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EE 201
Project Report
-----------DC power supply
Written by: Zhang Zhong
With lab partner: Li Jing
Lab section F – Wednesday 6:10-8:00.
Lab Instructor(s): Bob Sheldon and Levi Weiss
Introduction
 In the project, we will design a circuit to transfer AC power to DC power by
using cheap components. We actually need to take 120 𝑉𝑅𝑀𝑆 at the input and
provides two different kinds of outputs. The first one is an unregulated output
with an unloaded DC voltage around 10 V. The second one is regulated, with a
changeable output ranging from 5 V to 10 V, and we let the output current on
load smaller than 20mA for both regulated and unregulated output with ripple
both less than 0.1V.

We needed components like 4 normal diodes, two 5V Zener diodes, a big
capacitors, a couple of resistors, a 1KΩ potentiometer and a transformer that can
transfer 120 𝑉𝑅𝑀𝑆 to a small voltage like 18 𝑉𝑅𝑀𝑆 .
Design, calculations
1. First of all, we need to change the negative part of transferred AC wave (18𝑉𝑅𝑀𝑆 )
to be all positive, as below:
⟹
By using the bridge rectifier as below:
2. Then we will use a big capacitor (300uF) to keep the voltage as below:
As we can see in the graph above, the transferred AC voltage (18𝑉𝑅𝑀𝑆 ) was cut
and kept at around 16 𝑉𝑅𝑀𝑆 .

𝑉𝑝𝑒𝑎𝑘 = 18 𝑉𝑅𝑀𝑆

𝑉𝑟𝑖𝑝𝑝𝑙𝑒 = 𝑉𝑝𝑒𝑎𝑘 − 𝑉𝑚𝑖𝑛 = 𝑉𝑝𝑒𝑎𝑘 − 𝑉𝑝𝑒𝑎𝑘 𝑒 −𝑅𝐶 = 𝑉𝑝𝑒𝑎𝑘 (1 − 𝑒 −𝑅𝐶 )= 4 𝑉𝑅𝑀𝑆

𝑉𝐷𝐶 = 𝑉𝑝𝑒𝑎𝑘 − 2 𝑉𝑟𝑖𝑝𝑝𝑙𝑒 = 16 𝑉𝑅𝑀𝑆
𝑡
𝑡
1
In order to make 𝑉𝐷𝐶 bigger, we need to make 𝑉𝑚𝑖𝑛 bigger so as to make
𝑉𝑟𝑖𝑝𝑝𝑙𝑒 smaller, so that’s why we need bigger capacitance.
3. In addition, we will apply two 5V Zener diodes to keep the output voltage to be
10V, and a divider resistor to disport some voltage from the transferred AC power
source in case of burning of Zener diodes.
4. We will then connect a 100Ω load resistor and 60Ω divider resistor to the circuit
as our unregulated output:

In order to keep the current on the load output less than 100mA, we plan to let
the current equal to 100mA before it goes into the load output, so that we can
figure out the resistance of the divider resistor:
16𝑉 − 10𝑉
= 100𝑚𝐴 → 𝑅𝑑𝑖𝑣𝑖𝑑𝑒𝑟 = 60Ω
𝑅𝑑𝑖𝑣𝑖𝑑𝑒𝑟

The circuit are as below:

The graph of output voltage is as below:

Note: In the circuit building in my Pspice, I used D1N750 as my Zener diode,
which is 4.7V, and that’s reason the voltage shown above is below 10V.
5. Finally, we will build up the regulated circuit, and instead of a 60Ω divider
resistor, we will use a 330Ω one, and we will connect 1KΩ potentiometer on the
load part.

In order to keep the current on the load output less than 20mA, we plan to let the
current less than 20 mA before it goes into the load output, so that we can figure
out the resistance of the new divider resistor:
16𝑉 − 10𝑉
< 20𝑚𝐴 → 𝑅𝑑𝑖𝑣𝑖𝑑𝑒𝑟 = 330Ω
𝑅𝑑𝑖𝑣𝑖𝑑𝑒𝑟

The circuit of regulated output ranging from 5V-10V is as below:

The graph when potentiometer is 0Ω:

Note: In the circuit building in my Pspice, I used D1N750 as my Zener diode,
which is 4.7V, and that’s reason the voltage shown above is below 10V.

The graph when potentiometer is 1KΩ:

Note: In the circuit building in my Pspice, I used D1N750 as my Zener diode,
which is 4.7V, and that’s reason the voltage shown above is below 5V.
Implementation
We then did the regulated circuit in lab, because we know if the regulated output
works, the unregulated output can work, too.

The picture of our circuit on board with wires:

The picture of our circuit without wires:

Transformer we used in lab transferring 120 VRMS to 18 VRMS :


Our result:
Potentiometer is 1kΩ
Potentiometer is 0Ω
Output voltage
4.77V
9.76V
Current on the output
17.65mA
We showed those values to TA during the lab class time.
Conclusion



The design of this final project needs some concepts that are ahead of what I just
learnt from the class, so I searched for some related information and tutorials of
what are the principles of bridge rectifier and Zener diodes, how to connect them
to the circuit and what dangers or loss they may cause.
I learnt from this project that understanding the concept of components is far not
enough; we also need to know how to effectively implement them and combine
them in different structures so as to make different effects as we want.
The error we made in our implementing is because we didn’t adjust the resistor
potentiometer accurately, and we didn’t finish the experiment for just once, so I
guess some pieces of Zener diodes were burning so that Zener diodes could not
show us the accurate 10V.