Yes - the minimum input to a linear regulator is usually something like desired Vout + 1.2 volts. The sum of "drop out" voltage and desired Vout is probably the closest analogy to minimum input voltage.
Thanks, Josh On Sun, Nov 15, 2020 at 10:57 PM Kevin Schilf <[email protected]> wrote: > 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 < > [email protected]> 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 < > [email protected]> 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 > > > _______________________________________________ > Triangle, NC Embedded Computing mailing list > > To post message: [email protected] > List info: http://mail.triembed.org/mailman/listinfo/triembed_triembed.org > TriEmbed web site: http://TriEmbed.org > To unsubscribe, click link and send a blank message: mailto: > [email protected]?subject=unsubscribe > > _______________________________________________ > Triangle, NC Embedded Computing mailing list > > To post message: [email protected] > List info: http://mail.triembed.org/mailman/listinfo/triembed_triembed.org > TriEmbed web site: http://TriEmbed.org > To unsubscribe, click link and send a blank message: mailto: > [email protected]?subject=unsubscribe > >
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