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Integration > Electrical > Flashcards

Electrical Flashcards

1
Q

What is Ohm’s Law

A

V = IR

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2
Q

Conceptually describe Ohm’s Law

A

Ohm’s Law states that the current flowing through a conductor is directly proportional to the voltage across it.

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3
Q

What are some basic circuit analysis laws?

A

KCL / KVL

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4
Q

What is KCL?

A

Kirchoff’s Current Law states that the sum of all current entering and exiting a node is 0

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5
Q

What is KVL?

A

Kirchoff’s Voltage Law states that, for a closed loop in a circuit, the sum of voltages across all components is 0.

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6
Q

What is the equation to find power?

A

P = I^2 * R

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7
Q

Why is power loss often due to current, not voltage?

A

P=I^2R = IV. So power is proportional to I^2 and V^1

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8
Q

How can you mitigate sensor drift?

A

Periodic recalibration, algorithmic compensation (based on historical or current data), redundancy (allows drift detection), zeroing

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9
Q

Describe sensor calibration

A

Sensor calibration involves taking measurements with a sensor against a range of known values. Sensors that are linear over the range of interest can use 2 or 3 data points to fit a line, but nonlinear sensors need more in order to fit a curve.

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10
Q

What is the Nyquist Frequency

A

For a given sampling rate, the Nyquist Frequency is the highest frequency that can be sampled accuractely. IT is 0.5 * sampling rate. If the frequency of the signal to be sampled exceeds that it will start aliasing.

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11
Q

What is the equation for a voltage divider?

A

Series resistors, so, Vin = Veq = I(R1 + R2)
Also, I is same for R1 and R2, so I = Vin / (R1 + R2)
Vout = V2 = IR2 = (R2 / (R1 + R2)) * Vin

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12
Q

What is a Lowpass filter?

A

A lowpass filter allows low-frequency signals through while attentuating high-frequency. They are commonly used in audio and communication systems. For an RC lowpass filter, the output is taken across the capacitor

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13
Q

What is a Bandpass filter?

A

A Bandpass filter allows a specific range of frequencies through, attenuating both high and low frequencies. It is constructed of a combination of low and high pass filters

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14
Q

What is a Highpass filter?

A

A Highpass filter allows high-frequency signals to pass through. They are commonly used in communications systems to remove DC offset or baseline drift. For an RC lowpass filter, the output is taken across the resistor.

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15
Q

What is the cutoff frequency of an RC Lowpass filter?

A

f = 1 / (2piRC) Output taken across capacitor

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16
Q

What is the cutoff frequency of an RC Highpass filter?

A

f = 1 /(2piRC) Output taken across resistor

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17
Q

What is inductance?

A

Inductance is the tendency for an electrical conductor to oppose a change in the electric current flowing through it. The electric current produces a magnetic field around the conductor. Any change in a magnetic field through a circuit induces voltage or EMF in the conductors which opposes the change in current.

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18
Q

What are parasitics in passive components?

A

All passive components (resistors, capacitors, and inductors) have non-ideal electrical characteristics. E.g. resistors have capacitance and inductance. They can become relevant in high-frequency or precision circuits.

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19
Q

What are Op-Amps

A

Operational Amplifiers are voltage amplifying devices which can perform a wide number of analog signal processing tasks depending only on external components. One common type of op amp is a Differential Amplifier which amplifies the difference between the Non-inverting and Inverting input voltages.

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20
Q

What is Resistance?

A

Resistance measures a materials ability to oppose the flow of electric current through it.

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21
Q

What is resistance dependant on?

A

Resistance is dependent on material composition, length, resistivity, and cross sectional area. R = rho * L / A, where Rho is resistivity which is an inherent property of a material. Resistivity typically increases with temperature for metals

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22
Q

What is impedance?

A

Impedance is the opposition to alternating current presented by the combined effect of resistance and reactance in a circuit

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23
Q

How do you size pull-up or pull-down resistors?

A

Find the leakage current of the pin as well as the max/min voltage required for logic level high/low. The resistor value should be able to sink the required leakage current while still maintaining the correct logic level (high for pullup, low for pulldown). Pullup/down resistors also act as part of an RC circuit alongside the wire’s capacitance. If the RC value is too high, the rise time of the pin could be too slow.

24
Q

What is reactance?

A

Reactance is the opposition to alternating current by inductance and capacitance

25
Q

What is bandwidth in a sensor?

A

Sensor bandwidth is the ability of the sensor to follow changes in the sensed quantity

26
Q

What are inductors used for?

A

Inductors slow down current surges or spikes by temporarily storing energy in an electro-magnetic field and then releasing it back into the circuit. They are often used to attenuate or filter high-frequency noise in electrical circuits. They can be used in LC filters

27
Q

What’s the difference between an LC and an RC filter?

A

LC filters are typically used for high frequency ranges than RC. LC filters offer higher selectivity. LC Filters can handle higher power. RC filters are often small and more cost-effective, especially for low-frequency applications.

28
Q

What is a dielectric?

A

A dielectric is an insulator that can be polarised by an electric field

29
Q

What is a capacitor?

A

Capacitors are passive devices that store electrical energy by accumulating charges on two closely spaced surfaces that are insulated from each other by a dielectric or avacuum.

30
Q

What is the equation of a capacitor?

A

C = Q / V where Q is charge in Coulombs

31
Q

What are ground loops and how can they be avoided?

A

Ground loops occur when two or more points in a circuit that are intended to have the same ground potential have a different potential. Ground loops can occur when there is a voltage drop across a ground plane. Circular ground loops can occur via induction. One way to avoid ground loops is to have a single ground reference point. Differential signaling can’t get rid of ground noise but can mitigate its effects.

32
Q

What is the voltage across a discharged capacitor? Is it a short or open circuit?

A

0V, short

33
Q

What is the voltage across a charge capacitor? Is it a short or open circuit?

A

V = Q / C, open

34
Q

Equation for equivalent resistors in series - How is a voltage distributed across them?

A

Req = R1 + … + Rn. Voltage is divided across resistors. More R more V

35
Q

Equation for equivalent resistors in parallel - How is a voltage distributed across them?

A

1 / Req = 1 / R1 + … + 1 / Rn. Voltage is equivalent on each resistor

36
Q

Equation for equivalent capacitors in series - How is charge distributed across them?

A

1 / Ceq = 1 / C1 + … + 1 / Cn. Charge is the same on each capacitor

37
Q

Equation for equivalent capacitors in parallel - How is charge distributed across them?

A

Ceq = C1 + … + Cn. Charge is divided across them, more C more Q

38
Q

What’s the difference between a buck coverter and an LDO?

A

buck converters and ldos are both voltage regulators. Buck converters are switched-mode-power-supplies that steps down input voltage by switching the input across an inductor and then smoothing it. It is efficient. LDOs regulate by dissipating excess power as heat. LDOs are simpler but less efficient, especially when the input is much higher than the output. LDOs have a minimum difference between input and output to operate, bucks do not. Bucks have output noise and ripple, LDOs have low output noise and ripple.

39
Q

What is PWM?

A

Pulse Width Modulation is a method for controlling the amount of power delivered to a load by rapidly switching a digital signal on and off. The width of the on-time relative to the total cycle time determines the average power. Duty Cycle is the ratio of high to low. PWM is efficient because power is either on or off which minimizes dissipation

40
Q

What are some common battery chemistries?

A

NiCAD, LiPol, Li-Ion

41
Q

How are batteries characterized?

A

Voltage, Capacity, Energy Density, Power Density, Cycle Life, Self Discharge Rate, Temp Range

42
Q

How can you charge / discharge a battery safely?

A

Avoid overcharging, rapid dischargin, charge at a ideal temp, avoid overdischarging or rapid discharging

43
Q

What are some characteristics of Li-ion batteries?

A

high energy density, high discharge rate, fast charging, low self discharge rate, long cycle life, no memory effect

44
Q

What factors limit battery life?

A

Calendar life, cycle life, heat, cold, high charge, high discharge, fast charge / discharge rates.

45
Q

How can battery life be preserved?

A

Avoiding very high and very low states of charge. Avoiding very high charge rates (faster than C/2). Avoid charging in extreme cold. Avoiding very high discharge rates

46
Q

What are common failure modes of Lithium Ion Batteries?

A

Thermal runaway, short circuits can be caused by the electrolyte evaporating in extremely high temperatures, mechanical load can damage separator.

47
Q

How can LiB failures be mitigated?

A

Intrisic safety involves material modifications to improve stability, protection device sinclude vents, circuit breakers, fuses, current interrupt devices, and positive temperature coefficient devices. Early stage fire identification and suppression is critical. Battery thermal management mechanisms like air, liquid, and phase-change material based cooling.

48
Q

How do high and low temperatures affect LiBs?

A

Low temperatures diminish capacity and power density. High temperatures increase internal resistance. Extremely high temperatures can lead to short-circuits and thermal-runaway.

49
Q

What is most in a battery pack generated by? How can it be cooled?

A

It’s due to resistance in the battery circuit, although some comes from chemical reactions as well. Typically battery cooling systems run on Water Ethylene Gylcol mixtures. Forced air typically is not effective enough

50
Q

What is the importance of Cell Balancing?

A

Maximize capacity, lifespan, and safety of the battery pack. Maintained by resistive bleeding, zener diode shunting, state of charge balancing

51
Q

What is the structure of LiBs?

A

LiBs are comprised of two current collectors which are coated by a Lithium Oxide and a graphite matrix respectively which are then separated by an organic salt electrolyte.

52
Q

How do LiBs operate?

A

During charging, a voltage is placed across the battery cell. This voltage breaks the Lithium Ions out of their oxide and, since they are unstable, they shed their single electron. The electron is then attracted to the positive terminal of the battery while the positively charged Lithium Ions flow across the electrolyte towards the negative terminal and are held in a graphite grid. When the external voltage is removed and a load added, the lithium ions want to return to their stable state in the oxide and the electrons flow across the load to join them there.

53
Q

How can you measure sensor bandwidth?

A

The bandwidth of a sensor is the frequency corresponding to the point where a signal is attenuated to -3db. The sensor can be ran through a sine sweep with constant amplitude and the point where the sensor output is attenuated to -3db is the

54
Q

What is the bandwidth of a signal?

A

The frequency range of the signal. E.g. if a signal is composed of sinusoids, it’s fmax - fmin.

55
Q

What is a battery’s C rating?

A

Maximum safe discharge rate relative to the battery’s capacity. E.g. 2A / 1 Ah = 2C

56
Q

What is memory effect of a battery?

A

Seen in NiCd and NiMh batteries, battery capacity can be conditioned to a reduced capacity if only partially discharged before recharge

Integration (10 decks)

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