[introduction]To understand the power comsumption problem in operation amplifier circuit, we understand above all have electricity of small static state (IQ) amplifier and raise the concern between feedback network resistance and power comsumption.

Ask: Know the power comsumption design in operation amplifier circuit

To understand the power comsumption problem in operation amplifier circuit, we understand above all have electricity of small static state (the amplifier of IQ) and raise the concern between feedback network resistance and power comsumption.

Let us consider to may need to pay close attention to the circuit of give typical examples of power above all: The sensor of batteries power supply generates the imitate sine signal of 50mV extent and 50mV deflection when 1kHz. Signal need enlarge comes to 0V the limits of 3V adjusts with undertaking signal (graph 1) , want to save batteries n as far as possible at the same time, this is need gain the inphase amplifier configuration of 30V/V, if pursue,2 are shown. So, how we should optimize the power comsumption of this circuit?

Graph 1: The input in circuit of give typical examples and output signal (picture origin: Texas Instruments)

Graph 2: Sensor enlarge circuit (picture origin: Texas Instruments)

The power comsumption of operation amplifier circuit is comprised by a variety of elements, it is power of static power, operation amplifier output and laden power respectively. Static power (or abbreviation PQuiescent) is the power that retains amplifier open place to need, in data table general with IQ (static electric current) express, in laying a plan for exampleTexas Instruments OPA391 The indication in norms book.

Graph 3: The static electric current that TI OPA391 carry puts (picture origin: Texas Instruments)

Output power (POutput) is the power that when operation amplifier outputs class drive load, consumes. Finally, laden power (PLoad) is the power that laden itself consumes.

In this exemple, we have amplifier of operation of an only power source, its sine outputs signal to have volts d.c. deflection. Accordingly, we will use the following equality to calculate total average power (Ptotal Avg) . Power source voltage expresses by V+ , voff is the dc deflection that outputs signal, vamp is the extent that outputs signal, RLoad is the total laden resistor of operation amplifier. Need is advertent, average general power and IQ are direct and relevant into direct ratio, and become inverse ratio with RLoad.

The choice has appropriate IQ yuan of parts of an apparatus

As a result of from above formula 5 and 6 in have many alterable, choosing one had better consider only when makings. Choosing the amplifier that has low IQ is the most immediate strategy that drops integral power comsumption. Of course, there are a few balances in this process. For example, the facility that has inferior IQ has inferior bandwidth, bigger noise normally and likelihood more stabilize hard.

Because differ,the IQ of the operation amplifier of the type may exist the difference of diploid class, because this spends time choice,appropriate amplifier is worthiness. TI TLV9042, OPA2333, OPA391 and TLV8802 cite to make under quite. Pure the analysis from the number, to need most the application of high-power efficiency, TLV8802 will be a very good choice.

Express 1: Amplifier of operation of of all kinds low power comsumption compares a list

Reduce the resistance of laden network

Continue to consider formula now 5 with 6 medium the others. Vamp mutual and quits, to Ptotal, avg and Voff do not have an influence, normally by the predefine in application. In other words, the system cannot use Voff to reduce power comsumption. Similar, v+ course voltage is installed by voltage of power source of the practicable in circuit normally. Additional, RLoad also is by what apply predefine. But, RLoad is the package that includes any laden output, is laden resistor not only RL. In the graph a case that shows circuit falls, RLoad will include RL and feedback component R1 and R2. Accordingly, RLoad will by equality 7 be as follows with 8 definitions.

Through raising the cost of feedback resistor, the output power of the amplifier in the system also is reduced accordingly. When Poutput controls PQuiescent, this technology is particularly effective, but also have its limitation. If turn over resistor of make a present of to become apparent,be more than RL, criterion RLoad of RL general dominant, make power comsumption stops to drop thereby. Big feedback resistor returns the input capacitance interaction of meeting and amplifier, make circuit not stable and produce apparent noise.

The noise that reduces these component for utmost ground arises, best end will be inputted in every operation amplifier (see figure below 4) the density of voltage noise spectrum of the thermal noise of the equivalent resistance that see and amplifier undertakes comparative. Experience law is to ensure the norms of density of input voltage noise of amplifier is 3 times of the voltage noise that carries observed equivalent resistor from every input of amplifier at least.

Graph 4: Resistor thermal noise (picture origin: Texas Instruments)

The example in real world

Use these low power comsumption to design a technology, let us return first issue: The 0 batteries to 100mV imitate signal are generated to need the signal magnifying power of 30V/V for electric sensor below 1kHz. Next graphs 5 compared two kinds of designs. The left 3.3V power source that designs use model, dimension is taken no account of energy-saving resistor andTLV9002Current operation amplifier. The design on the right side of uses greater resistance and lower power comsumption TLV9042Operation amplifier. Ask an attention, turn over photograph input to carry equivalent resistor to be 9.667k Ω about when TLV9042, noise spectrum density is little 1/3 of the broadband noise at amplifier, in order to ensure the noise of operation amplifier takes dominant place in any noise in resistor generation.

Graph 5: Typical design and subtle design (picture origin: Texas Instruments)

Use graph standard of 5 medium values, design and two norms of operation amplifier, can use formula the 6 Ptotal that reach TLV9002 design and TLV9042 are designed respectively, avg. The result shows respectively at formula 9 with 10.

Reach from above result, the power comsumption that TLV9002 designs is TLV9042 design is fourfold much. This is taller amplifier the result of IQ, also show the operation amplifier that uses tall IQ, below the circumstance that calculates an attempt to use low feedback resistance, also won’t remarkable power comsumption is saved. We have above case two skill, increase resistance and the operation amplifier that choose to have electricity of inferior static state namely. These two kinds of strategy are usable in application of most operation amplifier.

Use low voltage course to omit report

Review formula again the average power comsumption of the circuit of 1 amplifier of operation of only power source that has sine signal and dc deflection voltage with 6 definitions:

Additional, from formula the power source course that 6 medium V+ are delegate circuitry (V+) , it is direct become direct ratio with power comsumption, so power source course (V+) setting is voltage of power source of practicable of the lowest in circuit, this also is a method that reduces power comsumption. The limits of voltage of lowermost power source of a lot of operation amplifier is 2.7V or 3.3V. Have the reason of this limitation, maintain the lowermost voltage that needs the place inside working limits in place to concern with will in-house transistor. Design of amplifier of a few operation is used at low to 1.8V lower even voltage. For example, amplifier of TLV9042 current operation can be below 1.2V voltage course the job.

Article origin: Get nimble electron DigiKey

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