Theoretically this would reduce ripple after a SMPS too, correct? Ryan On 6 March 2015 at 17:34, Bob Blick wrote: > It wouldn't work the same. As the load on the circuit increases, the > base current also increases, so the voltage drops both due to the > overall voltage drop, and also due to the increases base drive. > Hopefully keeping the transistor from dropping out (and letting ripple > through). > > If you used a MOSFET, you could get gobs of ripple reduction (the > resistor can be much larger), more than with a BJT. But as you increase > the load, the output voltage only tracks the voltage drop, not the > increased load current. > > A 78xx regulator would need the ground lead to be less than the output, > unlike a BJT or MOSFET. So you'd need to use a voltage divider (off the > input, to ground). It would track the input voltage, but due to the > voltage divider, to a lesser extent than a BJT or MOSFET. > > Friendly regards, Bob > > On Thu, Mar 5, 2015, at 07:25 PM, Ryan O'Connor wrote: > > Does it have to be a BJT? What about a mosfet or a 78xx regulator with = a > > cap on its adjust pin? > > > > Ryan > > On 6/03/2015 4:17 PM, "Bob Blick" wrote: > > > > > Hi Ryan, > > > You are right! It does not increase the storage of the filter > capacitor. > > > If you have an unregulated power supply with a filter capacitor (an > > > old-school DC wall-wart, for example) there will be ripple under load= .. > > > The greater the load, the greater the ripple. What the described > circuit > > > can do (with appropriate transistor/resistor/capacitor choices) is > > > maintain the output voltage a little under the lowest peak of the > > > ripple. The ripple on the output is less than, but follows, a multipl= e > > > of the circuit's capacitor. The nice thing about it is that the outpu= t > > > voltage drops with load, so it almost tracks the lower ripple peak, > > > something a 78xx regulator can't do. It also has less insertion loss. > > > Cheerful regards, Bob > > > > > > On Thu, Mar 5, 2015, at 06:50 PM, Ryan O'Connor wrote: > > > > That page is really informative. However, I'm left wondering about > the > > > > physics. How can a capacitor which stores charge possibly be > "multiplied" > > > > without any additional storage? > > > > > > > > Ryan > > > > > > > > On 6 March 2015 at 02:46, Adam Field wrote: > > > > > > > > > On Wed, Mar 4, 2015 at 12:17 PM, Bob Blick > wrote: > > > > > > Hi Joe, > > > > > > You could use a one transistor pass element to multiply a > capacitor. > > > Let > > > > > > me see if I can find an example on the web... nope. here's napk= in > > > art. > > > > > > > > > > > > Bob > > > > > > > > > > ESP has a good page on the concept: > > > > > > > > > > http://sound.westhost.com/project15.htm > > -- > http://www.fastmail.com - Access your email from home and the web > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .