[circuit design] peak voltage and surge current

One 、 Peak voltage Spike Voltage

Voltage spikes are characterized by tens of subtle and hundreds of volts , Caused by lightning stroke or inductive coupling of load step , It belongs to surge voltage . The motor 、 Capacitors and power conversion equipment （ Such as variable speed drive ） It is the main factor causing peak voltage .

Popular said , That is, the system voltage is unstable , Or when you suddenly call , Due to the inductance of electronic components 、 Functions of capacitors and other components , It will cause the instantaneous high voltage in the system that is many times or even several times higher than the normal working voltage , The highest value of this high voltage is the peak voltage .

The voltage spike is Inductive freewheeling Caused by the ：
The inductance that causes the voltage spike may be ： Transformer leakage inductance 、 Line distributed inductance 、 Inductive components in the device equivalent model ;
The current that causes the voltage spike may be ： Topological Current 、 Diode reverse recovery current 、 Improper resonant current, etc .

Reduce voltage spikes

The main measures to reduce voltage spikes are ：
（1） Reduce the inductance that may cause voltage spikes , Such as leakage inductance 、 Wiring inductance, etc ;
（2） Reduce the current that may cause voltage spikes , Such as diode reverse recovery current ;
（3） Transfer the above inductive energy elsewhere .

After taking the above measures, the voltage spike is still unacceptable , Before considering the absorption circuit . Absorption is a technical measure of last resort .

Peak absorption buffer circuit

Simple buffer circuit is right Impulse peak current for , The causes of current spikes are as follows ：
（1） diode （ Including body diode ） Reverse recovery current ;
（2） Charge and discharge current of capacitor . These capacitors may be ： Circuit distributed capacitance 、 Equivalent distributed capacitance of transformer winding 、 Improperly designed absorption capacitor 、 Improperly designed resonant capacitor 、 Capacitance components in the equivalent model of the device .

The basic method of buffering ： On the path of impulse current spikes String in Some kind of inductance , Common in BUCK In circuit .

notes ： Because the series connection of buffer inductors will significantly increase the workload of absorption , Therefore, the buffer circuit generally needs to be used with the absorption circuit ; The buffer circuit delays the impulse of conduction current , It can realize a certain degree of soft opening （ZIS）.

Peak voltage Absorption circuit There are three main design schemes ：
（1） Using zener diode and ultrafast recovery diode （SRD） Form a zener clamping circuit ;
（2） It is composed of resistance capacitance element and ultrafast recovery diode R、C、SRD Soft clamping circuit ;
（3） It is composed of resistance and capacitance elements RC Buffer absorption circuit .

In the switching power supply circuit , Usually through the regulator 7805 after , Add a small ceramic chip capacitor next to the large electrolytic capacitor , Small capacitance filters out high dV/dt Peak voltage .

Two 、 Surge current Surge Current

The circuit is being struck by lightning and connected 、 Switching off inductive loads or large loads often produces high operating overvoltages , This instantaneous overvoltage （ Or overcurrent ） be called Surge voltage （ Or surge current ）, It is a kind of transient interference . As mentioned above , Peak voltage is also a kind of surge voltage .

In the usual sense , Surge current refers to the moment when the power is turned on , Peak current flowing into the power supply . because The input filter capacitor charges quickly , Therefore, the peak current is much larger than the steady-state input current .

The hazards caused by surge mainly include ：
（1） Data loss in memory
（2） I/O Interface circuit reset , Cause the control process to be interrupted
（3） Components on the circuit board are damaged
（4） The preset calibration value drifts
（5） The program flies 、 System deadlock
（6） Frequency converter 、 The input rectifier module of DC motor driver, etc. fails
（7） The controller sends an incorrect command , Cause system malfunction

Surge protective device

Surge protective device （Surge Protection Device, SPD） It is used to limit transient overvoltage and discharge corresponding transient overcurrent , Device for protecting the safety of electronic and electrical equipment , Also known as surge protector （ Or lightning arrester 、 Lightning protector 、 Lightning arrester, etc ）. It should contain at least one nonlinear element . Surge protector is actually an equipotential connector .

Linear surge suppressor IC

LT4363 High voltage surge suppressor ：

Under normal operating conditions , An external N Ditch MOSFET Driven to all pass , And act as a transmission device with a very small voltage drop . If the output voltage rises above FB The voltage stabilizing value set by the resistance voltage divider on the pin ,MOSFET Just adjust OUT The voltage on the pin , Thus, the load circuit can continue to operate during the transient event .

SNS and OUT Optional resistors between pins are used to control overcurrent events , Current limiting loop control MOSFET Grid voltage on , To limit the detection voltage at both ends of the resistor to 50mV.

Whether over-voltage or over-current events will start a current source to connect to TMR Pin capacitor charging . The charging current is related to the voltage difference between input and output , In order to shorten the timer cycle with the increasingly serious fault , Thus ensuring MOSFET Keep within its safe working area .

---

Reference link

1. Peak voltage
2. Baidu Encyclopedia - Surge voltage
3. Protect against voltage surges 、 Spike and ripple measures
4. Absorption buffer circuit of switching power supply