Hi,
I am pretty new here but have used many of the resources from the website for a couple of my past projects. I am working on a handheld device and want to use +/-3.3V to power some opamps. I have been searching quite a lot to learn how to make a dual power supply. During my search, I came across this schematic. However, I don't understand how the inductors L1 and L2 helps in stepping down the voltage. Can someone help explain this circuit ?

 

U4 is a 12V input, +/-5V output DC to Dc converter smps, which will have high frequency noise on its outputs. L2 and L3 acting with C17 and C18 form a low-pass filter to get rid of the noise.

 

XP POWER IA0512S CONVERTER, DC TO DC, 5V TO +/-12V, 1W.

 

U4 is a 12V input, +/-5V output DC to Dc converter smps, which will have high frequency noise on its outputs. L2 and L3 acting with C17 and C18 form a low-pass filter to get rid of the noise.

As can be seen here , U4 is a 5 to +/-12 V DC/DC converter. What I don't understand is how the inductors and resistors are used to get the voltage down from 12V to 5V

 

As can be seen here , U4 is a 5 to +/-12 V DC/DC converter. What I don't understand is how the inductors and resistors are used to get the voltage down from 12V to 5V

No, the input to the brick is 12Vdc. The output from the brick is +/-5Vdc, but noisy. The inductors are there to help filter the noisy 5V.

 

No, the input to the brick is 12Vdc. The output from the brick is +/-5Vdc, but noisy. The inductors are there to help filter the noisy 5V.

This is the rating from the data sheet. I know input isn't 12, because J2 draws power from a USB

 

Ok, I see Scott found the data sheet. The schematic is mislabeled. The output terminals should say +12V and -12V. The inductors are still part of the final filtering to get the smps switching noise off the outputs.

 

As can be seen here , U4 is a 5 to +/-12 V DC/DC converter. What I don't understand is how the inductors and resistors are used to get the voltage down from 12V to 5V

They don't. The outputs on your schematic are labeled incorrectly, but the title is correct. The outputs are +/-12 V, and that's that. Each inductors is part of an output L-C filter to remove switching noise. The converter, not the filters, is doing the converting.

ak

 

Thank you guys. I was trying to understand this circuit for ever. Are R15 and R16 also a part of the filter?

 

Thank you guys. I was trying to understand this circuit for ever. Are R15 and R16 also a part of the filter?

The spec sheet says the output ripple of that supply is 75mVpp with a fundamental switching frequency of 80kHz.
The output filter will reduce that noise (likely needed if you are powering sensitive analog circuits).

I think R15 and R16 are to add damping to the filter to minimize ringing at the LC resonant frequency.

 

No, the input to the brick is 12Vdc. The output from the brick is +/-5Vdc, but noisy. The inductors are there to help filter the noisy 5V.

The picture posted (link) elsewhere doesn't look like a heatsink job, so unlikely a linear - my guess is those inductors are external buck inductors. It may require further filtering.

Technically; the buck coil and output capacitor are a LPF in their own right - the question is; which are those shown in the application example?