LM34927: Power supply to IC LM34927SD/NOPB

Hello,

For details on how to connect the IC for an inverting configuration please refer to the following app note: Working with Inverting Buck-Boost Converters (Rev. A) 

Regards,

Harrison Overturf 

Hello,

This Document shows how  to "Generating a negative output voltage rail from a positive input voltage rail can be done by reconfiguring an ordinary buck regulator." This is not my query. My doubt is we have negative supply and how to give supply to LM34927SD/NOPB IC.

Hello,

My apologies for the misunderstanding. 

Is your intention to use the LM34927 to generate a positive output voltage from a negative (-48V) input voltage rail?

Please share your desired input and output voltage requirements. 

Regards,

Harrison Overturf 

Hello, 

This is the circuit of our need

We have -48V and 0V at input side and our outputs are Vout1= 12V (voltage in primary side of XFMR) and Vout2= 12V , Vout3= 3.6V.

As you can see in application circuit there are one output at secondary side but we have two output because we used center taped XFMR.

Is power supply for IC in above circuit Correct? If not how can I supply this circuit?

Hello, 

I believe you will need to implement a boost converter topology in order to implement the negative input to positive output voltage polarity you desire. 

Take a look at the following app. note: Negative Input to Positive Output made SIMPLE 

That being said, you'll need to select a boost converter IC such as the LM2587 mentioned in the app. note. Let me reassign this thread to the Boost team and they can assist you in finding an appropriate IC. 

Regards,

Harrison Overturf 

Hi Arvind,

based on your schematic your output voltages are isolated from the input voltage.

So the polarity on the input is more or less a don't care - you just swap the supply input the the converter sees again a positive input and the same on the output side. 

This EVM shows and example of the Flyback with multiple isolated outputs:

LM5157EVM-FLY Evaluation board | TI.com

Best regards,

 Stefan

Hello Stefan,

Thanks for your reply.

I understand about our secondary output voltages.

But I have some uncleared doubt : 

1. Does this IC works in negative Power Supply Condition? As shown in above my Schematic VIN pin has 0V and RTN pin has -48V. Does this connection will work? I have this doubt because in Datasheet you have shown this operating input voltage range-

Thanks.

Hi Arvind,

no, the device need positive input voltage but if you connect your

- your systems -48V to the GND of the SMSP circuit

- your systems 0V to the VIN of the SMSP circuit 

The Device still would see a positive supply again. As mention due to the the isolation of the output signals this would not be an issue so polarity is relative.

Note: I forgot to mentioned the device on the reference board i listed above is only able to work with 45 V input voltages but you can use the LM5158 (if the current is enough) or go for the LM5156 (with external FET) this support up to 60V Vin.

Best regards,

 Stefan