High-precision op amps allow system designers to maintain the accuracy of the original signal while conditioning the signal (amplification, filtering, and buffering). When the information is contained in a very small signal, it is essential that the op amp on the signal path has very low DC and AC error performance during operation. The overall system accuracy depends on how accurately the signal path is maintained.
In some applications, it may happen that a voltage other than the supply voltage drives the op amp input—this is called an overvoltage condition. For example, if the op amp is configured with a +15 V positive supply and a −15 V negative supply, the op amp internal ESD whenever the input pin voltage is greater than one diode drop + supply rail voltage (eg ±15.7 V) The protection diode is forward biased and begins to conduct current. Excessive input current for long periods of time (or even short periods of time - if the current is high enough) can damage the op amp. Such damage may cause electrical specifications to deviate from the limits guaranteed by the data sheet and may even cause permanent damage to the op amp. Faced with this possibility, system designers typically add an overvoltage protection (OVP) circuit to the amplifier input. Therefore, it is difficult to introduce an OVP circuit without increasing the error (loss of system accuracy).
How does the overvoltage condition occur?Many different conditions can cause overvoltage conditions. Consider a system where the remote sensor is located in the field—such as liquid flow in the refinery and send the signal through the cable to the data acquisition electronics at another physical location. The first stage of the data acquisition electronic signal path is typically an operational amplifier configured as a buffer or gain amplifier. The input of the op amp is exposed to the outside world and may be affected by an overvoltage event—such as a short circuit caused by cable damage or a misconnection of the cable to the data acquisition electronics.
Similarly, a situation that can result in an overvoltage condition is that the input signal (usually within the amplifier's input voltage range) suddenly receives an external stimulus, causing the transient spike to exceed the op amp's supply voltage.
A third condition that can cause an input overvoltage condition comes from the power-up sequence of the op amp and other components on the signal path. For example, if a signal source (such as a sensor) is powered up before the op amp, the source can output a voltage while the op amp power pin is not powered. This can lead to overvoltage conditions, which can force excessive current to flow through the op amp input and reach ground (unpowered power pin).
Clamp: a classic overvoltage protection technologyFigure 1 shows a common method of OVP (overvoltage protection). When the input signal (VIN) amplitude exceeds one of the supply voltage plus the diode forward voltage, the diode (DOVPP or DOVPN) will be forward biased and current will flow to the supply rail. Excessive current can damage the op amp. In this application, we used the ADA4077, an extremely accurate op amp with a maximum power supply range of 30 V (or ±15 V).
The clamp diodes are 1N5177 Schottky diodes because their forward voltage is equal to approximately 0.4 V, which is lower than the forward voltage of the op amp input electrostatic discharge (ESD) protection diode; therefore, the clamp diode will be before the ESD diode Start to conduct current. The overvoltage protection resistor, ROVP, limits the forward current flowing through the clamp diode to keep it below the maximum current rating to prevent damage from excessive current. The feedback loop resistor RFB is used because any input bias current on the non-inverting input flows through the ROVP to produce an input voltage error—increasing the RFB value eliminates the error because it produces a similar voltage at the inverting input.
Figure 1. Classic clamp circuit for overvoltage protection.
mini pen vape,hot selling vape pen,high quality vape pen,free vape pen,free shipping vape pen
Shenzhen Aierbaita Technology Co., Ltd. , https://www.aierbaitavape.com