[TriEmbed] Powering ESP32 from an 8v golf cart battery

[Kevin Schilf]

 Hi Paul,
To answer your question about minimum input voltage, you need to think about Vdropout.
You apply a Vin and expect the Linear Regulator to provide Vout.  Vdifference (Vin - Vout) is dropped across the pass element inside the regulator which works like a variable "resistor."  This is why the linear regulator while small, simple, and quiet can be very inefficient (short battery life).
Ex.  Vin 9V, Vout 5V, Vdifference = 4V

44.4% of the power is consumed by the regulator (4 / 9)
As the input drops (battery), the efficiency increases until Vdifference approaches Vdropout.  Vdropout is a function of load current and specific regulator.  In the LDO you mention, Vdropout is 100mV at a current of 100mA.  This is an effective dropout resistance of 1 ohm.
When Vdifference <= Vdropout, the regulator is no longer regulating.  It becomes a fixed in-line resistor between the battery and the load about 1 ohm in this case.

Sincerely,
Kevin S.





    On Sunday, November 15, 2020, 7:47:19 PM EST, Josh Wyatt via TriEmbed <triembed at triembed.org> wrote:  
 
 Why not use something like AMS1117-3.3? Minimum voltage on your 8 volt battery is going to be something like 6VDC.

-j
On Sun, Nov 15, 2020 at 7:38 PM The MacDougals via TriEmbed <triembed at triembed.org> wrote:


How do I find an LDO that operates on 8 – 8.8 v?

I looked at a couple of datasheets and found linear regulators that take 9v (max) input.

I did not see a (min) spec for input v.

 

How can I tell if it works at 8?

 

For example:

https://www.njr.com/electronic_device/PDF/NJM2888_E.pdf

 

 

---> Paul

 
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