Agilent Overvoltage Protection in Power Supplies - Application Note 5989-9395EN c20140722 [4] free download

File name Overvoltage Protection in Power Supplies - Application Note 5989-9395EN c20140722 [4].pdf

Keysight Technologies Overvoltage Protection in Power Supplies Application Note Introduction Overvoltage Crowbar Overvoltage (OVP) is an important security feature in power supplies. An operator error or a component failure in the regulating feedback loop can drive By using this feature, we can protect a power supply's output voltage to many times its preset value. The function of the the device under test (DUT) from a crowbar circuit is to protect the load against this possibility. The circuit ensures higher voltage than the DUT was that the power supply voltage across the load will never exceed a preset limit. designed to handle. OVP is useful in This protection is valuable because of the extreme voltage sensitivity of today's a variety of applications in electronics semiconductor devices. manufacturing and the educational market. The basic elements used in most crowbars are some method of sensing the output voltage, a silicon controlled rectifier (SCR) that will short the output, and a circuit Overvoltage protection is also available that will reliably trigger the SCR within a time period that is brief enough to avoid if required during constant current damage to the load. operation. The constant voltage/ constant current (CV/CC) and The sensing circuit can be a simple bridge or voltage divider network that compares constant voltage/current limit (CV/ the output voltage to the internal crowbar reference voltage. The best trigger circuit CL) automatic crossover circuitry is is the one that turns on the SCR most quickly. The fastest SCR turn-on is ideal for these purposes because it accomplished by a fast rise-time pulse circuit such as a blocking oscillator or allows you to select the maximum safe Schmitt trigger. current or voltage for your particular load device. Keysight Technologies, Inc. E36001 and U8000 series power supplies are short- circuit proof and can operate under any current overload condition indefinitely, without the risk of internal damage. It uses an overvoltage crowbar in which the crowbar circuit is connected across the output terminals. This provides protection against any output overvoltage condition that might occur because of operator error or failure within the power supply or load. This application note explains the architecture of OVP and describes its applications. It discusses what you need to pay attention to when you use this feature. Figure 1. General crowbar overvoltage protection circuit Figure 1 shows the general crowbar overvoltage protection circuit. The circuit compares the output voltage with a reference voltage +V.