# Designing a Voltage Regulated Power Supply

• andyleo
In summary, the conversation discusses a voltage regulated power supply that consists of a full bridge rectifier, filter capacitor, and NPN bipolar junction transistor. It is fed from a 240V 50Hz source and must produce a +15V output for load currents up to 2A. The rectifier diodes have a constant forward voltage drop of 1.0V. The conversation covers the circuit arrangement, calculation of peak rectified voltage, selection of zener breakdown voltage, design of bias resistor, determination of BJT voltages, and calculation of average power dissipated. It is recommended to have practical experience with constructing and investigating such a power supply for better understanding.

## Homework Statement

A voltage regulated power supply consists of a full bridge rectifier feeding into a filter capacitor,
and then into an NPN bipolar junction transistor (BJT) operating as an emitter follower, and
with the base of the BJT biased using a resistor and a zener diode. The power supply is fed from
a 240V (rms) 50Hz source, which is stepped down through a 15:1 transformer. The power
supply must produce a +15V output for load currents up to 2A. The rectifier diodes have a
forward voltage drop that is a constant 1.0V irrespective of the load current.
a. Sketch the circuit arrangement for this type of voltage regulated power supply.
b. Calculate the peak rectified voltage that appears across the filter capacitor.
c. Select the zener breakdown voltage required to achieve the target regulated voltage.
d. Choose an acceptable voltage ripple for the rectifier, and hence design the required bias
resistor.
e. Determine the maximum and minimum collector-emitter voltages for the BJT.
f. Hence calculate the average power dissipated in the BJT.

## Homework Equations

Vz=V°+0.7
Iz*Rz + Ibe*Rz ≤ Vp - Vripple - Vz
I(output current)= C * ( dv/dt )

## The Attempt at a Solution

I took a photo of what I did so far ... :
http://imageshack.us/photo/my-images/573/img00289201110260009.jpg/

I'm not sure how I would solve this problem .. can you guys help me ?

I was good with the sketch, I'm not sure about the rectified voltage and the BJT voltages required it to operate... I'm lost please HELP!

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It helps considerably if you have constructed & investigated such a power supply. I think it would be difficult if you haven't. Three is no substitute for hands-on practical lab work.