So I just ordered some lm1117 but in the meantime I want a 3.7V source. I was thinking of using a wall adapter which is 5V out and using resistors to split up the Vo to get 3.7 and run my ESP8266 that way. Is this safe? Is it commonly done? Whats the best way of getting 3.7v steady source, no batteries?

 

You cannot generally use a voltage divider to power a device. The current drawn by the load affects the voltage output. If the current is variable, you cannot even adjust for it and got a constant voltage.

This is why we have voltage regulators.

Bob

 

As said above, a voltage divider does not regulate. It's usually used for voltage references. Treat your controller nicely and use a regulated supply. Also, as far as I know, the operating voltage for ESP8266 is between 3-3.6V max, ideally 3.3V. Why do you want 3.7V?

 

Sorry, I meant 3.3V. I was thinking of the lipos.

OK so that means that the recommended way would be to supply 5v (from a wall wart) and feed it thru the lm1117 to get the 3.3V?

 

Hi,
Quite good idea.
http://www.twovolt.com/2016/08/14/3-3v-regulator-board-using-lm1117-3-3v-ic/

 

While you're waiting for your LM1117, here's a simple 3V3 reg :

The two yellow traces show the output at two extreme temperatures.

Edit: This circuit would be unsuitable for handling start-up surge currents of a ESP8266 (which I understand can be ~800mA).

 

Is'nt the problem with that approach no regulation ?



Regards, Dana.

 

Sorry, had the wrong transistor there.



Regards, Dana.

 

This gives a little bit better regulation -



Regards, Dana.

 

The circuit at #6 is a "Vbe multiplier." You can reduce the resistor values for better "regulation" (finite hFE degrades regulation) but you must also consider that until the voltage across R2 reaches Vbe of the transistor the voltage drop depends entirely on the load current. A multiplier with a Darlington with high R2/R1 ratio & highish R2 might work, but the multiplication factor required would be only about 1.2.

Two silicon PN diodes in series might get the voltage down sufficiently, but it is very marginal. A single PN and two Schottkys might work, but I suspect the TS probably doesn't have suitable Schottkys on hand.

 

Dana, try a couple of 1N4001 or similar. Real diodes aren't well versed in the theory of voltage v. current. Bigger diodes at lowish current usually behave better because bulk resistance is less of a factor.

In one of his books Bob Pease published VI curves of a number of diodes and expressed surprise at how much some of them departed from theoretical expectation. I don't know if those curves were every published in any of his web-available articles, but they are interesting

 

1N4001 better regulation, but desired 3.3 on high side.

How about just using a 1,8V 5% Zener ? Probably most of us do
not have that handy.

Sim attached of 4001s


Regards, Dana.