John Larkin schrieb:> Relays will jitter many microseconds. The mechanical bits ring in a > zillion modes, like a church full of bells, after every hit.Hello, when I wrote of some 100 ns jitter, I already thought of several microseconds but I dont wanted to be too pessimistic. Cheers
Circuit for producing 10ns pulses of several amps
Started by ●July 20, 2012
Reply by ●July 23, 20122012-07-23
Reply by ●July 23, 20122012-07-23
On Mon, 23 Jul 2012 18:15:54 +0200, Uwe Hercksen <hercksen@mew.uni-erlangen.de> wrote:> > >John Larkin schrieb: > >> Relays will jitter many microseconds. The mechanical bits ring in a >> zillion modes, like a church full of bells, after every hit. > >Hello, > >when I wrote of some 100 ns jitter, I already thought of several >microseconds but I dont wanted to be too pessimistic. > >CheersIt's fun to look at the coil voltage of a regular or a reed relay, with a scope, after the drive device opens up. There's usually enough residual magnetism to make the various vibrations induce signals into the coil. It tends to be a frightful mess of superimposed mechanical resonances. Reeds are terrible for low-level signal switching for that same reason: long messy twangs. I once designed a delay generator to replace a piezoacoustic delay line, a few microseconds delay as I recall. The piezo delay line worked, sort of, but it would twang for tens of milliseconds after generating that short delay. It cost $2000, too. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Reply by ●July 23, 20122012-07-23
John Larkin wrote:> On Fri, 20 Jul 2012 16:51:33 -0400, Spehro Pefhany > <speffSNIP@interlogDOTyou.knowwhat> wrote: > >> On Fri, 20 Jul 2012 20:24:31 GMT, nico@puntnl.niks (Nico Coesel) >> wrote: >> >>> "Mr.CRC" <crobcBOGUS@REMOVETHISsbcglobal.net> wrote: >>> >>>> Nico Coesel wrote: >>>>> "Mr.CRC" <crobcBOGUS@REMOVETHISsbcglobal.net> wrote: >>>>> >>>>>> Hi: >>>>>> >>>>>> I have been using MOSFET drivers to pulse LEDs at currents of up to 21A >>>>>> (for 100s of ns to several microsecond pulses) and down to about 22ns >>>>>> for 1A pulses into 1mm^2 power LEDs. >>>>> What kind of MOSFETs are you using? The lower the RDSon the slower due >>>>> to the enormous gate capacitance. >>>> >>>> So far I haven't used any, except for a IRF530 in LTspice. >>> That one is quite old. >>> >>>> The physical circuits I've used are just the MOSFET gate drivers mentioned. >>>> >>>> But yes, in principle I would expect that some trade off btw RDSon/Qg >>>> and speed would apply. >>> It does apply. Last year I've designed a forward converter. A MOSFET >>> with a 10 times lower RDSon was less efficient. IMHO the most >>> efficient (and therefore fastest) MOSFET for a particular application >>> barely meets the specs. It will have the lowest gate capacitance. >> How about a GaN FET with matching driver? >> >> eg. EPC1014/LM5113 >> >> Rather prototyping-unfriendly package on the FET. > > Nice part, 10 amps and 280 pF, maybe a little big for CRC's LED driver > requirement, but it would work fine. You could drive it from my > TinyLogic gates, or from some paralleled 74AC gates... it only needs > 2-3 volts of gate drive. EPC2012 might be a better fit. >Does anyone know how fast they really switch, given a zero to 5V gate drive? The datasheets for those are rather paltry, not much info in them.> There are PHEMTS with Idss in the amps, and they sometimes enhance > about 2:1 better than that. They can switch at sub-ns speeds with > fairly easy gate drive. Avago has some enhancement parts. >I've got a situation where even using several 7002 in parallel won't muscle around a few hundred pF of load capacitance fast enough. I am trying to get down to around a nanosecond. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●July 23, 20122012-07-23
On Mon, 23 Jul 2012 15:59:29 +0100, Ian Field wrote:> Have you examined datasheet/appnotes for ZTX415 avalanch transistor - its > all in the tuned co-ax line (apparently).There's a fast LED driver described in there, without using a transmission line. 40 amps pulse, 10ns wide. Don't believe the Spice model they supply, it's nowhere near the published datasheet figures. Or real life. Nice device. -- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)
Reply by ●July 23, 20122012-07-23
On Mon, 23 Jul 2012 10:13:35 -0700, Joerg <invalid@invalid.invalid> wrote:>John Larkin wrote: >> On Fri, 20 Jul 2012 16:51:33 -0400, Spehro Pefhany >> <speffSNIP@interlogDOTyou.knowwhat> wrote: >> >>> On Fri, 20 Jul 2012 20:24:31 GMT, nico@puntnl.niks (Nico Coesel) >>> wrote: >>> >>>> "Mr.CRC" <crobcBOGUS@REMOVETHISsbcglobal.net> wrote: >>>> >>>>> Nico Coesel wrote: >>>>>> "Mr.CRC" <crobcBOGUS@REMOVETHISsbcglobal.net> wrote: >>>>>> >>>>>>> Hi: >>>>>>> >>>>>>> I have been using MOSFET drivers to pulse LEDs at currents of up to 21A >>>>>>> (for 100s of ns to several microsecond pulses) and down to about 22ns >>>>>>> for 1A pulses into 1mm^2 power LEDs. >>>>>> What kind of MOSFETs are you using? The lower the RDSon the slower due >>>>>> to the enormous gate capacitance. >>>>> >>>>> So far I haven't used any, except for a IRF530 in LTspice. >>>> That one is quite old. >>>> >>>>> The physical circuits I've used are just the MOSFET gate drivers mentioned. >>>>> >>>>> But yes, in principle I would expect that some trade off btw RDSon/Qg >>>>> and speed would apply. >>>> It does apply. Last year I've designed a forward converter. A MOSFET >>>> with a 10 times lower RDSon was less efficient. IMHO the most >>>> efficient (and therefore fastest) MOSFET for a particular application >>>> barely meets the specs. It will have the lowest gate capacitance. >>> How about a GaN FET with matching driver? >>> >>> eg. EPC1014/LM5113 >>> >>> Rather prototyping-unfriendly package on the FET. >> >> Nice part, 10 amps and 280 pF, maybe a little big for CRC's LED driver >> requirement, but it would work fine. You could drive it from my >> TinyLogic gates, or from some paralleled 74AC gates... it only needs >> 2-3 volts of gate drive. EPC2012 might be a better fit. >> > >Does anyone know how fast they really switch, given a zero to 5V gate >drive? The datasheets for those are rather paltry, not much info in them.By "they", do you mean the Tiny buffers? Figure about 600 ps rise/fall and, if you put three sections in parallel, maybe 8-10 ohms drive impedance. At 12 cents for a triple buffer, using several is feasible.> > >> There are PHEMTS with Idss in the amps, and they sometimes enhance >> about 2:1 better than that. They can switch at sub-ns speeds with >> fairly easy gate drive. Avago has some enhancement parts. >> > >I've got a situation where even using several 7002 in parallel won't >muscle around a few hundred pF of load capacitance fast enough. I am >trying to get down to around a nanosecond.What are you driving the 2N7002 gates with? I can make a 2N7002 sink about an amp in under 1 ns, driving its gate hard. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Reply by ●July 23, 20122012-07-23
John Larkin wrote:> On Mon, 23 Jul 2012 10:13:35 -0700, Joerg <invalid@invalid.invalid> > wrote: > >> John Larkin wrote: >>> On Fri, 20 Jul 2012 16:51:33 -0400, Spehro Pefhany >>> <speffSNIP@interlogDOTyou.knowwhat> wrote: >>> >>>> On Fri, 20 Jul 2012 20:24:31 GMT, nico@puntnl.niks (Nico Coesel) >>>> wrote: >>>> >>>>> "Mr.CRC" <crobcBOGUS@REMOVETHISsbcglobal.net> wrote: >>>>> >>>>>> Nico Coesel wrote: >>>>>>> "Mr.CRC" <crobcBOGUS@REMOVETHISsbcglobal.net> wrote: >>>>>>> >>>>>>>> Hi: >>>>>>>> >>>>>>>> I have been using MOSFET drivers to pulse LEDs at currents of up to 21A >>>>>>>> (for 100s of ns to several microsecond pulses) and down to about 22ns >>>>>>>> for 1A pulses into 1mm^2 power LEDs. >>>>>>> What kind of MOSFETs are you using? The lower the RDSon the slower due >>>>>>> to the enormous gate capacitance. >>>>>> So far I haven't used any, except for a IRF530 in LTspice. >>>>> That one is quite old. >>>>> >>>>>> The physical circuits I've used are just the MOSFET gate drivers mentioned. >>>>>> >>>>>> But yes, in principle I would expect that some trade off btw RDSon/Qg >>>>>> and speed would apply. >>>>> It does apply. Last year I've designed a forward converter. A MOSFET >>>>> with a 10 times lower RDSon was less efficient. IMHO the most >>>>> efficient (and therefore fastest) MOSFET for a particular application >>>>> barely meets the specs. It will have the lowest gate capacitance. >>>> How about a GaN FET with matching driver? >>>> >>>> eg. EPC1014/LM5113 >>>> >>>> Rather prototyping-unfriendly package on the FET. >>> Nice part, 10 amps and 280 pF, maybe a little big for CRC's LED driver >>> requirement, but it would work fine. You could drive it from my >>> TinyLogic gates, or from some paralleled 74AC gates... it only needs >>> 2-3 volts of gate drive. EPC2012 might be a better fit. >>> >> Does anyone know how fast they really switch, given a zero to 5V gate >> drive? The datasheets for those are rather paltry, not much info in them. > > By "they", do you mean the Tiny buffers? Figure about 600 ps rise/fall > and, if you put three sections in parallel, maybe 8-10 ohms drive > impedance. At 12 cents for a triple buffer, using several is feasible. >The buffers can do it but can the EPC2012? I've looked up and down their site and none of the scope plots in switcher apps looked all that mouthwatering. No hard timing data that I could find either.>> >>> There are PHEMTS with Idss in the amps, and they sometimes enhance >>> about 2:1 better than that. They can switch at sub-ns speeds with >>> fairly easy gate drive. Avago has some enhancement parts. >>> >> I've got a situation where even using several 7002 in parallel won't >> muscle around a few hundred pF of load capacitance fast enough. I am >> trying to get down to around a nanosecond. > > What are you driving the 2N7002 gates with? I can make a 2N7002 sink > about an amp in under 1 ns, driving its gate hard. >NL37WZ16. I'll have to see the layout, maybe something has gone wrong there (that art was out of my hands). -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●July 23, 20122012-07-23
On 07/23/2012 11:47 AM, Uwe Hercksen wrote:> > > Phil Hobbs schrieb: > >> You do it by connecting a charged, open-circuited coax stub via the >> relay. The coax empties itself out in a time t = 2L/sqrt(epsilon). > > Hello, > > ah, the length of the pulse is determined by the coax stub only. > Pulses of some 100 ps should be possible too. > But if you want periodic pulses with a period of some ms I would expect > a jitter of some 100 ns even when the relay is driven with a good XTAL > based clock. > > Cheers > >I'd be very surprised if the jitter were better than tens of microseconds for a mercury relay. But that's what the sampling scope's delay line is for. ;) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●July 23, 20122012-07-23
On Mon, 23 Jul 2012 13:20:40 -0700, Joerg <invalid@invalid.invalid> wrote:>John Larkin wrote: >> On Mon, 23 Jul 2012 10:13:35 -0700, Joerg <invalid@invalid.invalid> >> wrote: >> >>> John Larkin wrote: >>>> On Fri, 20 Jul 2012 16:51:33 -0400, Spehro Pefhany >>>> <speffSNIP@interlogDOTyou.knowwhat> wrote: >>>> >>>>> On Fri, 20 Jul 2012 20:24:31 GMT, nico@puntnl.niks (Nico Coesel) >>>>> wrote: >>>>> >>>>>> "Mr.CRC" <crobcBOGUS@REMOVETHISsbcglobal.net> wrote: >>>>>> >>>>>>> Nico Coesel wrote: >>>>>>>> "Mr.CRC" <crobcBOGUS@REMOVETHISsbcglobal.net> wrote: >>>>>>>> >>>>>>>>> Hi: >>>>>>>>> >>>>>>>>> I have been using MOSFET drivers to pulse LEDs at currents of up to 21A >>>>>>>>> (for 100s of ns to several microsecond pulses) and down to about 22ns >>>>>>>>> for 1A pulses into 1mm^2 power LEDs. >>>>>>>> What kind of MOSFETs are you using? The lower the RDSon the slower due >>>>>>>> to the enormous gate capacitance. >>>>>>> So far I haven't used any, except for a IRF530 in LTspice. >>>>>> That one is quite old. >>>>>> >>>>>>> The physical circuits I've used are just the MOSFET gate drivers mentioned. >>>>>>> >>>>>>> But yes, in principle I would expect that some trade off btw RDSon/Qg >>>>>>> and speed would apply. >>>>>> It does apply. Last year I've designed a forward converter. A MOSFET >>>>>> with a 10 times lower RDSon was less efficient. IMHO the most >>>>>> efficient (and therefore fastest) MOSFET for a particular application >>>>>> barely meets the specs. It will have the lowest gate capacitance. >>>>> How about a GaN FET with matching driver? >>>>> >>>>> eg. EPC1014/LM5113 >>>>> >>>>> Rather prototyping-unfriendly package on the FET. >>>> Nice part, 10 amps and 280 pF, maybe a little big for CRC's LED driver >>>> requirement, but it would work fine. You could drive it from my >>>> TinyLogic gates, or from some paralleled 74AC gates... it only needs >>>> 2-3 volts of gate drive. EPC2012 might be a better fit. >>>> >>> Does anyone know how fast they really switch, given a zero to 5V gate >>> drive? The datasheets for those are rather paltry, not much info in them. >> >> By "they", do you mean the Tiny buffers? Figure about 600 ps rise/fall >> and, if you put three sections in parallel, maybe 8-10 ohms drive >> impedance. At 12 cents for a triple buffer, using several is feasible. >> > >The buffers can do it but can the EPC2012? I've looked up and down their >site and none of the scope plots in switcher apps looked all that >mouthwatering. No hard timing data that I could find either. > >>> >>>> There are PHEMTS with Idss in the amps, and they sometimes enhance >>>> about 2:1 better than that. They can switch at sub-ns speeds with >>>> fairly easy gate drive. Avago has some enhancement parts. >>>> >>> I've got a situation where even using several 7002 in parallel won't >>> muscle around a few hundred pF of load capacitance fast enough. I am >>> trying to get down to around a nanosecond. >> >> What are you driving the 2N7002 gates with? I can make a 2N7002 sink >> about an amp in under 1 ns, driving its gate hard. >> > >NL37WZ16. I'll have to see the layout, maybe something has gone wrong >there (that art was out of my hands).Send me some screen snaps of the PCB layers, and I'll review it. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Reply by ●July 23, 20122012-07-23
John Larkin wrote:> On Mon, 23 Jul 2012 13:20:40 -0700, Joerg <invalid@invalid.invalid> > wrote: > >> John Larkin wrote: >>> On Mon, 23 Jul 2012 10:13:35 -0700, Joerg <invalid@invalid.invalid> >>> wrote: >>> >>>> John Larkin wrote: >>>>> On Fri, 20 Jul 2012 16:51:33 -0400, Spehro Pefhany >>>>> <speffSNIP@interlogDOTyou.knowwhat> wrote: >>>>> >>>>>> On Fri, 20 Jul 2012 20:24:31 GMT, nico@puntnl.niks (Nico Coesel) >>>>>> wrote: >>>>>> >>>>>>> "Mr.CRC" <crobcBOGUS@REMOVETHISsbcglobal.net> wrote: >>>>>>> >>>>>>>> Nico Coesel wrote: >>>>>>>>> "Mr.CRC" <crobcBOGUS@REMOVETHISsbcglobal.net> wrote: >>>>>>>>> >>>>>>>>>> Hi: >>>>>>>>>> >>>>>>>>>> I have been using MOSFET drivers to pulse LEDs at currents of up to 21A >>>>>>>>>> (for 100s of ns to several microsecond pulses) and down to about 22ns >>>>>>>>>> for 1A pulses into 1mm^2 power LEDs. >>>>>>>>> What kind of MOSFETs are you using? The lower the RDSon the slower due >>>>>>>>> to the enormous gate capacitance. >>>>>>>> So far I haven't used any, except for a IRF530 in LTspice. >>>>>>> That one is quite old. >>>>>>> >>>>>>>> The physical circuits I've used are just the MOSFET gate drivers mentioned. >>>>>>>> >>>>>>>> But yes, in principle I would expect that some trade off btw RDSon/Qg >>>>>>>> and speed would apply. >>>>>>> It does apply. Last year I've designed a forward converter. A MOSFET >>>>>>> with a 10 times lower RDSon was less efficient. IMHO the most >>>>>>> efficient (and therefore fastest) MOSFET for a particular application >>>>>>> barely meets the specs. It will have the lowest gate capacitance. >>>>>> How about a GaN FET with matching driver? >>>>>> >>>>>> eg. EPC1014/LM5113 >>>>>> >>>>>> Rather prototyping-unfriendly package on the FET. >>>>> Nice part, 10 amps and 280 pF, maybe a little big for CRC's LED driver >>>>> requirement, but it would work fine. You could drive it from my >>>>> TinyLogic gates, or from some paralleled 74AC gates... it only needs >>>>> 2-3 volts of gate drive. EPC2012 might be a better fit. >>>>> >>>> Does anyone know how fast they really switch, given a zero to 5V gate >>>> drive? The datasheets for those are rather paltry, not much info in them. >>> By "they", do you mean the Tiny buffers? Figure about 600 ps rise/fall >>> and, if you put three sections in parallel, maybe 8-10 ohms drive >>> impedance. At 12 cents for a triple buffer, using several is feasible. >>> >> The buffers can do it but can the EPC2012? I've looked up and down their >> site and none of the scope plots in switcher apps looked all that >> mouthwatering. No hard timing data that I could find either. >> >>>>> There are PHEMTS with Idss in the amps, and they sometimes enhance >>>>> about 2:1 better than that. They can switch at sub-ns speeds with >>>>> fairly easy gate drive. Avago has some enhancement parts. >>>>> >>>> I've got a situation where even using several 7002 in parallel won't >>>> muscle around a few hundred pF of load capacitance fast enough. I am >>>> trying to get down to around a nanosecond. >>> What are you driving the 2N7002 gates with? I can make a 2N7002 sink >>> about an amp in under 1 ns, driving its gate hard. >>> >> NL37WZ16. I'll have to see the layout, maybe something has gone wrong >> there (that art was out of my hands). > > Send me some screen snaps of the PCB layers, and I'll review it. >Thanks. But I don't have them myself yet. It pretty much needs to follow RF design rules and usually they are pretty good at that. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●July 23, 20122012-07-23
