CompTIA A+ Cert Exam Guide Ch. 10 - Power Supplies Flashcards Preview

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Flashcards in CompTIA A+ Cert Exam Guide Ch. 10 - Power Supplies Deck (77)

What is a basic definition of electricity?

The slow of negatively charged particles, called electrons, through matter. All matter enables the flow of electrons to some extent.


What is Voltage?

Measured in volts, V; The pressure of the electrons in the wire


What is current or amperage?

Measured in amperes, amps or A; The amount of electrons moving past a certain point on a wire


What is wattage?

Watts or W; the amount of amps and volts needed so that a particular device will function


What is the formula for wattage?

V x A = W


What are ohms?

Ω; The measure of resistance to the flow of electrons


What is a circuit breaker?

A heat sensitive electrical switch rated at a certain amperage. If you push too much electricity through the circuit breaker, the wiring inside detects the increase in heat and automatically opens, stopping the flow of electricity before the wiring overheats and breaks.


What is a ground wire?

A wire that provides a path of least resistance for electrons to flow back to the ground in case of an accidental overflow.


What is an overflow of electricity and what happens?

An overflow is when more electricity is passed to a wire than it can handle. When this occurs, the wire overheats and breaks. The electrons then seek a path to the ground.


What is DC?

Direct Current; the electrons flow in one direction around a continuous circuit


What is AC?

Alternating Current; the flow of electrons alternates direction back and forth in a circuit


What voltages are used to provide power?

110-120 VAC in the US and 220-240 VAC in the rest of the world (VAC - Volts Alternating Current)


What is a fixed-input power supply?

A power supply that has a switch to change from 110-120 to 220-240 VAC


What is an autoswitching power supply?

A power supply that does not require the user to manually switch between 110-120 to 220-240 VAC


What is an IEC-320 connector?

A standard power cable used to connect a power supply to a wall outlet. It consists of three holes: hot, neutral, and ground


What are the three components, from top to bottom, of a power supply?

• A hard on/off switch
• The 115/230 switch
• The IEC-320 connector


What function do the wires that connect to the three holes of a IEC-320 connector serve?

Hot wire: carries electrical voltage
Neutral wire: carries no voltage; completes the circuit by returning electricity to the source
Ground: Makes it possible for excess electricity to return safely to the ground


What three things do you want to check for when testing AC power?

• The hot outputs approx. 115 V
• The neutral connects to ground (0 V)
• The ground connects to ground (0 V)


What tools can you use to test electrical current?

A miltimeter (volt-ohm meter, VOM) or a Digital multimeter (DMM)


What voltages should you expect to see using a multimeter?

• Hot to Neutral - 115 V
• Neutral to Ground - 0 V
• Hot to Ground - 115 V


V ⎓

Direct current


V ~

Alternating current


What 4 tests do multimeters perform?

1. Continuity
2. Resistance
3. AC voltage (VAC)
4. DC voltage (VDC)


What does continuity test for?

Continuity tests whether electrons can flow from one end of a wire to the other end. You can use this test to determine whether or not a fuse is good or if there are breaks in the line.


What does resistance test for?

This will test whether or not a fuse or wire is good. A good fuse/wire will show no resistance whereas a bad fuse/wire will show infinite resistance.


What does testing the AC and DC voltage do?

Ensures the voltage is within the appropriate range, 110-120 V for the US and 220-240 V for everywhere else


What is an AC adapter?

An external device that converts AC power to DC for the device using it. An example is the power brick that comes with a laptop computer.


What is a major difference between a power supply and an AC adapter?

AC adapters are rarely interchangeable. You cannot plug he AC adapter for one device into another and expect that it will work.


What three things must match in order to use an AC adapter with a device?

1. Voltage
2. Amperage
3. Polarity


What will happen if you plug an AC adapter into a device where the voltage/amperage is too low or the polarity is reversed?

The device will not run


What will happen if you plug an AC adapter into a device where the voltage/amperage is too high?

You will likely fry the device


In terms of electricity, what is a Sag?

The voltage from the power company drops well below the standard 115 V


In terms of electricity, what is a surge/spike?

The voltage shoots from the power company shoots well above the standard 115 V


What is a brownout?

Large sags in electricity


What is a blackout?

When power cuts out completely


What two devices handle spikes and sags in the supply of AC?

• Surge suppressors
• Uninterruptible Power Supplies (UPS)


Of surges/spikes and sage, which is more dangerous to your electronics and why?

Surges/spikes are more dangerous. A sag will only cut power to your device, potentially forcing it to turn off. A surge/spike can physically damage your devices


What rating should your surge suppressor have to ensure that it will protect your devices?

Underwriters Laboratories UL 1449 for 330-V rating


What is a joule?

A unit of electricity


What measurement should you check before buying a surge suppressor?

The joules rating. This determines how much energy a suppressor can handle before failing. A good minimum is around 800 joules


Can surges come from telephone and cable connections?



How can you ensure that your surge suppressor is still good?

Use the test/reset button


What three things should ensure in a surge suppressor before buying one?

• Underwriters Laboratories UL 1449 for 330-V rating
• A joules rating of 800 or higher
• A Test/Reset button


What is power conditioning?

The filtering out of the electromagnetic and radio frequency interference power lines might pick up and deliver to your house


What is an Uninterruptible Power Supply?

UPS; A device that stands between your electronic device(s) and the wall outlet. It offers protection against power sags or outages by providing power.


In what units are UPS devices measured?

Watts and volt-amps


What are the three types of UPS devices?

• Online
• Standby
• Line-interactive


How does an online UPS function?

Devices are constantly powered through the IPS's battery


How does a standby UPS function?

Devices receive batter power only when the AC sags below 80-90 V


How does a line-interactive UPS function?

It handles moderate sags and surges without the need to switch to battery power.


To what DC voltages does a power supply convert AC current into?

5.0, 12.0, and 3.3 V


What is the most common size of power supply?

150 mm x 140 mm x 86 mm


What devices use 12.0 voltage?

Motors on devices, such as the HDD and optical drives


What devices use the 5.0 and 3.3 voltages?

Generally, onboard electronics


What are the three types of connectors on a power supply?

Molex, mini, and SATA


Molex connector

The molex connector is used to connect devices that need 5 or 12 V of power. It has notches called chamfers.


What is a chamfer?

The notches on a molex power connector


Mini connector

Supplies 5 and 12 V to peripherals; also known as the floppy power connector. This connector was mainly used for floppy drives.


SATA connector

15-ping connector that provides 3.3, 5.0, and 12.0 V to devices. The larger pin count supports SATAs hot-swappable feature.


How do you test a power supply using a multimeter?

• P1 must be connected to the motherboard and the system must be turned on.
• Plug the red lead into the red wire socket of a free molex connector and the black lead into a black wire socket. Then move the red lead to the yellow wire socket. The readings should be as follows: 5 V for red, 12 V for yellow
• Push the red and black leads into the top of the P1 connector, sliding alongside the wires until they bottom out. The readings should be the same as above.


What is a P1 power connector?

A 20- or 24-pin connector that supplies power to the motherboard. Some motherboards use special 4-, 6-, or 8-pin connectors.


What are the two distinguishing features of the original ATX power supply?

• The 20-pin P1 single cable motherboard power connector It had at least two other cables populated with two or more molex connectors
• Soft Power


What is soft power?

Some motherboards are always on even when powered down. For an ATX system, the PSU keeps the motherboard continually powered. The power switch, then, is not an actual power button but a switch that informs the BIOS to and OS to boot up the machine.


What are some advantages of soft power?

• It prevents the user from accidentally turning off a system before the OS shuts down
• It allows the PC to use power saving modes, such as standby and hibernation


ATX12V 1.3 power supply

The first update to the ATX power supply. It added two new power connectors to add more power to the motherboard.
• P4 motherboard power connector added more 12 V power. Used by Intel CPUs
• 6-pin AUX auxillary connector supplies increased 3.3- and 5.0 V current to the motherboard. Used by AMD CPUs
PSUs typically came with either the P4 or the AUX, but not both.


ESP12V power supply

A power supply intended to provide better support for the power needs of server motherboards. It offered more current and thus more stability.
• 24-pin main motherboard power connector (resembling the 20-pin ATX connector)
• P4
• 8-pin connector


What is a rail?

A rail is essentially a voltage regulator used to split the DC current into the needed voltage. A power supply uses rails to split DC current into the 3.0-, 5.0-, and 12.0 voltages.
Each rail has a maximum amount of power it can supply. Rather than include multiple rails to handle heavier power loads, manufacturers have increased the loads a 12 V rail can handle.


What are harmonics where power is concerned?

Harmonics are abrupt pulsating currents that are the result of devices like power supplies turning off an on at the peak of the sinsoidal wave of incoming electrical current. These pulsating currents create reflective currents back into the power distribution system.


What is Active Power Factor Correction?

Extra circuitry within a power supply that smooths out the way the power supply takes power from the power company and eliminates harmonics.


What happens when you attempt to boot a computer with a power supply that does not provide the maximum amount of wattage required by all components?

Because most devices in the PC require maximum wattage when first starting, the result is a dead PC. To confirm this, pull a non-essential part form the PC and attempt to boot again. If it boots, the problem is likely the power supply.


Does a power supply convert 100% of AC current coming in into DC current?

No. Manufacturers allow a certain minimum efficiency level. ATX12V 2.0 power supplies require a power supply to operate at 70% efficiency. So a power supply claiming 500 watts is only require to provide 350 watts.


What benefits do you gain from buying an efficient, higher-wattage power supply?

1. A power supply only puts out the amount of power required by the machine it is connected to and no more. The power supply running at less than 100% will last longer.
2. You will have plenty of power for component upgrades/additions in the future


What are some important considerations concerning cooling?

• Keeping your case closed allows the fans to create airflow. This includes keeping all slots covered.
• Heat rises so orient your fans with the intake at the bottom of the case and the outtake at the top


What can you do to lower the amount of noise from your PC fans?

• Buy manually adjusting fans and adjust the speed
• Buy fans with a larger diameter. They will spin slower, creating less noise
• Buy low-noise fans that use better fan bearings than the standard fans


By how much can a power supply safely vary voltage to a computer?

+/- 10%;
12 V - 10.8 to 13.2 V
5.0 V - 4.5 to 5.5 V
3.3 V - 2.97 to 3.63 V


How do you test the power switch to verify that it is working?

Short the soft power jumpers using a screwdriver or key. This will help determine whether or not the power supply is good.


What are the various types of fire extinguishers?

Class A: Ordinary free-burning combustible, such as wood or paper
Class B: Flammable liquids, such as gasoline, solvents, or paint
Class C: Live electrical equipment
Class D: Combustible metals such as titanium or magnesium