A major meltdown last Friday for my 8ns 1kV SiC MOSFET
pulser. After set of tests at 400V and 4MHz repetition
rate, with everything working fine, I had to increase
the frequency. A loose hand slip and I was at 10MHz.
That's when the smoke appeared. Blew out a 1-ohm gate
resistor, both TO-247 MOSFETs, both 24V gate drivers,
the flying regulator and the 150Mbps 50kV/us isolator,
and a 0.1-ohm current-sense resistor! Plus a scorch
damage region on the PCB. In the painful process of
getting it going again took out another gate driver.
(No more stock now for those.)
So yesterday after Tuesday's rebuild, I took it slow
and easy, checking temps with the Flir IR camera as I
went, looking for the operating limits. Can do 10MHz
in long bursts, check, 8MHz continuous with HV off,
check, 5MHz at 500V, nice.
500V, 5MHz, 5A square waves anyone?
OK, saved scope screen shots, turned everything off,
went home. Now I find the burned out 100-watt 50-ohm
non-inductive resistor, mounted on 100W heatsink + fan.
MP9100, "Caddock's Micronox� resistance film fired
onto flat ceramic substrate, 100 Watts at +25�C Case".
(Need 50-ohm back termination to drive output coax.)
Sheesh, but thankfully my 150-watt attenuator is OK.
Those are expensive, even on eBay!
--
Thanks,
- Win
Damn, burned out my 100-watt 50-ohm resistor!
Started by ●August 18, 2016
Reply by ●August 18, 20162016-08-18
On Thursday, August 18, 2016 at 2:05:10 PM UTC-4, Winfield Hill wrote:> A major meltdown last Friday for my 8ns 1kV SiC MOSFET > pulser. After set of tests at 400V and 4MHz repetition > rate, with everything working fine, I had to increase > the frequency. A loose hand slip and I was at 10MHz. > That's when the smoke appeared. Blew out a 1-ohm gate > resistor, both TO-247 MOSFETs, both 24V gate drivers, > the flying regulator and the 150Mbps 50kV/us isolator, > and a 0.1-ohm current-sense resistor! Plus a scorch > damage region on the PCB. In the painful process of > getting it going again took out another gate driver. > (No more stock now for those.) > > So yesterday after Tuesday's rebuild, I took it slow > and easy, checking temps with the Flir IR camera as I > went, looking for the operating limits. Can do 10MHz > in long bursts, check, 8MHz continuous with HV off, > check, 5MHz at 500V, nice. > > 500V, 5MHz, 5A square waves anyone? > > OK, saved scope screen shots, turned everything off, > went home. Now I find the burned out 100-watt 50-ohm > non-inductive resistor, mounted on 100W heatsink + fan. > MP9100, "Caddock's Micronox® resistance film fired > onto flat ceramic substrate, 100 Watts at +25°C Case". > (Need 50-ohm back termination to drive output coax.) > Sheesh, but thankfully my 150-watt attenuator is OK. > Those are expensive, even on eBay! > > > -- > Thanks, > - WinLook at " RF Termination Microwave Resistor Dummy Load RFP 150W 50ohm 150watt G150N50W4B " on Ebay. eBay item number: 311601466625 Dan
Reply by ●August 18, 20162016-08-18
On 18 Aug 2016 11:04:56 -0700, Winfield Hill <hill@rowland.harvard.edu> wrote:> A major meltdown last Friday for my 8ns 1kV SiC MOSFET > pulser. After set of tests at 400V and 4MHz repetition > rate, with everything working fine, I had to increase > the frequency. A loose hand slip and I was at 10MHz. > That's when the smoke appeared. Blew out a 1-ohm gate > resistor, both TO-247 MOSFETs, both 24V gate drivers, > the flying regulator and the 150Mbps 50kV/us isolator, > and a 0.1-ohm current-sense resistor! Plus a scorch > damage region on the PCB. In the painful process of > getting it going again took out another gate driver. > (No more stock now for those.) > > So yesterday after Tuesday's rebuild, I took it slow > and easy, checking temps with the Flir IR camera as I > went, looking for the operating limits. Can do 10MHz > in long bursts, check, 8MHz continuous with HV off, > check, 5MHz at 500V, nice. > > 500V, 5MHz, 5A square waves anyone? > > OK, saved scope screen shots, turned everything off, > went home. Now I find the burned out 100-watt 50-ohm > non-inductive resistor, mounted on 100W heatsink + fan. > MP9100, "Caddock's Micronox� resistance film fired > onto flat ceramic substrate, 100 Watts at +25�C Case". > (Need 50-ohm back termination to drive output coax.) > Sheesh, but thankfully my 150-watt attenuator is OK. > Those are expensive, even on eBay!Back in my amateur radio days (K7ZAE, 2M, ~1964), I made a dummy load with two sheets of FR-4 and 40 2K/2W/Composition resistors in parallel between the two sheets (and a fan of course). Gave an outstanding good VSWR at 144MHz: ================= _|_ _|_ _|_ | || || | | || || | |_ _||_ _||_ _| | | | ================= ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I'm looking for work... see my website.
Reply by ●August 18, 20162016-08-18
dcaster@krl.org wrote...> > On Thursday, August 18, 2016, Winfield Hill wrote: >> OK, saved scope screen shots, turned everything off, >> went home. Now I find the burned out 100-watt 50-ohm >> non-inductive resistor, mounted on 100W heatsink + fan. >> MP9100, "Caddock's Micronox=C2=AE resistance film fired >> onto flat ceramic substrate, 100 Watts at +25=C2=B0C Case". >> (Need 50-ohm back termination to drive output coax.) >> Sheesh, but thankfully my 150-watt attenuator is OK. >> Those are expensive, even on eBay! > > Look at " RF Termination Microwave Resistor Dummy Load > RFP 150W 50ohm 150watt G150N50W4B " on Ebay.Hey Dan, that's a simple dummy load, not a GHz bandwidth precision 20dB attenuator, with configurable connectors. -- Thanks, - Win
Reply by ●August 18, 20162016-08-18
Jim Thompson wrote...> > Back in my amateur radio days (K7ZAE, 2M, ~1964), I made a dummy load > with two sheets of FR-4 and 40 2K/2W/Composition resistors in parallel > between the two sheets (and a fan of course). Gave an outstanding > good VSWR at 144MHz: > >================= > _|_ _|_ _|_ > | || || | > | || || | > |_ _||_ _||_ _| > | | | >=================Yep. Mmodern RF power resistors are nice, my 100-watt TO-247 part is only $11 on DigiKey, http://www.digikey.com/product-search/en?keywords=MP9100-50.0F-ND But as I said to Dan, I worried for my precision attenuator, those are invaluable in RF power work. E.g., $500 at Fairview Microwave for 150W units. -- Thanks, - Win
Reply by ●August 18, 20162016-08-18
On 18 Aug 2016 12:11:54 -0700, Winfield Hill <hill@rowland.harvard.edu> wrote:>Jim Thompson wrote... >> >> Back in my amateur radio days (K7ZAE, 2M, ~1964), I made a dummy load >> with two sheets of FR-4 and 40 2K/2W/Composition resistors in parallel >> between the two sheets (and a fan of course). Gave an outstanding >> good VSWR at 144MHz: >> >>================= >> _|_ _|_ _|_ >> | || || | >> | || || | >> |_ _||_ _||_ _| >> | | | >>================= > > Yep. Mmodern RF power resistors are nice, my > 100-watt TO-247 part is only $11 on DigiKey, > http://www.digikey.com/product-search/en?keywords=MP9100-50.0F-ND > > But as I said to Dan, I worried for my precision > attenuator, those are invaluable in RF power work. > E.g., $500 at Fairview Microwave for 150W units.That will give you indigestion ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I'm looking for work... see my website.
Reply by ●August 18, 20162016-08-18
On Thursday, August 18, 2016 at 2:42:25 PM UTC-4, Winfield Hill wrote:> dcaster@krl.org wrote... > > > > On Thursday, August 18, 2016, Winfield Hill wrote: > >> OK, saved scope screen shots, turned everything off, > >> went home. Now I find the burned out 100-watt 50-ohm > >> non-inductive resistor, mounted on 100W heatsink + fan. > >> MP9100, "Caddock's Micronox=C2=AE resistance film fired > >> onto flat ceramic substrate, 100 Watts at +25=C2=B0C Case". > >> (Need 50-ohm back termination to drive output coax.) > >> Sheesh, but thankfully my 150-watt attenuator is OK. > >> Those are expensive, even on eBay! > > > > Look at " RF Termination Microwave Resistor Dummy Load > > RFP 150W 50ohm 150watt G150N50W4B " on Ebay. > > Hey Dan, that's a simple dummy load, not a GHz bandwidth > precision 20dB attenuator, with configurable connectors. > > > -- > Thanks, > - WinI am just confused. I thought you said your 100 watt 50 ohm load was burned out. And that your 150 watt attenuator was okay. Dan
Reply by ●August 18, 20162016-08-18
dcaster@krl.org wrote...> >On Thursday, August 18, 2016, Winfield Hill wrote: >> dcaster@krl.org wrote... >>> >>> On Thursday, August 18, 2016, Winfield Hill wrote: >>>> OK, saved scope screen shots, turned everything off, >>>> went home. Now I find the burned out 100-watt 50-ohm >>>> non-inductive resistor, mounted on 100W heatsink + fan. >>>> MP9100, "Caddock's Micronox=C2=AE resistance film fired >>>> onto flat ceramic substrate, 100 Watts at +25=C2=B0C Case". >>>> (Need 50-ohm back termination to drive output coax.) >>>> Sheesh, but thankfully my 150-watt attenuator is OK. >>>> Those are expensive, even on eBay! >>> >>> Look at " RF Termination Microwave Resistor Dummy Load >>> RFP 150W 50ohm 150watt G150N50W4B " on Ebay. >> >> Hey Dan, that's a simple dummy load, not a GHz bandwidth >> precision 20dB attenuator, with configurable connectors. > > I am just confused. I thought you said your 100 watt > 50 ohm load was burned out. And that your 150 watt > attenuator was okay.The two are in series and dissipate the same power level. Right, I'm thankful the $11 100W TO-247 guy burned out, and saved the $250 150W attenuator guy. Next I'm going to tear up the PCB layout, double the power capability of the heatsink + fan, and use two of the 100-watt resistors in parallel. -- Thanks, - Win
Reply by ●August 18, 20162016-08-18
On Thursday, August 18, 2016 at 5:08:42 PM UTC-4, Winfield Hill wrote:> Next I'm going to tear up the PCB layout, double > the power capability of the heatsink + fan, and > use two of the 100-watt resistors in parallel. > > > -- > Thanks, > - WinStill confused. Assuming the resistors are 50 ohm, would you not need to put two in series and parallel those with two more 50 ohm resistors ? Do not worry about replying. I am sure you found a better way like using 100 ohm resistors. Dan
Reply by ●August 18, 20162016-08-18
dcaster@krl.org wrote...> >On Thursday, August 18, 2016 at 5:08:42 PM UTC-4, Winfield Hill wrote: > >> Next I'm going to tear up the PCB layout, double >> the power capability of the heatsink + fan, and >> use two of the 100-watt resistors in parallel. > > Still confused. ... > > Do not worry about replying. I am sure you found a better > way like using 100 ohm resistors.Right, although 100 ohms is the highest value available and there's low inventory at Digi-Key, two 25-ohm in series is better. I'm beginning to like these guys. -- Thanks, - Win
