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??

 

It has what is called "foldback" output characteristics to reduce the power dissipation when the output is short circuited.

Les.

 

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.

 

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:

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.

 

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.

 

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

 

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?
If you limit the current by any external means then if would not be the short-circuit current.

 

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.

 

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

 

hi,
Check this link.
http://www.righto.com/2014/09/reverse-engineering-counterfeit-7805.html

I would say that a 'dead short' would hold the Vout at close to 0v.
The loss of Vout will unbalance the internal biassing of the 7805, which will enable only a limited Isc out of 750mA.
E

 

something about the latching nature of "foldback" just doesn't feel right.

A foldback circuit doesn't have to latch. It just reduces the maximum output current as the output voltage drops.