On sometimes the low pressure power line’s transient voltage peak-to-peak value can achieve the nominal voltage many times. This kind of situation requests to the equipment protection to prevent some people frequently to use not the suitable power level. Prevents the sensitive electric circuit overvoltage the commonly used method is increases inlays the position electric circuit parallel. Before the fuse or other current limiting component are in these to inlay the position electric circuit’s high energy absorbancy. Because other situations install or the replacement fuse, the working conditions with difficulty cannot approach or need the non-stop run to request the use high pressure series protection circuit (, but is not inlays position electric circuit parallel). Shown in Figure 1 the series protection circuit to use series connected high-pressured N trench MOSFET power switch Q1 and a fast overvoltage detector closes the power switch. The power switch and series power supply rectifier D1 can prevent in the load to appear reaches as high as ±500V the transient high pressure and the continual overvoltage.
Figure 1, this electric circuit may prevent with the right side two termination load not to appear with the left side two termination power source transient overvoltage and the transient high voltage.
In this kind provides the 1A load current with the 12V nominal voltage power line in the electric circuit, high-end switch driver IC1 to the power switch which puts through completely provides the bias. You may through change D1 and Q1 enhance the most high loading electric current. In order to prevent presents the very low supply voltage, IC1 contains one when the supply voltage is higher than 10V can work undervoltage locking circuit. In order to prevent to present the pressure, this electric circuit uses one to be composed, the non-bias electric current, 50 nanosecond overvoltage detectors by 3 transistors, when this detector in the input voltage achieves about 20V the trigger action. This time, Q4 fast short-circuits supply voltage’s electronics grid to the place, closes the power source forcefully. Elevates the overvoltage first causes the zener diode D2 breakover, D2 to inlay the IC both sides voltage the position to protect about 18V IC. The zener electric current winds through 2.2kΩ the resistor, produces one to cause the Q2 breakover the bias voltage. The Q2 breakover initiates a series of fast movements: The Q3 breakover, causes the Q4 breakover, also causes the Q1 grid capacity rapid discharge to cause Q1 to cut off.
Figure 2, adds to shown in Figure 1 on electric circuit’s VIN 150V transient voltage not to affect nearly to VOUT.
You may confirm this electric circuit’s performance like this: This electric circuit outputs the 1A electric current when the 12V supply voltage, on the supply voltage adds a 150V transient voltage (Figure 2). The transient voltage power source’s internal impedance for 1Ω, adds the voltage the rising time is 1ms. This electric circuit when normal work absorbs the 20mA electric current, 3mA by overvoltage locking, the voltage survey divider is absorbed, 17mA is absorbed by IC1. If your design needs to work under the hot conditions, then please note IC1 the grid current output to be opposite is limited. You when carry on the high temperature design calculation, needs to pay attention to other circuit element to produce closely leaks the electric current.
