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walid

SMP power supply

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Hi
In the Fig shown below is the input part of a switching mode ps
as most of us know the 220VAC is connected directly to the rectifer (4 diodes) through a filtering network
the rectifier o/p is about 310VDC
in some SMPS there is a one main filter capacitor 400v 220uF or so
in another there are two main filter capacitors 400v 220uF or so (C53 and C54 )in the sch below)
then this 310VDC is connected to the collector of Q16 and a snubars diode (damping diode)

My questions are:
1) Why using 2 caps (C53 and C54 ) instecd of only one
2) why using two transistors Q16 and 15 instead of one
3) if the voltage at the collector of Q16 is 310VDC what it should be at the Emitter of the same transistor
4) can u summarize the operation of this part of the circuit

thank u very much

post-2833-14279143182999_thumb.jpg

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Two capacitors are sometimes used to increase the voltage rating. the capacitors are connected in series making its voltage rating double of that of a single capacitor.
Two transistors are used to make the power supply a symmetrical one. the primary of the high frequency has either two symmetrical coils or a center tapped coil so to make the power input symmetrical , two transistor are used at either ends of the coil and the centre tap is connected to +Ve or -Ve.

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hi
the circuit shold have been shown fully instead of masking valid portions-- thus it appears deliberatein the sence, it may perhaps be a question in an exam? right!!

the dual caps and ajuper near the bridge provide forchange over between  two versions of incoming AC Supply -- like 110 V/60Hz of Japan, US, even canada if i am right; while 230V/50Hz in most other countries.

Others Qs are to be thought over

sarma

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