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Output with short circuit protection and current limiter

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kangyunmei

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Hello all,
can anybody show me how to improve the following circuit for the following needs:
- input voltage should be 12 V
- output voltage @ < 50 mA should be near 12 V (low drop out)
- very sharp current limiter curve
- the circuit should cut very sharp at 50 mA
- short circuit protection

My idea was to use anything like a TL431 with its very sharp curve to improve the circuit.
 

kangyunmei said:
Hello all,
can anybody show me how to improve the following circuit for the following needs:
- input voltage should be 12 V
- output voltage @ < 50 mA should be near 12 V (low drop out)
- very sharp current limiter curve
- the circuit should cut very sharp at 50 mA
- short circuit protection

My idea was to use anything like a TL431 with its very sharp curve to improve the circuit.
Click to expand...
Not sure exactly what 'the circuit should cut very sharp' means. Do you mean very accurate limiting point? What kind of limiting do you want? The TL431 is a shunt voltage regulator, how do you envision using it as a current limiter? Maybe you should show a circuit?
 

Hi,

You could use a current shunt monitor to trigger a comparator with a voltage reference controlling a MOSFET pass device maybe.
 

Your requirement that vout roughly equals Vin requires a small current sense shunt and an amplifier to measure that shunt combined with a switch. At 12V a PFET switch may work nicely.

Many TL431 style current limiting circuits need to drop 2.5V before they trigger the TL431 (1.2V variants exist, but that still sounds too high for you).

Look at a chip like INA202 which has built in high side shunt sense and comparator.

There are very nice fully integrated 'load switches' like FPF2700 but their current sense thresholds have poor accuracy.
 

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