The damage to higher integration circuit boards nowadays can cause many unnecessary troubles, and the significance of circuit protection has many aspects. Preventing circuit damage is one of the more important aspects. For example, the usage environment of many car mounted devices is more harsh than that of general electronic products, and they will generate a large instantaneous peak voltage when starting and stopping. At this time, it is necessary to use overvoltage protection components in the power adapter of these electronic devices.
For example, communication equipment is often troubled by surges, which include surge voltage and surge current. They are a type of spike pulse with extremely fast rising speed and short duration, which can instantly exceed the peak value of the device's stable value. This requires the use of a combination of multiple voltage transient and surge protection devices to form a multi-level protection circuit to ensure foolproof operation.
Of course, in addition to preventing accidental circuit damage, it can be seen that the working voltage of semiconductor device ICs is developing towards lower and lower trends. Protecting their circuits can also reduce energy loss, reduce circuit heating, and extend the service life of ICs.
The development of integrated circuits has driven the increasing diversification and complexity of electronic circuit products, resulting in more situations that may harm circuits. Circuit protection has become increasingly important.
Devices required for different circuit protection
Overvoltage protection is already an essential part of the circuit. Overvoltage protection devices are responsible for protecting the circuit from high voltage. The principle of this device is to use the potential difference to achieve the effect of circuit protection. When the voltage in the circuit exceeds the specified value, the internal circuit structure of the overvoltage protection device generates a certain potential difference with the circuit, thereby enabling the circuit to achieve protection through impedance changes.
At the same time, the internal current and voltage protection device of the overvoltage protection device will disconnect the circuit, preventing the current from further flowing to the protected electrical appliance or equipment, achieving the effect of protecting the electrical appliance or equipment.
Typical overvoltage protection devices are varistors and transient suppressors (TVS). Varistors can be said to be the most commonly used overvoltage protection device, with low cost, good effect, and high cost-effectiveness. The ns level response speed enables it to handle overvoltage protection work in the vast majority of cases.
Based on the nonlinear volt ampere characteristics of varistors, under normal circumstances, varistors act as a switch in an open state. When an overvoltage exceeds their rated voltage in a circuit, the resistance value of the varistor rapidly decreases to reduce the impact of overvoltage on subsequent circuits.
The characteristic of TVS is its fast response. When the transient voltage is too high, the TVS diode produces avalanche, causing the instantaneous large current to be diverted from the low resistance path, avoiding circuit damage as a result. Both have their own focuses, and TVS has more advantages in dealing with transient overvoltage impacts.
Overcurrent devices often use various fuses, such as glass tube fuses, chip fuses, and polymer fuses. They are simple to use and have obvious effects. Polymer fuses limit current by increasing resistance and have excellent recoverable characteristics. When used for overcurrent protection, the circuit can automatically return to a conductive state.
Glass tube fuses and chip fuses are directly fusing conductive fuses. Nowadays, there are more and more solutions using eFusion, which directly tracks current and has its unique advantages.
In circuit protection, there are also some electrostatic protection components involved, especially in high integration circuits where ESD protection is not installed. The high-voltage ESD impact generated through interface connections can cause high current peaks to directly flow into the integrated circuit, causing damage. To protect sensitive circuits from electrical overstress faults, the ESD protection diode should be connected to each signal line between the interface connector and the integrated circuit, with different interface speeds corresponding to different capacitance values of the ESD diode.
