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DC to DC conversion Help

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picstudent

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Hello

I need to measure a DC voltage that varies from +55V to +75V approximately.
I can do it using a PIC Micro. But I need to derive the +5V DC from the voltage I need to measure.

Which is the best method to derive +5v from this source. Linear supply using 78xx reg will generate heat at this input output difference?

I need to run a PIC micro and three seven segments digits from this supply. Maximum 500ma or something altogether.

Please suggest the best method.

Thanks

Roy
 
Can the Pic Vss be connected to the minus side of the +55 to+75V supply?

The Pic A/D converter can strapped to be ratiometric w.r.t. it's own Vdd, or it can be fed from an external reference. You have two options: regulate the PIC's Vdd to sufficient accuracy, or dont worry about the exact PIC Vdd, and buy a voltage reference chip.

As to the efficiency question, use a "buck" switcher. Look at National's or Linear Technology's chip solutions, or buy a ready made one. Any decent switcher will have an efficiency of at least 85%.
 
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Can the Pic Vss be connected to the minus side of the +55 to+75V supply?
Yes, Ground can be (is) common. The input to my system will be a ~ + 60Vdc and Ground. For reference Voltage I can use 2.5V or 2.048V ref chips.(2.5V is Very cheep and available locally) But my main requirement is the information to derive Vdd for PIC using a DC to DC converter. +5 Volt @ 500mA from +60vdc and Ground.

As to the efficiency question, use a "buck" switcher. Look at National's or Linear Technology's chip solutions, or buy a ready made one. Any decent switcher will have an efficiency of at least 85%.
To be frank, slight lower percentage of efficiency is not a problem in my case. But I need to avoid this heating up 78XX. I am interested in learning and implimenting a swicher based power supply. I think that is what we call by dc to dc converter. right?.(Correct me if I am wrong)

looking for app notes or example designs.

Thanks a lot
 
**broken link removed**
 
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