TPS23758: Is diode rectified flyback available in TPS23785

Tim Hsu

Part Number: TPS23758
Other Parts Discussed in Thread: TPS23755, , TIDA-010083

Hi,

I have some questions about TPS23758. According to the specification,TPS23758 is using in synchronous rectified flyback.

Is it any possibility for us to use diode rectified flyback in TPS23758?

Our system is designed for a 5V output, and no opto-coupler flyback.

Best Regards,
Tim Hsu

over 5 years ago

0 Michael Pahl over 5 years ago

TI__Mastermind 21320 points

Hello Tim,

The TPS23758 is meant for synchronous rectified flybacks only. However, the TPS23755 does support diode rectified flybacks.

Regards,

Michael Pahl

0 Hector Chen over 5 years ago in reply to Michael Pahl

Intellectual 410 points

Hi Michael,

Can we use 24V as input of TPS23758 EVM ? Any issues we should concern if we use lower input voltage. Thanks.

Hector

0 Michael Pahl over 5 years ago in reply to Hector Chen

TI__Mastermind 21320 points

Hector,

No, the TPS23758 PoE input range is 37V-57V, and the adapter input is 48V.

To have a 24V input the transformer would need to be a wide Vin.

Regards,
Michael Pahl

0 Tim Hsu over 5 years ago in reply to Michael Pahl

Prodigy 70 points

Hi Micheal

We've already tried DC 30V input on TPS23758EVM-080 Evaluation Module, and 5V output seems fine in this condition(DC24-30V input 13W loading) .

I'm wondering if we operate in lower DC input,will any fatal side effects occurs in this flyback system?

Best Regards,

Tim Hsu

0 Michael Pahl over 5 years ago in reply to Tim Hsu

TI__Mastermind 21320 points

Hello,

Lowering the input voltage will cause the transformer to saturate and you could damage that part. The transformer on the EVM is rated for 37-57V, so 24V could risk major saturation. As I said in first post, a new transformer with a wide Vin is required.

Additionally, the peak current will be increased and this could damage the internal FET of the IC. I estimated the current would be close to 1.9A when loaded with 2.3A load, which is too close to the absolute max rating. The load current would need to be lowered if 24V is going to be used on the input.

Regards,

Michael Pahl

0 Hector Chen over 5 years ago in reply to Michael Pahl

Intellectual 410 points

Hi Michael,

If a transfomer can support wide Vin, considering peak current limit, how low Vin can we use ?

Thanks

Hector

0 Michael Pahl over 5 years ago in reply to Hector Chen

TI__Mastermind 21320 points

Hello Hector,

That will depend on the load of the system. What I recommend doing is using the TI Power Stage Designer Tool, configure a Flyback with the same Vin, Vout, switching frequency, load current, etc. to estimate it. That will give you an idea of how input voltage and load current affect the peak current on the FET. The recommended operating current for the IC is 1.6A and I would strongly suggest not going over that in case of variance.

http://www.ti.com/tool/POWERSTAGE-DESIGNER

Then if you need more specifics, please use the following application note along with the TPS23758 and the transformer specs to calculate the exact values:http://www.ti.com/lit/an/slva305c/slva305c.pdf

Regards,

Michael Pahl

0 Israel Aminov over 5 years ago in reply to Michael Pahl

Prodigy 120 points

tidm244.pdf

Michael Pahl said:

Hector,

No, the TPS23758 PoE input range is 37V-57V, and the adapter input is 48V.

To have a 24V input the transformer would need to be a wide Vin.

Regards,
Michael Pahl

Hi Michael

There is a reference design TIDA-010083 that shows 24VDC conenction to TPS23758 (see attached file)

This reference design uses the same transformer as on the TPS23758 EVB

So I'm confused - can we use 24V for auxiliary power input?

0 Michael Pahl over 5 years ago in reply to Israel Aminov

TI__Mastermind 21320 points

Resolved on another post.

https://e2e.ti.com/support/power-management/f/196/p/869416/3216641#3216641

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TPS23758: Is diode rectified flyback available in TPS23785