Reply by Mr.CRC July 24, 20122012-07-24
legg wrote:
> On Sat, 21 Jul 2012 00:12:11 -0500, legg <legg@nospam.magma.ca> wrote: > >> On Fri, 20 Jul 2012 10:52:32 -0700, "Mr.CRC" >> <crobcBOGUS@REMOVETHISsbcglobal.net> wrote: >> > <snip> >>> I wish to achieve 10-20ns pulses of 1-10 amps. >>> > <snip> >> Some fairly short, high current pulses can be harvested as >> cross-conduction phenomena in (unloaded) gate drive circuits - their >> periods being equivalent to the rise or fall time of the pre-driver >> output. >> >> Problems with this include stray inductance in the current path, >> minimum capacitive loading of the pre-driver, headroom/gate threshold >> relationships and techniques in tailoring the current fall time. Using >> discrete parts, the cross conduction can be intentionally manipulated. > > Talking to myself, it seems.
Thanks for your reply. I saw it but the idea seemed a bit obscure for my to spend time on. My limitation, not yours. I'll have a look at your sim below, but it may take me a couple days...
> A quick LTspice simulation follows, using the cross-conduction alone. > > RL > > [edit]
Thanks for the consideration! -- _____________________ Mr.CRC crobcBOGUS@REMOVETHISsbcglobal.net SuSE 10.3 Linux 2.6.22.17
Reply by Mr.CRC July 24, 20122012-07-24
jc.al.robbins@gmail.com wrote:
> In case this has not already been cited, I have successfully used the > following circuit as the laser driver in a distance measuring > application > > UHRING W., ZINT C.V., BARTRINGER J., A low-cost high-repetition-rate > picosecond laser diode pulse generator, Proc. SPIE 5452, 2004, pp. > 583-590, Photonics Europe 2004, Strasbourg (France), April 26-30, > 2004, edited by D. Lenstra, G. Morthier, T. Erneux, M. Pessa, ISBN > 0-8194-5375-7. Lien > > JohnR
Thanks. I'll try to get my hands on that. My work library should be able to provide it. I also have this bookmarked, but haven't gotten it yet: http://ieeexplore.ieee.org/Xplore/login.jsp?url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F7361%2F5752398%2F05643093.pdf%3Farnumber%3D5643093&authDecision=-203 -- _____________________ Mr.CRC crobcBOGUS@REMOVETHISsbcglobal.net SuSE 10.3 Linux 2.6.22.17
Reply by July 24, 20122012-07-24
In case this has not already been cited, I have successfully used the following circuit as the laser driver in a distance measuring application

UHRING W., ZINT C.V., BARTRINGER J., 
A low-cost high-repetition-rate picosecond laser diode pulse generator, Proc. SPIE 5452, 2004, pp. 583-590, Photonics Europe 2004, Strasbourg (France), April 26-30, 2004, edited by D. Lenstra, G. Morthier, T. Erneux, M. Pessa, ISBN 0-8194-5375-7. Lien 

JohnR
Reply by krw...@att.bizzzzzzzzzzzz July 23, 20122012-07-23
On Mon, 23 Jul 2012 17:50:13 -0700 (PDT), bitterlemon40@yahoo.ie wrote:

>I think the usual way to shorten the pulses is to put a low value inductor in parallel with the LED. Therefore the current can only flow through the LED for a short while until the all the current available is shunted through the inductor instead.
That's a pretty big inductor. Why would you burn power unnecessarily?
Reply by July 23, 20122012-07-23
I think the usual way to shorten the pulses is to put a low value inductor in parallel with the LED.  Therefore the current can only flow through the LED for a short while until the all the current available is shunted through the inductor instead. 
Reply by Joerg 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 John Larkin 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 Phil Hobbs 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 Joerg 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 John Larkin 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