LM111 Differential Comparator

23 December 2019 - 0 Comments

LM111 Differential Comparator

LM111 Pinout

The LM111 is a single high-speed voltage comparator. These devices are designed to operate from a wide range of power supply voltages, including ±15-V supplies for operational amplifiers and 5-V supplies for logic systems.

Pin Description of LM111

Pin Number	Pin Name	Description
1	EMIT OUT	Output Emitter Comparator
2	Non-Inverting Input (IN+)	The Non-Inverting Pin of the comparator gives a variable voltage to compare
3	Inverting Input (IN-)	The Inverting pin is also given a fixed voltage which is compared with the (IN+)
4	Ground (VCC-)	Ground pin connected to the case
5	Balance	This pin can be used to turn off the DC-offset voltage
6	Balance/Strobe	This pin can be used to turn off the output stage
7	COL OUTPUT	Output Collector Comparator
8	VCC+	Provide the operating voltage for the Op-Amp. For LT111 it is up to +15V

LM111 features and specifications

Max Input Voltage (V_I) : ±15V
Maximum Input Bias Current: 300nA
Differential input voltage (V_ID) : ±30
Maximum Input Offset Current: 70nA
Max Response Time: 165nS
Min. Voltage Gain: 200,000
±30V Differential Input Voltage
Drives 50mA Loads At Up To 50V.

Note: Complete Technical Details can be found at the LM111 datasheet given at the end of this page.

Equivalent for LM111: LM211, LM311

Alternatives Comparator Op-Amp IC: LM741, LM358, LM339, LM324

Where to use the LM111 Comparator Op-Amp:

The LM111 Differential Comparator Op-Amp is a very popular comparator IC from Texas Instruments that have been used for Voltage comparisons for a long time in electronic designs. Any Op-Amp can be made to work as a voltage comparator, but the LM111 proves itself to be advantaged by housing an Output Transistor inside its package. The collector and Emitter pin of this Transistor can also be controlled by the hardware, this makes it’s suitable for many applications. The simplified schematics of the IC is shown below

LM111 Schematic

This transistor has can drive loads up to 50V and 50mA which is suitable for driving most of the TTL, MOS and RTL loads. The transistor can also make the Load to be isolated from the system ground. So if you are looking for a Voltage comparator to drive loads of these specifications then this IC might be the right choice for you.

How to use LM111:

Like all voltage Comparators, the LM111 also has an Inverting Pin and a Non-Inverting Pin. If the voltage at the Non-Inverting Terminal (pin 2) is high than the Inverting Terminal (pin 2) the output (pin 7) will also be high else the output will be low.

The LM311 can work in a Single supply voltage or dual supply mode. For now, let’s concentrate on the +5V supply voltage circuit since this is the most used design for digital circuits. In this type, the VCC+ (pin 8) is connected to +5V supply voltage and the VCC- (pin 4) is grounded to hold it at 0V potential. A sample circuit is shown below in which the Inverting Terminal is set to 2.5V and the Non-Inverting Terminal voltage is varied using a potentiometer. You can note that the Output voltage stays high when pin 2 has a higher voltage than pin 7 and vice versa.

LM111 Working

The pins 5 and 6 on the Op-amp are used to set the balance voltage if you want to manually adjust the DC-Offset voltage. Normally these pins are not used since the Input Offset itself is much better controlled. When not in use the pins 5 and 6 should be shorted as shown above. You can also notice that the Collector pin (pin 7) of the transistor is used for output and the emitter pin (pin 1) is grounded this type of design is called “Collector output Circuit.”