Projects: AC To DC 10V Rectifier

Objective:

Objective:

 

My objective is to take a 40VAC signal, which is obtained from a transformer that is connected to a standard US power outlet at 60Hz, and convert it into a 10VDC constant voltage supply with the following characteristics.  Output Power ≥ 1.0W, Output Ripple ≤ 50mVpp, and Load Regulation ≤ 0.2%.

 

Design and Simulation:

 

In order to complete our objectives for this project we split up the design into two parts, rectification and regulation.  Please see Figure 1 below for the schematic of our designed system.

 

Figure 1 (Design Schematic for 10VDC Regulator)

 

Rectification:

 

The rectifier part of the circuit is basically an absolute value circuit.  What ever voltage is put in, see Vsin in Figure 1, the magnitude of that value will come out, with a slight voltage drop due to the diodes.  Please see Figure 2 below for a picture description of full wave rectification.  It is important to note that having done a full wave rectification our frequency has doubled form 60Hz to 120Hz.

 

Figure 2 (Full Wave Rectification)

We then added a capacitor between the positive output of the rectifier and ground in order to get rid of some of the ripple.  See Figure 3 below for the rectified signal with the capacitor and our input signal.

 

Figure 3 (Input AC Signal Vs. Output of Rectifier with 1000uF cap Simulation)

 

Regulation:

 

Now that we have a semi DC signal as seen in Figure 3 above we send it through a regulation circuit as seen in Figure 1 above.  The diode D9, PNP transistors Q3, and resisters R1 and R2 is the pre regulator.  The zener diode D9 gives the PNP transistor Q3 a constant reference voltage of 6.8V, thus a constant current is fed into the base of the Darlington Pair NPN transistor Q1 in our regulation circuit.  Our regulation circuit consists of the Darlington Pair NPN transistor Q1,  NPN transistor Q4, zener diode D8, and resistors R3, R4 and R_Var from Figure 1 above.  The emitter of Q1 is fed into the voltage devider creaded by R3 and R4.  The output voltage of the voltage devideer is then sent into the base of the NPN transistor.  Because the emitter of Q1 is also the output of the system any change in voltage will be noticed by Q4 which will alter the base current and thus correcting the output of Q1.  It is important to note that the 6.8V zener diode Q8 is placed on the emitter of Q4 to give it a constant emitter voltage of 6.8V.  The resistor R_Var is placed between the emitter of Q1 and Q4 for fine tuning of the system.  As you alter the value of R_Var it will slightly alter the emitter voltage of Q4 and thus adjusting the current through the base of Q1.

 

A final 1000uF capacitor is placed across the output as a final noise filter.  Please see Figure 4, and Figure 5 below for the output voltage across a 100 Ohm Load at 10V and Figure 6 for the output voltage at no load.  Please see Table 1 below for the table of the ripple voltage, average voltage, power, and Load Regulation for the load and no load systems.

 

Load

Min Voltage

Max Voltage

Average Voltage

Power (Watts)

Ripple Voltage mVpp

Load Regulation (%)

No-Load

10.0138

10.0139

10.01385

0

0.100

0.0095%

100 Ohm

10.0128

10.013

10.0129

1.0027

0.200

 

Table 1 (Characteristics of the Load and No-Load Simulated System Simulated)

 

 

 

 

Figure 4 (Voltage across the system with a 100 Ohm Load Simulated)

 

Figure 5 (Voltage across the system with a 100 Ohm Load Simulated)

 

Figure 6 (Voltage across the system with No-Load Simulated)


Testing:

 

We then constructed our system and adjusted our part values in order to get the results that we wanted.  One of the main ways that we adjusted the output voltage was to adjust the voltage divider created by R3 and R4 in Figure 1 above.  We were having load regulation problems so we increased the size of each of the resistors in the voltage divider but made sure to keep the same working ratio.  We were still having problems with out loaded regulation so we tried changing our zener diodes D8 and D9 to 3.3V zener diodes.  It is important to note we had to change the ratio of our voltage divider to keep the same output voltage with the new zener diodes.  Please see Figure 7 below for our final circuit with the actual values that we used.  It is important to note that the voltage divider ratio or output to input voltage in Figure 7 is 0.451∙Vin.

 

Figure 7 (Tested 10VDC Regulation Circuit)

 

Please see Figure 8 and Figure 8 for the output voltages loaded with a 98.28 Ohm resistor and the circuit with no load respectively.  Please see Table 2 below for the table of the ripple voltage, average voltage, power, and Load Regulation for the load and no load systems.

 

Load (Ohms)

Min Voltage

Max Voltage

Average Voltage

Power (Watts)

Ripple Voltage (mVpp)

Load Regulation

No-Load

10.01

10.02

10.015

0

12.500

0.1947%

98.28

9.981

10.01

9.9955

1.017043142

31.250

 

Table 2 (Characteristics of the Load and No-Load Simulate)

 

Figure 8 (Voltage across the system with a 98.28 Ohm Load)

 

Figure 9 (Voltage across the system with No-Load)

 

Results and Conclusion:

 

We have successfully obtained a system with all of the attributes that we had initially been given for our 10VDC AC to DC Voltage Regulator, namely:  Output Power ≥ 1.0W, Output Ripple ≤ 50mVpp, and Load Regulation ≤ 0.2%.  Please see Table 2 above for the values that we have achieved.

 

Our main problem that we had during the design and creation of our 10VDC regulator was getting our output ripple voltage under 50mVpp.  We found that using the simulation software PSpice the zener diode that we used did not matter too much but when we made it in the lab we needed to move from a 6.8V zener diodes to 3.3V to give us a wider range of regulation. 

 

It is also important to note that the feedback design is not discrete but continuous, thus all of the steps in the feedback happen at the same time, giving us good regulation.  It is also important to note that when picking an RC combination for the AC filters you need to take into account that the frequency of the fully rectified circuit is 120Hz and not 60Hz.  The larger your capacitor the better your AC filtering will be because the time constant will be much longer with a larger capacitor given the same resistance.

 

Overall we have achieved all of our original goals.