ECL: Why'd they use negative voltages?
in [Design]
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From: John Larkin on 8 Jun 2010 12:22 On Tue, 08 Jun 2010 09:05:42 -0700, Joerg <invalid(a)invalid.invalid> wrote: >John Larkin wrote: >> On Tue, 08 Jun 2010 09:12:24 +0200, Jeroen Belleman >> <jeroen(a)nospam.please> wrote: >> >>> John Larkin wrote: >>>> 10KH type ECL does work fine at Vcc=5, Vee=0. That's called "PECL" >>>> mode, originally "pseudo ECL" and lately "positive ECL". One generally >>>> references all the signals to a nice 5-volt copper pour. >>> I once designed a VME module with a lot of PECL with signals terminated >>> into +3V, and which also had some circuitry running between +3V and >>> GND. The +3V net was shared. Since the combined current of all the PECL >>> terminators largely exceeded the consumption of the stuff between +3V >>> and GND, I used a negative regulator with its input connected to GND to >>> make the +3V. >>> >>> That raised some eyebrows, but it worked fine. >>> >>> Jeroen Belleman >> >> >> It's fun to use regulators "upside down." >> >> We need a good bipolar-drive regulator. I use LM8261s for small stuff, >> and occasionaly LT1010s for bigger stuff. >> > >Check out the big fat audio amp hybrids. Of course, one has to be >careful and pick one that isn't going obsolete next year because a >particular car stereo was discontinued. > >Heck, if you want to go green on this you might even consider class-D. >Then claim your carbon offset :-) A non-H-bridge class D amp can have circulating-current problems... it takes current out of one supply rail and dumps it into the other. Conservation of energy. John
From: GregS on 8 Jun 2010 14:39 In article <kvms06l6nnokp4fbg3ma5ickoqgk8ruanl(a)4ax.com>, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Tue, 08 Jun 2010 09:12:24 +0200, Jeroen Belleman ><jeroen(a)nospam.please> wrote: > >>John Larkin wrote: >>> >>> 10KH type ECL does work fine at Vcc=5, Vee=0. That's called "PECL" >>> mode, originally "pseudo ECL" and lately "positive ECL". One generally >>> references all the signals to a nice 5-volt copper pour. >> >>I once designed a VME module with a lot of PECL with signals terminated >>into +3V, and which also had some circuitry running between +3V and >>GND. The +3V net was shared. Since the combined current of all the PECL >>terminators largely exceeded the consumption of the stuff between +3V >>and GND, I used a negative regulator with its input connected to GND to >>make the +3V. >> >>That raised some eyebrows, but it worked fine. >> >>Jeroen Belleman > > >It's fun to use regulators "upside down." > >We need a good bipolar-drive regulator. I use LM8261s for small stuff, >and occasionaly LT1010s for bigger stuff. > Its been a while since I made upside down units. I was just thinking about the logics I have worked on, but I don't remember all the details. I think Collins logic used some negative voltages, and I think I have worked on negative logic as well.. There was Dec logic which I never really learned. There was Zerox logic, and I did learn General Dynamics dynamic logic, pulse or no pulse. greg
From: Tim Williams on 8 Jun 2010 14:48 "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message news:gdrs06pnjif182aijuqflgmvt3kcig8as0(a)4ax.com... > A non-H-bridge class D amp can have circulating-current problems... it > takes current out of one supply rail and dumps it into the other. > Conservation of energy. Quite so. I encountered this problem while doing research on class D tube amplifiers: http://webpages.charter.net/dawill/tmoranwms/Elec_Compound3.gif In classical tube style, I simply burned the excess energy in a resistor. This makes it a class D-A amplifier: the switch is constantly running, and the output network is resistive coupled, drawing bias current and, for the most part, wasting it. Since it's class A, RC coupled, it has 25% maximum efficiency. I got somewhere around 22% overall efficiency. The plate efficiency was quite high, over 80%. It also had remarkably low output impedance, about 100 ohms, despite having no global NFB. This is due to the pentode's "Rpk(on)". Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: John Larkin on 8 Jun 2010 15:19 On Tue, 8 Jun 2010 13:48:34 -0500, "Tim Williams" <tmoranwms(a)charter.net> wrote: >"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message >news:gdrs06pnjif182aijuqflgmvt3kcig8as0(a)4ax.com... >> A non-H-bridge class D amp can have circulating-current problems... it >> takes current out of one supply rail and dumps it into the other. >> Conservation of energy. > >Quite so. I encountered this problem while doing research on class D tube >amplifiers: >http://webpages.charter.net/dawill/tmoranwms/Elec_Compound3.gif >In classical tube style, I simply burned the excess energy in a resistor. > >This makes it a class D-A amplifier: the switch is constantly running, and >the output network is resistive coupled, drawing bias current and, for the >most part, wasting it. > >Since it's class A, RC coupled, it has 25% maximum efficiency. I got >somewhere around 22% overall efficiency. The plate efficiency was quite >high, over 80%. It also had remarkably low output impedance, about 100 >ohms, despite having no global NFB. This is due to the pentode's "Rpk(on)". > >Tim One of the old Motorola books has a class-D amp that uses bipolar supplies, half-bridge mosfets, LC filter, DC coupled to a grounded loudspeaker. The problem is that, if you're swinging the load, say, positive, you take power out of the + supply and pump power *into* the - supply, and blow up its filter caps. Their fix was cute: an idler circuit off to the side, a pair of mosfets switching at 50% duty cycle, pumping V+ and V- into a dummy grounded inductor. That automagically equalized the supply voltages. John
From: Vladimir Vassilevsky on 8 Jun 2010 15:42
John Larkin wrote: > One of the old Motorola books has a class-D amp that uses bipolar > supplies, half-bridge mosfets, LC filter, DC coupled to a grounded > loudspeaker. The problem is that, if you're swinging the load, say, > positive, you take power out of the + supply and pump power *into* the > - supply, and blow up its filter caps. The problem is known as "rail pumping". > Their fix was cute: an idler > circuit off to the side, a pair of mosfets switching at 50% duty > cycle, pumping V+ and V- into a dummy grounded inductor. That > automagically equalized the supply voltages. There is one small problem with this solution: it doesn't work. If anything is slightly off balance, that creates virtually unlimited current. It could be managed if the idler is controlled by some sort of intelligent loop, however that makes things complicated and expensive. (Remember, auduo is extremely cost sensitive!). Better solution is the synchronous rectifier in the power supply which dumps the energy back to the primary. But this is expensive, too. The only practical solution is having enough of capacitance on the power rails, and provide for overvoltage shut off just in case. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com |