gehan_s
Member level 3
hi all,
i am designing a linear power supply and i want to add a current limiting option to it. i am using a LM317 and driving its adj pin via a filtered, amplified PWM signal from a PIC to set the voltage.
for current limiting i have 2 options.
1.
i get the limiting current value to the pic (as a voltage) set by a pot (using A/D converter of the PIC). i get the current flowing in the circuit via a 1ohm sense resistor and compare the two. if the current limit has exceed i will reduce the PWM on time until the current drops to the maximum level set.
2. second one is without the PIC handling the current limiting i will compare the two currents using a comparator and if the current limit has exceeded, the comparator will switch on a transistor which will drag the adj pin of the LM317 down.
my question is which one is better ???
if both are bad can you suggest a better method???
in the second option will the system try to oscillate ????
thanks in advance !!!!!!!!!
i am designing a linear power supply and i want to add a current limiting option to it. i am using a LM317 and driving its adj pin via a filtered, amplified PWM signal from a PIC to set the voltage.
for current limiting i have 2 options.
1.
i get the limiting current value to the pic (as a voltage) set by a pot (using A/D converter of the PIC). i get the current flowing in the circuit via a 1ohm sense resistor and compare the two. if the current limit has exceed i will reduce the PWM on time until the current drops to the maximum level set.
2. second one is without the PIC handling the current limiting i will compare the two currents using a comparator and if the current limit has exceeded, the comparator will switch on a transistor which will drag the adj pin of the LM317 down.
my question is which one is better ???
if both are bad can you suggest a better method???
in the second option will the system try to oscillate ????
thanks in advance !!!!!!!!!