TL431: .

Aban Varghese

Prodigy 160 points

Part Number: TL431
Other Parts Discussed in Thread: UCC28740

I'm trying to design a power supply with the following calculations:

INPUT: 85VAC - 265VAC

OUTPUT: 80 volt, 0.6A

Topology: flyback with opto-coupler feedback

Voltage reference: TL431

controller IC: ucc28740

Transformer (designed using ucc28740 design calculator): PQ26/25 core, Nps = 1.172, Npa = 11.4, Lp = 172.6uH

The datasheet of TL431 states the maximum Vka = 37V, so I assume its not suitable for my use, but I found a flyback power supply design that uses the same TL431 for an output of 110 volts. I'm new to this kind of things hence require help...

thank you!

over 4 years ago

0 Marcoo Z over 4 years ago

TI__Mastermind 19370 points

Hi Aban,

Can you share the 110V design so i can be familiar with the design?

0 Aban Varghese over 4 years ago in reply to Marcoo Z

Prodigy 160 points

Hello Marcoo,

Thanks for the reply...

Please find the link with 110V design.

https://www.onsemi.com/pub/Collateral/AN1080-D.PDF

0 Marcoo Z over 4 years ago in reply to Aban Varghese

TI__Mastermind 19370 points

Hi Aban,

Our device TL431 is P2P to the device used in that app note so you can use our device in that configuration.

While the system can have a regulated 100V output, the TL431 is only regulating the 100V output through the 8V output.

Does your system only have 1 80V rail or multiple such as a 80V and a sub 36V?

0 Aban Varghese over 4 years ago in reply to Marcoo Z

Prodigy 160 points

Hello Marcoo,

My design has 80v and 0.6a rail on secondary and a 15v (for powering the controller IC) on auxillary winding, but can change the design to include a 12v on secondary to power TL431.

Will this effect the efficiency or cause any other issue?

0 Marcoo Z over 4 years ago in reply to Aban Varghese

TI__Mastermind 19370 points

Hi Aban,

Since you have a 15V and 80V rail. The design used in the app note you linked can work with our TL431. The feedback will be from the 80V rail while the TL431 cathode goes to the 15V rail.

The concern is if there was only 80V rail because the cathode of the TL431 cannot be larger than 36V. During a fault the cathode would be 80V. With the cathode connected to a 15V rail, during a fault the cathode will only see 15V which works.

0 Aban Varghese over 4 years ago in reply to Marcoo Z

Prodigy 160 points

Thank you Marcoo!

My design is supposed to work on Universal input.

So far I came to know 2 ways to use universal input...

1. Using a voltage doubler and switching the system based on high and low input voltages using a triac or so, as in the app note.

2. Designing the turns ratio using the minimum universal input (100VDC i.e = 80VAC * 1.414) to obtain required 80V. The output is stabilised to 80V through feedback as the input changes from 80VAC to 265VAC (approx. 100VDC to 400VDC).

These are my assumptions I don't know if I'm right...

Is there any other way or can you correct me if I'm wrong?

Best regards...

0 Marcoo Z over 4 years ago in reply to Aban Varghese

TI__Mastermind 19370 points

I have notified the UCC28740 team to help you with those questions. I can only support on the TL431.

0 Aban Varghese over 4 years ago in reply to Marcoo Z

Prodigy 160 points

Thank you so much!

0 Eric Faraci over 4 years ago in reply to Aban Varghese

TI__Expert 8210 points

Aban

UCC28740 can support a universal AC input of 85-265VAC without any additional circuit on the input. We don't have a reference design that is close to your requirement, but Webench can generate a design with estimated performance which you can access here webench.ti.com/.../SDP.cgi

Best Regards,

Eric

0 Aban Varghese over 4 years ago in reply to Eric Faraci

Prodigy 160 points

Hello Eric,

I have gone through the webench design. I have some doubts like

1. Is the SR controller necessary? I'm concerned about the BOM count.

2. The design doesn't have a flyback diode at the secondary.

I'm attaching a design produced from the UCC28740 design calculator. This design got me confused in 2 points. One the feedback side, which was cleared by Marcoo. The second problem was with the transformer design where I have the turns ratios, but not sure how to determine the individual no. of turns.

So now there is two designs... which one is better?80V_power_supply.pdf

thank you!

0 Eric Faraci over 4 years ago in reply to Aban Varghese

TI__Expert 8210 points

Aban

No, SR is not necessary. You can replace the SR with a diode if you prefer.

For the transformer design, the number of turns is set by the magnetizing inductance (which is 192.5μH in your excel design calculator). The exact number of turns is dependent on other properties of the transformer, such as core material, geometry and size of air gap. The excel tool has enough information for transformer design for a magnetic vendor to be able to design a transformer that will meet your design.

Best Regards,

Eric

0 Aban Varghese over 4 years ago in reply to Eric Faraci

Prodigy 160 points

Thank you for clearing my doubt.

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