constant power (APC) current driver design
in [Design]
|
From: Power boy on 19 Mar 2010 00:24 Hi, I am thinking over current source again in this year. Previously I did current source but I never got into the RF field. I am wondering how to design a constant power current source with a modulation frequency from DC to 150 MHz? I saw some circuits with fast DAC to control a line driver to provide up to 0 to 1A analogue current. But the limit is up to 30 MHz. Right now suppose I need 0 to 1A with 0-150MHz analogue modulation, how to do it? Any design notes or journal paper talked about it? I found little. To use a RF mosfet with simple feed back from some power sensing monitor or use a VxI chip? impossible since most of this type of chips have bandwidth in kHz level. Really have no idea now. Thanks, PB
From: Power boy on 19 Mar 2010 00:44 On Mar 19, 12:24 am, Power boy <bigca...(a)gmail.com> wrote: > Hi, > > I am thinking over current source again in this year. Previously I did > current source but I never got into the RF field. > > I am wondering how to design a constant power current source with a > modulation frequency from DC to 150 MHz? > > I saw some circuits with fast DAC to control a line driver to provide > up to 0 to 1A analogue current. But the limit is up to 30 MHz. > > Right now suppose I need 0 to 1A with 0-150MHz analogue modulation, > how to do it? Any design notes or journal paper talked about it? I > found little. > > To use a RF mosfet with simple feed back from some power sensing > monitor or use a VxI chip? impossible since most of this type of chips > have bandwidth in kHz level. > > Really have no idea now. > > Thanks, > PB and I suddenly realize that PID is not efficient as in power electronics, the type III bandwidth usually has bandwidth of 20khz, way too slow.
From: whit3rd on 19 Mar 2010 17:55 On Mar 18, 9:24 pm, Power boy <bigca...(a)gmail.com> wrote: > I am thinking over current source again in this year. Previously I did > current source but I never got into the RF field. > > I am wondering how to design a constant power current source with a > modulation frequency from DC to 150 MHz? > Right now suppose I need 0 to 1A with 0-150MHz analogue modulation, > how to do it? An emitter-coupled pair with current source on the emitters (an inductor, at high frequency) will steer current effectively, and 1A/150 MHz is not out of the question. You won't like the results if you insist on '0' in the range, that gets into hard base-drive requirements (but you could always leave the transistor turned ON and steal some current...). Doesn't need to be bipolar, of course, a source-coupled pair of MOSFETs could do something similar. I'm dubious that the output impedance will be high enough to be 'practically infinite', like a good DC current source.
From: Power boy on 20 Mar 2010 22:58 On Mar 19, 5:55 pm, whit3rd <whit...(a)gmail.com> wrote: > On Mar 18, 9:24 pm, Power boy <bigca...(a)gmail.com> wrote: > > > I am thinking over current source again in this year. Previously I did > > current source but I never got into the RF field. > > > I am wondering how to design a constant power current source with a > > modulation frequency from DC to 150 MHz? > > Right now suppose I need 0 to 1A with 0-150MHz analogue modulation, > > how to do it? > > An emitter-coupled pair with current source on the emitters (an > inductor, > at high frequency) will steer current effectively, and 1A/150 MHz > is not out of the question. You won't like the results if you insist > on '0' in the range, that gets into hard base-drive requirements (but > you could always leave the transistor turned ON and steal some > current...). > > Doesn't need to be bipolar, of course, a source-coupled pair of > MOSFETs could do something similar. > > I'm dubious that the output impedance will be high enough to be > 'practically infinite', like a good DC current source. it seems working on open loop only. the feedback is a big issue, at @150MHz need to do feedback to keep constant power output.
From: Mark on 21 Mar 2010 09:15
On Mar 20, 10:58 pm, Power boy <bigca...(a)gmail.com> wrote: > On Mar 19, 5:55 pm, whit3rd <whit...(a)gmail.com> wrote: > > > > > On Mar 18, 9:24 pm, Power boy <bigca...(a)gmail.com> wrote: > > > > I am thinking over current source again in this year. Previously I did > > > current source but I never got into the RF field. > > > > I am wondering how to design a constant power current source with a > > > modulation frequency from DC to 150 MHz? > > > Right now suppose I need 0 to 1A with 0-150MHz analogue modulation, > > > how to do it? > > > An emitter-coupled pair with current source on the emitters (an > > inductor, > > at high frequency) will steer current effectively, and 1A/150 MHz > > is not out of the question. You won't like the results if you insist > > on '0' in the range, that gets into hard base-drive requirements (but > > you could always leave the transistor turned ON and steal some > > current...). > > > Doesn't need to be bipolar, of course, a source-coupled pair of > > MOSFETs could do something similar. > > > I'm dubious that the output impedance will be high enough to be > > 'practically infinite', like a good DC current source. > > it seems working on open loop only. > the feedback is a big issue, at @150MHz need to do feedback to keep > constant power output. "constant power" and "current source" are contradictory. You can have one or the other but not both. Which do you want? Mark |