LM5026: as Flyback controller?

H.Tian

Part Number: LM5026
Other Parts Discussed in Thread: UCC28780, UCC28782, LM5023, UCC28600, UCC28742, UCC28704, UCC28740

Hi team,

can LM5026 be used in the flyback topology like diagram below? If no, why?

Thank you.

over 2 years ago

0 Eric Reicher over 2 years ago

TI__Expert 7900 points

Hello H. Tian,

The LM5026 is an Active Clamp Flyback controller.

The Typical Application Circuit from page 1 of the data sheet is show below.

There are some differences at the output of T1.

The LM5026 data sheet can be found here:

https://www.ti.com/lit/ds/symlink/lm5026.pdf?ts=1628277185268&ref_url=https%253A%252F%252Fwww.ti.com%252Fsitesearch%252Fdocs%252Funiversalsearch.tsp%253FlangPref%253Den-US%2526searchTerm%253Dlm5026%2526nr%253D99

An EVM for the LM5026 can be found here:

https://www.ti.com/lit/ug/snva117a/snva117a.pdf?ts=1628277404654&ref_url=https%253A%252F%252Fwww.ti.com%252Ftool%252FLM5026EVAL%253FkeyMatch%253DLM5026

Best regards,

Eric

0 H.Tian over 2 years ago in reply to Eric Reicher

Prodigy 30 points

Hello Eric

Thank you for your reply.

I saw the typical application from LM5026 is for forward circuit (so the diffrences at the output of T1). My question is: is LM5026 also suitable for a DC-DC Flyback Converter? You said, "The LM5026 is an Active Clamp Flyback controller". It means, i can use it in my flyback converter circuit? Sorry, i am little confused.

Let me tell you more details about my application: my circuit is a DC to DC auxiliary power supply, i want to improve the efficency by recovering the leakage inductance energy. I want to avoid to use the highside clamp fet, like the typicial application from UCC28780 or UCC28782. Is there any controller for my application?

thank you.

0 Eric Reicher over 2 years ago in reply to H.Tian

TI__Expert 7900 points

Hello H. Tian,

I have connected with Hong Huang, internally at TI. He is the expert who usually supports this product line. So, I am transferring this thread to him. Thank you, Eric

0 Hong Huang over 2 years ago in reply to Eric Reicher

TI__Guru 51065 points

Hi,

You can use LM5026 in either flyback or forward. My understanding to your need is you want to get a Quasi Resonant controller. If so, you may take a look at LM5023 or UCC28600.

0 Hong Huang over 2 years ago in reply to Hong Huang

TI__Guru 51065 points

Hi,

You can also consider UCC28740, and UCC28742 for QR flyback. If you can use the primary side regulation you may consider UCC28704.

0 H.Tian over 2 years ago in reply to Hong Huang

Prodigy 30 points

Hi Hong Huang,

Thanks for the tips. I use the secondary side regulation (the flyback transformer has no auxiliary winding) and my circuit works in CCM mode with a swiching frequency about 200kHz.

Another question: the active clamp flyback use typically highside Fet as clamp. What is the advantage compared to lowside clamp fet?

Thanks

best regards

0 Hong Huang over 2 years ago in reply to H.Tian

TI__Guru 51065 points

Hi,

Low-side clamp uses P-channel MOSFET which drive is on the same reference as the LM5026. High-side uses N-channel MOSFET which needs voltage level shift with a gate transformer or a high-side MOSFET driver. Usually P-channel MOSFET cost more than N-channel. But level shift may need to have additional cost. It is difficult to find P-channel MOSFET with voltage rating > 200V, or very expensive.

0 H.Tian over 2 years ago in reply to Hong Huang

Prodigy 30 points

Hi Hong Huang

Thanks a lot.

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LM5026: as Flyback controller?