Characteristic parameters of diode

characteristic parameter

The technical indicators used to indicate the performance and applicability of diodes are called diode parameters, and different types of diodes have different characteristic parameters.

Volt ampere characteristic

A diode has unidirectional conductivity and its volt ampere characteristic curve.

When a forward voltage is applied to a diode, the current is extremely small when the voltage value is low; When the voltage exceeds 0.6V, the current begins to increase exponentially, which is commonly referred to as the turn-on voltage of the diode;

When the voltage reaches about 0.7V, the diode is in a fully conductive state, usually referred to as the conduction voltage of the diode, represented by the symbol UD.

For germanium diodes, the turn-on voltage is 0.2V and the conduction voltage UD is approximately 0.3V. When a reverse voltage is applied to a diode, the current is extremely small when the voltage value is low, and its current value is the reverse saturation current IS.

When the reverse voltage exceeds a certain value, the current begins to increase sharply, which is called reverse breakdown. This voltage is called the reverse breakdown voltage of the diode and is represented by the symbol UBR. Different types of diodes

The breakdown voltage UBR value varies greatly, ranging from tens of volts to several thousand volts.

Positive characteristics

When a forward voltage is applied, at the beginning of the forward characteristic, the forward voltage is very small and not enough to overcome the blocking effect of the electric field inside the PN junction. The forward current is almost zero, and this section is called the dead zone. This is not

The forward voltage that can make a diode conduct is called the dead zone voltage.

When the forward voltage is greater than the dead zone voltage, the electric field inside the PN junction is overcome, the diode conducts in the forward direction, and the current rapidly increases with the increase of voltage. Within the normal range of current usage, the diode conducts when conducting

The terminal voltage of the diode remains almost constant, and 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 increases rapidly, and the diode conducts in the forward direction. It is called threshold voltage or threshold voltage, and the silicon transistor is about 0.5V,

The germanium diode is about 0.1V. The forward conduction voltage drop of silicon diodes is about 0.6~0.8V, and the forward conduction voltage drop of germanium diodes is about 0.2~0.3V.

Reverse characteristic

When the applied reverse voltage does not exceed a certain range, the current passing through the diode is the reverse current formed by the drift motion of minority carriers. Due to the small reverse current, the diode is in a cut-off state. This anti

The reverse saturation current, also known as leakage current, of a diode is greatly affected by temperature.

The reverse current of a typical silicon transistor is much smaller than that of a germanium transistor. The reverse saturation current of a low-power silicon transistor is in the order of nA, while that of a low-power germanium transistor is in the order of μ A. When the temperature rises, the semiconductor is excited by heat, and a small amount of current is carried

As the number of subunits increases, the reverse saturation current also increases.

breakdown characteristics

When the applied reverse voltage exceeds a certain value, the reverse current will suddenly increase, which is called electrical breakdown. The critical voltage that causes electrical breakdown is called the diode reverse breakdown voltage. Diode loss during electrical breakdown

Remove unidirectional conductivity. If the diode does not overheat due to electrical breakdown, its unidirectional conductivity may not be permanently destroyed. Its performance can still be restored after removing the applied voltage, otherwise the diode will be damaged

It's broken. Therefore, excessive reverse voltage applied to the diode should be avoided during use.

Reverse breakdown can be divided into two types based on the mechanism: Zener breakdown and Avalanche breakdown. In the case of high doping concentration, due to the small width of the barrier region and the high reverse voltage, the covalent bond structure within the barrier region is disrupted,

The breakdown that causes valence electrons to break free from covalent bonds, resulting in electron hole pairs and a sharp increase in current, is called Zener breakdown.

If the doping concentration is low and the width of the barrier region is wide, it is not easy to cause Zener breakdown.

Another type of breakdown is avalanche breakdown. When the reverse voltage increases to a large value, the applied electric field accelerates the electron drift speed, causing it to collide with the valence electrons in the covalent bond, resulting in the valence electrons being knocked out of the covalent bond

New electron hole pairs. The newly generated electron hole pairs are accelerated by an electric field and collide with other valence electrons, causing an avalanche like increase in charge carriers and a sharp increase in current. This type of breakdown is called avalanche breakdown. Regardless of the type of breakdown,

If the current is not restricted, it may cause permanent damage to the PN junction.

Reverse current

Reverse current refers to the reverse current flowing through a diode at room temperature (25 ℃) and the highest reverse voltage. The smaller the reverse current, the better the unidirectional conductivity of the diode. It is worth noting that the reverse current

It is closely related to temperature, and for every 10 ℃ increase in temperature, the reverse current doubles. For example, if the reverse current of a 2AP1 germanium diode is 250 μ A at 25 ℃ and the temperature rises to 35 ℃, the reverse current will increase

Rising to 500 μ A, and so on, at 75 ℃, its reverse current has reached 8mA, not only losing its unidirectional conductivity, but also causing the diode to overheat and be damaged. For example, 2CP10 silicon diode, reverse current at 25 ℃

The current is only 5 μ A, and when the temperature rises to 75 ℃, the reverse current is only 160 μ A. Therefore, silicon diodes have better stability than germanium diodes at high temperatures.

Dynamic resistance

The ratio of the change in voltage near the static operating point of the diode characteristic curve to the corresponding change in current.

Voltage temperature coefficient

The voltage temperature coefficient refers to the relative change in stable voltage for every one degree Celsius increase in temperature.

Maximum operating frequency

The maximum operating frequency is the upper limit frequency of diode operation. Because diodes, like PN junctions, have a junction capacitance composed of barrier capacitors. So the maximum operating frequency mainly depends on the size of the PN junction capacitance. If it exceeds

This value will affect the unidirectional conductivity.

Maximum rectified current

The maximum rectified current refers to the maximum forward average current allowed to pass through a diode during long-term continuous operation, which is related to the PN junction area and external heat dissipation conditions. Because when current passes through the diode, it causes the core to heat up and warm up

When the temperature rises and exceeds the allowable limit (around 141 ℃ for silicon diodes and around 90 ℃ for germanium diodes), it will cause the chip to overheat and be damaged. So under the specified heat dissipation conditions, do not exceed the maximum limit of the diode during use

Rectified current value.

Maximum reverse operating voltage

When the reverse voltage applied across the diode reaches a certain value, it will break down the diode and lose its unidirectional conductivity. In order to ensure safety during use, the maximum reverse working voltage value has been specified.