In this paper, the reverse recovery behavior of the body diode of a sic mosfet is evaluated. Reverse recovery losses due to bootstrap diode reverse recovery time. Just like a normal pn diode, the body diode of the mosfet will store charge during conduction. During this reverse recovery time, the charge stored in the diffusion capacitance is removed, turning the. Both, reverserecovery charge and current can be reduced significantly.
Modeling and understanding the gate driver circuit. The reverse recovery starts to flow at tt2, and at tt3, the reverse recovery current reaches its peak value irr. We have already discussed about the power diode basic s and power diode structur e in our previous posts. Low reverse recovery charge q rr increases reliability in zero voltage switching topologies ultralow onresistance and gate charge reduce conduction and switching losses. Then we have our reverse recover charge and reverse recovery time, which pertain to the diode characteristics. In halfbridge topologies there is always a finite time during which the body diode conducts due to the dead. The mosfet integral rectifier has a low voltage drop but reverse recovery. Mosfet gate driver circuit toshiba electronic devices. Prr synchronous rectifier mosfet bodydiode reverse recovery power loss psw mosfet switching loss qg total gate charge qrr bodydiode reverse recovery charge q1 control mosfet q2 synchronous rectifier mosfet rdson mosfet draintosource on resistance rg mosfet external discrete gate resistance rgi mosfet. Sic mosfet offers significant advantages over silicon one, in particular the main benefit deriving from the use of sic mosfet when the bidirectional dcdc converter works in boost mode is the strong reduction of reverse recovery charge leading to lower switchinglosses. The forward voltage of the body diode, vsd, decreases with temperature by about 2. New generation mosfets typically have gate resistance in the 1 to 2 ohm range, much less than a mid size gate driver, so most heat ends up in the driver.
The mosfet body diode recovery time trr, recovery charge qrr, and reverse recovery softness factor rrsf play an important role in determining peak voltage spikes and ringing levels. Optimizing mosfet characteristics by adjusting gate drive. Regarding the reverse recovery time trr of the body diode, figure 1. E the lower mosfet switches off and the inductor again forces the current to flow through the body diode, storing reverse recovery charge qrr. Spike of buck converter influenced by reverse recovery current. C 072018 c3m0065100k silicon carbide power mosfet c3m tm mosfet technology nchannel enhancement mode features new c3mtm sic mosfet technology optimized package with separate driver source pin 8mm of creepage distance between drain and source high blocking voltage with low onresistance highspeed switching with low capacitances. When switching from the conducting to the blocking state, a diode or rectifier has stored charge that must first be discharged before the diode blocks reverse current. In this post let us see the dynamic characteristics of the power diode. Pdf the influence of turnoff dead time on the reverserecovery. The ch2 width measurement at the right is a measure of the width of the waveform at the 10% reverse voltage point 20v, which can be interpreted as t rr.
No modulation on hv side prevent sic mosfet from achieving. Power mosfet features low gate charge qg results in simple drive requirement improved gate, avalanche and dynamic dvdt. This discharge takes a finite amount of time known as the reverse recovery time. Diode is employed to eliminate the parasitic ringings between the junction capacitance of and. Freewheeling diode reverse recovery failure modes in igbt applications ieee page 1 of 10 marchapril 2001 freewheeling diode reverse recovery failure modes in igbt applications m. Due to the junction capacitance, there is a capacitive. This loss is divided between the gate driver and the mosfet depending on the impedance ratio of those components. Mosfet body diode reverse recovery page 1 eevblog electronics community forum. High external gate resistance reduces chargedischarge current tofrom the gate.
Additional parasitic capacitance across the gan fet is minimized to less than 1 pf to reduce additional switching losses. The lmg1210 is a 200v, halfbridge mosfet and gallium nitride field effect transistor gan fet driver designed for ultrahigh frequency, highefficiency applications that features adjustable deadtime capability, very small propagation delay, and 3. This document uses ucc27710, tis 620v halfbridge gate driver with interlock to present the. This time is also known as the storage time because it is the time that is taken to sweep out the excess charge, qrr. Typical rectifier response for reverse recovery v f v rmrec v r i f t rr t a b i rmrec i r 0. New fast body diode nchannel mosfets improve reliability. Igbt reverse conduction characteristics hardswitching and. Resulting from reduced gate charge qg, bestinclass reverse recovery charge qrr and improved turn off behavior coolmos cfd7 offers highest efficiency in resonant topologies. The mosfet then turns off and blocks current flow thereafter. Mosfet failure modes in the zerovoltageswitched fullbridge. Freewheeling diode reverse recovery failure modes in igbt. Fredfet is not optimized for reverse recovery like a discrete diode is. Hard commutation of power mosfet infineon technologies.
Electrical characteristics of mosfets body diode idridrp. The silicon mosfet serves as the control unit while the sic jfet provides high voltage blocking in the off state. As part of infineons fast body diode portfolio, this new product series blends all advantages of. For the components shown, this condition persists for about 100msec while the capacitor discharges through the regulator. Key mosfet parameters for motor control applications. A shammas abstractin this paper, reverse recovery failure modes in modern fast power diodes are investigated. New fast body diode nchannel mosfets improve reliability, save energy in soft switching topologies product benefits. So, in switching on the diode charges its internal capacitor in the presence of the two resistors. Therefore, the fastest switching action is determined by the reverse recovery. A pchannel mosfet q1 protects the driver u1 from reversebattery insertion.
How can i calculate the diode reverse recovery losses for. The reverse recovery charge qrr is never released in the circuit. Discrete mosfet gate driver problems all about circuits. The charge required to recover the body diode can be found in the mosfets data sheet, under diode characteristics, labeled qrr. Body diode reverse recovery time the trench power mosfet and the parasitic body diode is shown in fig. Reverse recovery time is the time required for the injected minority carriers to be swept away from the depletion region during turnoff of the diode. The stored energy in the parasitic inductor is 2 2 1 eloop. F after the deadtime interval, the upper mosfet switches on. I account for reverse recovery loss in the conventional way. An internal switch turns the bootstrap diode off when the low side is off, effectively preventing the highside bootstrap from overcharging and minimizing the reverse recovery charge. Power diode switching characteristics reverse recovery. Qoss affects efficiency in the application such as switching power supplies especially driving in. When the high side mosfet qhs is on, net a is high and the qls body diode is reverse biased.
Diode reverse recovery charge electrical engineering. In a boost converter, the source terminal of the mosfet is connected to the circuit ground, which is referred to a lowside mosfet. Parasitic bipolar transistor the layered mosfet structure also forms a parasitic. Thus, substituting a mosfet for the diode provides an immediate improvement in. This type of commutation is the focus of this document. Power dissipation due to reverse recovery can be calculated by computing the average reverse current due tor reverse recovery charge times the reverse voltage across the diode. Reverse recovery charge, current and time eeweb community. A technique for reducing rectifier reverserecovery.
It displays the classis reverse recovery waveform, with a reasonably fast t rr of 154 ns. Sic sbds schottky barrier diodes with breakdown voltage from 600v which far exceeds the upper limit for silicon sbds and up are readily available. Like any conventional silicon diode, body diode reverse recovery charge and time depend on temperature, didt, and current. But it will become forward biased as qhs turned off, entering the dead time moment and the inductor reverses its voltage polarity. Coolmos cfd7 comes with reduced gate charge qg, improved turnoff behavior and a reverse recovery charge qrr of up to 69% lower compared to the. Ecen5817 diode reverse recovery in a boost converter reverse recovery of the diode d in the boost converter shown in fig. An1090d understanding and predicting power mosfet switching behavior. How can i calculate the diode reverse recovery losses for an igbt inverter.
The switching speed depends on the speed at which a gate driver can charge. Electrolytic capacitors are usually not enough for the latter role, thats why c2 is present in. Device ruggedness the ruggedness of power mosfet can be described by the following three major. Igbt reverse conduction characteristics hardswitching and softswitching energy saving products bu july 20. Also, the controlling charge and accordingly the storage time in the mosfet. A diodes reverse recovery characteristics are quantified by three parameters. Diode reverse recovery and its effect on switching losses peter haaf, senior field applications engineer jon harper, market development manager. I take qrr as specified in the data sheet and multiply by the frequency and input voltage for a buck converter or output voltage for a boost converter. During power mosfet turnoff transient, the parasitic body diode is stored minority charge and the stored charge must be removed. Mosfet driver with very low output resistance feeding a. Diode or mosfet data sheets typically specify a reverserecovery time and a reverserecovery charge. Compared to silicon frds fast recovery diodes, sic sbds have much lower reverse recovery current and recovery. Reversecurrent circuitry protection application note.
Low reverserecovery charge, qrr 112 nc soft reverserecovery body diode enables high efficiency in synchronous rectification fast switching speed 100% uil tested this device is pbfree, halogen freebfr free and is rohs compliant description this nchannel mosfet is. The following discusses the reverse recovery process of the body diode, commutation types and definitions, hard commutation test setup, and the key parameter of this subject reverse recovery charge. During this reverse recovery time, the charge stored in the diffusion capacitance is removed, turning the diode off. Wolfspeed c3m0280090j 900v sic mosfet is optimized for highfrequency power applications, including renewable energy inverters. Reverse recovery behavior of the body diode of the sic mosfet. How can i measure the reverse recovery time of power. Diode reverse recovery and its effect on switching losses. Reverse recovery time and recovered charge specified. The area of the body diode is the same as the area of the mosfet or fredfet, whereas the area of a discrete diode for the same function can be much smaller and hence have much lower recovery charge. Irr, trr and qrr are the three main parameters that are used to characterize the diodes reverse recovery behavior, and are typically specified on the. First we have the output charge qoss, which is located under dynamic characteristics. Irr 7 where l pcb is pcb parasitic inductor, and irr is reverse recovery peak current.
Higher reverse recovery charge means higher igbt turnon losses diode has its own recovery losses, as well. Due to the extremely low reverse voltage, the reverse recovery charges might not be swept out before turning. Ciss is the input capacitance, crss is the reverse transfer. Novel 100v power mosfet technology with soft body diode. Note that this power loss will occur in the highside mosfet, as it is the turn on of this device that has to recover the lowsides body diode. Diode is employed to eliminate the parasitic ringings between the junction capacitance. Hard commutation of a mosfet, in short, refers to the condition where the body diode of a mosfet experiences reverse recovery, i. Reverse recovery time an overview sciencedirect topics. The time t rr and the amount of charge q rr required for the reverse recovery current to reach zero during the reverse recovery operation of the body diode under the specified test conditions. Unfortunately, the lower body diode is in reverse recovery, resulting in a large reverse recovery current irr.
Figure 2 shows a simplified circuit featuring the configuration of the high and lowside gate driver and the mosfets half bridge for one phase leg in figure 1. The following schematic shows connections to rohms gate driver ic bm6103fvc with supply. The body diode of a mosfet or even a fredfet is not optimized for reverse recovery. Looking at the diode current curve i d t we see that the diode current is negative for a time period t rr, called the reverse recovery time. You can assume that the diode remains forward biased and that the diode. Spike of buck converter influenced by reverse recovery. An intuitive explanation of the diode reverse recovery phenomenon and its implications. The intrinsic capacitances, resistance, gate charge and the reverse recovery. Diode dvdt capability dvdt the maximum voltage ramp allowed during the reverse recovery time of the diode.
The first waveform shows the results obtained with an on semiconductor 1n4937 diode. Diode switching characteristics reverse recovery characteristics. Sic mosfet performance in a bidirectional dcdc converter. Emv optimized current controlled gate drivers up to 150ma possible. One common issue is that the diode recovery characteristics change as the power stage operating conditions change, especially as the diode forward current varies.
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