220 VAC to 12VDC 4A Convertor

Dear All,
I need to make a converter from 220VAC to 12VDC -4A to operate a solenoid
i required this circuit for pulse shot only (800ms -1s)
please tell me any circuit i can not use Transformer .
only linear circuit.

You can use 12V switching supply used with 12V/50W spotlight bulb. Its cheap and easily available from electrical stores.

If you need pulse shot why don`t you use an invertor??? Or the idea is different???

220VAC to 12VDC 4A linear circuit without transformer would be VERY inefficient and would produce LOTS of heat. Even though it's needed for short time, how frequently is it going to be used to produce the 4A output?
You might look for a cheap 12V power supply at some electronics store or eBay. A switching circuit for 12V 4A should be available at quite reasonable price.

Hope this helps.
Tahmid.

I need to shot a solenoid which is enclosed in a door lock.
i need to open the door i need it to be shot for Maximum 1 second .
if i used switching supply for this purpose then it will be overkill.

please advice

The supply i mentioned is so common that it cost only 40 rupees. People call it choke. If you ask for choke for 12V spotlight, you will get it.

It is strange to note the price of bulb on ebay. its available 3 for $1 in our local market.
**broken link removed**
The driver for this bulb provides more than 4A continuously.
eBay: driver 12 Halogen Light Bulb
**broken link removed**

If simplicity and cost are a paramount of your design i can only see two options: Use a tranformer like the one mentioned before or find a 220 V coil.

I would never recommend linear methods. A first approximation of the dissipated power: P = V * I = (220-12)*4 = 832 W for 1 second... Almost 1 kJ of wasted energy .

12V at 4A works out to a 3 ohm load. 48 watts.

You can store the energy in a capacitor. It would need to be a lot of uF.

How many uF? I calculate about 330,000. One-third farad.

How? I estimate a time constant of 1 should maintain the load above 6V for a second. Since TC=RC, and load is 3 ohms, then capacitance = 1/3.

Better to use maybe 4 capacitors, each delivering 1A. Such a bank might take up as much room as a C battery. You can fire it once, and then it will need time to charge to 12V again.

This may take several seconds. A popular way to obtain low V from mains is to use a capacitor. It generates reactance. Far less heat is involved. The schematic at this link would need several changes, in order to charge your capacitor fast enough to be practical. To limit it to 12V, you would substitute two 12V zener diodes in the diode bridge.

Transformerless power supply (electroschematics.com):

TransformerLess Power Supply 12V 100mA

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In considering other methods:

Resistance: To drop 220VAC to 12VDC at 4A implies that you will put in a resistance of 55 ohms, which can handle 832 W for one second. It may be okay for a second, if you parallel several power resistors.

Reactance: Put a coil, or capacitor, inline with your solenoid. Not too practical since current is 4 amps. Needs either a beefy coil or a beefy cap.

Hello my friends
If you don't want use transformer , and isolation isn't important for you , you can use a simple buck converter . and it is very good for this aim . but if isolation is important you can use a forward converter with HF transformer ( very small ).
Best Wishes
Goldsmith

ALERTLINKS said:

The supply i mentioned is so common that it cost only 40 rupees. People call it choke. If you ask for choke for 12V spotlight, you will get it.

It is strange to note the price of bulb on ebay. its available 3 for $1 in our local market.
**broken link removed**
The driver for this bulb provides more than 4A continuously.
eBay: driver 12 Halogen Light Bulb
**broken link removed**

Click to expand...

is this bulb commonly available in pakistani market?

Qaiser,
Yes it is available very commonly in our market and at surprising price, too.