How to Drive a Load from a Microcontroller

Question 1

What does an MCU act as in an active high

Answer 1

a source of current to the load

Question 2

What does an MCU act as in an active low

Answer 2

a sink of current from the load

Question 3

Which acts as a source of current, active high or active low

Answer 3

active high

Question 4

which acts as a sink, active high or active low

Answer 4

active low

Question 5

Why is a resistor in series with an Led

Answer 5

To limit current in LED to safe value

Question 6

What is the voltage across the load resistor equal to (in series with LED)

Answer 6

VR=VDD-VLED

Question 7

Which switch is between the load and the ground

Answer 7

Low side switch

Question 8

Which switch is between the load and the supply voltage

Answer 8

High side switch

Question 9

What type of switch must the current be reversible

Answer 9

H-bridge

Question 10

What type of MOSFET does a low side switch use

Answer 10

n-channel

Question 11

What type of MOSFET does a high side switch use

Answer 11

p-channel

Question 12

What switch is more common low side or high side

Answer 12

Low side

Question 13

For a low side switch what does the VG equal when the MCU is high

Answer 13

VGC=VsupplyMCU

Question 14

For a high side switch what and why is the current through the load when the output of MCYU is high

Answer 14

No current as the MOSFET switches off

Question 15

For a high side switch when the MOSFET is switched on is the MCU high or low

Answer 15

low

Question 16

What cannot change instantaneously in a capacitor and why

Answer 16

Current, produces ver high back EMF which causes something to blow

Question 17

What must every inductive circuit provide a path for and what is often used

Answer 17

the current when switch is turned off, diode

Question 18

what is the name for the protective diode

Answer 18

Catch, Clamp, Flyback or freewheeling diode

Question 19

For pulse width modulation what is the equation for average voltage assuming that Voff is 0

Answer 19

Vaverage=D*Von

Question 20

What does BJT stand for

Answer 20

Bipolar Junction Transistor

Question 21

In a BTJ what does acts and the input and what is the output

Answer 21

input is base and output is the collector

Question 22

In the BJT what does the base emitter junction behave like

Answer 22

Diode

Question 23

At what value does a BTJ become saturated

Answer 23

0.2V

Question 24

What is a pair of BTJ’S

Answer 24

Darlington Pair

Question 25

When are Darlington Pairs used

Answer 25

When the current is beyond the capability of the MCU

Question 26

What is Beta

Answer 26

The current Gain

Question 27

What are MOSFETs usually the best choice for

Answer 27

Low power switches

Question 28

What works better n-channel or p-channel

Answer 28

n-channel

Question 29

What is the voltage that the Vgc must be greater

Answer 29

The Threshold Voltage

Question 30

What does a MOSFET act like

Answer 30

A capacitor

Question 31

When turned on as a switch the MOSFET acts like a

Answer 31

Resistor

Question 32

Why should the voltage drop ne kept small for a MOSFET

Answer 32

It influences the Power dissipation

Question 33

What is a relay

Answer 33

A type of Electromechanical switch

Question 34

Good qualities of Relays

Answer 34

Safety, wide choice, can switch high voltages and currents, little power loss

Question 35

Poor qualities of Relays

Answer 35

Slow, expensive, large, cannot be driven directly from MCU

Question 36

If you want a circuit to be grounded should you use an active high or an active low

Answer 36

Active low

Question 37

If you need to dissipate heat should you use an active high or active low circuit

Answer 37

Active low

Question 38

When would you use a low side circuit

Answer 38

When the Voltage supply is greater than the MCU voltage

Question 39

When would you use a high side switch

Answer 39

When the voltage supply is equal to the MCU voltage

Question 40

What type of MOSFET does a low side switch use

Answer 40

n-channel MOSFET

Question 41

What type of MOSFET does a high side switch use

Answer 41

p-channel MOSFET

Question 42

What sort of loads can be connected directly to the MCU

Answer 42

Very Light loads

Question 43

What is the voltage drop for a bipolar junction transistor

Answer 43

Constant

Question 44

When would you use a relay

Answer 44

For a load powered directly from AC Mains