Structure, principle and function of fast recovery diode

Source: Network Organization Posted in : 2021-09-11 16:55:14

 Overview of Fast Recovery Diode
    Fast Recovery Diode (FRD for short) is a kind of fast recovery diode (FRD) with good switching characteristics and short reverse recovery time. It is mainly used in switching power supplies, PWM pulse width modulators, frequency converters and other electronic circuits, as high-frequency rectifier diodes, freewheeling diodes or damping diodes.
    Fast recovery diodes use gold doping, simple diffusion and other processes in the manufacturing process, which can achieve higher switching speed and higher withstand voltage. At present, fast recovery diodes are mainly used as rectifier components in inverter power supplies.
    Fast recovery diode structure
    The internal structure of fast recovery diode is different from ordinary pn junction diode, it belongs to PIN junction diode, that is, in P-type silicon material A base region I is added between the N-type silicon material to form a PIN silicon wafer.
    Since the main active region of the PD is the barrier region, the sensitivity can be improved by widening the barrier region. The p-i-n junction fast recovery diode actually artificially extends the width of the barrier region of the p-n junction, that is, a wider intrinsic semiconductor (i) layer is used to replace the barrier region and becomes a p-i-n junction.
    The effective region of the p-i-n junction fast recovery diode is mainly the i-type layer (barrier region) with an electric field, so the effective region for generating photogenerated carriers increases, and the influence of diffusion weakened, and the junction capacitance is also greatly reduced, so the sensitivity and response speed of its light detection have been greatly improved.
    The working principle of the fast recovery diode
    The working principle of the fast recovery diode
    The internal structure of the fast recovery diode is in P A base region I is added between the N-type silicon material and the N-type silicon material to form a PIN silicon wafer. Because the base region is very thin, the reverse recovery charge is very small, which not only greatly reduces the TRR value, but also reduces the transient forward voltage drop, so that the tube can withstand a high reverse working voltage.
    The reverse recovery time of fast recovery diodes is generally hundreds of nanoseconds, the forward voltage drop is about 0.6V, the forward current is several amperes to several thousand amperes, and the reverse peak voltage can be up to several hundred to several thousand volts. The reverse recovery charge of the ultrafast recovery diode is further reduced, enabling its trr to be as low as tens of nanoseconds. Fast recovery and ultra-fast recovery diodes below 20A are mostly packaged in TO-220.
    When a negative voltage (or zero bias voltage) is applied, the fast recovery diode is equivalent to a capacitor resistance; when a positive voltage is applied, the fast recovery diode is equivalent to a small resistance. By changing the structure size and selecting the parameters of the fast recovery diode, the reflection phase (reference phase) of the short-circuit stepped ridge waveguide is the same as the reflection phase of the short-circuit waveguide controlled by the positive voltage PIN tube. It is also required that the reflection phase of the short-circuit waveguide controlled by the fast recovery diode with negative voltage (or 0 bias) is opposite to the standard phase (between -164° and 164°).
    Main Features of Fast Recovery Diode
    , the ultrafast recovery diode can even reach tens of nanoseconds.
    The working principle of the fast recovery diode
    The figure is the waveform diagram of the reverse recovery current. In the figure, IF is the forward current, IRM is the reverse recovery current, and Irr is the reverse recovery current. Usually, Irr=0.1IRM is specified. When t≤t0, forward current I=IF. When t>t0, since the forward voltage on the rectifier suddenly becomes a reverse voltage, the forward current decreases rapidly, and at t=t1, I=0. Then the reverse current IR on the rectifier increases gradually; at t=t2, the reverse recovery current IRM value is reached. After that, under the action of the forward voltage, the reverse current gradually decreases, and reaches the specified value Irr at the time of t=t3. The reverse recovery process from t2 to t3 is similar to the capacitor discharge process. The time interval from t1 to t3 is the reverse recovery time trr.
    The role of fast recovery diodes in DC circuits
    The characteristics of high current resistance. Since it is used as a switch, it is generally required to have a faster switching speed. In addition, proper selection of the characteristics of the freewheeling diode, especially the reverse recovery characteristics, such as reverse recovery time and reverse recovery softness, can significantly reduce the power consumption of switching devices, diodes and other circuit components, and reduce the power consumption caused by the freewheeling current. Voltage spikes, electromagnetic interference caused by diodes, thereby minimizing or even eliminating the absorption circuit.
    Working principle of fast recovery diode
    Generally speaking, the forward voltage drop of fast recovery diode is small, about 0.4V, while ordinary silicon tube is About 0.6V, in order to reduce the loss, a fast recovery diode is used.
    If the reverse breakdown voltage of the fast recovery diode is 40V, it can recover quickly after reverse breakdown; if the reverse breakdown voltage of the fast recovery diode is 1000V, there is no reverse breakdown problem, so this point can be ignored in the DC circuit.