Lab2

Laboratory 3 Power supply, voltage regulation and power consumption

Lab4 [27/2]

1. Specifications

Our goals for this laboratory session will represent two projects:

(1) Review the main ideas behind typical AC/DC conversion techniques for powering electronic applications. Study how the Arduino board is powered.

(2) Design and prototype a simple AA - AAA 1.2 V nickel metal hydride (NiMH) batteries charger.

 

---

Basic context on power electronics

This is a good time for browsing the internet many resources on this topic. A convenient web to start:

Quantities of interest: voltage, power, current, , energy, load resistance, electrical isolation and electrical security.

AC/DC adapters

AC/DC power conversion from 50/60 Hz mains plug. Transformers have low power losses. The same with rectifier diodes that work as ideal switches. The smoothing capacitor simply accumulates energy. The voltage regulator is the critical block if our concern is power efficiency.

Fig. 1. Block diagram of a typical power supply input front-end  (ref.)

 

Linear voltage regulation

Fig. 2. Typical linear regulator using operational amplifier to establish the feedback control loop (ref.) (ref.)

Study some training boards power supply circuits. Focus your attention analysing the circuit for powering the Arduino board.

 

Linear current regulation

How to derive a current supply from a voltage supply? What is like your phone charger? Design a charger for AAA and AA batteries.  How to add a timer, for instance, a 15 h timer, to the charger so that the charging process stops when batteries full? How much energy is lost (dissipated as heat) by the charger in the process of charging four AA batteries for 16 h?

Fig. 3. Typical adjustable current source  where the control loop allows constant current to be selected. This circuit can be used as a battery charger (ref.) (ref.) (LM317 chip). LED driver may be as well designed using current sources.

 

Switching DC/DC converters

Describe the currently used switching topologies for DC/DC conversion. Which is the design equation?

Buck converter. Step-down voltage.

Fig. 4. Buck topology to convert power with high efficiently. (ref.). Equations in continuous conduction mode (CCM).

Boost converter. Step-up voltage.

ç

Fig. 5. Boost topology. Ref. TI power topologies handbook: slYu036.. Equations in continuous conduction mode (CCM).

Inverting Buck-Boost converter. Step up/down voltage.

Fig. 6. Buck-Boost topology. (ref.). Equations in continuous conduction mode (CCM).

Isolated power-converter Flyback topology.

Fig. 7. Flyback topology  offers the advantage of isolating input and output. (ref.) (ref.)

 

Non-isolated (off-line) power supply (only for very specific applications)

Fig. 8. Example block diagram of an off-line AC to DC Converter (ref. Design Guide: TIDA-010060 )

 

---

Thermal analysis. Heatsink calculations

Selecting mechanical heatsinks. Other references. Thermal resistance (qth) and junction temperature Tj. Design examples and equations.

Fig. 9. Example of aluminum heatsink and fan to reduce thermal resistance (picture ref.).

Design a 12 V / 4 A (48 W) linear power supply using AO and a Darlington BJT transistor pair. What is the advantage of using LDO voltage regulators? What are the heatsink requirements to keep the power transistors in their safe operating area?

 

---

Analysis project 1 on power supplies

---

2. Planning

 Read books and internet pages on power electronic circuits and try to find design equations and the main features, advantages and drawbacks of each topology.

Print the Arduino UNO schematic and try to deduce how it works. What is the maximum current/power available for each converter? How many regulated and unregulated voltages are available? Calculate the maximum power available for powering the board circuits and external circuits.

 Justify why the Arduino board regulators do not require heatsing.

 

3. Development

Analyse the circuit of the laboratory power supply. Is the laboratory power supply linear or switch mode? Calculate the headsinks required by the TO3 power transistors.

 

4. Testing

Measure and characterise the DC and AC components of your AC/DC adapter when working at full load (use a power resistor capable of dissipating the adapter rated power.

 

---

Topics in EMC

 

Identify in the Arduino scheamtic the elemented added for EMC.

 

5. Reporting

Studying and reporting this analysis proejct includes four sections of handwritten sheets of paper and printed images:

(1) Specifications.

(2) Planning.

(3) Developing.

(4) Test

 

---

Design project 2 on a battery charger

---

2. Planning

 Propose a circuit using an old AC/DC adapter that can charge up to 6 batteries using fast and slow charge currents. 

Calculate its components. Does it require a heatsink? The idea is to calculate the heatsink requirements for a given application and even if it will be necessary a fan for extracting heat while keeping the semiconductors in safe operating conditions.

 Apply equations and  find transistors, chips and other components to design the battery charger prototype. 

This project will be located at:

C:\EMC\LAB3\Battery_charger\(files)

 

3. Development

We can calculate and simulate a linear voltage regulator in Proteus or  Multisim.

This is an example battery charger simulated in Proteus. Adapt it to our specifications.

 

4. Testing

Simulate your battery charger.

 

---

Topics in EMC

What circuit have to be included to protect the charger against ESD?

 

5. Prototyping

Solder your components in an universal prototype board. Measure how your circuit work.

 

---

PCB design

Use the previous project PCB as a template for making the battery charger PCB.

This PCB project will be located at:

C:\EMC\LAB3\Battery_charger\PCB\(files)

 

6. Reporting

Studying and reporting this LAB3  represents at least five sections of handwritten sheets of paper and printed images from the battery charger circuits.

(1) Specifications.

(2) Planning.

(3) Developing.

(4) Test

(5) Prototyping.  

 

---