Vout & Short Circuit Output Current: Need Help!

[shaqtus]

Homework Statement

Here is the problem: http://img507.imageshack.us/img507/6488/unled2b.jpg

What is the open circuit output voltage, Vout?
Estimate the short circuit output current

Can someone explain to me how to do these.

Homework Equations

Honestly... no idea. I know V=IR and all that but it doesn't seem to help here.

The Attempt at a Solution

 

[gneill]

You'll have to look up the characteristics of the LT1084C regulator to see how it operates. Perhaps download a datasheet.

The transistor Q1 looks like it might be for overload (short circuit?) protection. Its base bias resistors are in the path of the load current (returning back to the bridge rectifier). After some load current threshold it's going to turn on and pull the regulator's Adj pin low, dropping the output voltage. You should probably look into what load current will cause the transistor to turn on and start to pull the output voltage down.

 

[rude man]

For OC output voltage Vout, all you need is the values of R1, R2 and the mfr's spec on the relationship between Vout and the voltage at the ADJ pin.

For SC current, I'd look at the spec sheet for that info.