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This boost regulator is for those times when you have a 28v relay, but want to use it with a 12v source. The circuit is built around the National Semiconductor LM2585, and uses the energy stored in an inductor to boost the 12v to 28. Output voltage can be varied by adjusting the ratio of resistor values on the feedback pin.
The circuit does it's switching around 100 Khz, but generates no noise if SMT components are used. Output is good for about half an amp continuous, enough to power two or three large microwave relays. The board measures 1.5"x2".
It is important to note at least these three cautions before powering up the board:
If you are using a PC board I once supplied (I no longer stock
them), please refer to this
picture, and the schematic below. A close-up picture, to assist with component
placement, can be seen here.