How many threshold voltages does a single comparator have

Voltage detectors are commonly known as VD (voltage detectors). In the early days, VDDs were used in clocks and watches, and were also called battery detectors. Once the battery of a clock is depleted to a certain level, the second hand may move once every 1 second and become 2 seconds.

Using a voltage detector can detect the degree of drain on the battery and prevent the clock from stopping. The reset circuit is used for the CPU (IC) and is also used for battery monitoring. For details, please consult Shenzhen Huaben Tiancheng Electronics, the company was established in 2012, focusing on the research and development of brushless DC motor driver chips and solutions.

The products are mainly used in automotive electronics, water pumps, power tools, fans, fans, etc., and we rely on our rich R&D strength to provide customers with cost-effective brushless DC motor driver chips and complete solutions. We will adhere to the principle of "Break and Create...

There is only one threshold voltage for a single-limit comparator;

When setting the threshold voltage, it is necessary to pay attention to how large the common-mode input voltage of the comparator is, and when the threshold voltage exceeds the common-mode input voltage, it will not be compared. For a comparator like the 339, the common-mode input voltage range is 0.

To correct one, the standard name should be single-limit comparator, and the threshold voltage is only 1.

The working principle of a single-limit comparator is that the voltage between the two inputs will change when the output state crosses zero, because the input is often superimposed with small fluctuating voltages, and the differential mode voltage generated by these fluctuations will cause the output of the single-limit comparator to change continuously, in order to avoid output oscillation, the new single-limit comparator usually has a hysteresis voltage of a few mV.

A single-limit comparator can be used as a 1-bit analog-to-digital converter (ADC). Op amps can theoretically be used as single-limit comparators without negative feedback, but due to the very high open-loop gain of op amps, they can only handle signals with very small input differential voltages. In addition, in general, op amps have a long delay time and cannot meet the actual needs.

Single-limit comparators are tuned to provide very small time delays, but their frequency response characteristics are somewhat limited. To avoid output oscillation, many single-limit comparators also have internal hysteresis circuitry. The thresholds for single-limit comparators are fixed, with some having only one threshold and some having two thresholds.

Single-limit comparator circuit.

Figure 1a shows a basic single-limit comparator. The input signal UIN, i.e., the voltage to be compared, is added to the noninverting input and a reference voltage (threshold level) UR is connected at the inverting input termination. When the input voltage UIN" UR, the output is high UOH.

Figure 1b shows the transmission characteristics.

Single-limit comparator principle Threshold voltage and output waveform.

Figure 3 shows the overtemperature detection protection circuit in an instrument. It operates from a single power supply, 1 4LM339 with an inverting input plus a fixed reference voltage, the value of which depends on R1. The voltage at the inverting terminal is equal to the voltage drop of the thermal element RT.

When the temperature in the machine is below the set value, the "+ terminal voltage" is greater than the "-" terminal voltage, and the uo is a high potential. When the temperature rises above the set value, the voltage of the "-terminal" is greater than the "+" terminal, the comparator is reversed, and the UO output is zero potential, so that the protection circuit operates, and the value of R1 can be adjusted to change the threshold voltage, and the size of the temperature value is set.

Single-limit comparator principle Threshold voltage and output waveform.

Theoretical analysis and calculation of single-limit comparators.

Single-limit comparator principle Threshold voltage and output waveform.

As can be seen from the figure, the inverting input of the integrated op amp is grounded by the resistor R3, so when the input voltage U1 changes, if the potential of the inverting input u = u+=0, the state of the output will change. According to the characteristics of the virtual fault, and by using the superposition theorem, the potential of the inverting input terminal is u =(r2 (r1+r2))u1+(r1 (r1+r2))uref so that u = 0, and the threshold level can be solved by the above equation as ut=u1=-r1 r2uref.

How a single-limit voltage comparator works.

1. The working principle of the voltage comparator is very simple: the potential of the normal phase input terminal is higher than that of the inverting input terminal, and the output level is high; The potential of the inverting input is higher than that of the normal-phase input, and the output is low.

2. When the potential of the reverse input terminal is a fixed value, the forward input terminal is the comparison terminal; When the forward input is fixed, the reverse input is the comparison end. The output level of the comparator conforms to the above law.

Single-limit comparator principle Threshold voltage and output waveform.

Single-limit comparator threshold voltage calculation.

The op amp has two inputs, and the inverting terminal is grounded, then the potential is 0, then only the inverting terminal is the input terminal. When up un, the op amp outputs +uom, and when up un, the op amp outputs -uom, then, un is 0, so it is a 0 comparator, and the threshold voltage is 0v