Application Note: CPWR-AN3, Rev. B Hard-Switched Silicon s? Cut Switching Losses in Half Silicon Carbide Schottky s by Jim Richmond Replacing the Si Ultrafast soft-recovery diode used as the freewheeling component in hard-switched applications a Silicon Carbide (SiC) Schottky diode reduces the switching losses in the diode by % the switching losses in the by %. Introduction The Silicon, which combines the output switching characteristics of a bipolar transistor the ease of control of a MOSFET, has become the power switch of choice for hard-switched, high-voltage (greater than V) high-power (greater than watts) applications. Typical applications include motor-control inverters, uninterruptible power supplies, welding equipment switched-mode power supplies (SMPS). The ever-increasing dem in power electronics for improved efficiency, reduced cooling, decreased size weight, stricter EMI/RFI power quality requirements present new challenges to the designer. All of these requirements are greatly influenced by the high transient losses during turn-on when switching the inductive load found in hard-switched topologies. The reverse-recovery present at turn-off of the silicon freewheeling diode directly affects this turn-on transient. To compound matters, the diode reverse-recovery increases increasing operating temperature, diode, di/dt. The diode reverse-recovery the switching losses can be drastically reduced by replacing the silicon freewheeling PiN diode a SiC Schottky barrier diode (SBD). Due to the material properties of silicon, silicon Schottky diodes are not possible in the -plus volt range. SiC Schottky s The is commercially available -volt -volt ratings. The -volt diodes are available -, -, -, -, -amp ratings. The -volt diodes are available - -amp ratings. The main advantage of a high-voltage lies in its superior dynamic performance. The reverse-recovery charge in the is extremely low is the result of junction capacitance, not stored charge. Furthermore, unlike the Si PiN diode, it is independent of di/dt, forward temperature. The maximum junction temperature of 7 C in the represents the actual useable temperature. The ultralow Q rr in s results in reduced switching losses in a typical hard-switched based application. This lowers the case temperature of the, improving the system efficiency possibly allowing for a reduction in size of the silicon. In order to measure the benefit of these high-performance rectifiers, an inductive switching test circuit was used to measure the diode switching losses. This allowed for a switching-loss comparison between an Ultrafast soft-recovery silicon diode the Cree Zero Recovery SBD, as well as the impact their reverse recovery has on the switching losses of an. Switching Measurement shows the inductive test circuit used for making the switching measurements. During operation, a double pulse is used to drive the gate. For the -volt device testing, a -ohm gate drive resistor is used to set the di/dt to 7 A/µs. A -ohm resistor was used the -volt devices for a di/dt of A/µs. At time T, the is turned on through the inductor ramps up until it reaches the desired test at time T. At time T, the is turned off the inductor is transferred to the diode. The turn-off losses diode turn-on losses are measured at the T transition. The inductor continues to flow through the diode until the is turned back on at time T3. Now inductor is transferred from the diode back to the. The turn-on losses diode turn-off losses are measured at the T3 transition. Subject to change out notice.
volt devices for a di/dt of A/µs. diode (similar to what would be copackaged in a A ultrafast ) a A, V, along the switching losses of a A, V Silicon. The losses were measured at a voltage of V of A. 9 7 3 - - - - - - - - 3. Inductive Test Circuit operating waveforms. At time T, the is turned on through the inductor ramps up until it reaches the desired test at time T. At time T, the is turned off the : Inductive test circuit operating waveforms. inductor is transferred to the diode. -Volt The Switching turn-off Comparison losses diode turn-on losses are measured at the T transition. Switching parameters The inductor were measured continues for a -A, to-v flow Ultrafast soft-recovery through thesilicon diode diode until(similar the to what is turned would be co-packaged in a -A Ultrafast ) a -A, - back on at time T3. Now inductor is V, along the switching losses of a -A, - V silicon. The losses were measured at a voltage of V of A. CPWR-AN3, Rev A Page /9 shows the turn-off voltage, instantaneous power measured at a junction temperature of C of the Si Ultrafast diode. This shows a peak reverse-recovery of 3 amps, a recovery time of ns, a peak instantaneous power of 7 kw. Also shown is the -volt overshoot caused by the high di/dt during the reverse-recovery snap-off. Copyright 3- All rights reserved. The information in this document is subject to change out notice. Cree CPWR-AN3, Rev. B - -. : -volt Si Si Ultrafast diode turn-off off voltage, voltage, instantaneous instantaneous power at power C. at C. shows the turn-off voltage, instantaneous power measured at a junction temperature of C of the Si ultrafast diode. This shows a peak reverse power is due to the only having to recovery of 3 amps, a recovery dissipate a small capacitive charge, which time of ns, a peak instantaneous happens while the diode voltage is low. The power of 7 kw. Also shown is the volt voltage overshoot seen in the Si diode is overshoot caused by the high di/dt during completely eliminated the. the reverse recovery snap-off. 3 is the turn-off waveforms for the at C. This shows a peak reverse recovery of amps, a reduction of, a recovery time of 33 ns, a reduction of 7%, a peak instantaneous power of. kw, a reduction of 9. The drastic reduction in switching power is due to the having to dissipate only a small capacitive charge, which happens while the diode voltage is low. The voltage overshoot seen in the Si diode is completely eliminated the. 9 3 is the turn-off waveforms for the SiC 7 SBD at C. This shows a peak reverse recovery of amps, a reduction of, a recovery time of 33 ns, a reduction of 7% a peak 3 - instantaneous power of. kw, a reduction - of 9. The drastic reduction in switching - - - - 3 - - 3. 3: -volt SiC turn-off SBD turn-off voltage, voltage, instantaneous instantaneous power at C. power at C. 7 3 3 3 Silicon Drive Durham, NC 773 USA Tel: +.99.33.3 Fax: +.99.33.77 - pea diss freq cau a m F curr at a IGB SBD % pow freq are resu 7 3 - - Figu
ng to hich. The de is. ltage, C. 3 3 - afast eous tage, 7 3 - - peak instantaneous power of kw frequency - -oscillations - - in the voltage caused when the Si Time diode (ns) snaps off. This is : -volt turn-on Si Ultrafast diode, instantaneous power at C. shows the turn-on voltage, a. The use of the SiC instantaneous power measured at a junction temperature of C SBDof results the in a peak a Si Ultrafast ofdiode. amps, During a the turn-on, % reduction, the diode reverse-recovery a peak instantaneous is added to the power of, 7. kw, resulting a % reduction. in a peak The highof amps. frequency A peak instantaneous oscillationspower in theof kw voltage is dissipated in the are. also Also eliminated shown are high-frequency the SiCoscillations SBD, in the voltage caused when the Si diode snaps off. This resulting in reduced RFI/EMI generation. is a major cause of RFI/EMI generation. Copyright 3- All rights reserved. The information in this document is subject to change out notice. Cree 3 CPWR-AN3, Rev. B 3 3 - APPLICATION NOTE is dissipated in the. Also shown are high a major cause of RFI/EMI generation. shows the turn-on voltage, instantaneous power measured at a junction temperature of C of the 7 3 - - - - - -. : -volt turn-on turn-on w/ SiC w/ SBD, SiC SBD, voltage, voltage, instantaneous instantaneous power at power C. at C. A comparison of the switching parameters of the SiC SDB the Si ultrafast diode are shown for measurements taken at a junction temperature of C in Table for measurements taken at a junction temperature of C in Table. The total switching loss reduction ( + ) is calculated to be % at C % at C. 3 3 - shows the turn-on voltage, instantaneous power measured at a junction temperature of C of the a. The use of the results in a peak of amps, a % reduction, a peak instantaneous power of 7. kw, a % reduction. The high-frequency oscillations in the voltage are also eliminated the, resulting in reduced RFI/ EMI generation. A comparison of the switching parameters of the SiC SDB the Si Ultrafast diode are shown for measurements taken at a junction temperature of C in Table for measurements taken at a junction temperature of C in Table. The total switching-loss reduction ( + ) is calculated to be % at C % at C. I C = A, V CC = V, Rg = ohm Peak Reverse Ipr (A) 3 9% Reverse recovery time Trr (ns) 3 3 % Recovery Charge Qrr (nc) 7 % loss turn-off Eoff (mj).. % loss turn-on Eon (mj).3. 3 loss total Ets (mj).. 7% loss turn-on Eon (mj).3.3 loss turn-off Eoff (mj)..3 loss total Ets (mj).9. % loss total Ets (mj).3.9 % Table : volt-switching parameter comparison between Si Ultrafast at C. I C = A, V CC = V, Rg = ohm Peak Reverse Ipr (A) 3 Reverse recovery time Trr (ns) 33 7% Recovery Charge Qrr (nc) 9 loss turn-off Eoff (mj).3. 9% loss turn-on Eon (mj).3. 3 loss total Ets (mj).. % loss turn-on Eon (mj).9. 7% loss turn-off Eoff (mj).9. % loss total Ets (mj).9. % loss total Ets (mj).9.9 % Table : -volt switching parameter comparison between Si Ultrafast at C. shows the turn-off s of the Si Ultrafast diode the at C C superimposed on one plot. The is unchanged temperature, a peak reverse of amps. The Si Ultrafast diode shows strong temperature dependence, increasing from 3 amps at C to 3 amps at C. Silicon Drive Durham, NC 773 USA Tel: +.99.33.3 Fax: +.99.33.77
duction 9% % % % % % % % eter SiC duction 7% % % % % % % eter SiC ts of D at plot. nt of trong from ts of SiC d on GBT trong erse the I (A) I (A) 3 3 - - - @ C @ C C - - @ C -3 -- - - - - @ C - : -volt turn-off of the Si Ultrafast - diode the at C C. - -3 Copyright 3- All rights reserved. The information in this document is subject to change out notice. Cree CPWR-AN3, Rev. B @ C C APPLICATION NOTE @ C 7 shows the turn-on s of the - - - - a Si Ultrafast diode a at C C, superimposed on one plot. The peak in the the : is unchanged volt turn off temperature. of thethe Si peak Ultrafast of the diode the the Si Ultrafast diode at C shows strong temperature C. dependence due to the reverse-recovery temperature dependence of the diode. 3 3 - w/ @ C w/ @ C w/ SBD @ C C - - - - - 7: 7: -volt volt turn-on turn-on of the of the w/ the Si Ultrafast diode the at C w/ the Si Ultrafast diode the SiC C. SBD at C C. shows the total diode switching losses (turn-on turn-off) in watts at switching frequencies from khz to khz temperatures of, C. The SBD has significantly lower switching losses (up to an % reduction) shows no change increased temperature. shows the total diode switching losses (turn-on turn-off) in watts C at switching frequencies from khz to khz C temperatures of, C. The SBD has significantly lower switching losses (up to C an % reduction) shows no change increased temperature. Switching Losses (watts) Switching Losses (watts) 3 C C C 3 7 9 3 7 9 9 shows the total switching losses (turn-on turn-off) in watts at switching frequencies from khz to : -volt switching power loss of khz at, C. The the Si Ultrafast diode the SBD at C, C, switching loss C. the is about half that of the the Si ultrafast diode. 9 shows Thethe 9 shows total the total the switching switching losses also (turn-on turn-off) losses (turn-on in watts at switching turn-off) frequencies in watts from at shows less increase in switching losses khz to khz at, C. The switching switching frequencies from khz to loss temperature. the Theis temperature about half that dependence of the the Si khz ofultrafast theat switching, diode. losses The C. in the the The SiC SBD the also shows switching SiC less SBD increase loss is due in switching tothe thesic losses increase SBD is intemperature. about The temperature half turn-off thattime of dependence the since the of turn-on the theswitching Si losses ultrafast losses are in the diode. The the is due theto SiC the increase SBD also in unchanged temperature. This dramatic turn-off time since the turn-on losses are unchanged shows less increase in switching losses temperature. improvement This dramatic theimprovement switching in the switching temperature. performance performance is The due is temperature solely due solely to theto dependence absence the absence of of reverse of reverse the recovery switching recovery in the losses SiC in the SBD. in SiCthe SBD. the is due to the increase in turn-off time since the turn-on losses are C unchanged temperature. This dramatic improvement C in the switching performance C is due solely to the absence of reverse recovery in the. Switching Losses (watts) Switching Losses (watts) 3 : volt switching power loss of thesi Ultrafast diode the SBD at C, C, C. C C C 3 7 9 9: 9: -volt switching power power loss w/ loss the Si Ultrafast the Si Ultrafast diode diode the SiC the SBDSiC at C, SBD at C, C, C, C. C. 3 7 9 9: volt switching power loss w/ the Si Ultrafast diode the at CPWR-AN3, Rev A C, C, C. Silicon Drive Durham, NC 773 USA Tel: +.99.33.3 Fax: +.99.33.77 meas recov be co switc The l meas recov temp be since co runawa switch The l curre tempe at a j since ultraf runaw recov of of. curre the at due a ju t ultrafa lower recov of of. the due to lower - - - Figur off vo at off vo at
-Volt Switching Comparison The switching parameters were measured for an -A, -V Ultrafast soft-recovery silicon diode (similar to what would be co-packaged in an -A Ultrafast ) a -A, -V SBD, along the switching losses of an -A, -V. The losses were measured at a voltage of V of A. The maximum temperature used in this testing was C since the started going into thermal runaway when biased at C. shows the turn-off voltage, instantaneous power measured at a junction temperature of C for the Si Ultrafast diode. This shows a peak reverse-recovery of amps, a recovery time of ns, a peak instantaneous power of. kw. The voltage overshoot seen the -volt Si diode is not pronounced here due to the -volt testing being done at a lower di/dt ( A/µs vs. 7 A/µs). lower di/dt ( A/µs vs. 7 A/µs). - - - - : -volt Si Ultrafast diode turn-off voltage, instantaneous power at C. is the turn-off waveforms for the at C. This shows a peak reverse-recovery of amp, a reduction of, a recovery time of 3 ns, a reduction of %, a peak instantaneous power of.3 kw, a reduction of 9%. The drastic reduction in switching power is due to the capacitive charge of the SBD dissipating while the diode voltage is low. - - - - - - - - - - - - - - - - - - - - - - - is the turn-off waveforms for the SiC. : SBD -volt at C. This showsturn-off voltage, a peak voltage, reverse recovery instantaneous instantaneous power of at C amp, power a at C. reduction of, is thea recovery turn-off waveforms time of 3 ns, for the a SiC reduction SBD at of C. % This showsa a peak reverse instantaneous is the turn-on recovery power voltage, of.3 kw, of a reduction instantaneous power measured at a junction temperature of amp, C for a the reduction of 9%. The a Si Ultrafast of, drastic diode. a recovery reduction During time in switching the of 3 ns, turn-on, the diode apower reduction reverse-recovery is due to of the capacitive % is charge added a to of peak the the, instantaneous SBD resulting dissipating a power peak while ofthe.3diode kw, of.7 avoltage reduction amps. A ispeak instantaneous of low. 9%. power The drastic of kw reduction is dissipated in switching in the. power is due to the capacitive charge of the SBD dissipating while the diode voltage is low. - - - - - - - - - - - -. volt turn-off voltage, instantaneous power at C :. -volt turn-on w/ Si Si Ultrafast Ultrafast diode, diode, voltage, instantaneous power at at C.. is thevolt turn-on voltage, turn-on w/ Si Ultrafast 3 shows diode, the turn-on voltage, voltage, instantaneous power measured at a instantaneous instantaneous power power measured at C. at a junction temperature of C junction for the temperature of a SBD. The for the use of the SBD is the turn-on voltage, instantaneous power measured at a junction CPWR-AN3, temperature Rev Aof C for the turnis ad peaka turn-o insta is in ad the peak insta in the - - F SBD, powe F SBD, curre powe at a Fi curre resul at redu a of. resulf reduc the S of C. The F the temps C am The stron temp from The am stron diode from ns a The the r diode temp ns a the temp Copyright 3- All rights reserved. The information in this document is subject to change out notice. Cree CPWR-AN3, Rev. B CPWR-AN3, Rev A Silicon Drive Durham, NC 773 USA Tel: +.99.33.3 Fax: +.99.33.77
results in a peak of.7 amps, a % reduction, a peak instantaneous power of. kw, a % reduction. in the. - - - - - 3: -volt turn-on SiC SBD, voltage, instantaneous power at C. shows the turn-off s of the Si Ultrafast diode the at C C superimposed on one plot. The is unchanged temperature, a peak reverse of amp. The Si Ultrafast diode shows a strong temperature dependence, increasing from amps at C to amps at C. The reverse recovery time of the Si Ultrafast diode increases from ns at C to ns at C while reverse-recovery time of the is unchanged temperature. I (A) - - - @ C - - - - Copyright 3- All rights reserved. The information in this document is subject to change out notice. Cree CPWR-AN3, Rev. B @ C C - @ C : -volt turn-off of the : volt turn-off of the Si Si Ultrafast diode the at C Ultrafast C. diode the at C C. shows the turn on s of the a Si ultrafast diode the at C C superimposed on one plot. The peak in the the is unchanged temperature. The peak reverse recovery time of the the Si Ultrafast diode the at C C. shows the turn on s of the a Si ultrafast diode the at C C superimposed on one plot. The peak in the shows the turn-on s of the a Si Ultrafast the diode SiC SBD the SiC issbd unchanged at C C superimposed temperature. on one The plot. peak The peak reverse in the the is unchanged temperature. The peak recovery time of the the Si reverse-recovery time of the the Si Ultrafast ultrafast diode diode shows shows a strong a strong temperature temperature dependence due to dependence the reverse-recovery due to the temperature reverse dependence recovery of the diode. temperature dependence of the diode. APPLICATION NOTE A CPWR-AN3, comparison Rev of A the switching parameters of the the Si ultrafast diode are shown for measurements taken at a junction temperature of C in Table 3, for measurements taken at a junction temperature of C in Table. All is measured % at C parameters % at C. show a major improvement the. The value of the SBD parameters are effectively unchanged increased temperature while the Silicon Ultrafast diode parameters increase. The total switching loss reduction ( + ) is % at C % at C. Ic = A, Vcc = V, Rg = ohm Peak reverse Ipr (A). % Reverse recovery time Trr (ns) 3 7% Recovery charge Qrr (nc) 9 9 loss turn-off Eoff (mj).. 7% loss turn-on Eon (mj).3. 3 loss total Ets (mj).. % loss turn-on Eon (mj).73. % loss turn-off Eoff (mj).33. % loss total Ets (mj)..3 % loss total Ets (mj).7.7 % Table 3: volt switching parameter comparison between Si Ultrafast SiC SBD at C. w/ @ C w/ @ C w/ SBD @ C C - - - - - : : -volt turn-on turn-on of the of the w/ the Si Ultrafast the diode Si Ultrafast the SiCdiode SBD at C the SiC C. SBD at C C. A comparison of the switching parameters of the the Si Ultrafast diode are shown for measurements taken at a junction temperature of C in Table 3, for measurements taken at a junction temperature of C in Table. All measured parameters show a major improvement the. The value of the SBD parameters are effectively unchanged increased temperature while the Silicon Ultrafast diode parameters increase. The total switching-loss reduction ( + ) Ic = A, Vcc = V, Rg = ohm Peak reverse Ipr (A) Silicon Drive Durham, NC 773 USA Tel: +.99.33.3 Fax: +.99.33.77 Dio IGB Table comp SBD P Peak r Revers Rec Dio IGB Table comp SBD switc watts to C switc temp in wa khz SBD
I C = A, V CC = V, Rg = ohm Peak Reverse Ipr (A). % Reverse recovery time Trr (ns) 3 7% Recovery Charge Qrr (nc) 9 9 loss turn-off Eoff (mj).. 7% loss turn-on Eon (mj).3. 3 loss total Ets (mj).. % loss turn-on Eon (mj).73. % loss turn-off Eoff (mj).33. % loss total Ets (mj)..3 % loss total Ets (mj).7.7 % Table 3: -volt switching parameter comparison between Si Ultrafast at C. I C = A, V CC = V, Rg = ohm Peak Reverse Ipr (A) Reverse recovery time Trr (ns) 3 % Recovery Charge Qrr (nc) 9% loss turn-off Eoff (mj).. % loss turn-on Eon (mj).3. 3 loss total Ets (mj).9. 79% loss turn-on Eon (mj).9. 7% loss turn-off Eoff (mj).7. % loss total Ets (mj)..9 % loss total Ets (mj).7.73 % Table : -volt switching-parameter comparison between Si Ultrafast at C. shows the total diode switching losses (turn-on turn-off) in watts at switching frequencies from khz to khz for temperatures of, 7 C. The SBD has significantly lower switching losses (up to a 79% reduction) shows no change increased temperature. 7 shows the total switching losses (turn-on turn-off) in watts at switching frequencies from khz to khz for temperatures of, 7 C. switching loss the SBD is about half that of the the Si Ultrafast diode. The the SBD also shows less increase in switching losses temperature. The temperature dependence of the switching losses in the the SBD is due to the increase in the turn-off time, since the turnon losses are unchanged temperature. This dramatic improvement in the switching performance is due solely to the absence of reverse recovery in the. the turn-off time, since the turn-on losses are unchanged temperature. This dramatic improvement in the switching performance is due solely to the absence of reverse recovery in the SiC SBD. Switching Losses (watts) Switching Losses (watts) 7 C 7 C C C C C 3 7 9 3 7 9 : -volt switching-power loss of the : Si Ultrafast volt switching diode power the loss SBD of at the C, Si Ultrafast 7 C, diode C. the SBD at C, 7 C, C. Switching Losses (watts) C 7 C C 3 7 9 CPWR-AN3, Rev A 7: -volt switching-power loss w/ w/ the the Si Si Ultrafast diode diode the the SBD SBD at C, at C, 7 C, 7 C, C. C. Conduction Total Losses Conduction Total Losses shows the forward IV of the volt Si ultrafast diode the at C C. At amps the shows the forward IV of the -volt Si Ultrafast diode the at C C. At amps the diode has.7-volt lower forward drop at C.-volt lower forward drop at C. This results in reduced conduction losses for the. Forward Current (amp) 3. v at C Tab losses a %. am device used. the da With t reduce are re loss r by sim a SiC c Tota c Tota T Table a con diode Copyright 3- All rights reserved. The information in this document is subject to change out notice. Cree 7 CPWR-AN3, Rev. B Silicon Drive Durham, NC 773 USA Tel: +.99.33.3 Fax: +.99.33.77
Forward Current (amp) 3 C C...... 3. Forward Voltage (volt) : Forward voltage of the -volt Si Ultrafast diode the SiC SBD at C C. Table shows the calculation of total losses for a -khz converter operating at a % duty cycle an average of. amps using the -volt devices. A device junction temperature of C was used. The conduction loss for the is the data sheet value of.9 volts at amps. With the, the total diode losses are reduced by % the total losses are reduced by %. This gives a % total loss reduction for the -volt converter by simply changing the Si Ultrafast diode to a. Conclusions The turn-on switching losses of the are strongly dependent on the reverse-recovery characteristics of its freewheeling diode. The impact of the on the switching performance of the freewheeling diode the is of great importance to the hard-switched circuit designer. Based on the measurements presented above, there are significant advantages offered by SiC Schottky diodes. While the reverse-recovery of the Si Ultrafast diode shows a strong temperature dependence, the is unaffected. At a high di/dt, the Si Ultrafast diode exhibits a voltage overshoot on turn-off due to snapoff during reverse recovery, but the is unaffected. The snap-off in the Si Ultrafast diode causes oscillations in the voltage, which generate RFI/EMI. This oscillation is not present the. The % reduction in switching losses can be applied in a number of ways to optimize the circuit design. The reduction in switching losses can be applied to increase efficiency, reduce cooling requirements, or reduce the rating of the. The operating frequency can be increased in order to allow the use of smaller passive components or to achieve acoustic requirements. The absence of a voltage overshoot eliminates the need for snubber networks. The absence of the high-frequency oscillation reduces the RFI/EMI filter requirements. The replacement of the Si Ultrafast diode a SiC Schottky diode such as the Cree Zero Recovery SBD results in a substantial reduction in switching losses in both the diode the, resulting in a significant system-level performance improvement. Si Pin % Reduction Switching loss (watt) 9 79% conduction loss (watt)..7 % Total loss (watt) 3..7 % Switching loss (watt) 9 % conduction loss (watt).. % Total loss (watt) 9. 3. % Total loss (watt) 99. % Table : Comparison of calculated losses in a converter the -volt Si Ultrafast diode the SBD at C. Copyright 3- All rights reserved. The information in this document is subject to change out notice. Cree CPWR-AN3, Rev. B Silicon Drive Durham, NC 773 USA Tel: +.99.33.3 Fax: +.99.33.77