High voltage surge stoppers ensure reliable operation during power surges: Page 2 of 5

March 28, 2012 //By Alison Steer, Linear Technology Corp.
High voltage surge stoppers ensure reliable operation during power surges
In automotive, industrial and avionic applications, high voltage power supply spikes with durations ranging from a few microseconds to hundreds of milliseconds are commonly encountered. The electronics within these systems must not only survive transient voltage spikes, but in many cases also operate reliably throughout the event. Recent surge stopper designs help to maintain these devices in the safe zone.
first released the LT4356 Surge Stopper in 2007 to address these challenges. The LT4356 operates from 4V to 80V and provides -60V of reverse protection on the input pins. During an overvoltage transient, the output clamps to a user-defined voltage, defined by the resistor divider network on the output. The LT4356 is capable of suppressing surges >100V as long as a resistor and TVS diode is used at the input to avoid exceeding the absolute maximum operating voltage (see Figure 2). Because the current sensing circuitry is upstream of the MOSFET, overcurrent protection must be disabled if the device is used to protect from transients above 100V.

Figure 2: LT4356 Withstands 150V at Input

Two new devices have recently been added to Linear Technology's surge stopper family, the LTC4366 High Voltage Floating Surge Stopper and the LT4363 High Voltage Surge Stopper with Overcurrent Protection. The LTC4366 is designed for systems that continuously operate at voltages above 100V, or where protection from extremely high voltage transients (>200V) is required (see Figure 3).

Figure 3: LTC4366 High Voltage Floating Surge Stopper

The LT4363 is a second generation version of the popular LT4356, moving the overcurrent sensing downstream of the pass FET so that it provides overcurrent protection while withstanding voltage transients greater than 100V (Figure 4).

However, like the LT4356, the absolute maximum rating for the LT4363 is 100V, so the input must be protected from high voltage transients >100V using a resistor and TVS diode as shown in Figure 3. In contrast, the LTC4366 uses a floating topology; external voltage dropping resistors allow it to float up with the supply, isolating it from the high voltage surge. The upper limit on the operating voltage is only limited by the availability of the high valued resistors and sizing the MOSFET to handle the power dissipated during voltage regulation.

Figure 4: LT4363 High Voltage Surge Stopper with Overcurrent Protection


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