It possible change the topology of step up converter to step down? like the SX1308, I see in aliexpress some module use the same IC to step down and step up in one board, I cant remember how called the topology used in these board, but it possible do it only change the place of the diode and inductor to do step down topology? I need do 3v to 1.5v.

 

Yes it is possible but depending On the chip used, some of them are only for stepping up, some stepping down and some for both. Check Buck regulator for stepping down and Boost for stepping up. You also would have to change how inductor, diodę and Talking capacitor are place so it's probably not so viable for the existing board but yoy can always prototypem something

 

The are buck-boost converters, such as a CUK type, that can either buck or boost the input voltage as needed to deliver a constant output voltage.

 

why not read the datasheet? first few lines usually tell you if the chosen product is capable of it:

 

¿Por qué no leer la hoja de datos? Las primeras líneas suelen indicarle si el producto elegido es capaz de hacerlo:
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I see some ic say Step Up and it is used in step down like the LM2596 LM2577

 

Yes it is possible but depending On the chip used, some of them are only for stepping up, some stepping down and some for both. Check Buck regulator for stepping down and Boost for stepping up. You also would have to change how inductor, diodę and Talking capacitor are place so it's probably not so viable for the existing board but yoy can always prototypem something

I see in aliexpress some use the same ic to do steup and step down but I only need step down,

 

These board use buck-boost use the SEPIC topology

But it posible only change the diode place?

 

To go from 3V to 1.5V you want a buck converter. What is the problem?

 

To go from 3V to 1.5V you want a buck converter. What is the problem?

I cant find one operate between 2.5- 4.2V to 1.5 V

 

but it possible do it only change the place of the diode and inductor to do step down topology? I need do 3v to 1.5v.

The boost and buck PWM look the same ( diode, inductor, IC, capacitors) but they are not the same and cannot simply be changed. The IC is different, and the parts are almost a mirror image. (simple answer)

 

I cant find one operate between 2.5- 4.2V to 1.5 V

How about this one?

 

This one below is a very old part.

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I can find many ICs that can do the job. How much current?

 

1-2 A

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This one below is a very old part.
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I can find many ICs that can do the job. How much current?

 

I see some ic say Step Up and it is used in step down like the LM2596 LM2577

then you must have better eyes. i have never seen statement that LM2596 can do boost.
the LM2577 is a different story since using SEPIC topology

But it posible only change the diode place?
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it is not JUST the diode location. note that the SWITCH location is different too. and in some ICs that switch in internal so rewiring is much harder .