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.
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.