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Re: transformers

On Wed, 6 Dec 2000, Larry Smith wrote:

How is this done, in addition to below? (voltage up.)

I think he's talking about "Switching Regulators". These use the
inductive kick from a tiny coil to step up the voltage. If you connect an
inductor to a voltage source, let the current build up, then suddenly
insert a capacitor and diode in series, then the capacitor will behave as
an open circuit and will charge up to a higher voltage than the power
supply, while the current through the inductor will fall to zero. Repeat
the process at 30,000 times per second, take your output across the
capacitor, and you've created a transformerless DC/DC step-up device.

I'm curious too. For our astronomy class we run two Meade telescopes which
call for 18 VDC from the car battery. There is a (literally) black box
which has one end labeled 18 V and the other end 12 V.

That might just be a "series regulator", where a transistor in series with
the +18V wire causes a voltage drop to 12v on the output. The transistor
actually forms a resistive voltage divider along with the external load
resistance. There is a feedback circuit as part of this, and the
transistor is constantly adjusted so that the voltage-division will always
produce 12VDC output. If you open up the black box, you might find an
even smaller black box, since these sorts of regulators often are entirely
built into the package of a single power transistor.

On the other hand, sometimes switching regulators are used as step-down
regulators. Putting a transistor in series with your power supply will
dissipate heat just like a resistor would. There are no big resistors
involved when switching currents through an inductor, so a switching
regulator can handle large currents while remaining ice cold, while a
series transistor regulator gets hot and needs a big heat sink in order to
handle currents over 1/4 amp.

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