HS gate drive transformer?
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From: Hammy on 22 Apr 2010 20:44 I wound a toroid to use as a HS gate drive transformer for a 100W two switch flyback. I'm using the typical DC restore technique AC couple the transformer. Here's my schematic; http://i42.tinypic.com/9gvyow.png I'm using a PIC and a FET driver to simulate the extremes of the PWM controller duty cycle and drive level and it works well with the exception of Burst Mode. Burst mode is when the controller modulates the original gate signal at light load for anyone who doesn't know. A picture is worth a thousand words. Here's my gate waveform at 90kHz 70% duty. A little sloping but acceptable. http://i39.tinypic.com/25kieyq.jpg Now here's where the fun begins I'm modulating the 90kHz to simulate burst mode. http://i44.tinypic.com/qy5l69.jpg Here's a zoom of one of the burst. http://i43.tinypic.com/2eumxbk.jpg My primary and secondary are 1:1 ; inductance of 1.5mH. Is there anyway to clean this up?
From: Jim Thompson on 22 Apr 2010 21:01 On Thu, 22 Apr 2010 20:44:03 -0400, Hammy <spam(a)spam.com> wrote: > > >I wound a toroid to use as a HS gate drive transformer for a 100W two >switch flyback. I'm using the typical DC restore technique AC couple >the transformer. > >Here's my schematic; > >http://i42.tinypic.com/9gvyow.png > >I'm using a PIC and a FET driver to simulate the extremes of the PWM >controller duty cycle and drive level and it works well with the >exception of Burst Mode. Burst mode is when the controller modulates >the original gate signal at light load for anyone who doesn't know. > >A picture is worth a thousand words. > >Here's my gate waveform at 90kHz 70% duty. A little sloping but >acceptable. > >http://i39.tinypic.com/25kieyq.jpg > >Now here's where the fun begins I'm modulating the 90kHz to simulate >burst mode. > >http://i44.tinypic.com/qy5l69.jpg > >Here's a zoom of one of the burst. > >http://i43.tinypic.com/2eumxbk.jpg > >My primary and secondary are 1:1 ; inductance of 1.5mH. > > Is there anyway to clean this up? Somewhere in the past I posted A DC restorer for transformer drive of MOSFET's... on the Hubble. Surf for it. ...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 | The only thing bipartisan in this country is hypocrisy
From: John Larkin on 22 Apr 2010 21:08 On Thu, 22 Apr 2010 20:44:03 -0400, Hammy <spam(a)spam.com> wrote: > > >I wound a toroid to use as a HS gate drive transformer for a 100W two >switch flyback. I'm using the typical DC restore technique AC couple >the transformer. > >Here's my schematic; > >http://i42.tinypic.com/9gvyow.png > >I'm using a PIC and a FET driver to simulate the extremes of the PWM >controller duty cycle and drive level and it works well with the >exception of Burst Mode. Burst mode is when the controller modulates >the original gate signal at light load for anyone who doesn't know. > >A picture is worth a thousand words. > >Here's my gate waveform at 90kHz 70% duty. A little sloping but >acceptable. > >http://i39.tinypic.com/25kieyq.jpg > >Now here's where the fun begins I'm modulating the 90kHz to simulate >burst mode. > >http://i44.tinypic.com/qy5l69.jpg > >Here's a zoom of one of the burst. > >http://i43.tinypic.com/2eumxbk.jpg > >My primary and secondary are 1:1 ; inductance of 1.5mH. > > Is there anyway to clean this up? What are the values of the parts? Something is resonating at 12 KHz. The burst has some very low-frequency DC components. Dump burst mode! John
From: Joerg on 22 Apr 2010 22:49 Hammy wrote: > > I wound a toroid to use as a HS gate drive transformer for a 100W two > switch flyback. I'm using the typical DC restore technique AC couple > the transformer. > > Here's my schematic; > > http://i42.tinypic.com/9gvyow.png > > I'm using a PIC and a FET driver to simulate the extremes of the PWM > controller duty cycle and drive level and it works well with the > exception of Burst Mode. Burst mode is when the controller modulates > the original gate signal at light load for anyone who doesn't know. > > A picture is worth a thousand words. > > Here's my gate waveform at 90kHz 70% duty. A little sloping but > acceptable. > > http://i39.tinypic.com/25kieyq.jpg > > Now here's where the fun begins I'm modulating the 90kHz to simulate > burst mode. > > http://i44.tinypic.com/qy5l69.jpg > Ah, another guy with an Instek scope. > Here's a zoom of one of the burst. > > http://i43.tinypic.com/2eumxbk.jpg > > My primary and secondary are 1:1 ; inductance of 1.5mH. > > Is there anyway to clean this up? Looks like you haven't wound your toroid transformer in bifilar fashion. That is essential for apps like this, leakage inductance must be minimized, else this rings like crazy. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Robert Baer on 23 Apr 2010 02:42 Hammy wrote: > > I wound a toroid to use as a HS gate drive transformer for a 100W two > switch flyback. I'm using the typical DC restore technique AC couple > the transformer. > > Here's my schematic; > > http://i42.tinypic.com/9gvyow.png > > I'm using a PIC and a FET driver to simulate the extremes of the PWM > controller duty cycle and drive level and it works well with the > exception of Burst Mode. Burst mode is when the controller modulates > the original gate signal at light load for anyone who doesn't know. > > A picture is worth a thousand words. > > Here's my gate waveform at 90kHz 70% duty. A little sloping but > acceptable. > > http://i39.tinypic.com/25kieyq.jpg > > Now here's where the fun begins I'm modulating the 90kHz to simulate > burst mode. > > http://i44.tinypic.com/qy5l69.jpg > > Here's a zoom of one of the burst. > > http://i43.tinypic.com/2eumxbk.jpg > > My primary and secondary are 1:1 ; inductance of 1.5mH. > > Is there anyway to clean this up? That is the one thing i hate about those stupid "controllers" that supposedly are good for DC-DC conversion. Why simulate? Toss the verdammdt controller and use the PIC directly; then you can have the program be as dirty or clean (or both) as you want... ...Namely slow non-giga-amp startup current spikes!
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