Yes, power handling was one of my concerns.
#Ferrite core inductor calculations full
If the amplifier has zero ripple reduction, output buzz is very roughly -75dB from full output. In this case the designer got to 2x22,000uFd before he either met his ripple spec or ran out of space/money.Ĥ4,000uFd at 100Hz is 0.036 ohms. Then super-size the capacitors, spending about equally on C1 and C2. At these currents, 2mH may be as good as it gets without custom-winding a heavy hunk of iron. So the answer seems to be: find the biggest practical choke. Taking 1,000uFd and sticking with 1mH, 1000uFd at 100Hz is 1.6 ohms, choke is 0.6 ohms, ripple is reduced about as 1.6/(0.6+1.6) or 1:0.7, still not much. On today's market, caps of any size are a commodity product, chokes are all "specials". This works really well when caps are cheap, as they have been since 1940. Since the choke can't be as good as we like, we pick a cap with very-very-very low impedance. We would like the capacitor's AC impedance to be very low. We would like the choke's AC (100Hz) impedance to be very high (with low DC resistance), but that may not be easy. And in the real world, a bag of same-size caps is cheaper than an assortment of different values. Both act as reservoirs, the choke prevents the amp from getting full use of C1, so C2 should be large too. A good first-guess is that C2 should also be >1,000uFd. Note that C1 "has" to be >1,000uFd for tolerable ripple in a speaker-amp. However this calls for 50V/2,000mA= 25mH. > desired output voltage (V) / total current draw (mA) => inductor size (H)Īn OK starting point.
The ripple reduction is about 0.6/(0.6||50), or about 1:0.99, not much at all.
Using the above values, 32mFd is 50 ohms at 100Hz and 1mH is 0.6 ohms at 100Hz. (However, even if the air-core choke acts like a resistor at 100Hz, it can have high impedance at 1,000Hz, which will reduce the most annoying part of the ripple.) Iron/etc-core will give higher AC impedance at lower DC resistance. In fact air-core is not a lot of good for reducing 100Hz ripple, unless you use a LOT of copper (big, costly). However, as air-core, we will probably find ~1 ohm DC resistance. 1mH is readily available (you can use a pound of fat magnet wire on a plastic spool). In 60Hz lands it will be 120Hz ripple, but we don't need to be precise and I'm lazy.ģ2uFd is 50 ohms at 100Hz. Take 100Hz as the ripple frequency (double the line frequency). Speaker amp power supply impedance is around 50 ohms. For best ripple reduction, the impedance of the C should be much less than the load R, the impedance of the R or L should be more than the load R. If that is not clean enough, add a R-C or L-C filter. Generally you aim for 5% ripple, though you may have to re-consider this. Pick C1 as a reasonable compromise between ripple and cost/size. The exact inductance is not critical, and the inductor current is known. (Cored chokes sold for speaker use "should" have a reasonably constant inductance up to rated current.) You MUST be sure it is rated for more current than you have, and you must accept that the actual inductance could vary 2:1 from low current to rated current. Iron/ferrite/powder cores allow a smaller (and sometimes cheaper) part, but the inductance declines at high current. behave the same way as a ferrite core inductor,Īir-core has a constant inductance at any current (until it melts, which is a huge current).
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