Selection of Buck Regulator

Prajakta Ghatage

Other Parts Discussed in Thread: LM5155, LM25118, LM34936

I am trying to design a two-output forward converter where 1st output will be controlled by feedback while other should be controlled by a buck regulator. The operating frequency of my circuit is 1MHz and I want an output of 15V and 0.625A. Is there any regulator available that can meet these specifications.

over 6 years ago

0 Ed Walker over 6 years ago

Prodigy 5 points

Hello Prajakta,
There are 2 ways to create the second output.

1. Secondary Side Post Regulator. SSPR
http://www.ti.com/product/LM25115A
http://www.ti.com/product/UCC2583

This is a buck topology more suited for designs that have a main loop controlled output and need a second output.
TI's offerings here are generally 500kHz or less.

2. Synchronous Buck Regulator
There are many of these in TI's portfolio.
I can help selection if you can provide what input voltage would be available for the buck.

Here is one example of a 1Amp 36Vin synchronous buck that could be considered.
2.2MHZ maximum frequency.

LMR23610 - SIMPLE SWITCHER, 36V 1A Synchronous Step-Down Converter

0 Prajakta Ghatage over 6 years ago

Prodigy 40 points

Thank you so much.

0 Prajakta Ghatage over 6 years ago

Prodigy 40 points

For the synchronous buck regulator, the input voltage would be 12V to 20V. And the output needed is 15V.

0 Youhao Xi over 6 years ago in reply to Prajakta Ghatage

TI__Guru* 79085 points

Hi Prajakta,

This cannot be supported by a buck. You need a buck-boost or SEPIC converter. What is the max load current at the 15V output rail?

Thanks,

Youhao Xi, Applications Engineering, BCS Product Line

0 Prajakta Ghatage over 6 years ago in reply to Youhao Xi

Prodigy 40 points

Max load current is 0.8 A in the 15V rail. If the input voltage to buck converter lies between 15.5V to 24V can we use a buck converter?

0 Youhao Xi over 6 years ago in reply to Prajakta Ghatage

TI__Guru* 79085 points

If you Vin is only 15.5, it may be difficult to get 15Vout owing the the max duty cycle limit. It requires about 97% duty. Anyway, if you just consider buck, let know and I can forward this thread to our buck group.

If you can consider a buck-boost or sepic. You may consider the LM5155 in SEPIC, or the LM25118 or LM34936 for buck-boost.

Thanks,

Youhao

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Selection of Buck Regulator