Today’s microprocessors need a regulated 3.3-V supply that can provide several amperes of current. To obtain this, a synchronous switching regulator (LTC1266-3.3) using a 5-V supply is usually used with a p-channel top-side MOSFET and an n-channel bottom-side MOSFET. However, because a p-channel MOSFET has higher RDS(on) and higher gate capacitance than that of a comparable n-channel MOSFET, there would be a higher voltage drop across the MOSFET. This contributes to higher overall power loss. Such a drop in efficiency becomes even more obvious under high current situations. The ideal configuration would use n-channel MOSFETs for both top- and bottomside switches.

To replace the p-channel MOSFET with an n-channel, a secondary input voltage capable of fully enhancing the n-channel MOSFET is needed. Because this secondary input only drives the gate of the charging MOSFET, little current would be drawn. A simple and compact charge pump (LTC1263) that converts 5 V to 12 V does the job. As shown, both the switcher and the charge pump are powered by the 5-V supply while the 12-V output of the charge pump drives the V_in pin of the switcher.

The charge pump has a somewhat lower efficiency than that of an inductor-based switcher. However, it’s preferred over a boost switching regulator because of the charge pump’s simplicity and its need for fewer and smaller external components. These advantages outweigh the drawback of its lower efficiency.

Since both the LTC1266-3.3 switcher and the LTC1263 charge pump have shutdown pins, both of them can be connected directly to an I/O line from a microprocessor. This way, the system can save much current and power during standby mode.

With these two new regulated supplies of 12 V/60 mA and 3.3 V/5 A generated from the original 5-V supply, many previously tough power supply problems are eliminated.

See associated figure

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Reader Comments please send me ckt diag. for +5v & -5v regulated power supply using center tap transformers separately, to avoid confusion vishal meshram -October 22, 2008 i need DC to DC converter circuit diagram with dual power supply output............. Anonymous -October 08, 2008 please just send the power supply. Anonymous -June 04, 2008 Please send me a schematic diagram of a regulated power supply with output voltage of 5V. Charles -October 31, 2007 What's the bet most of these people saying "o plz send me the wiring for that voltage regulator" wouldn't even make it anyway? Damn freeloaders. MasterCJ -August 25, 2007 Please send me a circuit diagram of a DUAL Output Supply LDO voltage regulator, from Vin=+5V, Vout1=+3.3V, Vout2=+2.5V thank you joe -May 15, 2007 Please send me a schematic diagram of a regulated power supply with output voltage of 5V, 7V and 9V, in one circuit. Please i badly need it. thanks. Eric trinidad -April 29, 2007 send me wiring layout, in a server with dual power supply facility shared when system is configured with two power supply is that a. two different phase of same source of power supply b. same phase of two source of power supply Anonymous -March 29, 2007 please send me a circuit diagram for 5v input to 12v output regulator michael -December 19, 2006 Please send me a circuit diagram of a DUAL Output Supply LDO voltage regulator, from Vin=+5V, Vout1=+3.3V, Vout2=+2.5V thank you and more power!!! carlos -August 29, 2006 please send me the circuit diagrame of of the above mentioned LTC 1266-3.3V to obtain 12v & 3.3v from 5v DEEPAK SEHGAL -December 06, 2005 please i want circit for dc dc converter in put+5 volt output +/- 12 volt 300ma small size thank you for help me best regard ahmed dawod ahmed dawod -June 29, 2005
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