## ⚡ Electronics #1

Transistors and some applications

## Contents: Transistors

• Bipolar Junction Transistors
• MOSFETs
• Darlington Pair
• IGBT

## Contents: Applications

• Low battery detection
• Variable Resistor & Regulators
• LDO
• Buck Regulator
• Boost Regulator
• Motor Driver
• Solenoid Switch

### Transistors?

From Wikipedia:

“A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power.”

From Arduino’s Tutorial:

“pins can source (provide positive current) or sink (provide negative current) up to 40 mA (milliamps) of current to other devices/circuits. […] attempting to run high current devices from them, can damage or destroy the output transistors in the pin, or damage the entire Atmega chip.”

Assuming Arduino runs at 5v,

$Watts=Voltage\times Amps$ $2.5W=5V\times Amps$

$Amps=0.5A>>>0.04A$ 💥

### Problems

• slow
• prone to hardware failure
• big
• arcing

∴ A “digital” solution is required

There are many different types of transistors, but the first important one made was the
bipolar junction transistor (BJT)

It is commonly used as an amplifier, eg. for microphones and speakers

For switching a lightbulb, a BJT isn’t the most suitable…

metal–oxide–semiconductor field-effect transistor (MOSFET) is another type of transistor, the gate is insulated from the rest of circuit thus there is low input current and high input impedance

For a very high power lightbulb, power losses may become severe…

to solve the input issues of the MOSFET while acheiving the (relatively lower) output impedance of a BJT, a darlington pair configuration can be used

But Vce is doubled, so more power losses

insulated gate bipolar transistor (IGBT) combines the low output impedance of a BJT, high input impedance and high switching speed of a MOSFET to make a very high powered transistor.

But this is usually a lot more expensive and large, for most cases it’s overkill

### For powering a lightbulb, a MOSFET is probably the most suitable

• A lightbulb isn’t THAT high power to require a IGBT or Darlington pair
• We are digitally controlling the lightbulb using a microcontroller, so we don’t need analog amplification
• Cost effective, small, easily available, commonly used

### Driving a linear solenoid

We usually run the solenoids at ~60V, ~2A. This results in huge spikes in current and voltage we have to contain.

We first used a relay, but we experienced arcing due to this large power draw and inductive nature of the solenoid.