Operation amplifier idle current
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Low Power Op Amps: Only 20μA for 1.3MHz, 240μA for 30MHz
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Please help, if you can. Discussion in ' Solid State ' started by Ollollo , Oct 30, Log in or Sign up. Messages: 62 Location: Sweden.
Hi Does more idle current translate into a more class A before the amp switches to AB? Last edited: Oct 30, Ollollo , Oct 30, Theory sounds good but many other conditions come into play. I have read this many places and on the surface sounds like you can't hurt anything BUT Changing the idling output transistor current might overtax the power supply and you might lose valuable "head room" on peaks, feedback may no longer be "optimal" for the now shifted operating point, heat dissipation in the output stages may be compromised, possibly leading to thermal "runaway".
What I am saying is the amplifier was designed for a "given" operating point and by "deciding" you want to shift that point MIGHT effect many other points in the original design, and if that effect causes other problems is hard to tell.
Too little "class A" bias results crossover distortion, a "little is good, but more is better" doesn't always work here. Yes, you may make an improvement in distortion at lower levels, but what are you trading off to get this one effect? Mark T. From what I understand For a normal, run of the mill AB amp, pushing idle current has no effect on class operation.
They are always in class AB mode. Pushing idle current just turns the transistor "more on". Pushing the power. That would make it more "powerful" but add stress and heat. Many vintage amps may be running "hot" since they are out of adjustment.
It will effect the sound quality since the system wasn't designed to be run that way for the spec'd THD. It could also cause clipping easier at higher volume. Hmmm, I wonder if it effects the AB overlap and would actually be detrimental to quality Messages: 1, Before answering this question, one should know what Class AB is.
The term refers to push-pull amplifiers where a pair of transistors handle the output in a particular manner. So although it is true that "pushing idle current has no effect on class operation. Switch over from Class A to Class B at too low a level and the "handover" between the two output transistors becomes uneven due to nonlinearity in the transistors.
The result is crossover distortion, a particularly nasty-sounding distortion that is made even worse on the ear because it occurs mostly at low power where sheer loudness doesn't swamp it. Switch over at too high a level and the output transistors will generate excessive heat, even as crossover distortion is pushed down to minuscule levels.
Since it is likely that the bean counters will have seen to it that the heatsinks on a commercial amplifier will be only just barely enough for operation in stock, factory-specified form, this will generally result in the heatsink running too hot and thus not being able to properly cool the output transistors.
Excessively "Pushing idle current" does NOT "push the power," whatever that was intended to mean. But at the same time it is decreasing crossover distortion, it DOES add stress and heat, which could cause reliability issues if the design isn't intended to handle that heat. The amplifier could probably sound better, but not for long! Last edited: Oct 31, GP49 , Oct 31, How does a class AB amp run in class A at low power? Messages: 1, Location: Pittsburgh, PA.
Messages: 73 Location: Antwerp, Belgium. The quiescent current, or bias current, has nothing at all to do with volume level. It is a small standing i. DC current which passes through both output transistors which are in series with NO signal applied.
Normally there are low value resistors between the two emitters, and you tweak a preset for a given voltage across them - with no input signal. What this is doing is setting the amount by which the devices are already turned on before they try to produce any output swing away from 0V.
When signal is applied, one device starts supplying current into the load, and the output moves away from 0V. At the same time, the other device still passes the set quiescent current. The basic idea is that the transistors are not completely off with no input signal. They are already operating in a more or less linear region. So when they are asked to drive current into the load, they can do so in a linear fashion. If they had to start from an off state, they would pass through a very non-linear portion of their transfer function - causing a lot of crossover distortion.
At least, that is how I understand it. Messages: 1, Location: Leesburg, VA. The short answer to the OP's question is "yes". Whether the output stage is thermally stable with higher bias is another question.
Guys like John Curl go to a lot of effort to insure that their high-bias amps are thermally stable, and don't turn into crispy critters. Messages: 2, Location: Ottawa, ON. The bias or quiescent current setting for an amplifier, whether it is single ended or push-pull, determines its class of operation: class B, class AB , or class A.
In a push-pull amplifier operating in class A, both halves of the circuit share the signal simultaneously; the output transistors are always completely "on" and dissipating as heat the full output capacity of the amplifier, even in the absence of signal. Class AB push-pull amplifiers are essentially a compromise between class A and class B.
Class AB amplifiers operate in class A at low power levels, and become class B amplifiers at higher output currents. Whether an amplifier can be biased for class A operation is dependent on the capacity of the power supply and the heat dissipation capacity of the heatsinks. As an example: A 50W per channel class A amplifier will be likely be the same size and weight as a W per channel class AB amplifier. Leestereo , Oct 31, Messages: 3, Location: Northern Jersey Transistors add a noise spike to the signal when they turn on and off That will reduce the switching noise of the transistor shutting off They heat up pretty quickly Just my take..
Thanks everyone for your replies, I learned a lot! I think I'll bump the voltage a bit this weekend and see if I can hear any difference. Default is 30 mV, I'll see where I end up. I'm guessing I will be on the safe side as long as the temperature of the heatsing doesn't go above 50 degrees C. Ollollo , Oct 31, Messages: 13, Location: Ottawa Ontario. Lee, I think you meant a 50w class a amp. Messages: Location: Michigan. I can really hear a difference. I have always wondered if a larger wattage class AB amp would generally stay in class A longer?
NeonDriver , Oct 31, Messages: 2, Rod Elliott discusses increasing idle current in an AB amp so it would stay in Class A longer, at the end of this article here. The power supply rails also become unbalanced so he advocates two separate power supplies rather than a conventional split rail. I would keep biasing to the min.. This will run the amp in high power range most of the most time, cause the transistor's switching noise to be at lower spdb levels to be far less audible.
You will not hear it. The reverse of this approach is when people use high efficiency speakers with a high wattage amp in a small bright room and wonder why it sounds like crap I have an amp capable of clipping at wpc into 4 ohms. I use low efficiency speakers. I have a mid size listening room. It sounds wonderful at lower listening level No one recommends a super high power amp with super high efficiency speaker in a small Bright room
What is the input offset voltage of an op-amp?
While all these functions may sound similar, they can have very different meanings depending on the specific amplifier and the manufacturer. We use the terms power-down and shutdown to represent the state of an amplifier when the quiescent supply current is lowered from its normal operating level. The supply current is typically throttled back by reducing the current in the amplifier's internal bias circuitry. For example, an amplifier that draws milliamps of quiescent current in normal mode may draw only microamps or even nanoamps in power-down mode. We use the term disable to represent the state of an amplifier whose quiescent supply current is reduced from the normal on state of the amplifier, but with the additional feature that the output goes to a high-impedance state when the device is put into disable mode.
More idle current = more class A?
Op-amp Tutorial Includes: Introduction Op amp gain Bandwidth Op amp slew rate Offset null Input impedance Output impedance Understanding specifications How to choose an op amp Op amp circuits summary The offset null connections present on many operational amplifiers chips can be used to null any small DC offsets that might appear if the capability were not used. Although the op amp offset null may not be important where AC coupling is used, there are some electronic circuits where DC amplifiers are used. Here it can be of particular importance, enabling high DC gains to be employed without large offsets that can be present. Using the offset null capability is easy, and often just requires the addition of a single electronic component: a potentiometer to the circuit, although in some instances digital techniques may be also employed. There are few changes to the electronic circuit design that are needed: typically the addition of the single potentiometer to null the offset, or the digital nulling capability. An op amp is a differential amplifier. This means that when there is no difference between the two inputs, e. Unfortunately under these circumstances there is always a small offset because no operational amplifier is ever perfect and completely balanced. There is always a small input offset voltage.
Leaving Class A
It addresses voltages from 1. Hi guys, I am looking for LM replacement. It's a dual Op-amp IC means it contain two op-amp inside. They take an input potential voltage and produce an output potential that's tens, hundreds, or thousands of times the magnitude of the input potential.
Linear amplifier schematic
Our op amp family has expanded with industry-leading speed versus supply current. In combination with 1. Figure 1 shows the configuration. Setting R IN1 to 2. C IN1 can be larger or smaller, with more or less filtering accordingly.
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RV converters are necessary components of your RV electrical system, doing exactly what their name implies. It's converting standard shore power into DC power, meant to charge your batteries or run certain appliances that only work on DC power. Know more from RV Profy. Answer: A. Answer: B. The output V o of the circuit is. Obtain an expression for V o in terms of V s , R and the reverse saturation current I s of the transistor.
Operational Amplifier (op-amp) in Digital Electronics
One of the most important functions of electronic circuitry is amplification. In the absence of amplification, many other specific circuits would not work. For example, oscillators to produce sine waves, square waves, pulse or any other desired wave shapes would not be possible without amplifier circuits. The operational amplifier or op-amp enables a very high-performance and highly stable amplification circuit with very few passive components, so in this tutorial, we are going to know about the most commonly used Op-amp ICs and how to choose an op-amp for your application.
Op Amp Offset Null
An operational amplifier , often called an 'op-amp', is a DC-coupled high-gain electronic voltage amplifier with differential inputs and, usually, a single output. Typically the output of the op-amp is controlled either by negative feedback, which largely determines the magnitude of its output voltage gain, or by positive feedback, which facilitates regenerative gain and oscillation. High input impedance at the input terminals and low output impedance are typical characteristics. Op-amps are among the most widely used electronic devices, used in a vast array of consumer, industrial, and scientific devices. Modern designs are electronically more rugged than earlier implementations and some can sustain direct short-circuits on their outputs without damage.
David, aka Grumpy, needs our help. Great news. David is home! It was quite the ordeal to get him home and into the house, but it is done. Thank you to everyone for their support.
In electronics, the open-loop voltage gain of the actual operational amplifier is very large, which can be seen a differential amplifier with infinite open loop gain, infinite input resistance and zero output resistance. In addition, it has positive and negative inputs which allow circuits that use feedback to achieve a wide range of functions. And meanwhile, it can be further simplified into an ideal op amp model, referred to as an ideal op amp also called ideal OPAMP. When analyzing various application circuits of operational amplifiers, the integrated operational amplifier is often regarded as an ideal operational amplifier.
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