On 28 Dec 2005 17:01:01 -0800, "
wrote:

Which shutdown circuit is turning the set off?


To ones who are not famillar with this Hitachi's design, I find this
nice that this doesn't blow up SMPS and easier to track problem down,
just with scope and voltage meter plus 4 green LEDs on 4 of voltage
outputs.

The core shut down circuit is frightfully simple: small SCR hooked to
the low voltage via resistor to limit current via SCR to ground
feeding to the protection shutdown optisolator via this on hot side to
the oscillator pin on STR6511, red LED is hooked to this IC's osc pin
also for visual status: dark: no power or no oscillation, half
brightness is normal (slight brightness changes is OK), full
brightness is tripped condition via that SCR.

Ok, the trip circuits are monitoring the voltage outputs for loss
using diodes, over current circuits are done with transistors across
low value resistors in series, voltage rises with current increase, if
high enough breaks through one of those zeners and SCR latches. Oh,
Scan loss, vertical problems is included. Short and voltage outputs
loss via diodes.

All this goes right to the one SCR.

IMHO, this is what should be this way in other makes but thanks to the
young MDA in business people, left this features out. :P

Even I wish RCA used this concept to stop the SMPS oscillation instead
of trying to driving into shorted load and blow up like CTC203 does.

Cheers, Wizard