Jamie
- posted
9 years ago
Jamie
Well, it could. Why does it need that third transformer winding and stuff? Why doesn't it just connect to the opto output?
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com
Input/Output Isolation? ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et |
if you want and isolated output you need an isolated supply for the control
-Lasse
Don't see why. The IC has internal power, derived from the primary side. Why can't it pull up the phototransistor?
I think they are assuming that the phototransistor is always partly on, enough to actually power the chip internals. So that third winding really powers the chip after startup. But it doesn't have to.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com
rol
yes looks like the control input powers the chip after startup, duty-cycle controlled by current shunted by the internal regulator I don't think you can use the internal supply except for startup, looks like it switches to the control input when the shunt regulator hits 5.7V and is in regulation
-Lasse
OK, even simpler: get rid of the opto and do the sensing on the primary side. Then the regulator becomes a 2-terminal device.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com
The document says the feedback current is its power source. Its internal regulator just does kickstarts.
A linear regulator off 600 V would probably require some not-simple cooling.
the datasheet says the range is 2-6mA so it is "only" ~3.6W
-Lasse
Maybe they make/sell the transformers for extra income?
...but an iso-optulator already does that.
Check!
Then steal power from the TOPswitch,,
trol
afaict you'll need something like 12V at upto 6mA
-Lasse
You could use a capacitor power supply to overcome this issue. Then, on the other hand the additional X-capacitor is both more bulky and more costly than the third winding. BTW, find it irritating that they correctly note C7 as Y1 class, but don't specify X1 for C6 (figure 8).
Klaus
Note the returns... and AC _common_ and output _common_. ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et |
Most people like to GND reference their power supplies, without the isolati on you would end up shorting the rectifier, then the input voltage on this is fairly huge so that even at a few milliamps loading there is fairly huge power savings by running the IC off a low voltage winding, then most cheap bastards run their transformer windings at the highest allowable current d ensities making the winding regulation with loading poor so the output leve l sensing needs to be done there. The stuff with zener and opto is pure una dulterated garbage, they should be using that TL431/opto combo thing, anyth ing else is a hope and a prayer.
On Fri, 25 Apr 2014 17:01:33 -0700, John Larkin Gave us:
You have never heard of feedback or control loops?
How did you ever make it in this industry?
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