Driving capacitive loads with an H bridge
in [Design]
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From: Grant on 25 Jul 2010 18:49 On Sun, 25 Jul 2010 10:38:53 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Wed, 21 Jul 2010 19:12:10 -0700 (PDT), amark ><amarkpalmer(a)gmail.com> wrote: > >>On Jul 21, 9:48 pm, "markp" <map.nos...(a)f2s.com> wrote: >>> Hi All, >>> >>> I need to drive capacitor with a triangle wave with no DC across the >>> capacitor (i.e. a symmetrical bipolar drive but triangular) but it has to be >>> efficient, i.e some kind of energy retrieval. >>> >>> Is it possible to use standard H bridge circuits to do this? Does anyone >>> have any links or app notes? >>> >>> Thanks! >>> Mark. >> >>There is a classic circuit which is an op-amp integrator, followed by >>an inverting comparator whose o/p is fed back to the integrator. >>What's an H bridge? > >The four switches here > >ftp://jjlarkin.lmi.net/Triangle_Cap.JPG > >make an h-bridge. The a-a and b-b switch pairs are alternately turned >on. So the power source can be connected to the load (the capacitor >here) in one direction or the other. Or the two bottom switches could >be turned on to short the load, or all four turned off to open it. The >switches are usually transistors of some sort, and fully integrated >h-bridge chips are common. > >H-bridges are commonly used to drive motors and speakers, using >pulse-width modulation to control how much drive goes into the load. >The power source would ususlly be a voltage, not a current like in my >circuit. They allow you to, theoretically, make a 100% efficient >amplifier. But then one may consider delivering a constant current into / from a cap as not being efficient, since not a tuned circuit? Can you really have this both ways? Anyway, we don't know if the 'capacitor' is the load, or something there to swamp it, in order to define and make a known waveform? > >This particular circuit can drive a triangle wave into the capacitive >load with, theoretically, zero power required after startup. In >practise, it would be far more efficient than a linear amplifier. Yes. > >Hmmm, you can also turn on all four switches in an h-bridge. Yeah, that's to pop the main fuse and protect the load from EMP :) Grant. > > >John > >
From: Grant on 25 Jul 2010 18:53 On Sun, 25 Jul 2010 13:38:16 -0500, "Tim Williams" <tmoranwms(a)charter.net> wrote: >"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message news:4qso4618ig6ls9d2vq67vrh681l39mqe19(a)4ax.com... >> ftp://jjlarkin.lmi.net/Triangle_Cap.JPG >> >> make an h-bridge. The a-a and b-b switch pairs are alternately turned >> on. So the power source can be connected to the load (the capacitor >> here) in one direction or the other. Or the two bottom switches could >> be turned on to short the load, or all four turned off to open it. The >> switches are usually transistors of some sort, and fully integrated >> h-bridge chips are common. > >Hard to do for more than a few milivolts, though. For large signals, you have to use back-to-back MOSFETs and *lots* of floating gate drives. > >Incidentially, I recently made a synchronous rectifier with BJTs. PP, not bridge. It passes up to +/-200mV in either direction. PP, whazzat? Mind blank. Grant. > >Tim
From: Jim Thompson on 25 Jul 2010 18:53 On Mon, 26 Jul 2010 08:49:12 +1000, Grant <omg(a)grrr.id.au> wrote: >On Sun, 25 Jul 2010 10:38:53 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Wed, 21 Jul 2010 19:12:10 -0700 (PDT), amark >><amarkpalmer(a)gmail.com> wrote: >> >>>On Jul 21, 9:48�pm, "markp" <map.nos...(a)f2s.com> wrote: >>>> Hi All, >>>> >>>> I need to drive capacitor with a triangle wave with no DC across the >>>> capacitor (i.e. a symmetrical bipolar drive but triangular) but it has to be >>>> efficient, i.e some kind of energy retrieval. >>>> >>>> Is it possible to use standard H bridge circuits to do this? Does anyone >>>> have any links or app notes? >>>> >>>> Thanks! >>>> Mark. >>> >>>There is a classic circuit which is an op-amp integrator, followed by >>>an inverting comparator whose o/p is fed back to the integrator. >>>What's an H bridge? >> >>The four switches here >> >>ftp://jjlarkin.lmi.net/Triangle_Cap.JPG >> >>make an h-bridge. The a-a and b-b switch pairs are alternately turned >>on. So the power source can be connected to the load (the capacitor >>here) in one direction or the other. Or the two bottom switches could >>be turned on to short the load, or all four turned off to open it. The >>switches are usually transistors of some sort, and fully integrated >>h-bridge chips are common. >> >>H-bridges are commonly used to drive motors and speakers, using >>pulse-width modulation to control how much drive goes into the load. >>The power source would ususlly be a voltage, not a current like in my >>circuit. They allow you to, theoretically, make a 100% efficient >>amplifier. > >But then one may consider delivering a constant current into / from >a cap as not being efficient, since not a tuned circuit? Can you >really have this both ways? > >Anyway, we don't know if the 'capacitor' is the load, or something >there to swamp it, in order to define and make a known waveform? >> >>This particular circuit can drive a triangle wave into the capacitive >>load with, theoretically, zero power required after startup. In >>practise, it would be far more efficient than a linear amplifier. > >Yes. >> >>Hmmm, you can also turn on all four switches in an h-bridge. > >Yeah, that's to pop the main fuse and protect the load from EMP :) Not instantaneously. The inductor is still there. What we have going on here is mixing in the idea of RESONANT charging with an essentially constant current drive. Calling it energy conserving is a _big_ stretch. Maybe _someone_ will draw up a _real_ circuit that works? > >Grant. >> >> >>John >> >> ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Spice is like a sports car... Only as good as the person behind the wheel.
From: John Larkin on 25 Jul 2010 19:00 On Mon, 26 Jul 2010 08:49:12 +1000, Grant <omg(a)grrr.id.au> wrote: >>The four switches here >> >>ftp://jjlarkin.lmi.net/Triangle_Cap.JPG >> >>make an h-bridge. The a-a and b-b switch pairs are alternately turned >>on. So the power source can be connected to the load (the capacitor >>here) in one direction or the other. Or the two bottom switches could >>be turned on to short the load, or all four turned off to open it. The >>switches are usually transistors of some sort, and fully integrated >>h-bridge chips are common. >> >>H-bridges are commonly used to drive motors and speakers, using >>pulse-width modulation to control how much drive goes into the load. >>The power source would ususlly be a voltage, not a current like in my >>circuit. They allow you to, theoretically, make a 100% efficient >>amplifier. > >But then one may consider delivering a constant current into / from >a cap as not being efficient, since not a tuned circuit? Can you >really have this both ways? Sure. The sim works with no lossy parts at all, just one L and one C and the switches. An actual implementation could have only minor losses. This *is* a resonant circuit. The switches just time-warp it in big jumps so that we only use the segments of the sine wave that appeal to us. Just skip over the parts you don't like. John
From: Jim Thompson on 25 Jul 2010 19:31
On Wed, 21 Jul 2010 16:45:42 +0100, "markp" <map.nospam(a)f2s.com> wrote: ><langwadt(a)fonz.dk> wrote in message >news:a02cd398-9bd8-4315-8c89-4b86481a609e(a)f33g2000yqe.googlegroups.com... >> On 21 Jul., 13:48, "markp" <map.nos...(a)f2s.com> wrote: >>> Hi All, >>> >>> I need to drive capacitor with a triangle wave with no DC across the >>> capacitor (i.e. a symmetrical bipolar drive but triangular) but it has to >>> be >>> efficient, i.e some kind of energy retrieval. >>> >>> Is it possible to use standard H bridge circuits to do this? Does anyone >>> have any links or app notes? >>> >>> Thanks! >>> Mark. >> >> what kind of frequencies, voltages? >> >> class-d audio amplifier? >> >> -Lasse > >I can't say much for NDA reasons, but assume >40V AC (true RMS) For a triangle wave, 40V RMS = 138.56V peak-to-peak > and a few >hundred Hertz, I take that as 200Hz >so there are potentially a few amps I take that as 2A >flying about in the load >capacitor. > >Mark > That works out to a capacitor value of 36uF At resonance, you'd need a 17.6mH inductor. To get relatively straight "triangle" slopes, you'd need an inductor much greater than that value... maybe John Fields' 1 Henry. Am I in the ball-park? Or do you need to restate the problem? ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Spice is like a sports car... Only as good as the person behind the wheel. |