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petra electrical components are surge absorbers/varistor assemblies. Due to their nonlinear resistance change with voltage, they exhibit symmetry in both directions (positive and negative). They respond to abnormal voltages on the line, absorbing most of the surge/lightning energy, while suppressing the abnormal voltage to a safe range, thereby improving the safety and stability of the circuit. In the standby state, the surge absorber (varistor) has very high impedance (several megohms) relative to the protected electronic components and does not affect the characteristics of the original design circuit. However, when an instantaneous surge voltage appears (exceeding the breakdown voltage of the surge absorber), the impedance of the surge absorber drops low (only a few ohms), causing a short circuit in the line, thus protecting electronic products or more expensive components.

petra electrical component characteristics

(1) Volt-ampere characteristics: When a forward voltage is applied to the diode, if the voltage value is small, the current is extremely small; when the voltage exceeds a certain value, the current begins to increase exponentially. This is usually called the turn-on voltage of the diode. The diode is in a fully conductive state, and this voltage is usually called the conduction voltage of the diode. For germanium diodes, when a reverse voltage is applied to the diode, if the voltage value is small, the current is extremely small, and its current value is the reverse saturation current. When the reverse voltage exceeds a certain value, the current increases sharply, which is called reverse breakdown, and this voltage is called the reverse breakdown voltage of the diode. The breakdown voltage values of different models of diodes vary greatly, from tens of volts to thousands of volts. (2) Forward characteristics: When a forward voltage is applied, in the initial part of the forward characteristics, the forward voltage is very small and insufficient to overcome the blocking effect of the electric field within the PN junction. The forward current is almost zero, and this section is called the dead zone. This forward voltage that cannot make the diode conduct is called the dead zone voltage. When the forward voltage is greater than the dead zone voltage, the electric field within the PN junction is overcome, the diode conducts in the forward direction, and the current rises rapidly as the voltage increases. Within the normal operating current range, the terminal voltage of the diode during conduction remains almost constant; this voltage is called the forward voltage of the diode. When the forward voltage across the diode exceeds a certain value, the internal electric field is quickly weakened, the characteristic current grows rapidly, and the diode conducts in the forward direction. This is called the threshold voltage or threshold voltage. (3) Reverse characteristics: When the applied reverse voltage does not exceed a certain range, the current flowing through the diode is the reverse current formed by the drift motion of minority carriers. Since the reverse current is very small, the diode is in the cutoff state. This reverse current is also called reverse saturation current or leakage current. The reverse saturation current of the diode is greatly affected by temperature. Generally, the reverse current of silicon tubes is much smaller than that of germanium tubes. The reverse saturation current of low-power silicon tubes is in the order of nA, and that of low-power germanium tubes is in the order of μA. When the temperature rises, the semiconductor is heated and excited, the number of minority carriers increases, and the reverse saturation current also increases. (4) Breakdown characteristics: When the applied reverse voltage exceeds a certain value, the reverse current will suddenly increase. This phenomenon is called electrical breakdown. The critical voltage causing electrical breakdown is called the diode reverse breakdown voltage. During electrical breakdown, the diode loses its unidirectional conductivity. If the diode does not overheat due to electrical breakdown, the unidirectional conductivity will not necessarily be permanently destroyed. After removing the applied voltage, its performance can still be recovered; otherwise, the diode will be damaged. Therefore, excessive reverse voltage applied to the diode should be avoided during use. Reverse breakdown is divided into two types according to the mechanism: Zener breakdown and avalanche breakdown. In the case of high doping concentration, because the width of the barrier region is very small, when the reverse voltage is large, the covalent bond structure in the barrier region is destroyed, causing valence electrons to break free from covalent bonds and generate electron-hole pairs, resulting in a sharp increase in current. This breakdown is called Zener breakdown. If the doping concentration is low and the barrier region is wide, Zener breakdown is not easy to occur. Another type of breakdown is avalanche breakdown. When the reverse voltage increases to a large value, the external electric field accelerates the electron drift speed, causing collisions with valence electrons in covalent bonds, knocking valence electrons out of covalent bonds and generating new electron-hole pairs. The newly generated electron-hole pairs are accelerated by the electric field and knock out other valence electrons, causing an avalanche increase in carriers and a sharp increase in current. This breakdown is called avalanche breakdown. Regardless of the type of breakdown, if the current is not limited, it may cause permanent damage to the PN junction. (5) Reverse current: Reverse current refers to the current flowing through the diode when the diode is at room temperature and under the maximum reverse voltage. The smaller the reverse current, the better the unidirectional conductivity of the tube. It is worth noting that reverse current is closely related to temperature; the reverse current doubles. Therefore, silicon diodes have better stability at high temperatures than germanium diodes. (6) Dynamic resistance: The ratio of the change in voltage to the corresponding change in current near the static operating point of the diode characteristic curve. (7) Voltage temperature coefficient: The voltage temperature coefficient refers to the relative change in stable voltage for every one degree Celsius increase in temperature. (8) Maximum operating frequency: The maximum operating frequency is the upper limit frequency for diode operation. Since the diode, like the PN junction, has junction capacitance composed of barrier capacitance, the value of the maximum operating frequency mainly depends on the size of the PN junction capacitance. If this value is exceeded, the unidirectional conductivity will be affected. (9) Maximum rectified current: The maximum rectified current refers to the maximum allowable forward average current value when the diode operates continuously for a long time. Its value is related to the PN junction area and external heat dissipation conditions. Because current passing through the tube causes the core to heat up and the temperature to rise, if the temperature exceeds the allowable limit, the core will overheat and be damaged. Therefore, under specified heat dissipation conditions, the diode should not exceed the maximum rectified current value during use.(10) Maximum reverse working voltage: When the reverse voltage applied across the diode reaches a certain value, the tube will break down and lose its unidirectional conductivity. To ensure safe use, the maximum reverse working voltage value is specified.

petra electrical component parameters

1. Nominal varistor voltage: Refers to the voltage value across the varistor when a pulse current of specified duration passes through it. 2. Voltage ratio: Refers to the ratio of the voltage value generated by the current of the varistor to the voltage value generated by the current of the varistor. 3. Maximum clamping voltage: The peak voltage across the varistor under the maximum pulse peak current Ip that the varistor can withstand and under the specified waveform. 4. Residual voltage ratio: When the current passing through the varistor is a certain value, the voltage generated across it is called the residual voltage for this current value. The residual voltage ratio is the ratio of the residual voltage to the nominal voltage. 5. Surge current capacity: Surge current capacity, also known as surge current, refers to the maximum pulse current value allowed to pass through the varistor under specified conditions. 6. Leakage current: Leakage current, also known as standby current, refers to the current flowing through the varistor at the specified temperature and maximum DC voltage. 7. Voltage temperature coefficient: Refers to the rate of change of the nominal voltage of the varistor within the specified temperature range, i.e., the relative change in voltage across the varistor when the temperature changes while the current passing through the varistor remains constant. 8. Current temperature coefficient: Refers to the relative change in the current flowing through the varistor when the temperature changes while the voltage across the varistor remains constant. 9. Voltage nonlinearity coefficient: Refers to the ratio of the static resistance value to the dynamic resistance value of the varistor under a given applied voltage. 10. Insulation resistance: Refers to the resistance value between the lead wires of the varistor and the insulating surface of the resistor body. 11. Static capacitance: Refers to the inherent capacitance of the varistor itself. 12. Rated power: The maximum power that causes a change in varistor voltage when operating at a specific ambient temperature. 16. Maximum impulse current: The maximum impulse current that causes a change in varistor voltage when the varistor is impacted by a specific pulse current once or twice.

petra electrical component composition

A diode is composed of a PN junction with corresponding electrode leads and package casing. Using different doping processes and diffusion, P-type semiconductors and N-type semiconductors are fabricated on the same semiconductor substrate (usually silicon or germanium). A space charge region, called the PN junction, is formed at their interface. The electrode led out from the P region is called the anode, and the electrode led out from the N region is called the cathode. Due to the unidirectional conductivity of the PN junction, when the diode conducts, the current flows from the anode through the interior of the tube to the cathode. The diode has two electrodes: the electrode led out from the P region is the positive pole, also called the anode; the electrode led out from the N region is the negative pole, also called the cathode.

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