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LM339 based voltage comparator application circuits

Published on Mar 14 2011 // Device application circuits

LM339 Manifold with four separate internal voltage comparator, the voltage comparator is characterized by: 1) The offset voltage is small, typically 2mV; 2) Supply voltage range, single-supply for the 2-36V, dual power supply is ± 1V-± 18V; 3) Comparison of the signal source resistance of the wide limits; 4) a large common mode range for the 0 ~ (Ucc-1.5V) Vo; 5) large differential input voltage range, large to be equal to the supply voltage; 6), potential output can be flexible and easy to use.
LM339 integrated block-type package using C-14, Figure 1 shows the shape and pin permutation. LM339 used as a flexible, widely used, so the world’s leading IC manufacturers, the company went so far as to launch its own four-phase comparator, such as the IR2339, ANI339, SF339, etc., consistent with their parameters, used interchangeably.

LM339 based voltage comparator application circuits 1

LM339 is similar to operational amplifier gain is not adjustable. Each comparator has two inputs and one output. Called with two inputs phase input, use "+" indicates the other is called the inverting input, use the "-" indicates. For comparing two voltages, any increase to a fixed voltage input a reference voltage (also known as the threshold level, it can choose LM339 input common mode range at any point), the other side plus a signal voltage to be compared. When the "+" terminal voltage higher than the "-" terminal, the output tube cut-off, equivalent to the output open. When the "-" terminal voltage above the "+" side, the output tube saturation, the equivalent output termination of low potential. Difference between the two is greater than 10mV input voltage output from a state can ensure a reliable converted to another state, therefore, the LM339 used in weak signal detection is an ideal occasion. Output of LM339 will not receive the equivalent of a transistor collector resistance while in use is the power output to be connected a general resistance (referred to as pull-up resistor, select 3-15K). Select different resistance pull-up resistor will affect the output of the high potential value. Because the deadline when the output transistor, its collector voltage is basically dependent on the pull-up resistor and load values. In addition, the comparator output to allow connection with the use.

 LM339 based voltage comparator application circuits 2

Single limit comparator circuit
Figure 2a shows a basic single-limit comparator. Input signal Uin, the voltage to be compared, it is added to the inverting input, the inverting input is terminated with a reference voltage (threshold level) Ur. When the input voltage UinUr, the output is high UOH. Figure 2b for its transmission characteristics.

LM339 based voltage comparator application circuits 3

Figure 3 shows the detection of a thermal protection circuit in the instrument. It uses a single power supply, 1/4LM339 the inverting input plus a fixed reference voltage, its value depends on the R1 to R2. UR = R2 / (R1 + R2) * UCC. Phase terminal voltage equal to the thermal component of the voltage drop Rt. When the internal temperature below the set value, "+" terminal voltage is greater than "-" terminal voltage, Uo high potential. When the temperature rises above the set value, "-" terminal voltage is greater than "+" side, the comparator reversal, Uo output zero potential, the protection circuit operation, adjust the value of R1 can change the threshold voltage, both set The size of temperature.

LM339 based voltage comparator application circuits 4

Hysteresis comparator
Comparator hysteresis can be understood as a single limit plus positive feedback comparator. Described earlier the comparator single limit, if the input signal Uin slightly in the vicinity of the threshold of interference, the output voltage will produce a corresponding jitter (fluctuations). The introduction of positive feedback in the circuit can overcome this shortcoming.
Figure 4a shows a hysteresis comparator, people familiar with the "Schmidt" circuit is a hysteresis comparator. Figure 4b for the transmission characteristics of the comparator hysteresis.

LM339 based voltage comparator application circuits 5

It is obvious that when the output state once the conversion, as long as the transition voltage ΔU near the interference does not exceed the value, the value of the output voltage will be stable. However, followed by a lower resolution. Because of the hysteresis comparator, it can not distinguish the two different input voltage is less than the value of ΔU. Plus hysteresis comparator has a positive feedback can speed up the response speed of the comparator, which is one of its advantages. In addition, the hysteresis comparator plus a strong positive feedback, the circuit than the parasitic coupling much stronger, so the hysteresis comparator circuit can also remove the parasitic coupling of the resulting self-excited oscillation.
If you need a transition point is fixed at a certain reference voltage value on the positive feedback circuit in the access to a non-linear components, such as crystal diode, using diode one-way conductivity, can achieve these requirements. Figure 5 for schematic.

LM339 based voltage comparator application circuits 6

Figure 6 Induction circuit for a power grid over-voltage detection circuit part. Grid voltage is normal, 1/4LM339 the U42.8V, U5 = 2.8V, output open-circuit, over voltage protection circuit does not work, as a positive feedback emitter follower BG1 is conduction. When the grid when the voltage is greater than 242V, U42.8V, flip the comparator output is 0V, BG1 end, U5 completely determined by the voltage on the partial pressure of R1 and R2 values for 2.7V, to promote greater in U4 U5, This makes a very stable condition after turning to avoid pressure points over a small vicinity of the grid voltage fluctuation caused by the phenomenon of instability. As the making of a certain amount of hysteresis (hysteresis) in the over-voltage protection, power voltage to be reduced to 242-5 = 237V when, U4U3, induction cooker before work began. This is what we expect.

LM339 based voltage comparator application circuits 7

Dual limit comparator (window comparator)
Figure 7 circuit is composed of a window by two LM339 comparator. When comparing the signal voltage Uin is located is between the threshold voltage (UR1UinUR2), the output is high voltage (UO = UOH). When the threshold is not Uin is between the potential range, (UinUR2 or UinUR1) output is low voltage (UO = UOL), the window voltage ΔU = UR2-UR1. It can be used to determine whether the input signal potential between the potential at the specified threshold.

 LM339 based voltage comparator application circuits 8

Composition of the oscillator with the LM339
Figure 8 is composed of a 1/4LM339 audio square wave oscillator circuit. C1 can be changed to change the frequency of the output square wave. This circuit, when C1 = 0.1uF time. f = 53Hz; when C1 = 0.01uF time, f = 530Hz; when C1 = 0.001uF time, f = 5300Hz.
LM339 can be composed of high-voltage digital logic gates, and directly with TTL, CMOS circuit interface.