Active rectifier/peak detector @ up to 150kHz...
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From: John Larkin on 5 Apr 2010 12:49 On Mon, 5 Apr 2010 09:34:54 -0700 (PDT), Nicko <nick(a)desmith.net> wrote: >On 5 Apr, 16:33, "Tim Williams" <tmoran...(a)charter.net> wrote: >> Inductors don't resonate. �What are you really doing? �Sounds similar to my >> induction heater. > >Its a resonant RC tank circuit that can be detuned by external >influences, so I track it using a uP - similar to an induction heater >where you want the circuit to resonate but where you might change your >work coils and thus move the resonant frequency - either way you don't >want your bridge FETs/IGBTs to over cook... We make power amps that have a uP constantly (2000 times a second) digitizing everything of interest (voltages, currents, temperatures) and protecting our fets. We run a thermal simulation of junction temperatures and shut down at what we compute to be 140C. Nowadays a $4 CPU could run the same model at 100K per second, if that helped any. A $4 CPU is worth it to get the maximum safe performance out of $300 worth of fets. You might random-sample-digitize the current waveform and do math on that. Things like abs val, square, lowpass filter, whatever. That's much more versatile than things like hardware current limits. A cheap uP with a built-in 10 or 12-bit ADC actually makes a pretty good true-RMS voltmeter. The low-end ARMs are now going for under $1. John
From: Jan Panteltje on 5 Apr 2010 14:37 On a sunny day (Mon, 5 Apr 2010 09:34:54 -0700 (PDT)) it happened Nicko <nick(a)desmith.net> wrote in <948b5354-5c23-408a-92f3-6bdb6bcd7698(a)i25g2000yqm.googlegroups.com>: >Its a resonant RC tank circuit Not likely :-)
From: Michael A. Terrell on 5 Apr 2010 15:10 Tim Williams wrote: > > Inductors don't resonate. What are you really doing? Sounds similar to my > induction heater. Really? Then why worry about SRF? -- Lead free solder is Belgium's version of 'Hold my beer and watch this!'
From: Tim Williams on 6 Apr 2010 03:46 "Michael A. Terrell" <mike.terrell(a)earthlink.net> wrote in message news:4BBA35A1.7565787D(a)earthlink.net... >> Inductors don't resonate. > > Really? Then why worry about SRF? Pure inductances are inductive from DC to light. Who knows what the OP actually has. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: MooseFET on 6 Apr 2010 05:36
On Apr 5, 1:27 am, Nicko <n...(a)desmith.net> wrote: > Hi, > > I've got a current transformer looking at AC pulses to an inductor - > these can get quite big due a feedback mechanism that tunes the > circuit for resonance & maximum current. In order not to detonate the > driving bridge, I want to inhibit the bridge very quickly (in the next > cycle) should the peak (not RMS) current start getting too high - we > are talking a range of 20-200A depending on the drivers. Frequency is > up to 150kHz. The output of the transformer can go directly to a couple of comparators. You can shut down if either one says there is too much current. This will be fewer parts than making the rectifier because the comparators come two to a package and a "wire-or" does the OR function. > > My current transformer produces 100mV/A (its a Pearson 410) and is > pretty linear. I was thinking of using an active rectifier followed by > a comparator, but am so out of touch with "current" thinking, I was > wondering if there is any other approach I should look at - a simple > bridge and comparator doesn't work at the lower currents due to the > forward drop of the diodes... > > Thanks |