How to Drive a Load from a Microcontroller Flashcards
What does an MCU act as in an active high
a source of current to the load
What does an MCU act as in an active low
a sink of current from the load
Which acts as a source of current, active high or active low
active high
which acts as a sink, active high or active low
active low
Why is a resistor in series with an Led
To limit current in LED to safe value
What is the voltage across the load resistor equal to (in series with LED)
VR=VDD-VLED
Which switch is between the load and the ground
Low side switch
Which switch is between the load and the supply voltage
High side switch
What type of switch must the current be reversible
H-bridge
What type of MOSFET does a low side switch use
n-channel
What type of MOSFET does a high side switch use
p-channel
What switch is more common low side or high side
Low side
For a low side switch what does the VG equal when the MCU is high
VGC=VsupplyMCU
For a high side switch what and why is the current through the load when the output of MCYU is high
No current as the MOSFET switches off
For a high side switch when the MOSFET is switched on is the MCU high or low
low
What cannot change instantaneously in a capacitor and why
Current, produces ver high back EMF which causes something to blow
What must every inductive circuit provide a path for and what is often used
the current when switch is turned off, diode
what is the name for the protective diode
Catch, Clamp, Flyback or freewheeling diode
For pulse width modulation what is the equation for average voltage assuming that Voff is 0
Vaverage=D*Von
What does BJT stand for
Bipolar Junction Transistor
In a BTJ what does acts and the input and what is the output
input is base and output is the collector
In the BJT what does the base emitter junction behave like
Diode
At what value does a BTJ become saturated
0.2V
What is a pair of BTJ’S
Darlington Pair
When are Darlington Pairs used
When the current is beyond the capability of the MCU
What is Beta
The current Gain
What are MOSFETs usually the best choice for
Low power switches
What works better n-channel or p-channel
n-channel
What is the voltage that the Vgc must be greater
The Threshold Voltage
What does a MOSFET act like
A capacitor
When turned on as a switch the MOSFET acts like a
Resistor
Why should the voltage drop ne kept small for a MOSFET
It influences the Power dissipation
What is a relay
A type of Electromechanical switch
Good qualities of Relays
Safety, wide choice, can switch high voltages and currents, little power loss
Poor qualities of Relays
Slow, expensive, large, cannot be driven directly from MCU
If you want a circuit to be grounded should you use an active high or an active low
Active low
If you need to dissipate heat should you use an active high or active low circuit
Active low
When would you use a low side circuit
When the Voltage supply is greater than the MCU voltage
When would you use a high side switch
When the voltage supply is equal to the MCU voltage
What type of MOSFET does a low side switch use
n-channel MOSFET
What type of MOSFET does a high side switch use
p-channel MOSFET
What sort of loads can be connected directly to the MCU
Very Light loads
What is the voltage drop for a bipolar junction transistor
Constant
When would you use a relay
For a load powered directly from AC Mains
