This is a multi-part message in MIME format. ------=_NextPart_000_00E9_01C13225.FF09DDE0 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: 7bit Here's a revised circuit of the BooBu converter - addition of D3 is the only change. This should do exactly what is wanted to hold the converter in boost phase until all inductor energy is expended. Again, where shown compionent values should be ignored. It works (hopefully) like this - Afetr current input phase with Q3 and Q4 on the voltage on C2 rises, as before, until Z1 conducts. This causes regenerative turnoff action and L flips polarity so that the LH end is at near ground potential and the RH end rises until current flows via D1 to the load and CBUK2. Q3 is off and the cathode of D1 has voltage present ONLY because of the collapsing magnetic field in L. D3 conducts and holds Q1 on thus keeping the converter in the "off" phase. C2 discharges to zero to wait anothe rturn on cycle. Only when the energy in L is dissipated and the rh end of L falls to near ground will D3 stop conducting. At this stage Q1 again turns on and the cycle repeats EXCEPT that if this last cycle has caused Vout to reach it's design level then ZBUK1 wikll be conducting and will hold the conveter off until Vout again falls. D3 could instead be a zener and series diode to allow the inductor rh end to not have to return fully to ground before the cycle restarts. As before, under certain circumstances a design MAY be able to combine Q2 and Q4 but this would be more as a fun exercise than a useful cost saving. 3 of the 4 transistors are low current NPNs and could be in a single small outline package leading to a very compact design. 4 x SOT-23 are also fairly tiny. Even 4 x TO92 pkgs are rarther compact given the single inductor winding and relatively few other components. The terminally enthusiastic may be able to eliminate RBUK4 and PBUK1 but again this would be more for fun than a sensible approach. regards, Russell McMahon ------=_NextPart_000_00E9_01C13225.FF09DDE0 Content-Type: image/gif; name="boobu2.gif" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="boobu2.gif" R0lGODlh0wF/AYAAAAAAAP///yH5BAAAAAAALAAAAADTAX8BAAL/jI+py+0Po5w0gXNRrrz7D4bi SJbmiabqem4bC8fyTNf2jeeoq70BAPTphsSi8YhMKn8Yi9MgXEqn1Kr1ersIfTys9wsOi8NaBbc5 TqvX7PbODNSg3fS6/Y7P6/f8vv8PGCg4SFhoeIiYqLiIGETlqAjJOEnZI5kUFNeYWdk5mQkaKjpK Wmp6ipqqusra6vmaCColu3kJeytoi6kZy4v7GxiF+QlcHGwlXJhszEy3bPSc2zydF01kDYhNvY2l nePdB849viRuY66HTr5+jUzMDu+lPjN/Vx+PH3MPs++c/z/LHaN+AAuOIKgCIRuFBhtyYNjincOJ 5wQugkgxIwOM/yU4ivGoMSSTKiDBlBRJ8SQIld1QuoxIUuLLmSstRqKJ8wNLDztt5vwZoedDmUCL NhBaAekUpUanMZXwVEnUpsWmPrB6BCvVW1o3Et1KtesCsUPIgqVkVs7As2fTzrnJtiipgGvjAo1i 1m0Wu3fH0r3I9yfev3AD0xxc7qthkYilKl6ssfGwupBdIuaE4VKXkZzfBn1ceeLlOZtLQ4GTFHTo 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