What does this strange SMPS design do (strange thing about L2 and diode D2 vs D3)? Is it a power factor correction circuit? And how does it actually work?
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- 1\$\begingroup\$ Where did the schematic come from? What is the video link for? \$\endgroup\$Andy aka– Andy aka2025-11-17 16:32:46 +00:00Commented Nov 17 at 16:32
- 2\$\begingroup\$ I recognize the DAP006 which was, indeed, the NCP1200 that I have introduced in 2000 : ) Yes, the extra elements on top of the transformer help passing the PF standard but far from a unity value of course. There is OPP on the CS pin and they shunt the DRV pin to CS in case of too high an input voltage, kinda bad for the IC in my opinion. The low-side SCR latches off the IC in case of over-temperature issue. Notice the Zener diode across the optocoupler, necessary in case of short-circuit between the HV pin and any other pins from the controller (safety requirements for preserving isolation). \$\endgroup\$Verbal Kint– Verbal Kint2025-11-17 16:50:43 +00:00Commented Nov 17 at 16:50
- 1\$\begingroup\$ I don't think it is a DAP006 because it was derived after NCP1207 which was a QR controller (my bad in the above comment) and there is no demagnetization pin here. I therefore believe it is a DAP007, released as a special NCP1200. \$\endgroup\$Verbal Kint– Verbal Kint2025-11-17 18:17:07 +00:00Commented Nov 17 at 18:17
- \$\begingroup\$ Hi @HilumineHuyền - Where did the image come from? To comply with the site referencing rule, details of the original source of any copied/adapted material must be provided by you, next to each copied / adapted item. If the original source is online, please edit the question & add the webpage/PDF/video name + timestamp & its link (URL) (e.g. website name + webpage title + URL). (I doubt it applies here, but if the source is offline (e.g. printed book / private intranet) then add source details "to the best of your ability" e.g. title, authors, page, edition etc.) TY \$\endgroup\$SamGibson– SamGibson ♦2025-11-18 05:36:39 +00:00Commented Nov 18 at 5:36
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1 Answer
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4 Short answer:
- No, it's not power factor corrected (but it does a bit of it).
- Those components bias the transformer to allow for a smaller core
Long answer:
That IC is the DAP006 "PWM Current−Mode Controller for Free Running Quasi−Resonant Operation" from On Semi. (It took a long time to find that spec sheet because it's a custom version for a specific customer of the now-discontinued NCP1207.)
The IC's specialty is to operate the transformer at the very edge of its saturation.
Onto your question. It appears that D2 and D3 generate a full-wave rectified sine wave (unfiltered by a capacitor) and feed it as a constant DC current (L2 filters the switching noise) into the transformer, to bias it at one end. That lets the IC operate the transformer over its entire magnetization range (without it, it would only operate it between 0 and North). Therefore, the transformer core is half as big as it would be with a standard circuit.
The lack of filtering on D2 D3 means that the bias point moves up and down with the absolute phase of the line frequency. Doing so improves the power factor, though this is not a PFC power supply.
{Source: me}
- 1\$\begingroup\$ the DAP006 is indeed a QR controller but it was derived from the NCP1207 - the NCP1200 was derived as DAP007 for Delta Electronics. A QR controller does not operate the transformer at the edge of saturation but it forces so-called boundary conduction mode (BCM) which imposes a permanent discontinuous operation and lower turn-on losses with a small delay inserted after the aux winding. However, looking back at the circuit drawn, I would say it is not a QR because there is no demag pin on the controller, so most likely DAP007. \$\endgroup\$Verbal Kint– Verbal Kint2025-11-17 18:14:15 +00:00Commented Nov 17 at 18:14
- \$\begingroup\$ OP's schematic specifically says '6', not '7'. \$\endgroup\$Davide Andrea– Davide Andrea2025-11-17 20:28:08 +00:00Commented Nov 17 at 20:28
- 1\$\begingroup\$ I know for a fact that DAP006 is NCP1207 while DAP007 was NCP1200. The first one is a QR, the second a fixed-switching frequency. The pinout difference between the two is in pin 1: it is the demag detection in 006 while it is the skip level adjustment in 007. The labeling is misleading on the schematic and perhaps 1 should actually be labeled DMG. \$\endgroup\$Verbal Kint– Verbal Kint2025-11-17 21:01:58 +00:00Commented Nov 17 at 21:01
- \$\begingroup\$ Thank you. I corrected my answer accordingly. \$\endgroup\$Davide Andrea– Davide Andrea2025-11-17 22:23:14 +00:00Commented Nov 17 at 22:23