UCC28600-Q1: Efficient way to design an AC/DC converter with inputs ranging from 100 to 240AC in 50/60Hz, and an output of 48VDC (Isolated)

Hi Robert,

Thank you for the query on UCC28600.

I think all the flyback IC controlllers are cpable of operating at both 50 and 60hz and are configured for universal input applications. So there is no requirement for a switch to transition.

The UCC28600 is definitely a good option to proceed with with best in class QR switching algorithm and helps in best switching performance. You are also free to explore other devices like UCC28740 (which is also a secondary side controller), UCC28742 (SSR but without HV startup) and also also look at some PSR controllers like UCC28730/ UCC28710, UCC28700. So depending on cost and voltage regulation you can opt for one of the family of controllers which will give best tradeoff in terms of cost, BOM standby power and efficiency performance.

Here are some 48V designs for your reference:

https://www.ti.com/lit/df/tidrkt3a/tidrkt3a.pdf?ts=1700480045585&ref_url=https%253A%252F%252Fwww.ti.com%252Freference-designs%252Findex.html

https://www.ti.com/lit/df/tidrg47/tidrg47.pdf?ts=1700480052676&ref_url=https%253A%252F%252Fwww.ti.com%252Freference-designs%252Findex.html

Please let us know if you have further questions.

Regards,

Harish

Hello Harish,

Thank you for your support.

Regarding the AC/DC SMPS, do I need to include power factor correction (PFC) circuit? Is it a standard practice to include it in a design?

Also, is the green mode feature(UCC28600) different from PFC?

Kind regards,

Bright

Hi Robert,

Thank you for the query.

The PFC standards mandate the usage of power factor correction circuit when the power levels are greater than 75W. 

In 2001, the European Union put into effect the standard IEC/EN61000-3-2 to set limits on the harmonics of the AC input current up to the 40th harmonic for equipment above 75 W. The standard defines four classes of equipment depending on its type and current waveform. The most rigorous limits (class D) are established for personal computers, computer monitors, and TV receivers. To comply with these requirements, modern switched-mode power supplies normally include an additional power factor correction (PFC) stage.

Please refer the document below:

https://www.emcfastpass.com/wp-content/uploads/2017/04/Class_definitions.pdf

https://www.emcstandards.co.uk/files/61000-3-2_mains_harmonics.pdf

The greenmode feature helps disable the PFC stage (with STATUS pin set to 1) during extremely light loads which helps in efficiency enhancement at light loads.

Regards,

Harish

Good morning,

Thank you Harish for the detailed response. 

I notice that when PFC circuit is used, a high voltage start up is used as well to power the PFC circuit. After the start up has been completed, is the high voltage start up circuitry or IC deactivated and replaced with a Low Dropout regulator? Or will the high voltage start up continue to supply power to the PFC circuit?

Also, is brown out circuit a standard or optional practice when designing AC/DC converter?

Kind regards,

Bright

Hi Robert,

The following links show the use of UCC28600 with PFC stage.

https://www.ti.com/lit/ug/sluu256a/sluu256a.pdf?ts=1700558798166&ref_url=https%253A%252F%252Fwww.google.com%252F

https://www.ti.com/lit/an/slua399b/slua399b.pdf?ts=1700559523007&ref_url=https%253A%252F%252Fwww.google.com%252F#:~:text=To%20minimize%20leakage%20inductance%20and,for%20a%20successful%20transformer%20design.

PFc circuit's Vcc is fed by the PFC_bias signal which disables the PFC stage during light / burst mode. The startup resistors are going to dissipate power. The brown out circuit is generally taken care off in the PFC. 

The UCC28600 controller does not feature Brown-in or Brown-out functions.  These functions can be added externally.

Brown-in alone can be added by using a circuit tor drive a transistor which holds the SS input low until the Brown-in level is reached.
However, once started, the SS pin has no more function, so it cannot be used for Brown-out. 

Both Brown-in and Brown-out can be achieved with a circuit that releases or pulls down on VDD. This transistor must be capable of sinking a high peak current. We do not have any designs to showcase this,

Regrads,

Harish

Hello Harish,

Thank you for the comprehensive response. I really appreciate it. 

It appears that I do not need High voltage start circuitry start up or IC for the configuration example that you mentioned. The other  reference design - TIDA-01623 (www.ti.com/.../TIDA-01623) used a high voltage start up circuitry.  Thanks for that clarification. 

The other question is about the Brown out circuitry.  I have not used it in AC circuitry before, so any guidance or reference design on how to use brown out in AC application would be useful. I have question regarding where to connect the brown out circuit, is it after the bridge rectifier? Like the example in the schematic on page two of the link https://www.ti.com/lit/df/tidrxg9a/tidrxg9a.pdf?ts=1700572269845. The brown out circuit in this design seems complicated and I am not sure that I understand how it works there. So any explanation or simpler working of brown out circuit reference design for AC application will be appreciated.

Kind regards,

Bright 

Hi Robert,

Thank you for the quick reply.

For the brown in/out implementation, I would recommend the following circuit using LM8364 from one of the CCM PFC circuits.

brownout (1).pdf

https://www.ti.com/cn/lit/df/tidrqy2/tidrqy2.pdf?ts=1663301200007

Regards,

Harish

Hello Harish,

You are welcome.

Regarding the Brown out circuit, is it only connected to the PFC controller? https://www.ti.com/lit/ug/sluu256a/sluu256a.pdf?ts=1700558798166&ref_url=https%253A%252F%252Fwww.google.com%252F. How about the Quasi-Resonant Flyback Portion of the UCC28600?

If the PFC controller is turned off, will it switch off the output?

Kind regards,

Bright

Hi Bright,

Thank you for reaching out. Once brown out is detected in the PFC, it will stop switching the controller which would cause the output voltage to drop, but the flyback output could still be on. The main purpose of brown-out is to make protection on the primary side components of those with high current not exceeding each designed rating, or otherwise would need to design them with more margin. If the specs require turning aux power output off, then we would need additional circuit to achieve both Brown-in and Brown-out through a circuit that releases or pulls down on VDD as discussed above.

Regards,

Harish