#### PRIYADHARSHINI PALANISAMY

##### Member level 2

Hi all

I want to construct 1mA constant current source.Here I have attached my circuit.1mA current flows through 100E resistor.I change my resistor values upto 3.9K.If 1mA current flows through the resistor the voltage across the resistor

for 100E it will give 0.1V

for 3.9K it will give 3.9V

I will give this output to micro controller.But the problem with the circuit is the 1mA constant current decreases when I increased my resistor value above 2.5K.At that time the TL431 gives 3.3V instead constant 2.5V.What is the problem with this circuit?

Thanks in advance

I want to construct 1mA constant current source.Here I have attached my circuit.1mA current flows through 100E resistor.I change my resistor values upto 3.9K.If 1mA current flows through the resistor the voltage across the resistor

for 100E it will give 0.1V

for 3.9K it will give 3.9V

I will give this output to micro controller.But the problem with the circuit is the 1mA constant current decreases when I increased my resistor value above 2.5K.At that time the TL431 gives 3.3V instead constant 2.5V.What is the problem with this circuit?

Thanks in advance