A comparator might appear straightforward at first glance. It compares two signal voltages and adjusts its output accordingly—either high or low. But what happens if those two input voltages are extremely close? Even the tiniest bit of noise on the input could cause the output to rapidly switch between high and low logic levels. The simplest solution to this issue is increasing hysteresis.
Hysteresis refers to the system's ability to depend on its prior state. In a comparator, this means setting a higher threshold for the high-side switch while lowering the threshold for the low-side switch. If you think about it, this is fundamentally similar to how a thermostat in an air conditioner operates. Imagine if the thermostat lacked hysteresis—if the temperature fluctuated slightly around the setpoint, the air conditioner would turn on and off repeatedly within seconds. That would not only create unnecessary noise but also reduce energy efficiency and put extra strain on the system. Adding hysteresis ensures smoother operation.
Now, some comparators already come with built-in hysteresis, often just a few millivolts. While this may suffice for certain applications, there are cases where you need additional external hysteresis. For these scenarios, you’ll want to implement a setup that supports adjustable rise and fall thresholds tailored to your needs.
Hysteresis is achieved through positive feedback in the comparator’s circuitry—a rare instance where positive feedback actually improves performance rather than causing instability. Unlike traditional thresholding, hysteresis doesn’t rely on a single fixed point. Instead, it introduces distinct rising and falling thresholds, ensuring the output remains stable (either high or low) even when the input signal hovers near the reference voltage. This design is commonly referred to as a Schmitt trigger.
Take, for example, the ON Semiconductor TL331 configured as an inverting Schmitt trigger. The TL331 is a low-power, single-channel comparator with no internal hysteresis. By using a resistor divider formed by R1 and R2, you can establish both the reference voltage at the non-inverting pin and the switching threshold voltage at the output. Given that this is an open-collector comparator, it’s essential to attach a pull-up resistor to the output. To boost hysteresis via positive feedback, introduce a feedback resistor. Ideally, choose a feedback resistor value of at least 100 KΩ.
In this inverting configuration, whenever the input signal falls below the threshold, the output goes high, pulling the threshold voltage upward through the feedback resistor. As a result, minor fluctuations in the input signal won’t affect the comparator output unless the input voltage surpasses a higher, adjusted rising threshold. Once the input crosses that threshold, the output switches low, pulling the threshold voltage down through the feedback resistor to maintain a low output until the input drops below the regulated lower threshold.
The non-inverting configuration operates similarly but with a key difference: the threshold voltage determined by the resistor divider remains constant regardless of the feedback loop. Here, the feedback adjusts the input signal at the non-inverting node instead.
Below is a visual representation of this setup:
*Figure 1: Comparator Configuration for Inverting Schmitt Trigger*
In this arrangement, when the input signal is low, the output follows suit, dragging the non-inverting node voltage down. When the input rises sufficiently to push the non-inverting node above the reference voltage, the output flips high, elevating the non-inverting node further.
Both configurations demonstrate that adding hysteresis requires minimal external components—just one or two resistors whose values can be fine-tuned based on the specific application requirements. When applied correctly, increasing hysteresis offers a practical method to mitigate issues caused by input signal noise, especially when the voltages at the input pins tend to converge for extended periods.
By integrating hysteresis into your comparator design, you ensure reliable operation while minimizing sensitivity to environmental factors like noise. This small yet impactful tweak can significantly enhance the robustness and stability of your circuit.
Hydraulic pump
Hydraulic motor
The hydraulic cylinder
Hydraulic valve
The supercharger
All components used in hydraulic systems.
Can be divided into:
Power components, such as hydraulic pumps.
Control components, such as relief valve, sequence valve, directional valve, etc.
Actuators, such as hydraulic motors, hydraulic cylinders.
Auxiliary parts, such as: fuel tank, pipeline, etc.
Hydraulic system: is composed of a variety of hydraulic components, auxiliary components, the components are distributed in each part of the equipment, they are organically connected by the pipeline, pipe joints, connectors and other parts can independently complete a variety of working conditions of the system.
Hydraulic Precision Parts,Steel Hydraulic Hose Fitting,Stainless Steel Hydraulic Hose Fitting,Carbon Steel Hydraulic Hose Fitting
Tianhui Machine Co.,Ltd , https://www.thcastings.com