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I have a power supply from broken DVD player (if I remember correctly), and would like to make a new case for it and reuse as a power source for my hobby projects.

I have some experience building 220v AC to 1-24 v DC power sources (including making transformer myself), but it was long time ago. However, nowadays power sources have "green" feature, meaning, that there is some kind of feedback from the device, which switches off the power. The original monitor also used ON/OFF button.

The question is, how can I find a place to make the power source always on? I think, for experienced person this question is not a problem.

My own guess is, that one possible place is to replace photocoupler U2 (just besides the transformer) (not sure, should I replace it with a diode and resistor on "high voltage side" or just remove). Another idea is to plug into smaller connector (smaller one on the right). Connectors have voltages and GNDs, but also pins called "F+" and "F-" (not sure, what for they are, but maybe they are to control the power supply?)

TNY268P integrated circuit is used, if its not visible from the image. PCB817 photocoupler.

Maybe, its stupid idea...

enter image description here

enter image description here

UPDATE: Problem has been solved so far (as I about it wrote in the comment of disappeared answer) and PSU provides all voltages on power on. I will do further checks to see if the problem re-arises.

UPDATE 2: I've found datasheet for TNY268P, and it claims to have "Simple ON/OFF control – no loop compensation needed", and "High bandwidth provides fast turn on with no overshoot". Does it mean, that TNY268P is the one, which senses load and switches ON/OFF?

The question is not any more about removing eco-feature (as it means too big change), but rather have I understood PSU operation right?

UPDATE 3: TNY268P connected almost typically (like recommended in datasheet here http://mkpochtoi.narod.ru/TNY268_ds.pdf ) in the PSU, but in addition BP (bypass) has connection to the outmost transformer pin like this:

enter image description here

(cant recognize what kind of diode is D6)

Does this gives any further ideas?

UPDATE 4: this is what the funny PSU gives on one of the taps at transformer secondary. At least explains annoying high-freq noice it is making.

enter image description here

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  • \$\begingroup\$ The opto is not the device you want to remove. It is part of the control/regulation loop. The original device was able to power on/off the PSU with the optocoupler in place, so surely you should be able to do that too. Start by identifying the mains input pins at the primary side (you definitely don't want to touch those) and the GND pin(s) at secondary side. Then try to figure out the other pins at secondary side. Are some pins in parallel? Are they connected to a linear regualtor? Are there caps connected? There is probably a pin that controls the output and a pin that carries standby power \$\endgroup\$ – jippie Jul 12 '13 at 18:51
  • \$\begingroup\$ Try to draw a circuit diagram from it. \$\endgroup\$ – jippie Jul 12 '13 at 18:55
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    \$\begingroup\$ I would guess that the "green feature" is a soft power circuit on the device, tied to the on button. Via this circuit, the device can shut down the power supply when it is idle, which works by (de)asserting some pin going back to the power supply. That circuit itself keeps getting some power from the supply, though, which enables the power button to re-assert the line and power up the device. Perhaps you can force the supply to be on simply by finding out which pins control this behavior and tying them accordingly to the correct supply rails and logic levels. \$\endgroup\$ – Kaz Jul 12 '13 at 19:00
  • \$\begingroup\$ Thanks for the hints. What is "deasserting"? PSU connectors have only plus-minus voltages, GND, and "F+", "F-" (which I do not understand what they are for). \$\endgroup\$ – Roman Susi Jul 12 '13 at 19:09
  • \$\begingroup\$ @jippie I will try to draw the diagram, as now I am sure the device is working and I can continue with making PSU from it. \$\endgroup\$ – Roman Susi Jul 12 '13 at 19:11
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Bad idea.

The TNY268P along with the optocoupler is the heart of the regulation circuit. What makes the circuit 'green' is that minimizes the amount of power taken by constantly monitoring the load current. These supplies are about 78% efficient. Removing the heart is a sure way of killing the patient.

The left hand side of the circuit board (top picture) looks like a 240V mains AC input that is rectified by D1 to D4 then smoothed by the two big caps to produce a high voltage DC supply.

The TNY268P uses this high DC voltage to switch the primary of the transformer (GVG-TNY268M-A) on and off. Pin 5 - [DRAIN] to transformer and pins 2 & 3 [SOURCE] to ground (mains side of circuit)

The optocoupler monitors the voltage from the output side transformer and sends a control signal to pin 4 [EN/UV]

To the right of the transformer it looks like a bunch of schottky diodes, zeners, smoothing caps and inductors. They will determine the actual output voltages at the socket.

If there is something stopping the output my guess would be there's some form of link required in this socket (probably something that went off to the on/off switch).

More info: enter image description here

I've found the whole circuit - just google tny268_122 and download the pdf

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  • \$\begingroup\$ Thanks for cues. One small addition: I think GVG-TNY268M-A is probably a name of the whole PSU. By googling, I saw it sold for $35 and more. \$\endgroup\$ – Roman Susi Jul 13 '13 at 7:17
  • \$\begingroup\$ And board is GV-DPA268 \$\endgroup\$ – Roman Susi Jul 13 '13 at 8:14
  • \$\begingroup\$ I have recreated mains side's schematics, but I do not know if I can post it here, as it may constitute somebody's intellectual property. \$\endgroup\$ – Roman Susi Jul 13 '13 at 16:16
  • \$\begingroup\$ @RomanSusi I've found the circuit online - google tny268_122 and download the pdf \$\endgroup\$ – JIm Dearden Jul 13 '13 at 19:07
  • \$\begingroup\$ Lot of thanks! It seems to be the full one, because my and the one you posted a photo lack 3 transistors and some other components and have only 4 pins, not 6 on CON3. I will accept this answer, because the rest is my "homework". I will post an update, if I find a way to control standby mode. \$\endgroup\$ – Roman Susi Jul 13 '13 at 19:53

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