Why peak output current is greater than Short Circuit Output Current in 7805 voltage regulator?

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khatus

Joined Jul 2, 2018
84
This is the datasheet of 7805 voltage regulator produced by "Continental Device India Limited"My question is Why peak output current is greater than Short Circuit Output Current?? The Short Circuit Output Current should be > peak output current since at short circuit resistance is zero and maximum current will flow??
And at the time of theoretical calculation Which value(The peak value of current or short circuit output current) should i take as maximum output current??

 

LesJones

Joined Jan 8, 2017
2,639
It has what is called "foldback" output characteristics to reduce the power dissipation when the output is short circuited.

Les.
 

wayneh

Joined Sep 9, 2010
16,390
It's a timing difference. The peak is some instantaneous pulse. You'd have to read how this manufacturer defines the specified value. The short circuit is the continuous current draw.
 

crutschow

Joined Mar 14, 2008
24,969
The device appears to have "foldback current limiting" where the short-circuit current is less than the normal or peak operating current at 5V output, to reduce the stress and power dissipation of a short.
Some examples of this are shown below:

upload_2019-2-1_8-32-20.png
Which value(The peak value of current or short circuit output current) should i take as maximum output current?
The peak current is just for short, transient loads.
The load regulation is given at up to 1.5A, so I would use that as the maximum, but for continuous operation I wouldn't go higher than about 1A.
 

Tonyr1084

Joined Sep 24, 2015
4,535
It can SUSTAIN 2.2 amps continuous. When shorted it will "fold back" (can't rightfully explain that part) so that the current is 750 mA.

Consider this: 5 volts at 2.2 amps is 11 watts. A short circuit would quickly exceed that wattage and the temperature rise would shut down the regulator. (thermal protection)

[edit] @crutschow states the 2.2 amps is transient. I'd bet he knows more about it than I do. I may be incorrect in my statement of a sustained 2.2 amps. Honestly, that's how I would take the data sheet but I'm less experienced than many here.
 

AnalogKid

Joined Aug 1, 2013
8,464
There is nothing in the data quoted, and nothing in the history of the 78xx series, to indicate that foldback current limiting is at play here. My take is that the short circuit current spec is for continuous operation into a short, and that the peak current spec is what the chip can deliver *briefly* until the internal thermal protection kicks in.

ak
 

crutschow

Joined Mar 14, 2008
24,969
My take is that the short circuit current spec is for continuous operation into a short
But how is the short circuit current limited to 750mA when the maximum operating current is >1A if not by foldback limiting? o_O
If you limit the current by any external means then if would not be the short-circuit current.
 

AnalogKid

Joined Aug 1, 2013
8,464
Both Isc and Ipk are indicated by a Tj of 25 °C.
And, in the shown part of the datasheet, there are no notes on test time.
Yeah, I saw that; and I'm not 100% confident in my analysis. but something about the latching nature of "foldback" just doesn't feel right.

ak
 
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