This is a multi-part message in MIME format. ------=_NextPart_000_0015_01C12BBB.6B2155B0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit > Here's the circuit as it actually got implemented. Since everyone is throwing their circuits out there, I've decided to give in and throw out mine too. This circuit is a piece of a personal project I am currently working on and it was designed before this thread started. However, it hasn't been built yet, which is why I didn't want to let it out earlier. It is also intended for much higher currents, but the topology should scale down to lower currents nicely. This circuit is intended to take 12-20 V unregulated DC at "+12UNREG" and make a roughly regulated 10V out at "+10V" with the capability of 1.5A. This is a rather straight forward self oscillating buck converter. It is actually similar in concept to the "divine inspiration" circuit, although the source of this one was much more mundane common sense and some down to earth engineering with careful calculations. Some notes on this design: 1 - D6 need not be a fast recovery diode. The values of L3, C4, the hysterisis, and the 0-1.5A current draw range make sure that L3 is always done conducting before Q1 turns on for the next pulse. This allows D6 to be an ordinary power diode, which is very useful considering the currents envolved. 2 - Note that the *average* current thru Q1 and L3 is 1.5A max. Since this current will come in pulses, the peak current will be much larger. This is an important point that the other designs seemed to have missed. I chose these parts to handle a peak current of 6A, since this is some margin above the theoretical peak current. Note that this also effects the peak current rating of D6, because it will see the same peak current as L3. 3 - Oscillation is guaranteed due to the hysterisis provided by R4 and R2. This assumes that +5VREF is a zero impedance source. 4 - In my project, +5VREF is actually coming from a 5V regulator powered by the +12UNREG line. This is OK since the current draw on the +5VREG line is under 20mA. You could generate a good enough reference with a zener, resistor, and cap. The cap must be large enough so that its impedance is much less than R2 at the switching frequency. With a custom reference, the R6 and R5 divider could be eliminated and the output voltage fed directly into the minus input of the comparator. 5 - Q2 and Q3 provide the current amplification necessary to switch the FET gate quickly. Note that power FETs have considerable gate capacitance, and the slew rate of most ordinary op amps or comparators would slow down significantly if connected directly to the gate. Any reasonalbe small signal "junk box" transistors would do for Q2 and Q3. The ones show happen to be my junk box transistors I use for this purpose. They are available very cheaply from Jameco. 6 - The choice of LM6132 as comparator is not optimal. There happened to be one of these left over from the rest of the circuit and it should be good enough for this purpose. 7 - The max input voltage is limited by the max allowed FET gate voltage, which is 20V. This could easily be extended with a resistor between the op amp output and Q2/Q3 followed by a 12V zener clamp to the +12UNREG line. The next limit is the max power supply allowed by the LM6132, which is 24V. This could be extended another 10V or so by playing games with the negative supply input, but that gets messy. The right answer is to use a comparator better suited for the job or make something from a few discrete transistors that can all take the higher voltage. Keeping the Q2/Q3 current amplifier will be especially important then. ------=_NextPart_000_0015_01C12BBB.6B2155B0 Content-Type: image/gif; name="buck.gif" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="buck.gif" R0lGODlhewK0AfcAMQAAAAEBAQICAgMDAwQEBAUFBQYGBgcHBwgICAkJCQoKCgsLCwwMDA0NDQ4O Dg8PDxAQEBERERISEhMTExQUFBUVFRYWFhcXFxgYGBkZGRoaGhsbGxwcHB0dHR4eHh8fHyAgICEh ISIiIiMjIyQkJCUlJSYmJicnJygoKCkpKSoqKisrKywsLC0tLS4uLi8vLzAwMDExMTIyMjMzMzQ0 NDU1NTY2Njc3Nzg4ODk5OTo6Ojs7Ozw8PD09PT4+Pj8/P0BAQEFBQUJCQkNDQ0REREVFRUZGRkdH R0hISElJSUpKSktLS0xMTE1NTU5OTk9PT1BQUFFRUVJSUlNTU1RUVFVVVVZWVldXV1hYWFlZWVpa WltbW1xcXF1dXV5eXl9fX2BgYGFhYWJiYmNjY2RkZGVlZWZmZmdnZ2hoaGlpaWpqamtra2xsbG1t bW5ubm9vb3BwcHFxcXJycnNzc3R0dHV1dXZ2dnd3d3h4eHl5eXp6ent7e3x8fH19fX5+fn9/f4CA gIGBgYKCgoODg4SEhIWFhYaGhoeHh4iIiImJiYqKiouLi4yMjI2NjY6Ojo+Pj5CQkJGRkZKSkpOT k5SUlJWVlZaWlpeXl5iYmJmZmZqampubm5ycnJ2dnZ6enp+fn6CgoKGhoaKioqOjo6SkpKWlpaam 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