[MAMS] DC-DC boost converter

[Dr. Gerald N. Johnson]

A non isolated buck switching converter can do that inversion IF its 
input can stand the sum of the maximum input voltage and the desired 
output voltage. Say 14 volts in and -20 out so it needs to stand +34 
volts in. You ground the + output connection of the circuit, you apply 
+12-14 to the normal input, and you take -20 (providing you have the 
buck converter set for 20 volts output) off the normally grounded 
circuit connection.

Isolation is another way to get there but not required for the simple 
buck regulator connection. And the circuit can be set to regulate at 20 
volts and most all the commercial isolated converters don't allow for 20 
volts so you have to take 24 and add a three terminal regulator to get 
down to 20.

IIRC something like an LT1041 or LT1045 is ideal for this scheme taking 
few external components, like an inductor and some capacitors, and a 
couple resistors to set the output voltage. The scheme is on the data 
sheets of some regulators in that family.

73, Jerry, K0CQ

On 10/3/2012 12:47 PM, Dexter McIntyre W4DEX wrote:
> Dr. Gerald N. Johnson wrote:
>> Two critical questions: What's its minimum load? What's its noise output?
>>
> Also is the output fully isolated from the input?  That's needed to use
> a microwave brick oscillators that requires a negative voltage for an LO
> in a transverter powered by by a common 12 volt input.
>
> Dex
>
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