Lab 8

ENGR201 Lab 2018 Fall
Lab 8 Inductors and Boost Converters.
Outcome of this lab:
1. Practice on soldering.
2. Observe and analyze the voltage waveforms obtained when charging/discharging a inductor through a resistor.
3. Measure the (magnitude of) the frequency response of an RL low-pass filter and high-pass filter.
4. Build a voltage booster using inductors, resistors, diodes, and capacitors.

Instructions:

Watch the video for more instructions.

PDF Notes

An inductor is also a passive element designed to store energy but in its magnetic field. They are widely used in power supplies, transformers, radios, TVs, electric motors and so on. Inductors are unique in that they can be magnetically coupled such that a time-varying current in one will cause a voltage to be generated in a second inductor in close proximity. This ‘mutual inductance’ is the basis for the electrical transformer that is ubiquitous in the electric power industry. Transformers, with their impedance transforming property are also useful in electronic circuits over almost the entire frequency spectrum.

Also, inductors are usually formed into a cylindrical coil with many turns of conducting wire to enhance the inductive effect. Various inductors and transformers are shown in Fig. 1.

Fig. 1 Inductors
You can find coils (inductors) very often in different situations:

When current flows through a wire, it creates a magnetic field around it, more current, bigger field.

To increase the magnetic field created by current, you can make a coil out of a wire, and put a metal core inside the coil.

An inductor will have its maximum DC current limit. Too much DC current will burn the inductor.

The can be in nanohenry, microhenry, and milihenry range:
Nanohenry range inductor:

Microhenry range inductors:

Milihenry range inductor: (huge)

Tasks:
1. Build the following circuit in LTSpice and solder it on a PCB board.

What is the delay of the Vout compared to Vin? Compare your hand-calculation, simulation, and measurement on a Prototype PCB.

2. Change the input to a sinewave as shown in the following figure.

Why the output is attenuated? Can you explain this qualitatively?

What if you decrease the frequency? Does the output increase or decrease? Why? Explain this qualitatively.
What if you increase the frequency? Does the output increase or decrease? Why? Explain this qualitatively.

Build this circuit on a prototype PCB, show at which frequency (roughly), the signal starts being attenuated?

4. Boost converters:
Let's make something practical out of inductors and capacitors: (Super useful for DC-DC converters)

A boost converter (step-up converter) is a DC-to-DC power converter that steps up voltage (while stepping down current) from its input (supply) to its output (load). It is a class of switched-mode power supply (SMPS) containing at least two semiconductors (a diode and a transistor) and at least one energy storage element: a capacitor, inductor, or the two in combination.
The basic circuit model for a boost converter:

Because the switch is turning on and off so fast, the inductors magnetic field never fully collapses, so when the switch is opened again, this causes a higher voltage on the inductor as it adds to the magnetic field.

Watch the animation for better understanding of this circuit. (the video is re-capped from an Youtube Channel at here).

Let's build a Boost Converter in LTSpice!!!
Try the following circuit by yourself in LTSpice:

The datasheet for the transistor being used can be found here (CD4007): ground VSS, power up the chip at VDD, and connect Pin 6 to the square wave, connect Pin 8 to the same location of V2 in the simulation schematic.

The statement '.include cmosedu_models.txt' is a text file that defines the fabrication parameters of the NMOS transistor (M1) we used in the circuit. Here is the package you need for the simulation.

Keep in mind that the 'bar' painted on the diode indicates the cathode side of the diode.

Use the electronic components available in the lab to build the circuit on a bread board to test the input and output of the circuit. The purpose is to boost a 4 V DC power to a 10 V DC powe supply using your Boost Converter.

Make the input square wave to the transistor to be 20% duty cycle:

** Boost Converter Operations:

Step 1: When the MOSFET is on, current goes through the MOSFET and then to the GND. Energy is stored in the inductor in the form of a megnetic field. The voltage polarity across the inductor is 'Left plus and Right minus.'

Step 2: When the MOSFET is off, the previous megnetic field is destroyed and a new one is generated: 'Left minus and Right Plus'. Then you'll get two voltage sources in series so the output voltage is V1+Vind, this voltage will charge up the loading cap. Because the switch is turning on and off so fast, the inductors magnetic field never fully collapses, so when the switch is opened again, this causes a higher voltage on the inductor as it adds to the magnetic field.

The statement '.model D D(BV=10)' defines the Breakdown voltage of D2 (a zener diode). The function of the zener diode is to stabilize the output at 10 V. See the diagram of the Zener diode: The one we are using today is 1N5240 ZENER DIODE. The regular diode we will use is 1N5817 S&P DIODE.

Don't worry about these new things now, you just need to know there functions in this circuit but not the details of their physics. These things will be covered in ENGR 337 Analog Electronics.

* For more advanced Boost Converters with a feedback and stable output with a load, watch the video her e for your references. We do not have time to build this in this lab. Also, if you have a passion to make a product out of this and prototype it onto a PCB, try it yourself or pursue this as your senior seminar project.

Follow the lab report guidelines to avoid losing points.