LM3488: Dual output: -48V and +48V generation via Flyback Boost converter reference circuit

Prabhakar A

Part Number: LM3488
Other Parts Discussed in Thread: LM51551, LM2585

Hi E2E Team,

We have Li-ion battery operated device design which operates from 3V to 4.2V of battery voltage.

We are looking forward to generate dual output: -48V and +48V via Flyback Boost converter circuit.

We have come across LM3488 part. But we could not find reference circuit for Dual output: -48V and +48V via Flyback transformer with appropriate primary and secondary turns ratio.

1. Could you confirm whether we can use LM3488 for this requirement?.

2. There is reference Coilcraft Flyback transformer: CJ5143 which has Pri:Sec ratio 1:15. Can we use one of this transformer for -48V and another transformer for +48V (in center tap config)?. We will use 2 nos of this transformer..

SMT Flyback Transformer | Coilcraft

3. Please share reference circuit for this design req

4. We have come across Dual output Flyback converter for LM2885

LM2585 data sheet, product information and support | TI.com

Best regards, A Prabhakar

over 2 years ago

0 Prabhakar A over 2 years ago

Intellectual 260 points

Hi E2E Team,

I forgot add the current rating. Need dual output: -48V and +48V at 200mA load current.

0 Prabhakar A over 2 years ago in reply to Prabhakar A

Intellectual 260 points

Hi E2E Team,

Can you share possible answers for our design queries?.

Best regards, A Prabhakar

0 Youhao Xi over 2 years ago in reply to Prabhakar A

TI__Guru 68675 points

Hi Prabhakar,

Sorry for the delay. You post seems being missed due to the Thanksgiving holidays. We will have our engineer to answer your question soon.

Thanks,

Youhao

0 Richard Fu22 over 2 years ago

TI__Genius 17640 points

Hi Prabhakar,

Please see my following response:

1) It is possible to use the LM3488, but may I recommend using the LM51551? The LM5155x series is the next generation update of the LM34xx series, and is more suitable for your application.

2) Unfortunately, you will not be able to use this in a center tap configuration. You will need to find a flyback transformer that is suitable for 48V output, similiar to LM2585 Q4438-BL (as shown in T6): https://www.coilcraft.com/getmedia/aee52f91-8ce3-419a-8e8c-b5189c48a410/lm258x.pdf. You may need to contact a transformer vendor for a custom design.

3) The schematic should follow figure 26 on the LM2585 datasheet. https://www.ti.com/lit/ds/symlink/lm2585.pdf?ts=1639010141132&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM2585

Thanks!

Richard

0 Prabhakar A over 2 years ago in reply to Richard Fu22

Intellectual 260 points

Hi Richard,

Thanks for your inputs.

1. Sure, we will plan to use LM51551

2. Sure, we will use center tap config transformer as shown in T6 of https://www.coilcraft.com/getmedia/aee52f91-8ce3-419a-8e8c-b5189c48a410/lm258x.pdf

For this, We will try to use CUSTOM Flyback transfer with Center tap config as per Coilcraft CJ5143 specifications but with Pri:Sec1:Sec2 ratio 1:15:15

3. Sure, We will follow as per Figure 26 on LM2585 datasheet. But, we will use Opto coupler isolated feedback as shown in Figure-2 of How to design an isolated flyback using LM5155 (ti.com)

Best regards, A Prabhakar

0 Prabhakar A over 2 years ago in reply to Prabhakar A

Intellectual 260 points

Hi Richard,

Instead of using CUSTOM center tap transformer, We thought of using two CJ5143 which has Pri:Sec ratio 1:15 ( SMT Flyback Transformer | Coilcraft )

The circuit to be built is shown below for your review:

Is this circuit fine?.

Best regards, A Prabhakar

0 Richard Fu22 over 2 years ago in reply to Prabhakar A

TI__Genius 17640 points

Hi A Prabhakar,

I would not recommend this configuration. The reason for this is that imagine the reflected voltage back across the primary windings when the secondary side is conducting may not be equally matched. If there is a slight difference, I'm afraid that there will be a circulating current flowing through the two primary-side windings, since the resistance of the primary side windings is quite small. This may cause damage.

Best regards,

Richard

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LM3488: Dual output: -48V and +48V generation via Flyback Boost converter reference circuit