Electronics Part I Flashcards
Equation for Single Phase Half Wave Load Power?
(Eline^2/Rload)/2
Form Factor for Single Phase Half Wave?
0.45
Diode Amperage in a Single Phase Half Wave?
Equal to I load
Ripple Freq of a single phase half wave
X1
Peak Inverse Voltage Rating of a single phase half wave rectifying diode?
Eline • 1.41
Ripple voltage of a single phase half wave rectifier?
Epeak to zero
Number of diodes in a single phase full wave rectifying bridge?
4
Form factor a single phase full wave rectifying bridge?
0.9
Diode amperage of a single phase full wave bridge?
Iload/2
Power for a single phase full wave bridge?
Eline^2/Rload
Ripple frequency for a single phase full wave bridge?
Supply freq x 2
Piv rating of a diode in a single phase full wave bridge?
Eline times 1.41
Ripple voltage of a single phase full wave bridge?
Same as epeak which is line times 1.41
Form factor of a single phase full wave centre tap, and diode number
0.9 and 2
Diode amperage of a centre tap rectifier?
Iload/2
Power of a single phase full wave centre tap?
Eline2/Rload
Ripple frequency of a single phase full wave centre tap is…
Supply times 2
Piv rating of a centre tap diode in a full wave single phase?
Eline(using the secondary, aka line times 2) times 1.41
Ripple voltage of a centre tap?
Supply on the line (half the secondary) times 1.41
What is ripple
Voltage?
Max to min voltage of a rectifying circuit across a load (aka the max and min amount of ac voltage that appears on a dc load)
3 phase half wave rectifiers circuit FF and diode number?
0.675 and 3
What is form factor?
The dc output of an ac supply
Amperage per diode in a three phase half wave rectifier?
Iload/3
Power of a load in a 3 phase half wave rectification circuit?
Eload times Iload dc)
In a three phase, do we use line
Power ac or dc for power?
Dc
Ripple frequency of a three phase half wave rectifier?
3x the supply
Piv rating of a diode in a three phase half wave is using Eline or e phase?
Eline. It’s Eline times 1.41
Ripple voltage of a three phase half wave rectifier?
(Ephase times 1.41)/2 (at 50% between wave forms of various phases)
Form factor of a three phase full wave rectifier? How many diodes?
1.35 and 6.
Mneumonic: 1,3,5 and add first and last to get 6 for diode number
Diode amperage of a full wave three phase rectifier?
Iload/3
Power of a three phase full wave rectifier is Eline times Iload; t or f
F. It is Eload times Iload.
Ripple frequency of a 3 phase full wave rectifier?
Supply times 6
Piv rating of a diode in a three phase full wave?
Eline times 1.41
Do we ever use ephase for calculating piv?
Nope
When is the only time we use ephase for rectifying circuit formulas?
It’s for the ripple voltage
Of a three phase half wave only
Ripple voltage of a three phase full wave rectifier?
Eline times 1.41 times 0.134
Mneumonic: .134 for the ripple whores
How many valence electrons in a conductor?
1-3
How many valence electrons in an insulator?
5-8
Semiconductors have 4 valence electrons: t or f
T
Shells are 2-8-18 for filling the first three shells. T or f.
T
Fewer free electrons means more reactive; t or f
False: more free electrons means more reactive, and more conduction
Define current
Flow of electrons
What are 4 advantages of
Copper?
1) good amount of free e’s
2)non magnetic
3)high conduction rate (gives good current flow and it cools quickly when hot)
4)self regulating via a
Drop in conductivity as temperature rises
5) malleable
6) not oxidative
How does a solenoid work? Can it work with ac or dc only?
A non magnetic coil running current through itself allows the solenoid pull to in or drop out.
It can work with both. In dc, a magnetic current pulls it in. In ac, the alternating current changes polarity of the coil, but the solenoid is not magnetic (it’s steel or iron) and so will pull in regardless of
Polarity (a special device is used to make sure the solenoid stays pulled in as current crosses 0 in the sin wave to prevent chatter)
What is covalent bonding?
It’s when 2 or more atoms share valence electrons
Is a crystal lattice si structure conduction or not?
Not conductive; 4 valence electrons in each molecule bond together.
To make an N type, should pentavalent or trivalent impurity be added?
Pentavalent to allow for a net electron negative charge
What happens if you add boron to a silicon lattice?
Boron is trivalent and so it causes a P type semiconductor as as there is a net gain in “holes”
If boron is trivalent, what is antimony?
It’s pentavalent
Mneumonic: anti-money aka negative to money
How many valence e’S in germanium?
4
In a semiconductor, what is a way to
Increase current without adding impurities?
Increase temp.
What’s another name for the barrier region?
Depletion zone
Barrier voltage is how much?
0.7
The anode is to the p or the n side?
The positive p side
In conventional flow, what direction does current flow?
From positive to negative (think of it as representing the “holes” instead of the electrons)
In rev bias, the kathode is attached to negative; t or f
F. In reverse bias, the anode is attached to negative, and the kathode to the positive. Current conventionally then flows from the positive attached kathode to the anode.
A diode with two layers is known as a ?
PN junction diode
How many junctions, layers, and leads does a pn junction diode have?
Two layers, two leads, and one junction
A diode short circuits without a load in series with it; t or f
True
Describe Voltage control or regulation’s meaning in terms of a diode.
It’s the process of maintaining a stable 0.7V drop across the diode.
How does barrier voltage work?
It is the amount of “push” needed for electrons to collapse the depletion region by allowing electrons to
Fill
Holes on the anode side.
Peak inverse voltage is also known as breakover voltage; t or f
F. It’s known as blocking voltage. Piv is amount of voltage the diode can safely block. Reverse breakDOWN voltage (as highlighted by the maximum repetitive reverse voltage rating specification which is aka Vrrm) is the voltage that allows avalanching or breakDOWN in the reverse bias direction of a diode. Breakover is like in an scr, when current conducts in fwd bias without a gate pulse, or in a diac, where the current conducts in fwd bias (through the reverse biased Zener). Breakover isn’t so unhealthy for a diode as breakdown is (breakdown means device is done). Breakover is like the Vdrm of an scr.
How does a diode rectify?
It blocks negative ac, allowing only the positive dc through, aka, it gives voltage out that always has the same polarity.
What are 3 Diode Ratings?
1) piv (safe blocking voltage)
2) fwd current (refers to maximum amount of current that can flow through diode in forward bias safely)
3) forward voltage (0.7v)
4) power rating
5) temp rating
What are two applications of a pn junction diode or a zener diode?
1) rectifying an ac circuit
2) polarity protection of a dc load
3) charger isolation
4) surge suppression (clips the surges via a zener)
5) voltage regulation (via zeners)
The zener diode symbol is the same as a diode symbol; t or f
F. It has diagonal slants on the line that signals the kathode side.
A Zener is hooked in reverse bias but functions as a regular diode in forward bias; t or f.
T.
How come a Zener diode isn’t usually installed alone in an ax circuit?
Because, as polarity switches at the ac alternation, the Zener will drop 0.7v across the parallel load, rather than the Zener voltage (aka the normal
Operating voltage) across the load.
What is normal operating voltage?
The Zener voltage aka the “piv” of the Zener. This voltage is what is safely allowed through the Zener and allows current to flow (anything above is clipped)
Does current flow at below or above the Zener voltage?
It will only safely allow current to flow through it above the Zener voltage if the voltage and current together don’t exceed the power rating. If it does exceed it, it will burn up.
Below the Zener voltage, aka the breakdown voltage of the Zener, there will be leakage current which rises exponentially as the Zener voltage is reached. Thus, the Zener drop stays predictably steady (rms or dc average).
What is the difference between breakdown and breakover voltage?
Breakdown voltage is the voltage at which a diode burns up as reverse bias or piv voltage is exceeded, or the voltage at which a Zener conducts in reverse bias. Breakover voltage applies to scr’s and is the voltage where the scr conducts without gate current (Vbf)
In a working circuit, does Zener voltage ever change?
Nope. That’s why it’s used as voltage regulation.
To get the maximum current a Zener diode can allow…
Use the power rating. If given zener voltage, and dropping resistor resistance, can calculate voltage drop across dropping resistor (kirschoffs law), and already know what it is at Zener (never changes), then can get total current, even with a parallel load to Zener.
How would you use Zener diodes in an ac circuit for surge protection via clipping?
By installing the zener’s in inverse series, parallel with the load (drop
Would be 0.7v plus Zener voltage across the load).
In a centre tap, what is line 1, line 2, and secondary winding voltage?
Line 1 is to the centre tapped neutral, as is line 2. The secondary winding or secondary voltage is from line to line.
In a centre tap rectifier, what is used for piv?
The secondary voltage.
In a 3 phase full wave rectifier circuit, where is the 4 number diode?
It’s at the C phase after the load.
1 is at A, the “start”, before the load.
2 is at B phase after the load (as A “finish” is connected to B.
3 is connected to B before load.
4 is at C phase after the load.
5 is at C before the load.
6 is at A after the load.
What type of device is a BJT? And what does it stand for?
It’s a transistor. And it’s a bipolar junction transistor.
Why is it called a BJT?
It has 3 layers, with pnp or npn design.
How many leads in a BJT? And what are they?
3 leads. And they’re the collector, base, and emitter.
Emitter’s arrow shows electron flow; t or f.
F. It shows “hole” flow as it points from Positive to negative (ie. points to outside N towards the E in an NPN).
Base current is equal to?
Base current is equal to emitter current minus the collector current.
Emitter current always consists of…
Collector and base current.
What is beta gain?
The ratio of current in collector to the base. (Base c beta gives collector current).
How can you use the Beta value to get Base Current and Collector current? (Formula)
Base current • (Beta+1) = emitter current
Mneumonic: 1 and only child beta is based.
Is a diode voltage or current control?
Voltage
Is a transistor current or voltage control?
Current (base current is a MUST to flow)
What are the applications of a BJT?
1) amplifier (of current)
2) switching.
How does a BJT provide switching?
It can, via a variable resistor, cause base current to not meet minimum current needs (Ib)
At cut- off, why happens to Vce?
It’s the same as the course voltage.
What is saturation in a BJT?
Point at which current in the base is at its maximum rated value
What is Vbe at saturation?
0.7V unless otherwise stated.
What voltage is known of a BJT at saturation?
Vce is 0.1V.
The total voltage drop in the branch with the load in it in a BJT-having circuit should take into account Vce; t or f.
T.
Voltage of the variable resistor or fixed load is the only voltage drop in a branch with the base of the BJT; t or f.
F. The Vbe should also be added into account.
A BJT can be npn or pnp; t or f
T. Thus, it can have 2 anodes on either side of the base or 2 kathodes.
If the arrow of an emitter is towards the base, the transistor is oriented…
PNP.
A low reading in an ohmeter over BJT leads when not expected means…
It’s shorted (burnt out if high)
What does it mean when a BJT is in “linear”?
It’s not at cut off where base current is zero or saturated when base is at max. It’s in the
Middle, still conducting.
Does over saturation increase Ic, Ie, and Ib?
No, only Ib. Thus it won’t help to change anything in the load branch.
What is the thyristor we studied?
An SCR (silicon controlled rectifier)
What does scr stand for?
Silicon controlled resistor
Mneumonic: scissor. Sicr. Silicon controlled rectifier.
What are the characteristics of an scr? Name 3.
1) 4 layers.
2) three junctions.
3) 3 leads.
4) 2 current paths.
5) is current controlled via the gate.
What is Ig?
Gate current needed to start or trigger.
What is difference between Ig and Ih?
Gate current needed to trigger; holding current to keep scr conducting.
How does an SCR relate to a BJT transistor?
It’s basically two bjt’s joined internally.
What is natural vs forced commutation?
Natural commutation is when the ac sim wave goes below being able to supply the holding current, cutting off scr current from anode to kathode, switching the scr off. Forced commuting is when it is done on purpose.
Why use a thyristor vs a bit?
It’s better for higher power applications.
What is an application of an scr?
Solid state switching.
Why is better to use a thyristor (scr) as a solid state switch rather than a mechanical dc switch?
1) no moving parts
2) no corrosion
3) no arcing
4) no putting
5 no contact bounce
6) ranges from 0.25-5000 A
In a multimeter, what lead is negative?
The black common (it pushes electrons so to speak)
Should the red lead be connected to the anode or kathode when testing a diode.
Anode.
The anode is p-type semiconductor; t or f.
F. The anode ATTACHES to the p type silicon based semi conductor.
Terms related to SCR’s are It, Iave, Igt, Igm, Ih, Vdrm, Vrrm, Vgt, Vf or Von. What do they mean?
It is the maximum continuous current.
I average is the maximum current from a dc supply.
I gt is the required current to pulse the gate.
I gm is the max current through the gate.
I h is the holding current required from the anode to kathode to allow the scr to latch in the on state.
Vdrm is the forward breakover voltage, aka the max voltage we can block.
Vrrm rev breakover voltage, aka max voltage blocking in the piv direction.
Vgt is the voltage from the gate to the kathode.
Vf is the voltage drop forward from anode to kathode.
Can see from above, SCR’s are only put in forward bias.
Is natural commutation when current goes to 0 via the ac sin wave?
No. It’s when current goes below Ih via the ac sin wave.
What are the practical firing angles for an scr?
15-165 degrees.
Why do we use ephase to get the ripple voltage of a three phase half wave?
Because, as ripple voltage is the maximum and minimum of the ac wave that is seen across the load, and a three phase half wave system can’t have Eline shown across the load as there’s a neutral at the other end of the load, we use ephase.
How do you find the average dc output for a specific firing angle?
E Average is equal to Epeak•(((cos fa)+1)/2pi)
What’s the purpose of a gate protection diode, and where is it installed?
It protects the gate of an SCR by not allowing current to flow in the opposite direction to the intended (conventional flow has the kathode side closest to the gate, and current (but really, just the holes) flows anode to kathode, though in our way of thinking, current still flows the other way; it doesn’t affect calculations or installations). It is installed in the trigger circuit.
What is the firing angle of resistance only circuits?
0-90. But 15-90 realistically.
Why do we calculate instantaneous voltage in an scr?
It is the voltage drop in ac across the trigger branch (and the parallel branch) and we can then get the “ac” info in regards to firing angles; dc info doesn’t tell us a whole lot.
How many terminals does a full wave R triggering circuit have? And why?
4 terminals for the bridge rectifier (gives the full wave).
If a dc source supplies a dc load, and the polarity in the left of the dc load is a negative sign, then the top side terminal of the dc source will be..?
Negative. Current flows negative to positive at the source, negative to positive through a load, and negative to positive in the branches (but at the source, the line polarity is same as the last resistor’s closest polarity as it’s the same point and no load has been gone through).
Formula for a full wave trigger circuit?
E average is equal to e peak times (cos of the firing angle plus 1 divided by pie. )
What’s the range of control for a half wave scr? What about full wave resistance only? And what about half wave resistance and capacitor? And what about full wave RC trigger? Explain.
22.5-45 percent for half wave r only (45% is the form factor; 22.5 is the realistic r only scr trigger).
45-90 percent for a full wave. (Doubles as no blocking the second alteration)
0 - 45 percent for an rc half wave. (With a cap, the realistic firing angle can be much faster due to how quickly it can charge)
0-90 for a full wave rc.
Does the capacitor empty fully during a pulse?
No. Just a bit. Then, in the other ac alteration, it should empty fully (to keep same firing angle).
A capacitor bank shows no voltage until it nears full capacity; t or f.
T. Current is at 100% inflow until near the full point as well.
Lowering resistance does what to the voltage? What about the firing angle?
Increases it as firing angle decreases.
How does a full wave single phase scr trigger circuit differ if it has a bridge rectifier attached to the ac source or not?
If it has a bridge, during the polarity switch, the single scr still conducts in the correct direction. Without a bridge rectifier, two SCR’s are needed, one for each direction, connected in inverse parallel and in series with the load (with an internal trigger circuit attached in between both SCR’s).
How does a soft starter work?
It has 2 SCR’s connected in inverse parallel with an internal triggering circuit. The gate triggers at a high firing angle initially, causing less voltage and less current to come into the machine at startup. Slowly the firing angle decreases. Once we reach close to fla, bypass closes. When shutting off, we slowly bring the firing angle higher again via the SCR’s.
How fast can SCR’s switch? Hz.
25khz.
Describe a triac. Is it bi or unidirectional? Controlled by what? How many leads?
It’s two parallel inverse connected scr’s, with mt 1 on one side and mt 2 on the other side. They’re bidirectional and current controlled. It has 3 leads including a gate. It switches at 400Hz and used as a dimmer switch.
How does a triac function as a dimmer?
It controls the pulses sent to the lamp (smaller pulse means dimmer).
Is a triac a trigger device?
No. A triac IS triggered as it has a gate, BUT it itself is not a TRIGGER device. It is TRIGGERED. It doesn’t make its own trigger.
Name two trigger devices.
1) diac
2) ujt.
How is a diac voltage controlled?
Via the variable resistor in its branch.
How many leads does a diac have?
It’s a triac without a gate.
Describe a diac.
It’s 2 Zener diodes connnected in inverse series.
How fast can a diac fire a current into a connected gate?
50 nano seconds.
What is Vbo?
It’s breakover voltage for a diac (amount of voltage needed for it to conduct). Can be thought of as Zener voltage (or normal
Operating voltage of the Zener) plus the voltage drop of the other Zener diode in fwd bias.
What is a ujt? Is it compatible with ac like the other trigger device?
A uni junction transistor. It’s only compatible with dc. It looks like a BJT but only has one junction (top and bottom types surround middle type). It has an emitter, and b1 and b2 (base one and base 2). The emitter is central to the bases.
What are the leads in a ujt?
E, b1,b2.
What’s the advantage of a ujt? How do you calculate emitter current of it?
It has a built in variable resistor to adjust the voltage and thus the current (think of it as built in Rb). Emitter current is equal to currents of b1 and b2.
Mneumonic: drop the B for a UJT because the Rb is built in. Or UJT has Arbie’s built in.
What is a LASCR?
A light activated silicon controlled rectifier.
What are two ratings of a lascr?
Vgt and Igt.
Symbol for a LASCR has…
2 arrows pointing into it (pointed away means led).
How can we vary the pulse time of a LASCR?
If Igate (which is really the lens on the LASCR) is reached before we want it to, we can have the drain carry current to ground (via a variable resistor) meaning the Igate is reached later. (Note the drain “lead” is referred to as a gate still).
Binary is read left to right; t or f.
False. It’s read right to left.
What is the 2 to the power of in the second place to the right of the decimal in binary? Wb to the left?
To the power of -2. To the power of 1.
In an AND gate, if both inputs are 0, what is output? What about for an OR gate? What if they’re both 1 inputs?
Zero.
Zero.
With both 1’s,
It’s 1 and 1.
In an XOR with 1 and 1 as input, output is…
0.
In a not gate, an input of 1 gives output…
0
In NAND gate, with 0 and 0 input, output is…
1.
In a NOR gate, 1 and 0 inputs give output as…
0.
In an XNOR gate, inputs of 1 and 0
Give…
0.
When we are tasked with determining the maximum and minimum controllable load voltage, how do we do this?
The maximum will be the form factor maximum, and the minimum will be 0.225 the ac voltage (in a half wave r only) or 0.45 (in a full wave r only) or 0 percent of the ac voltage, depending on if it has an r or an rc in the trigger.
Explain why the range of control for a half wave resistance only circuit is 0.225 to 0.45.
0.45 is the form factor for a half wave rectifier. Now, at 90 degrees firing angle, we’ll get half that. 0.225. And in a half wave, we don’t double both the values.
In a capacitor circuit, range of control is zero to 0.45 because we can delay the firing angle to basically 180 degrees.
If capacitance increases, does it need more or less current to fill?
More. It’s capacity is greater.
Can the voltage across a trigger branch be greater than the line voltage (ac)?
Yes. The instant voltage can exceed Eline, reaching the peak even.
For a three phase half wave, is it required to divide power by 2?
No, dc voltage across load already used and accounts for the half wave.
What value determines difference between max and min voltage?
Ripple voltage. (Can use ripple to get min voltage for a 3 phase and such too)
Maximum typical amperage for a LASCR? Wb power?
3 A. 400 W.
Laser Reefers. Reefours. 3-4’s.
What device typically attached to case of scr?
A heat sink.
For a dc motor, which lead connects to the left or “top” side in a wiring diagram for it to spin CW?
Negative lead.
MOSFET is current or voltage controlled? How?
It’s voltage controlled via the gate.
What does a triac consist of?
2 SCR’s
What are the components of a IGBT? What 2 devices does it consist of?
It has 3 leads. It has a gate, collector, and emitter (a mosfet has a gate, supply, a drain, and a a substrate within, and The substrate has an arrow showcasing p to n flow (hole flow)). Igbt consists of a BJT and a mosfet.
What is needed for a current to flow in a IGBT? Where does it flow?
A voltage across gate to substrate squeezes the charge carriers to conduct or stop conducting.
In an IGBT, the gate is attached to…
Metal, which is attached to an insulating material
What does mosfet stand for?
Metal oxide silicon field effect transistor
(Can’t stop the acronym until reach transistor; I mean, the S can’t be semiconductor because that would stop the “flow” of the acronym).
In a symbol for mosfet, if the channel line is dotted and the arrow points outwards in the substrate line, what does this tell us? What would the symbol look like for IGBT?
If the line is dotted, gate voltage is needed to conduct. If the arrow points out, then it’s a PNP MOSFET as substrate is N and channel is P. This is known as a P type E (enhancement, vs depletion) mosfet. In an IGBT, the three leads are gate, emitter, and collector. E would point out depending on how IGBT is made; no relation to substrate (as is understood so far).
What’s an application for a IGBT?
In VFD’s, after rectification and filtration, it can pulse voltages at varying frequency, to change the frequency (SCR’s change voltage out). This helps give the same torque at a lower freq and voltage (same torque but smaller speed). This is called pulse width modulation.
What is pulse width modulation? What device is used?
It is the varying of frequency of the dc output. It’s done via IGBT.
2 ____’S make an SCR.
Bjt’s
In a triac, the SCR’s it consists of are connected…
In inverse parallel.
Gate protection diode is always placed in fwd bias.
In our systems at Bcit, yes. That’s why hate always attaches to inner p.
In conventional flow, the current path shown is the path of holes, so the current can be thought of as “hole flow”; t or f.
T. In conventional flow, current means hole flow (vs electron flow). This, current in convention (aka hole flow in convention) flows anode to kathode, positive to negative.
If a half wave single phase rectifier circuit is single pulse, and a full wave is 2 pulse, and 3 phase half wave is a 3 pulse, then a 3 phase full wave rectifier circuit is considered…
6 pulse (equal to the number we multiply supply frequency by to get the ripple frequency)
What’s an advantage of an IGBT and a mosfet?
Faster switching as it’s voltage controlled rather than current controlled.
Is a UJT a trigger device?
Yes.
Name 3 IGBT advantages.
1) faster switching
2) greater load current
3) high efficiency
4) low c to e voltage drop
5) 0 amps gate current needed
