On 05/01/2014 22:24, Arfa Daily wrote:


"N_Cook" wrote in message
...
Burnt and burst SMPS supervisor on this otherwise no-name and little
chance Chinese thing. As laser and motor/s in the DVD deck and
heatsink bonded to a video chip a reasonable power draw.
But the SMPS IC , in a conventional 8 pin DIP package also contains
the Tx driver transistor. So air gap under the IC and reverse side of
pcb enlarged pad of pcb-copper as some sort of vain attempt at
heatsink. Thermal connection to this is via just pins 4 and 5 combined
in normal soldering , connected to the Tx. There is a hole through the
pcb as though for some sort of clip to go perhaps top and bottom of
the IC and bolted through to this under pad but no sign of anything
having been fitted there, no deformation of the tinning over the pad
around the hole. Turning over the unit and shaking over paper meant
the blasted away top part , mainly, of the IC emerged but no clip at all.
Is it possible to have combined supervisor and driver transistor in an
8pin DIP package with no heatsink tab provision? or are there combined
SMPS TX with internal driver transistor buried in the base?
Also ps supply provision marked on pcb ac 85V - 250V
IC logi i in a reversed D
marked in 3 lines ICE 2?26 maybe more numbers, ? maybe a 4
logo then 0 and more
XK4.. probably more numbers
probable pinning
p1 0.1uF to 0V
p2 to optocoupler
p3 over current sense
p4-p5 to Tx low side
p6 n/c
p7 supply 25V
p8 0V


SMPS controller ICs with the letters "ICE" as the first part of their
type number are quite common. Such ICs are often coupled directly to a
power FET switching element, but are just as commonly connected directly
to a small SMPS Tx, particularly when it is a standby supply. I have
always been amazed that these chips can stand the better part of 400
volts across their internal FET, and that it can supply enough current
to drive the Tx directly. I guess the thermal issues are dictated by how
good the RDSon of the internal device is. The closer it is to zero ohms,
the lower the dissipation, and some these days are pretty damn close to
zero for all practical purposes.

Arfa

Its the first time I've come across such a situation, still does not
look right. For something like a set-top box with no motors or laser and
a graphics processor that does not require a heatsink, I could see it
was possible