The characteristics and use of LM339 comparator
LM339 (Four-Way Differential Motion Comparison) is a common integrated circuit with four independent voltage comparators inside the voltage comparator chip. It is mainly used in high voltage digital logic gate circuits. LM339 can easily form various voltage comparator circuits and oscillator circuits.
Characteristic
(1) The breakdown voltage is small, the typical value is 2mv;
(2) The range of the power supply voltage is wide, the single power supply is 2-36V, and the dual power supply voltage is ± 1V-± 18V;
(3) The internal resistance of the comparator signal source is relatively large;
(4) The common modular range is large, 0 ~ (ucc-1.5V) vo;
(5) Differential input voltage range is large, which can be equal to the power supply voltage;
(6) The output potential can be selected flexibly and easily.
LM339 application
(1) This type of circuit is very widely used in non-steady-state multi-resonant circuit, used in single-state trigger, TTL/MOS logic converter. "And" door circuit.
(2) The various oscillators composed of LM39 are shown in the figure below. The circuit is a voltage control oscillator. The operating frequency is determined by the input voltage. The two important applications of the voltage control oscillator are the locking loop and the simulation remote control system. This type of circuit can provide two types of output waveforms "square waves and triangular waves." The input control voltage is provided by a pressure device consisting of an RL potentiometer. Other control voltages can also be used. As long as the RL potentiometer is removed, the control signal will You can get between the input of the voltage control oscillator and the ground
(3) The amateur application of LM339
It can be used as a temperature control detection circuit. As shown in the figure below, the temperature controller determines the operating valve value of the alarm detection circuit. When the temperature exceeds the set temperature, the output inverter drives the load generator alarm. The comparator output can form a temperature control alarm with an upper and lower limit. If current is required, you can use the triode to expand.
Instructions for use
LM339 is a high-gain broadband device, like most comparators. If there is a parasitic capacitor from the output terminal to the input terminal, it is easy to oscillate. This occurs only when the output voltage transitions when the comparator is changed. Power supply plus bypass filtering does not solve this problem. The design of standard PC boards is helpful in reducing parasitic capacitance coupling between input and output. Reducing the input resistance to less than 10K will reduce the feedback signal, and increasing or even small positive feedback (stagnation 1.0 ~ 10mV) can cause rapid conversion, making it impossible to produce oscillations caused by parasitic capacitors. Unless lag is used, it will directly insert the IC and add pin resistance to the input-output oscillation in a short conversion cycle. need.
All useless comparator pins must be grounded.
The LM339 bias network establishes its static current to have nothing to do with the 2.0-30V supply voltage range.
Usually the power supply does not need to be added with bypass capacitors.
Differential input voltage may be greater than VCC and does not damage the device. The protection part must prevent the input voltage from exceeding -0.3V to the negative end.
The output portion of the LM339 is a set of collecting electrodes, and the NPN output transistor that emits polar ground may be provided with multiple sets of electrode outputs. The output load can be connected to any supply voltage within the allowable supply voltage range, and is not limited by the VCC -end voltage value. This output can be used as a simple ground SPS road (when the load resistance is not applied), and the output part of the trap is limited by the β value of the possible driving and devices that may be obtained. When the extreme current (16~) is reached, the output transistor will output and the output voltage will rise rapidly. The output saturated voltage is limited by the γsat restrictions of about 60ohm. When the load current is small, the low voltage (about 1.0mV) of the output transistor allows the output clamp to be zero.
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