This is an interesting task to do
and thankfully you don’t need an electrical engineering degree in order to
figure out how to do it. The best way to figure it out is to disassemble a Chinese
made flashlight and you can see that they use just capacitors to bring down the
voltage instead of a transformer. They use it to charge a small lead-acid
battery. The question now is how a
capacitor alone can be used to bring down 220volt down to 6 or 12 volt? What is capacitive power supply anyway?
A capacitive power supply is a
type of power supply that uses the capacitive reaction of a capacitor to reduce
the mains voltage to a lower voltage. There are
two important limitations. First the high withstanding voltage required of the
capacitor, along with the high-capacitance required for a given output current,
mean that this type of supply is generally used only in low-power applications.
Generally, a capacitor of a given size or budget can have a high voltage rating
or high capacitance but not both. The second is that due to the absence of
electrical isolation, the circuit must be encapsulated and isolated to avoid
direct galvanic contact with the users.
This process is extremely unsafe.
There are achievable but un economical methods to do so. You can use a
capacitor divider. Replace the resistors of a resistor divider with capacitor.
It is a possible way to reduce voltage. However there are two challenges. Unregulated
voltage. A regulator must be used. You will need capacitors that will let pass
3 amps.
Another way to convert AC to DC
without a transformer is to use electrostatic induction (capacitive dual of a
transformer). It is still immature technology but possible to be
modified to your application. You can use electronic circuits but they won’t be
able to provide a 3A output. It won’t be
more than .5A output. Why is India using 220 volts when the United States is
using 110 volts of power?
You need to know your supply
types and the pros and cons for each use of the product. A Capacitive supply
type is a higher cost than resistive. However it is more efficient than
resistive. The zero crossing is delayed. A Resistive supply type is the lowest
cost but also the least efficient. The zero crossing is not delayed. The Bridge
supply type is the highest cost but also the highest current capacity and
efficiency. The output voltage isn’t referenced to line or neutral so TRIAC
control isn’t possible.
They are using lots of transformer
less power supplies in China in their small appliance products. Because
transformers are big and heavy use a capacitor replace which is smaller and
lighter than a transformer as a power supply. The problem is that if you touch
the circuits you might get a electric shock. So, as I said before, it is
unsafe. The use of transformer less power supply dates back to about 15-20
years ago.
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