Hi all. I need a basic voltage mode PWM controller for a buck converter project. I need a wide duty cycle range, like 5 - 95%. I don't need an error-amp in the ic, since this part is placed elsewhere in my circuit. So, a basic Ramp generator and a PWM comparator, and an output stage. An UC3843 would suit if it were voltage controlled instead of current. I've gone through Fairchild, ONsemi websites without finding any suitable parts. Thanks for any hints! Regards PAF
Wanted: Voltage mode PWM controller
Started by ●March 27, 2009
Reply by ●March 27, 20092009-03-27
On 27 Mar., 06:52, powerampfreak <powerampfr...@hotmail.com> wrote:> Hi all. I need a basic voltage mode PWM controller for a buck > converter project. I need a wide duty cycle range, like 5 - 95%. I > don't need an error-amp in the ic, since this part is placed elsewhere > in my circuit. > So, a basic Ramp generator and a PWM comparator, and an output stage. > An UC3843 would suit if it were voltage controlled instead of current. > I've gone through Fairchild, ONsemi websites without finding any > suitable parts. > Thanks for any hints! > > Regards > PAFCheckout: http://groups.google.com/group/sci.electronics.design/browse_thread/thread/374ad1c7dfa3261e/b90a47d3c56c7d79?hl=da&lnk=gst&q=kragelund#b90a47d3c56c7d79
Reply by ●March 27, 20092009-03-27
On 27 Mar, 08:55, Klaus Kragelund <klausk...@hotmail.com> wrote:> On 27 Mar., 06:52, powerampfreak <powerampfr...@hotmail.com> wrote: > > > Hi all. I need a basic voltage mode PWM controller for a buck > > converter project. I need a wide duty cycle range, like 5 - 95%. I > > don't need an error-amp in the ic, since this part is placed elsewhere > > in my circuit. > > So, a basic Ramp generator and a PWM comparator, and an output stage. > > An UC3843 would suit if it were voltage controlled instead of current. > > I've gone through Fairchild, ONsemi websites without finding any > > suitable parts. > > Thanks for any hints! > > > Regards > > PAF > > Checkout: > > http://groups.google.com/group/sci.electronics.design/browse_thread/t...The UC3825 has two out of phase outputs. I need one output with full duty cycle from 5 - 95%
Reply by ●March 27, 20092009-03-27
On 27 Mar., 11:07, powerampfreak <powerampfr...@hotmail.com> wrote:> On 27 Mar, 08:55, Klaus Kragelund <klausk...@hotmail.com> wrote: > > > > > > > On 27 Mar., 06:52, powerampfreak <powerampfr...@hotmail.com> wrote: > > > > Hi all. I need a basic voltage mode PWM controller for a buck > > > converter project. I need a wide duty cycle range, like 5 - 95%. I > > > don't need an error-amp in the ic, since this part is placed elsewher=e> > > in my circuit. > > > So, a basic Ramp generator and a PWM comparator, and an output stage. > > > An UC3843 would suit if it were voltage controlled instead of current=.> > > I've gone through Fairchild, ONsemi websites without finding any > > > suitable parts. > > > Thanks for any hints! > > > > Regards > > > PAF > > > Checkout: > > >http://groups.google.com/group/sci.electronics.design/browse_thread/t... > > The UC3825 has two out of phase outputs. I need one output with full > duty cycle from 5 - 95%- Skjul tekst i anf=F8rselstegn - > > - Vis tekst i anf=F8rselstegn -Well, you said: "An UC3843 would suit if it were voltage controlled instead of current". Read the link to the post again=B4.
Reply by ●March 27, 20092009-03-27
On 27 Mar, 14:15, Klaus Kragelund <klausk...@hotmail.com> wrote:> On 27 Mar., 11:07, powerampfreak <powerampfr...@hotmail.com> wrote: > > > > > > > On 27 Mar, 08:55, Klaus Kragelund <klausk...@hotmail.com> wrote: > > > > On 27 Mar., 06:52, powerampfreak <powerampfr...@hotmail.com> wrote: > > > > > Hi all. I need a basic voltage mode PWM controller for a buck > > > > converter project. I need a wide duty cycle range, like 5 - 95%. I > > > > don't need an error-amp in the ic, since this part is placed elsewh=ere> > > > in my circuit. > > > > So, a basic Ramp generator and a PWM comparator, and an output stag=e.> > > > An UC3843 would suit if it were voltage controlled instead of curre=nt.> > > > I've gone through Fairchild, ONsemi websites without finding any > > > > suitable parts. > > > > Thanks for any hints! > > > > > Regards > > > > PAF > > > > Checkout: > > > >http://groups.google.com/group/sci.electronics.design/browse_thread/t.=..> > > The UC3825 has two out of phase outputs. I need one output with full > > duty cycle from 5 - 95%- Skjul tekst i anf=F8rselstegn - > > > - Vis tekst i anf=F8rselstegn - > > Well, you said: "An UC3843 would suit if it were voltage controlled > instead of current". Read the link to the post again=B4.- D=F6lj citerad =text -> > - Visa citerad text -Look, I said I want ONE output with full duty cycle (5-95%). The UC3843 does have that, but it's intended for current mode operation. If you take a look at the UC3825 datasheet: http://focus.ti.com/docs/prod/folders/print/uc3825.html You'll see it's a two output device most suitable for bridge type converters like half and full bridge. Each output provides a maximum of 50% duty cycle and that's too less for my application.
Reply by ●March 27, 20092009-03-27
On 27 Mar, 17:16, powerampfreak <powerampfr...@hotmail.com> wrote:> On 27 Mar, 14:15, Klaus Kragelund <klausk...@hotmail.com> wrote: > > > > > > > On 27 Mar., 11:07, powerampfreak <powerampfr...@hotmail.com> wrote: > > > > On 27 Mar, 08:55, Klaus Kragelund <klausk...@hotmail.com> wrote: > > > > > On 27 Mar., 06:52, powerampfreak <powerampfr...@hotmail.com> wrote: > > > > > > Hi all. I need a basic voltage mode PWM controller for a buck > > > > > converter project. I need a wide duty cycle range, like 5 - 95%. =I> > > > > don't need an error-amp in the ic, since this part is placed else=where> > > > > in my circuit. > > > > > So, a basic Ramp generator and a PWM comparator, and an output st=age.> > > > > An UC3843 would suit if it were voltage controlled instead of cur=rent.> > > > > I've gone through Fairchild, ONsemi websites without finding any > > > > > suitable parts. > > > > > Thanks for any hints! > > > > > > Regards > > > > > PAF > > > > > Checkout: > > > > >http://groups.google.com/group/sci.electronics.design/browse_thread/=t...> > > > The UC3825 has two out of phase outputs. I need one output with full > > > duty cycle from 5 - 95%- Skjul tekst i anf=F8rselstegn - > > > > - Vis tekst i anf=F8rselstegn - > > > Well, you said: "An UC3843 would suit if it were voltage controlled > > instead of current". Read the link to the post again=B4.- D=F6lj citera=d text -> > > - Visa citerad text - > > Look, I said I want ONE output with full duty cycle (5-95%). The > UC3843 does have that, but it's intended for current mode operation. > If you take a look at the UC3825 datasheet:http://focus.ti.com/docs/prod/=folders/print/uc3825.html> You'll see it's a two output device most suitable for bridge type > converters like half and full bridge. > Each output provides a maximum of 50% duty cycle and that's too less > for my application.- D=F6lj citerad text - > > - Visa citerad text -The good old NE5561 would do the job perfectly, if it was still available. Unfortunately it isn't. There must be a similair ic around.
Reply by ●March 27, 20092009-03-27
On Fri, 27 Mar 2009 11:51:12 -0700 (PDT), powerampfreak <powerampfreak@hotmail.com> wrote:> > >The good old NE5561 would do the job perfectly, if it was still >available. Unfortunately it isn't. >There must be a similair ic around. >There are lots of controllers like that. TEXAS INSTRUMENTS - TPS40200DRG4 - Voltage Mode Contoller http://canada.newark.com/texas-instruments/tps40200drg4/voltage-mode-contoller/dp/59M7211 SEMTECH - SC1103CSTRT - Pulse Width Modulation (PWM) Controller http://canada.newark.com/semtech/sc1103cstrt/pulse-width-modulation-pwm-controller/dp/63J8418 For that matter whats wrong with using a UC3842 IT HAS 95% DUTY. You dont have to use it in CMC there are no laws that I know of.From the datasheet typical application VMC Buck. http://i41.tinypic.com/1z5uazk.png UVLO is 16V for the 3842,if this isnt a problem. from this data sheet. http://lc.fie.umich.mx/~ifranco/DATASHEET/control_fuentes_conmutadas/slua143.pdf There is a way to use opto feedback using the comp pin,if you already have an EA.This seems more trouble then it's worth but it's doable.If you dont need isolation I wouldnt do it.I think Basso has an example floating around the net somewhere. If you really want to omit the EA you could search for primary side controllers or isolated controllers.These dont have or usually dont have EA's on board the control signal is sent acrross the isolation boundary by a transformer or optocoupler. Onsemi makes several of these NCP series comes to mind.
Reply by ●March 27, 20092009-03-27
On Thu, 26 Mar 2009 22:52:36 -0700, powerampfreak wrote:> Hi all. I need a basic voltage mode PWM controller for a buck > converter project. I need a wide duty cycle range, like 5 - 95%. I > don't need an error-amp in the ic, since this part is placed elsewhere > in my circuit. > So, a basic Ramp generator and a PWM comparator, and an output stage. > An UC3843 would suit if it were voltage controlled instead of current. > I've gone through Fairchild, ONsemi websites without finding any > suitable parts. > Thanks for any hints! >You can turn voltage into current with a resistor. ;-) Cheers! Rich
Reply by ●March 27, 20092009-03-27
On Mar 27, 5:52=EF=BF=BDam, powerampfreak <powerampfr...@hotmail.com> wrote= :> Hi all. I need a basic voltage mode PWM controller for a buck > converter project. I need a wide duty cycle range, like 5 - 95%. I > don't need an error-amp in the ic, since this part is placed elsewhere > in my circuit. > So, a basic Ramp generator and a PWM comparator, and an output stage. > An UC3843 would suit if it were voltage controlled instead of current. > I've gone through Fairchild, ONsemi websites without finding any > suitable parts. > Thanks for any hints! > > Regards > PAFsg3525
Reply by ●March 28, 20092009-03-28
On Fri, 27 Mar 2009 03:07:50 -0700 (PDT), powerampfreak <powerampfreak@hotmail.com> wrote:>On 27 Mar, 08:55, Klaus Kragelund <klausk...@hotmail.com> wrote: >> On 27 Mar., 06:52, powerampfreak <powerampfr...@hotmail.com> wrote: >> >> > Hi all. I need a basic voltage mode PWM controller for a buck >> > converter project. I need a wide duty cycle range, like 5 - 95%. I >> > don't need an error-amp in the ic, since this part is placed elsewhere >> > in my circuit. >> > So, a basic Ramp generator and a PWM comparator, and an output stage. >> > An UC3843 would suit if it were voltage controlled instead of current. >> > I've gone through Fairchild, ONsemi websites without finding any >> > suitable parts. >> > Thanks for any hints! >> >> > Regards >> > PAF >> >> Checkout: >> >> http://groups.google.com/group/sci.electronics.design/browse_thread/t... > >The UC3825 has two out of phase outputs. I need one output with full >duty cycle from 5 - 95%The thread points out the ease of converting the CMode circuit to voltage mode. For 3842/3 types, you could use the Rt/Ct waveform, suitably attenuated so as not to exceed 1V peak, as an input to the Csense pin to produce voltage mode control. Your external error signal is easily fed into the 'compensation' pin, if the local error amplifier input pin is grounded, but why not use the integrated part? It's free. I hesitate to go further, as you claim to have found no suitable parts in two fairly comprehensive mfr's product lines. Obviously it's not just voltage mode that is your stumbling block, or you would have found 78s40, 34060/3, 494/594 etc. Note that parts providing two-phase outputs can often be easily summed, paricularly when these outputs are open collector or other simple structures. PWM can be achieved fairly simply. An integrated device attempts to provide the bells and whistles that you might find you need in addition to that simple feature. Perhaps if you make a list of what actual properties you expect from the device, someone can help you. RL
