This is a multi-part message in MIME format. ------=_NextPart_000_007B_01C580C7.64968340 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original Content-Transfer-Encoding: 7bit Bob Blick wrote: > 2. Why did you make it current limiting? It also limits your lowest > supply voltage. I agree with Bob here. I know you put current limiting in the spec, but I would look for other ways to achieve the same thing, probably at a higher level. The schematic I posted was current limited as per spec, but I would rather just get rid of the emitter resistors and put base resistors in instead. I have revised my schematic (attached) to loose the current limiting. This is about a simple as it gets, with only 4 transistors. Only one of the inputs at R5 and R6 may be driven high at a time. This H bridge is desinged to supply a minimum of 300mA to the load with a minimum supply of 3V. The transistors are assumed to have a minimum gain of 50, which is quite reasonable for this voltage and current range. Power dissipation in the pass elements is minimal since they are always run in saturation when on. This also means minimal headroom is used by the H bridge and most of the voltage goes to the load. The control inputs are meant to be driven directly from PIC pins with the PIC supply being 3-5V. ------=_NextPart_000_007B_01C580C7.64968340 Content-Type: image/gif; name="hbridge.gif" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="hbridge.gif" R0lGODlhfgKnAfcAMQAAAAEBAQICAgMDAwQEBAUFBQYGBgcHBwgICAkJCQoKCgsLCwwMDA0NDQ4O Dg8PDxAQEBERERISEhMTExQUFBUVFRYWFhcXFxgYGBkZGRoaGhsbGxwcHB0dHR4eHh8fHyAgICEh ISIiIiMjIyQkJCUlJSYmJicnJygoKCkpKSoqKisrKywsLC0tLS4uLi8vLzAwMDExMTIyMjMzMzQ0 NDU1NTY2Njc3Nzg4ODk5OTo6Ojs7Ozw8PD09PT4+Pj8/P0BAQEFBQUJCQkNDQ0REREVFRUZGRkdH R0hISElJSUpKSktLS0xMTE1NTU5OTk9PT1BQUFFRUVJSUlNTU1RUVFVVVVZWVldXV1hYWFlZWVpa WltbW1xcXF1dXV5eXl9fX2BgYGFhYWJiYmNjY2RkZGVlZWZmZmdnZ2hoaGlpaWpqamtra2xsbG1t bW5ubm9vb3BwcHFxcXJycnNzc3R0dHV1dXZ2dnd3d3h4eHl5eXp6ent7e3x8fH19fX5+fn9/f4CA gIGBgYKCgoODg4SEhIWFhYaGhoeHh4iIiImJiYqKiouLi4yMjI2NjY6Ojo+Pj5CQkJGRkZKSkpOT k5SUlJWVlZaWlpeXl5iYmJmZmZqampubm5ycnJ2dnZ6enp+fn6CgoKGhoaKioqOjo6SkpKWlpaam 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