# What current is expected at the 6v input in the given circuit?

#### Joe Stavitsky

Joined Apr 5, 2020
109
Or, what current range is safe?

Thanks so much

Joe

#### ericgibbs

Joined Jan 29, 2010
18,213
hi.
The LM2940 is rated at 1amp maximum current.
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#### crutschow

Joined Mar 14, 2008
33,326
And that's if it's on an adequate sink.

#### ci139

Joined Jul 11, 2016
1,898
The OUTP "short" current is refered to be "internally limited" ... 1.9A typical - reducing by the die temperature rise

#### dl324

Joined Mar 30, 2015
16,111
Or, what current range is safe?
The regulator can handle 1A, but I'd be more concerned about the dropout voltage. 6V is the minimum voltage acceptable for the worst case dropout voltage. The diode exacerbates the problem.

It seems to me that the circuit isn't very robust. If the 6V input isn't connected, the peripheral won't get any power.

#### ScottWang

Joined Aug 23, 2012
7,389
The LM2940 rated Vin=6~26V, if your Vin is only 6V,
Vin(LM2940) = 6V-0.6V(1N5819) = 5.4V, so the input voltage will be too less, if the input side is using a battery then it also has less voltage issue when the voltage of the battery is going down.

#### ericgibbs

Joined Jan 29, 2010
18,213
hi,
This is what my d/s sheets for the LM2940 and IN5819.

Image #1 LM2940, Image #2 IN5819, so OK for a 6Vdc supply at 1A output.
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#### dl324

Joined Mar 30, 2015
16,111
OK for a 6Vdc supply at 1A output
That's for a typical device. The worst case dropout voltage at 1A is 1V.

Though most parts are more likely to be closer to typical than worst case, the OP has to be willing to cherry pick parts if this is a one off build. If this is a higher volume build, more conservative design practices should be used, or they could pay the manufacturer for tighter screening.

#### ericgibbs

Joined Jan 29, 2010
18,213
Hi dl324,
I know it's for a typical device.
I have found in many years of using electronic components, the typical specifications cover over 70% of the devices purchased from reliable sources.

Very rare to have problems, when the device supporting circuity has been correctly designed.

E

#### dl324

Joined Mar 30, 2015
16,111
Hi dl324,
I know it's for a typical device.
I have found in many years of using electronic components, the typical specifications cover over 70% of the devices purchased from reliable sources.

Very rare to have problems, when the device supporting circuity has been correctly designed.

E
As I said. The OP needs to know that a worst case device won't work. They can decide what to do with the information.

If this is a high volume design, it's a poor one.

#### ericgibbs

Joined Jan 29, 2010
18,213
As I said. The OP needs to know that a worst case device won't work
hi dl,
With due respect, the TS has asked what current range is safe?,

so how can you say 'that a worst case device won't work', for his application.?

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#### ci139

Joined Jul 11, 2016
1,898
the d/s specifies the Output voltage range of 4.75 ... 5.25 V for entire operating T - range (Vin 6.25 ... 26.0)
d/s : "Device dynamic performance is improved when the input voltage is at least 2 V greater than the output voltage."

however - what i don't see is the histogram for the 5V regulator being actually that 5V . . . for example for the TL431 the 2.5V may be from 1.8 up to 2.8V /!\

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