Electronics > Beginners
Foldback Current Limiting - an example
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iMo:
Here is a small simulation with calculation of the resistors for a Foldback Current Limiting.
Normally the current limiting with LM723 (or any other PSU with same current limiting wiring) works such the current flowing through the shorted output is aprox.
I_limit = 0.7V/R_shunt
With the Foldback Current Limiting the current during short is much lower, call it I_short.
Thus we have I_limit and I_short. After the output current approaches I_limit, it starts to drop down to I_short.
In the below example the I_short is aprox. 5x smaller than the I_limit.
Below is, as an example, a simulation with an LM723 and the calculation.
To find the right values is not straightforward, however.
The Rshunt is a much higher value as you would expect, and the both currents depend on the Rshunt value and R4/R5 ratio as well.
Excel sheet with the goal seeker is something which may help.
The simulation shows the calculation fits pretty well, with larger deviations when k < 0.8 ..
--- Code: --- I_limit I_short
Calc: 41mA 8.5mA
Sim: 39mA 8.7mA
--- End code ---
More on how it works here:
http://www.eeeguide.com/foldback-current-limiting/
ledtester:
FWIW, this lecture on the topic might also be helpful:
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