Overview
Operation amplifier and comparator no matter the exterior or blueprint sign are similar, so they have what distinction after all, how to distinguish in applying actually? I come today graph article is analysed in the round, tamp everybody’s foundation, make an engineer further upward.

 

The interior that sees them first distinguishs a graph:

 

 

 

From interior the graph can see the difference of operation amplifier and comparator depends on outputting circuit. Operation amplifier uses double transistor push-pull to output, and comparator uses a transistor only, collector connects output end, blast off extremely ground connection.

 

One is received to carry what carry to output to go up from positive electricity source outside comparator need help resistance, resistor is pulled to be equivalent to the collector resistor of transistor on this.

 

Operation amplifier can be used at linear enlarge circuit (negative feedback) , linear signal voltage compares usable also Yu Fei (open loop or make a present of of positive and negative) .

 

Voltage comparator can be used at signal voltage to compare only, cannot use at linear enlarge circuit (comparator does not have frequency to compensate) .

 

Both can be used at doing signal voltage to compare, but comparator is designed to be high speed switch, it has rapidder than operation amplifier changeover rate and shorter delay time.

 

 

As linear enlarge circuit, did not say more here (later need discusses amplifier alone) , this is in advocate board circuit plan is very common, use at stabilized voltage circuit commonly, use negative feedback circuit it and transistor cooperate to be equivalent to a 3 end manostat, but use rise more agile. Pursue as follows:

 

 

Below a lot of circumstances, in needing to know two signal which bigger, or when does a signal exceed the voltage that sets beforehand (use as voltage is compared) . With operation amplifier can build a simple circuit very easily to realize this function. When V+ voltage is more than V- voltage, output tall n. When V+ voltage is less than V- voltage, output low n. Pursue as follows:

 

 

 

Analyse circuit, cent of 2.5v classics resistor is pressed get 1V inputs V- end, when bus line voltage produces 1.2v normally, input V+ , voltage of V- of V+ report pressure ratio is right now tall, output a tall n to run the EN open base of chip to CPU power source. If bus line voltage is done not have,be outputted or abnormal little at 1v, voltage of V- of V+ report pressure ratio is right now low, output low n.

 

 

The inphase end when comparator voltage (V+ ) under carry voltage instead (V- ) when, output transistor guides, output ground connection low n; When carrying voltage prep above instead in phase, output transistor ends, the power source that helps resistance through going up outputs tall n. Pursue as follows:

 

 

 

Analyse this circuit, after resistor cent is being pressed through cent when the comparator U8A above should have VCC to output, the input arrives to be carried in phase (V+) , the input after its voltage is more than 5VSB to be pressed via cent arrives to be carried instead (the voltage of V-) , in-house transistor ends, the power source 12v that resistance helps on output classics (at the same time the comparator U8B below carries voltage to also be more than in phase carry instead, in-house transistor also is to end) , q37 of canal of field of N raceway groove guides, output VCC5V. At the same time field of P raceway groove is in charge of Q293 to end. Conversely, should carry voltage to be more than inphase end instead when voltage, in-house transistor guides, power source 12V is pulled on low for low n, field of N raceway groove is in charge of Q37 to end, at the same time Q293 of canal of field of P raceway groove guides, output 5VSB. This is 5VDUAL generation circuit.

 

The comparator in applying actually draws power source on need, and operation amplifier does not need commonly.

 

 

 

Amplifier works mostly in closed circuit condition, ask so after closed circuit cannot self-excitation. And comparator works mostly in open loop condition more pursuit speed. Can replace comparator more completely than inferior circumstance amplifier to frequency (want an idea to output n) , conversely comparator is major the circumstance cannot regard as amplifier is used.

 

Because comparator undertakes optimizing to raise rate, this kind optimizes the scope that reduced closed circuit stability however. And carry is put stabilize limits to undertake optimizing for closed circuit only, reason lowered rate. So the comparator of same price class and amplifier had better be each department its duty. Can use as as amplifier comparator is same, also cannot eliminate comparator to also can use as amplifier. But the price that you pay to make its closed circuit stable may add an amplifier more than!

 

Change character, seeing a carry put is to regard as the negative feedback depth that comparator or amplifier see circuit namely. So, the comparator of shallow closed circuit works likely in amplifier condition not self-excitation. But must make many test, in order to make sure all jobs in the product are stabilized below condition! At that time you are about cost / the risk is careful business accounting.

 

(2) calculate amplifier and comparator be exactly the same, tell simply, comparator carries put open loop applies namely, but the design of comparator is to be aimed at voltage to the door is restricted to compare and be used, the comparison of the requirement the door is restricted accurate, than latter output edge rises or decay time wants short, output accords with TTL/CMOS n / or OC, do not seek the accuracy of the link intermediate, drive ability is different also at the same time. General situation: Put with carry do comparator, most short of is full an output, or too longer than latter edge time, put because this design is medium less with carry do comparator to be beautiful.

 

 

Although be on circuit graph,comparator and carry are put the symbol is same, but these two kinds of parts of an apparatus have very big distinction truly, general not OK crossing-over, distinction is as follows:

 

1, of comparator retroflexion rate is rapid, be in about Ns amount class, and carry is put turn over rotate speed to spend class of the average amount that it is Us (special high speed carry puts except) .

 

2, carry is put can receive negative feedback circuit, and comparator cannot use negative feedback, although comparator also has,mix in phase instead two inputs end, but because of its interior does not have phasic compensation circuit, so, if receive negative feedback, circuit cannot stabilize the job. Interior does not have phasic compensation circuit, this also is comparator puts the main reason with a lot of rapidder rate than carry.

 

3, carry puts output level to use push-pull circuit commonly, bipolar output. And level of most comparator output is structure of collector open a way, resistance is helped on need so, odd polarity is outputted, join easily with digital circuit.

 

(3) comparator (LM339 and LM393) output are collector open a way (OC) structure, resistor ability is pulled to have the capacity that exports electricity external on need. And the structure that carries putting output level is push-pull, those who have semmetry pull electric current and ability of fill electric current. Additionally comparator answers speed to accelerate, intermediate class is very few, also do not have in-house frequency compensation. Carry put the need that works in the light of linear area to join compensation circuit. So comparator (luck of unwell cooperation of LM339 and LM393) is put with.

 

Carry is put in switch power source to basically be used at the feedback circuit, sampling enlarge that sheds protection too to wait a moment.