Driving capacitive loads with an H bridge
in [Design]
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From: John Larkin on 21 Jul 2010 11:13 On Wed, 21 Jul 2010 09:44:35 -0500, "Tim Williams" <tmoranwms(a)charter.net> wrote: >Assuming you mean triangle voltage waveform (= square current waveform), you can do this with an H bridge and an arbitrarily large inductor in series with the supply. You will actually have an arc segment of the LC oscillation, so you need a big L to make the frequency low enough that the arc looks straight. > >Tim The system becomes an LC lowpass filter, so there is in theory a higher-order filter that makes a better triangle wave. The first step would be a smaller LC ahead of the main LC, such as to tend to increase the drive to the output LC during the cycle. Tapped inductors, or a compensating series transformer, would be interesting too. A little saturation could be interesting, too, like the linearity correction inductor in an old teevee set. But, as usual, the problem is underspecified. John
From: markp on 21 Jul 2010 11:45 <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) and a few hundred Hertz, so there are potentially a few amps flying about in the load capacitor. Mark
From: Nunya on 21 Jul 2010 11:50 On Jul 21, 8:45 am, "markp" <map.nos...(a)f2s.com> wrote: > <langw...(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) and a few > hundred Hertz, so there are potentially a few amps flying about in the load > capacitor. > > Mark Talking about driving a capacitive load with HVDC is pretty easy when particulars are few or missing. Driving one with AC would require a bit more info. And you say it is in the area of a couple uF?! Sorry, NDA or not, you would need to explain more to get viable responses. You could float the voltage up just enough that it goes negative only for a tiny fragment of the waveform. It would still be AC then, technically.
From: markp on 21 Jul 2010 12:04 "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message news:cb3e46lt9jra176n20k902menqcsnv9vej(a)4ax.com... > On Wed, 21 Jul 2010 09:44:35 -0500, "Tim Williams" > <tmoranwms(a)charter.net> wrote: > >>Assuming you mean triangle voltage waveform (= square current waveform), >>you can do this with an H bridge and an arbitrarily large inductor in >>series with the supply. You will actually have an arc segment of the LC >>oscillation, so you need a big L to make the frequency low enough that the >>arc looks straight. >> >>Tim > > The system becomes an LC lowpass filter, so there is in theory a > higher-order filter that makes a better triangle wave. The first step > would be a smaller LC ahead of the main LC, such as to tend to > increase the drive to the output LC during the cycle. Tapped > inductors, or a compensating series transformer, would be interesting > too. > > A little saturation could be interesting, too, like the linearity > correction inductor in an old teevee set. > > But, as usual, the problem is underspecified. > > John > A little more info then, >40V AC (true RMS) across the load capacitor (a few uF) and at a few hundred Hertz. I'm wondering whether a single inductor with a half-bridge PWM'd might do. I could ground one end of the cap and use +/- V DC supplies to provide the high and low DC to the half-bridge. One problem with that might be the voltage swings at the PWM from a noise point of view, and like you say might require another filter prior to the load cap. Thoughts? Mark.
From: markp on 21 Jul 2010 12:13
"Nunya" <jack_shephard(a)cox.net> wrote in message news:836af8b3-6b92-4292-bbc5-63fabc53c3c4(a)s24g2000pri.googlegroups.com... On Jul 21, 8:45 am, "markp" <map.nos...(a)f2s.com> wrote: > <langw...(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) and a few >> hundred Hertz, so there are potentially a few amps flying about in the >> load >> capacitor. >> >> Mark > Talking about driving a capacitive load with HVDC is pretty easy > when > particulars are few or missing. Driving one with AC would require a > bit > more info. And you say it is in the area of a couple uF?! Sorry, NDA > or > not, you would need to explain more to get viable responses. > You could float the voltage up just enough that it goes negative only > for > a tiny fragment of the waveform. It would still be AC then, > technically. I'm not looking for a design as such, just a possible architecture. So far the info you've been given is a triangle waveform across the cap, bipolar so no DC component, >40V AC(true RMS), a few hundred Hertz and a question whether an H-bridge architecture could do it. I'm not sure how much more information you want...:) Mark |