ringing inductor in boost circuit
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From: Michael Robinson on 23 Jun 2010 17:42 I breadboarded a little voltage booster. Here's the business end of the circuit: +5v | ,------------+ | | | | | ) | )220uH /e ) -1k--| | \c ,----+--+-->|--+--out | | | | | | 68pF = | | | | | /c | | '--470--+--| - | | \e ^ = 4k7 | | | | | | | '----+--+------' | gnd The pnp is driven by a square wave. I also have feedback from the output, which I didn't show in this drawing, controlling the duty cycle to keep the output voltage steady at 16 volts. I used jelly bean transistors, Pn2222 and PN2907. The inductor has a fraction of an ohm resistance. The circuit is running at about 15kHz with light load. I only needed a few tenths of a watt for my purposes. I scoped the circuit. When the npn switch turns off the voltage at the collector jumps to 16 volts and clamps there, as it should. But when the voltage at the collector drops below the voltage on the filter cap, the inductor rings. The diode clamp across the emitter-collector and the 68pF cap are there to adress this. The diode clamps the initial negative excursion at the collector. The base-collector cap damps the ringing. Without that cap in place, ringing is quite pronounced. It starts out with a magnitude of ten volts, decays exponentially and is still ringing when the npn switch turns on in the next cycle. The cap cuts the intial amplitude of the ringing from about ten volts to about two, and it dies out much faster. Is the ringing of the inductor unavoidable in a circuit like this?
From: Hammy on 23 Jun 2010 19:15 On Wed, 23 Jun 2010 14:42:03 -0700, "Michael Robinson" <kellrobinson(a)yahoo.com> wrote: >I breadboarded a little voltage booster. >Here's the business end of the circuit: > > +5v > | > ,------------+ > | | > | | > | ) > | )220uH > /e ) >-1k--| | > \c ,----+--+-->|--+--out > | | | | | > | 68pF = | | | > | | /c | | > '--470--+--| - | > | \e ^ = > 4k7 | | | > | | | | > '----+--+------' > | > gnd > >The pnp is driven by a square wave. I also have feedback from the output, >which I didn't show in this drawing, controlling the duty cycle to keep the >output voltage steady at 16 volts. I used jelly bean transistors, Pn2222 >and PN2907. The inductor has a fraction of an ohm resistance. The circuit >is running at about 15kHz with light load. I only needed a few tenths of a >watt for my purposes. >I scoped the circuit. When the npn switch turns off the voltage at the >collector jumps to 16 volts and clamps there, as it should. But when the >voltage at the collector drops below the voltage on the filter cap, the >inductor rings. > >The diode clamp across the emitter-collector and the 68pF cap are there to >adress this. The diode clamps the initial negative excursion at the >collector. The base-collector cap damps the ringing. >Without that cap in place, ringing is quite pronounced. It starts out with >a magnitude of ten volts, decays exponentially and is still ringing when the >npn switch turns on in the next cycle. The cap cuts the intial amplitude of >the ringing from about ten volts to about two, and it dies out much faster. > >Is the ringing of the inductor unavoidable in a circuit like this? > Try an RC snubber across the output rectifier.
From: Hammy on 23 Jun 2010 19:31 On Wed, 23 Jun 2010 19:15:29 -0400, Hammy <spam(a)spam.com> wrote: >On Wed, 23 Jun 2010 14:42:03 -0700, "Michael Robinson" ><kellrobinson(a)yahoo.com> wrote: > >>I breadboarded a little voltage booster. >>Here's the business end of the circuit: >> >> +5v >> | >> ,------------+ >> | | >> | | >> | ) >> | )220uH >> /e ) >>-1k--| | >> \c ,----+--+-->|--+--out >> | | | | | >> | 68pF = | | | >> | | /c | | >> '--470--+--| - | >> | \e ^ = >> 4k7 | | | >> | | | | >> '----+--+------' >> | >> gnd >> >>The pnp is driven by a square wave. I also have feedback from the output, >>which I didn't show in this drawing, controlling the duty cycle to keep the >>output voltage steady at 16 volts. I used jelly bean transistors, Pn2222 >>and PN2907. The inductor has a fraction of an ohm resistance. The circuit >>is running at about 15kHz with light load. I only needed a few tenths of a >>watt for my purposes. >>I scoped the circuit. When the npn switch turns off the voltage at the >>collector jumps to 16 volts and clamps there, as it should. But when the >>voltage at the collector drops below the voltage on the filter cap, the >>inductor rings. >> >>The diode clamp across the emitter-collector and the 68pF cap are there to >>adress this. The diode clamps the initial negative excursion at the >>collector. The base-collector cap damps the ringing. >>Without that cap in place, ringing is quite pronounced. It starts out with >>a magnitude of ten volts, decays exponentially and is still ringing when the >>npn switch turns on in the next cycle. The cap cuts the intial amplitude of >>the ringing from about ten volts to about two, and it dies out much faster. >> >>Is the ringing of the inductor unavoidable in a circuit like this? >> >Try an RC snubber across the output rectifier. SMPS's are always noisy when you do them on a breadboard. you can also read through theis from TI for more suggestions. "Minimizing Ringing at the Switch Node of a Boost Converter " http://focus.ti.com/lit/an/slva255/slva255.pdf
From: John Larkin on 23 Jun 2010 19:51 On Wed, 23 Jun 2010 14:42:03 -0700, "Michael Robinson" <kellrobinson(a)yahoo.com> wrote: >I breadboarded a little voltage booster. >Here's the business end of the circuit: > > +5v > | > ,------------+ > | | > | | > | ) > | )220uH > /e ) >-1k--| | > \c ,----+--+-->|--+--out > | | | | | > | 68pF = | | | > | | /c | | > '--470--+--| - | > | \e ^ = > 4k7 | | | > | | | | > '----+--+------' > | > gnd > >The pnp is driven by a square wave. I also have feedback from the output, >which I didn't show in this drawing, controlling the duty cycle to keep the >output voltage steady at 16 volts. I used jelly bean transistors, Pn2222 >and PN2907. The inductor has a fraction of an ohm resistance. The circuit >is running at about 15kHz with light load. I only needed a few tenths of a >watt for my purposes. >I scoped the circuit. When the npn switch turns off the voltage at the >collector jumps to 16 volts and clamps there, as it should. But when the >voltage at the collector drops below the voltage on the filter cap, the >inductor rings. > >The diode clamp across the emitter-collector and the 68pF cap are there to >adress this. The diode clamps the initial negative excursion at the >collector. The base-collector cap damps the ringing. >Without that cap in place, ringing is quite pronounced. It starts out with >a magnitude of ten volts, decays exponentially and is still ringing when the >npn switch turns on in the next cycle. The cap cuts the intial amplitude of >the ringing from about ten volts to about two, and it dies out much faster. > >Is the ringing of the inductor unavoidable in a circuit like this? > If the L is bigger or the frequency is higher, you can run in continuous mode, where the upper diode keeps conducting until the transistor turns on again. Just make sure to limit the transisor duty cycle. Or use a snubber as suggested. Snubbing, or damping as you are doing, reduces efficiency a little. John
From: Jamie on 24 Jun 2010 18:55
Michael Robinson wrote: > I breadboarded a little voltage booster. > Here's the business end of the circuit: > > +5v > | > ,------------+ > | | > | | > | ) > | )220uH > /e ) > -1k--| | > \c ,----+--+-->|--+--out > | | | | | > | 68pF = | | | > | | /c | | > '--470--+--| - | > | \e ^ = > 4k7 | | | > | | | | > '----+--+------' > | > gnd > > The pnp is driven by a square wave. I also have feedback from the output, > which I didn't show in this drawing, controlling the duty cycle to keep the > output voltage steady at 16 volts. I used jelly bean transistors, Pn2222 > and PN2907. The inductor has a fraction of an ohm resistance. The circuit > is running at about 15kHz with light load. I only needed a few tenths of a > watt for my purposes. > I scoped the circuit. When the npn switch turns off the voltage at the > collector jumps to 16 volts and clamps there, as it should. But when the > voltage at the collector drops below the voltage on the filter cap, the > inductor rings. > > The diode clamp across the emitter-collector and the 68pF cap are there to > adress this. The diode clamps the initial negative excursion at the > collector. The base-collector cap damps the ringing. > Without that cap in place, ringing is quite pronounced. It starts out with > a magnitude of ten volts, decays exponentially and is still ringing when the > npn switch turns on in the next cycle. The cap cuts the intial amplitude of > the ringing from about ten volts to about two, and it dies out much faster. > > Is the ringing of the inductor unavoidable in a circuit like this? > > have you tried putting a small R in series with the inductor to lower the Q ? |