txr110 1v to 5v to 4 -20ma

Kamarul,

Can you measure the gate to source voltage at the MOSFET? Since the MOSFET used is P-channel, be sure that it is connected with correct polarity (drain outputs current). 

i checked it and i measured it ..what i got is around 24v dc like that ..the source is dropped from 2.5ma to 1.5ma after i took out the capacitor at the vcc to the ground.. the mosfet pin diagram i followed as screenshot 

sorry...mistaken.... not the source i measured..instead at the drain voltage and current....

ok....product type is txr110kp... as i know there is some faulty design which can gave undesireable output...

today i already measured the pin 14 .. and it gave 0.5v...which not enough to switch on the mosfet gate.....pls guide me....i dont know what to do anymore

Kamarul,

For a P-Channel MOSFET the source should be connected to the supply voltage, or in this case to pin 1 and pin 13 of the XTR110. Therefore if the gate drive pin (pin 14) was at 0.5V the MOSFET should be completely turned on. Assuming at 24V supply that would be a VGS of -23.5V (neglecting the drop across the internal 50 ohm resistor)! Can you tell me the part number of the MOSFET you are using? And could you measure the voltage from the gate to the source at the MOSFET?

2364.IRF9510_2.pdf   im used this kind of mosfet....voltage gate that is pin 14 is 1.3v  .... and the voltage gate to source is 22.7..and the voltage source is 23.87v ....voltage drain at mosfet is 20v at 1.24ma... i already set 5v at the input..and how can it be like this???

The absolute maximum rating for the VGS of the IRF9510 MOSFET is +/-20V, you are currently applying 22.7V so there is the potential that the MOSFET is damaged. I would replace the MOSFET and test the circuit with a lower power supply voltage to confirm proper functionality first. 

so if i replaced with a new mosfet...how can i reduced the voltage at the source of the mosfet.... can i put some resistor at it??how much resistance??? or can i used with a transistor??i got 2 source voltage...24v is from power source and the 5v is  from sensor....im afraid the drain output at mosfet is differ from i wanted to... as at the maximum 5v...i want to convert to 20ma...as i know the source and drain is joined...at the gate will control the flow which will be current.... ..please advised