![]() Prot on amplifier series#It can be argued that these diodes are sufficiently robust to handle an overvoltage if the current is limited through a series resistor however, each IC is different and ESD protection topologies can vary considerably. The most popular internal protection circuit employs ESD clamping diodes connected to the supply rails, thereby shunting ESD strikes to the power supplies. Most ICs have some form of internal electrostatic-discharge (ESD) protection. V R curves are found in the diode datasheet. The equation is a good model for the reverse-bias capacitance, as well as the forward-bias capacitance up to approximately half of the built-in potential. Equation 4 assumes V R is negative for a reverse-bias voltage and positive for a forward-bias voltage. T curves are found in the diode datasheet.Įquation 4 models the capacitance of a diode below its built-in potential (approximately 0.7V for silicon):Ĭ j0 is the PN junction capacitance at 0V, Φ 0 is the built-in potential, and M is the grading coefficient, which is unitless and quantifies the abruptness of the P material where it meets the N material. I 0 is the reverse current as specified at temperature T 0. Based on this rule and a reference point, we can use Equation 3 to calculate reverse current relative to temperature: V R curves are found in the diode datasheet.Ī widely accepted rule of thumb states that the reverse current of a PN junction doubles for every 10☌ rise in temperature. Where n can vary roughly from 2 to 4, depending on the manufacturer. Because the volume of the space-charge layer depends on applied reverse voltage, I R is typically modeled by Equation 2: I R is proportional to the volume of the space-charge layer in the PN junction. In practice, however, the reverse current is much higher than I S and is not constant across temperature and reverse-bias voltage. Operational amplifiers are used to illustrate protection methods, although many of the methods are useful for discrete amplifiers as well.Īfter inspecting the diode equation presented in Equation 1, one might assume that a reverse-biased diode draws a reverse current I R equal to I S. This article explains the basics of reverse-biased diodes, discusses several protection strategies, and provides a few solutions for reducing parasitic leakage and capacitance. These diodes exhibit capacitance and leakage current that contribute to distortion and limit bandwidth. Most amplifier overvoltage-protection methods utilize diodes to shunt overvoltage fault current to ground or to the supply rails. ![]() An overvoltage may be induced by human error, such as shorting the amplifier input to a higher supply voltage, or may be inherent to the application, such as a transducer that routinely produces voltages higher than the amplifier supply rails. For amplifier applications that require overvoltage protection (OVP), as well as low distortion, low noise, and high bandwidth, designers must pay careful attention to overvoltage protection design. ![]()
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