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Topic: Favourite way to bring 5 Volt signals down to 3,3 Volt (Read 3264 times) previous topic - next topic

mcufan

Speaking of LDO: I still haven't found the "perfect" one. I recently found this one: TPS7150
http://www.ti.com/product/tps7150
"...Because the PMOS device behaves as a low-value resistor, the dropout voltage is very low (maximum of 32 mV at an output current of 100 mA for the TPS7150)... ". Sound really good. What do you guys think?

Which LDO would you recommend?
As MarkT mentioned there is many of them with different characteristic. Some are also very sensitive on strong magnetic field etc...

If your device draws in max peaks 800mA, some voltage regulator supplies max 100 mA is far from suitable - it will burnout very quickly. In short, higher LDO value give you freedom to chose some "more common and cheaper". I would chose 4.2V battery at least, which would give maximum of 0.9V freedom of choice. As well, depends how much current battery can storage, i.e how much time you need device to run during specific period of time, until discharged, etc.

For TH components I usually use commonly found LF33CV which have max LDO of 0.45V at 800mA and much lower (0.2V, IIRC) at 100mA... If you use SMD components, there is also many choices under 1.2V LDO value.

All that depends on your overall device spec.

As well, be aware of the fact that battery rated 3.6V or 4.2V will not provide constant voltage all the time until total discharge. It will drop during time of use., which require to inspect closely the graph of the battery from its datasheet.

Zealot

Start with your requirements and do a filtered search
at one of the distributers' websites that allows parametric search.
Which site would you recommend?

mcufan

Any larger electronic supplier have extensive web based searching and filtering engine. It is your choice which to use.

Zealot

Adafruit seems to use a diode on the Adafruit HUZZAH ESP8266 Breakout board to connect 5V TX to 3,3V RX

https://learn.adafruit.com/system/assets/assets/000/024/745/original/adafruit_products_schem.png?1429900999

They us a 1 N 4148. Is this a good solution?

mcufan

Adafruit seems to use a diode on the Adafruit HUZZAH ESP8266 Breakout board to connect 5V TX to 3,3V RX

https://learn.adafruit.com/system/assets/assets/000/024/745/original/adafruit_products_schem.png?1429900999

They us a 1 N 4148. Is this a good solution?
It seems to me as an error in schematic...

1. D1 and D2 should point in different directions, i.e. from 5V source to 3.3V source. Well, RX after all mean "receive"...
2. Reverse voltage for 1N4148 is 0.7V, thus 5-0.7 is 4.3V.

For cheapest solutions it is usually 2x 1N4148 which drop voltage to 3.6V. However, that is on the maximum limit, which is not quite good in terms of product lifetime.

All in all, I would not involve such solutions, but instead use 74HC4050 for reliable product.

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