoff.and need to be discharged fast without coupling gate 1 to gate 2.
Hope this will solve your query

 

[Raza]

Hi neon,
This is the output transformer circuit of an inverter, Q and Q6 are the output MOSFETS and are being driven by the MCU (Micro Controller Unit) in PUSH-PULL action at the output windings of the trafo (5-6 and 4-7) and the winding 2-9 is used for supplying the MCU as the self-looped supply circuit. Hope this may satisfy you a bit. :smile:

 

[surjeetkmr5]

in this circuit u have missed center taping ,center taping will be ground and then it will work ,its woork is that bost the ac voltage as per requered battery charging