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20 votes

Effective capacitance of a capacitor under DC-bias voltage

The DC bias derating of an MLCC is a product of something called "spontaneous polarisation reversal inhibition". This sounds complicated, but it's not super difficult to wrap your head ...
Polynomial's user avatar
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14 votes
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Can I reverse bias the base-emitter of a BJT transistor?

The BE junction can be reverse biased, and your PNP will be off. The limit is the BE-junction breakdown voltage, as for any PN junction. As long as you don't exceed that breakdown voltage, you'll be ...
LorenzoDonati4Ukraine-OnStrike's user avatar
13 votes
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VBE Multiplier with Emitter Resistance Cancellation

I'd like to somewhat simplify the schematic you've got, so that we can temporarily avoid having to continually discuss the potentiometer when the real purpose is supposed to be trying to understand ...
jonk's user avatar
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10 votes
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Are film capacitors affected by DC bias?

Film capacitors have a very stable capacitance over DC bias. Look at this: But it comes to happen that film capacitors are not the only ones immune to DC bias: So, the actual question is why do ...
Enric Blanco's user avatar
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10 votes
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Why is the collector feedback bias popular in electret-mic preamp circuits?

Most of the hobbyist circuits you find by googling are crap originating from dubious tinkering and then copied from each other. The bias level of this circuit is not very predictable from BJT to BJT (...
Spehro Pefhany's user avatar
9 votes
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Rationale for operating the diode in the (reverse biased) breakdown region

Three reasons: First, operating in the forward orientation only allows operation at a single voltage, nominally about 0.7 volts for a silicon diode. Diode construction can be tailored to produce a ...
WhatRoughBeast's user avatar
9 votes
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Isolated audio without a transformer

Is there any reason this wouldn't work the way I think it would? You cannot expect that circuit to work because the guitar signal ground connection has to connect into the op-amp circuit ground node ...
Andy aka's user avatar
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9 votes

What is the advantage of gate resistor (R3) in this JFET voltage divider biasing circuit?

Historically, high value resistors (especially carbon film types) have tended to have a lot more drift (both with temperature and with time) than lower values. If one of the resistors in the divider ...
Spehro Pefhany's user avatar
8 votes

Can I reverse bias the base-emitter of a BJT transistor?

In general 3V reverse bias is okay for most jellybean transistors- typically the rating is 5V or so, and the actual breakdown more like 9V. This is not necessarily true for some RF transistors, which ...
Spehro Pefhany's user avatar
8 votes
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Pre-biased Bipolar Transistor (BJT) Tradeoffs

Pre-biased (also "resistor-equipped" or "digital") transistors indeed have a plain resistor in front of the base. Most also have a second resistor between base and emitter. Both resistors are used in ...
CL.'s user avatar
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8 votes
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Input coupling to Class AB amp with diode bias. One capacitor or two?

The purpose of the diodes is to set a bias voltage between the transistors' bases, which sets a small idle current through the push-pull. This makes it work in class-AB and lowers crossover distortion....
bobflux's user avatar
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8 votes
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What is the advantage of gate resistor (R3) in this JFET voltage divider biasing circuit?

If you add a large capacitor across R2 it will make a difference. In that case, the power supply noise won't be amplified by the amplifier. simulate this circuit – Schematic created using ...
G36's user avatar
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8 votes
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Where does one find the minimum voltage above the negative rail an op-amp can output in their datasheets?

DKNguyen’s answer addresses limitations on the input voltage swing, but I believe you asked about the output swing. That’s generally specified fairly directly in the data sheet as “output voltage ...
td127's user avatar
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8 votes

Class AB power amplifier from "Electronic Devices" by Thomas L. Floyd

What is the purpose of Q5 and how it is even biased and how the whole amplifier circuit is biased? Well, the 2nd picture is missing a couple of really quite vital components if you are going to make ...
Andy aka's user avatar
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8 votes

What is the purpose of these passives in a microphone pre-amplifier circuit?

The first group are bias for the microphone capsule. the top 2K reduces supply noise into the capacitor, and the bottom 2k provides bias current The second group set the bias voltage for the op-amp ...
Jasen  Слава Україні's user avatar
7 votes
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What can I use to replace an SV-04F bias diode?

This is from an old Sony service bulletin. It mentions SV04S (not F) but part numbers show SV04, SV04S and SV04F as equivalent, so it should work. It's a Vbe multiplier, also known as an adjustable ...
Luncheon Ticket's user avatar
7 votes
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Why are multiple bias voltages required to drive an LCD?

The voltages between BP and SEG for each segment need to fulfill two conditions: The average voltage over the duration of the frame must be 0 (= no DC) The RMS of the voltage must be high when we ...
AndreKR's user avatar
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7 votes

Where does one find the minimum voltage above the negative rail an op-amp can output in their datasheets?

It appears differently on different datasheets. I've seen two or three ways. Sometimes it will literally list the input common mode range relative to the voltage rails (i.e. Vcc - 3V and Vss + 3V). ...
DKNguyen's user avatar
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7 votes
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Why are pull-up inductors biasing the power amplifier output of radio transmitters chips needed?

Applying DC supply straight to the output pin would cause a dead short when the amplifier attempts to sink current to drive the output in an open-drain fashion, as documented in the datasheet: This ...
nanofarad's user avatar
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7 votes

What is the purpose of these passives in a microphone pre-amplifier circuit?

I refer to this datasheet. Starting with the microphone and its power/biasing: simulate this circuit – Schematic created using CircuitLab The microphone drops a few tenths of a volt (I assume 0....
Simon Fitch's user avatar
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6 votes

Biasing of a circuit with two transistors BJT

We are not here to do your homework for you. There are various ways to approach this. Here is one. As you say, the capacitors are open circuit for the purpose of finding the DC operating point. ...
Olin Lathrop's user avatar
5 votes
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Biasing an AC voltage for input to ADC

The ADC input floats to some DC voltage. If you disconnect your voltage divider from the ADC, you will see the voltage on the ADC float to some DC voltage. The ADC input looks something like this: ...
JRE's user avatar
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5 votes

Rationale for operating the diode in the (reverse biased) breakdown region

The obvious answer is ... that they were designed to do that. Not being facetious here, rectifying diodes are designed for forward operation and high withstand in reverse, regulating diodes are ...
placeholder's user avatar
  • 30.2k
5 votes

500V unity gain buffer

This is fairly simple. Use an isolated supply to produce (let's say) +/- 15 volts, and tie its output common to your output HI. Then use any op amp you like (selected for output current), powered by ...
WhatRoughBeast's user avatar
5 votes

Pre-biased Bipolar Transistor (BJT) Tradeoffs

As CL. said they have one or two built-in resistors. In addition to saving board space and money they also idiot proof if you use them within reason. Often the base resistor is dimensioned that ...
Nils Pipenbrinck's user avatar
5 votes
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Why is this comparator loading down a voltage divider?

The problem was that the input signal went below zero. It can go a little negative without problems but at around a diode forward drop it starts loading down the inputs. Sorry for wasting everyone's ...
Felix S's user avatar
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5 votes
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Opamp input voltage divider creates wrong voltage - what could be the cause?

... when 72v applied to the 30:1 voltage divider ... It's not 30:1, it's 31:1. \$ V_{OUT} = V_{IN} \frac {10k}{200k + 100k + 10k} \$. ... voltage across R1 is only 1.727 V instead of 2.4 V. But ...
Transistor's user avatar
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5 votes
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RS485 termination: AC + failsafe + parallel + bidirectional

This is an interesting question :-) Thumbs up for giving it a thorough thought - I see many people still using RS485 but hardly anyone trying to understand termination (hardly anyone even knowing the ...
frr's user avatar
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5 votes
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MOSFET H-Bridge Amplifier Unbalanced Gain

You are taking the U3 drive signal from the wrong place. Figure 1. Marked up schematic. Instead of taking the signal from (2) you should be taking it from (3). The problem is that (2) is a ...
Transistor's user avatar
  • 175k
5 votes

Single supply op amp to convert 0-5VDC to +/-2VDC (microcontroller to line level)

I think you are trying to make sure that your output signal does not have a DC offset with a peak voltage of 2 V. Simply you can remove a DC offset by inserting a series capacitance: simulate this ...
loudnoises's user avatar
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