Max Current and Shorted Current

[Electric1]

I am trying to solve the above circuit two parameters to be found out are



The maximum current is IL(max) = 0.7V / 1 Ohm = 0.7A.
My doubt is the shorted current is same as max current? Does it mean that RL=0 and no current flows through R2 and R3 , V-=0V, and the voltage at V- will never be same as V+. How do i solve this problem?

 

[danadak]

No Rl does not have to be 0 to force Q2 to rob Ibase of Q1. It just has to be a value
that hits the Ilmax you calculated. If it did go to 0 then V + - V- = 5.1 (Vz). The action
of the current limit outside OpAmp operates independently of OpAmp also trying to
force more Ibase into Q1 as Rload drops. Essentially Q2 with Rl = 0 robs/prevents
current into Q1. Once Imax is achieved.

Note OpAmp can only deliver so much output current so that affects operation as well.
Its short circuit current limit ~ 40 mA. If design needs more current one would change
Q1 to a darlington or consider a MOSFET.

 

[crutschow]

The shorted current will be slightly larger than the regulated voltage maximum current, due to the low gain of the current limit circuit.
The regulated output max current is when Q2 turns on sufficiently at the op amp output current limit.

Typically a resistor is added in series with the op amp output to better establish its maximum output current.

 

[Krishna Sankhyan]

Max current is what the device can safely supply under normal conditions, while short-circuit current is the much higher current that flows when the output is directly shorted (and usually only for a brief moment). Always design for protection, because short-circuit current can damage components quickly.

 

[danadak]

Max current is what the device can safely supply under normal conditions, while short-circuit current is the much higher current that flows when the output is directly shorted (and usually only for a brief moment). Always design for protection, because short-circuit current can damage components quickly.

Of course there are the parts that use foldback current limiting to manage that. As well as thermal limiting monitoring die
temp as well.