Help me solve the problem in my voltage regulator

[lhlbluesky]

i have designed a voltage regulator,the circuit is as follows:
a opamp with the ouput 474mV when the input is 1.22391V(generated by PTAT);
vtop=vref(1+R2/R1);vref is 1.2391V;in general. vref is precise enough,so vtop should be precise,too;but in reality,it doesn't work;and vout is either close to 0(about 60mV) or vdd(about 1.756V);please help me.what's the problem?
thaks.

 

[Audioguru]

ask for help

Your schematic has no part numbers.
I can't see if the Mosfet is N-channel or P-channel and I can't see which wire is drain or source.

I don't know any opamp or Mosfet that works from a supply voltage of only 1.8V.

 

[lhlbluesky]

ask for help

the mosfet is nmos,the lower end is source,any problem?

 

[Audioguru]

Re: ask for help

the mosfet is nmos,the lower end is source,any problem?

Yes, if the circuit had enough supply voltage to function then the opamp inverts and the Mosfet inverts so the entire circuit has positive feedback instead of negative feedback which would cause the output to saturate against the positive supply or to ground.

 

[rajanarender_suram]

ask for help

can u give me the figures of resistors u used.. shown in figure

 

[keoiuser]

Re: ask for help

try to use yhis LDO