Analysing a circuit(problem at diode)

[student52]

Hi all,

While I was working I landed up in analyzing a circuit.....I couldn't figure out how actually the voltage at Node A(I presume it is very high) can drive diode(I believe this diode gets burnt as the voltage is far above its maximum voltage). Please let me know how far this circuit works. Please find the circuit attached. I am stuck up with this for past 4hrs.....I expect some kind of help from you guys



Thanks in advance,

Regards.

BMP image replaced with gif image which is smaller and can be viewed in the browser [alexan_e]

 

[FvM]

presume it is very high

Why it should be? The voltage results from the current supplied by the 1Mohm resistor ( 120 uArms) and the LED characteristic, about 1 V at that low current level. For reasonable operation, the current should be raised to about 0.5 mA at least, see the PS2505 current transfer characteristic in datasheet.