Chip varistor is a transient surge voltage suppressor, which can protect IC and other circuits at the plate to prevent damage caused by electrostatic discharge ESD, surge and other transient currents. The current application range is from Mobile phones, DC power supplies, uninterruptible power supplies, computers, consumer electronics such as digital audio / video equipment, video games, digital cameras and laptops and smartphones.
Transient surge voltage is caused by lightning, electromagnetic pulses, spark discharges or electrostatic discharge, and it is found in almost every AC and DC electronic circuit. For the above surge voltage, previous circuit designers used resistors, capacitors, inductive elements, zinc oxide varistor and Zener diodes to protect the semiconductor components in the line. A new type of chip varistor developed in recent years can effectively suppress transient surge voltages in integrated circuits. Due to its small lead size, small size, fast response speed, large current capacity, low limiting voltage, and temperature Compared with the traditional lead-type varistor, it can effectively suppress transient surge voltage, so it has obtained IC protection, CMOS, MOSFET devices, automotive electronic circuit protection, I / O protection, etc. Wide application.
The chip varistor is a semi-conductor ceramic element in which electrode layers and semiconductor functional ceramic layers are alternately arranged and sintered in a casting process. Interlayer electrodes are staggered with end electrodes of the element to increase the effective area of the opposite electrode. Therefore, the ability of the component to withstand surge voltage is improved.
The varistor voltage of the chip varistor, that is, the surge response voltage, depends on the thickness between the two electrode layers, and has nothing to do with the thickness of the entire component. The flow capacity of the element is mainly determined by the number of staggered stacks, and it increases with the size of the element.
Basic electrical performance parameters
Varistor characteristics: Chip varistors are voltage-sensitive resistors with symmetrical volt-ampere characteristics. Their resistance value decreases non-linearly with the increase in applied voltage. When the voltage further rises within a certain range, This nonlinear response is more dramatic.
DC working voltage: Under the specified environmental conditions, the maximum DC voltage value that can be continuously applied to ensure the normal operation of the chip varistor is also used as a reference point for measuring leakage current. This voltage is usually less than the varistor voltage of the component.
AC working voltage: Under the specified environmental conditions, the maximum AC voltage value that can be continuously applied to ensure the normal operation of the chip varistor.
Maximum inrush current (peak current Ip): Under the specified pulse waveform (8 / 20us) and the corresponding voltage, the maximum current allowed to ensure the normal operation of the chip varistor. This pulse can be applied from either end of the element.
Maximum surge energy (energy tolerance Es): Under the specified pulse waveform (10 / 1000us), the maximum pulse energy that the chip varistor can withstand during normal operation is guaranteed.
Leakage current (IL): In non-conducting mode, this component has a very high impedance (approximately 1.0E + 9 ohms) and is open circuit in the system. At this time, the leakage current is very low (<5uA at room temperature). Unlike Zener diodes, chip varistors have low leakage current characteristics. At the highest operating temperature, the leakage current does not exceed 50uA.
The varistor voltage: This voltage is the voltage value of the chip varistor from the open state to the on state. The nominal varistor voltage is usually the voltage corresponding to the 1mA DC current.
Limit voltage: Under the specified pulse waveform (8 / 20us) and the corresponding current, the peak voltage generated across the element. It should be noted that the generation of peak voltage and peak current need not be consistent in time.
Capacitance: The capacitance of a component at a specified frequency (1MHZ or 1KHZ) and a bias voltage of 1.0V.
(1) Small size Compared with traditional radial leaded varistor and Zener diode, chip varistor is 1/4 to 1/3 of their volume. For example, the size of 1206 is 3.2mm in length and 1.5mm in width, and the size of 0603 is 1.6mm in length and 0.8mm in width.
(2) Fast response time The response time of traditional radial leaded varistor is generally 10 ~ 50ns. Because chip varistors have no leads and the inductance is almost zero, the response time can reach 0.5 ~ 10ns. With the above optimization, the response time of the chip varistor can reach 0.2ns, and the fast response characteristics can effectively suppress the transient surge, and it can be extended to the application of anti-static discharge and anti-electromagnetic pulse.
(3) Low limit voltage The measurement of the limit voltage is performed under a specified test current and waveform, such as 8 / 20us. The chip varistor can effectively limit the transient surge voltage below the breakdown voltage of the protected component, thereby preventing the component from being damaged by the surge voltage. The chip varistor has a very small impedance due to its special structure. It is only 1 to 10 ohms in the breakdown state. Therefore, the chip varistor can be changed without using a radial leaded varistor. Under the premise of line impedance and varistor installation position, reduce the limiting voltage.
(4) Excellent temperature characteristics The basic electrical properties of the chip varistor are in the temperature range of -55 ~ 125deg.c, which is almost unchanged.
(5) Powerful flow capacity. The special structure makes the multilayer electrode and semiconductor ceramic layer superimposed so that it has a large effective facing current area, so it can achieve a large flow capacity. For example, for the 1206 specification, the peak current can reach 300A.
(6) A wide range of capacitance. The stacking process can be used to design the number of layers of dielectric overprint to obtain the required capacitance. The capacitance can range from 1 to 10,000 pF.