What is the difference between an op amp and a comparator and what is the function of the diode on the output side of a comparator?

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What is the difference between an op amp and a comparator and what is the function of the diode on the output side of a comparator? [Copy link]

The output of the op amp is generally an emitter follower output or a push-pull output, as shown in the following figure:

This is a four-way comparator integrated chip LM339B. It can be seen that the output structure is collector output. What is the function of the diode across the base and emitter at the input pins IN+ and IN-?

maychang

What is the function of the diode across the base and emitter at the input pins IN+ and IN-? 】

Prevent the voltage between the IN+ pin and the IN- pin from being too large, causing the PNP tube emitter junction at the input end to break down.

qwqwqw2088

The output of the op amp should be a push-pull output, and an emitter follower output

Push-pull output can provide greater driving capability
. Emitter follower output is usually not a standard output type of op amp, but is suitable for use as a buffer.

乱世煮酒论天下

maychang published on 2024-8-10 17:32 [What is the role of the diodes across the base and emitter of the input pins IN+ and IN-? ] Prevent excessive voltage between the IN+ pin and the IN- pin from causing...

How to prevent the emitter junction from breaking down? Assuming that the voltage of the positive input pin of the op amp is higher than that of the negative input pin, the first-stage protection diode of the positive input pin is turned on and the second-stage is turned off; the first-stage protection diode of the negative input pin is turned off and the second-stage is turned on. At this time, the turned-on diode shunts the current flowing out of the upper current source, protecting the base current of the first-stage PNP transistor flowing through the current source, and preventing the current from being too large and causing breakdown?

乱世煮酒论天下

qwqwqw2088 posted on 2024-8-11 08:48 The output of the op amp should be push-pull output, and emitter follower output. Push-pull output can provide greater driving capability...

So how does a single-power-supply op amp output? Collector output or emitter output, both have relatively weak load capacity?

乱世煮酒论天下

Or there is another circuit structure, for example, the encoder is powered by a single 5V power supply, there is a negative power generation circuit inside, and the encoder output signal is ±2.5V

qwqwqw2088

Luan Shi Zhu Jiu Lun Tian Xia published on 2024-8-11 12:22 So how does the single-power-supply op amp output? Collector output or emitter output, the load capacity is relatively weak?

There are many emitter followers powered by a single power supply, which have stable output voltage and certain current driving capability.

It also depends on the op amp model selected

Gen_X

The previous diode is simple, so I won’t explain it.

The diode at the back (above) acts as an anti-saturation device. It limits the maximum current of the transistor by preventing it from entering deep saturation. The advantage is that it can effectively reduce the ringing effect of the output, but at the same time does not reduce the fast performance of the transistor as a switching characteristic (the diode does not work for small signals).