Transformer less power supply is used in electronic projects where low low voltages needed. Low voltage DC like 3v, 5v,6v 9v 12v required we use this kind of supply. In electronics circuits generally batteries are used but batteries need to be replaced after some time. So, to overcome this problem we use powers supplies to generate DC from 220v or 110v AC.
Straight forward and easy way is to use step-down transformer from AC to DC, but the transformers costly, heavy in weight and big in size. We already discussed different ways of converting AC to DC using transformers.
In this post we are going to discuss transformer less power supply to run LEDs drive, Led bulbs different toys and etc.
X-Rated Capacitor
X-Rated Capacitors are connected in the series with the AC Phase line to lower down the current. These capacitors are found in 230 volts, 600v.
Output current and output voltage of X-rated capacitors
Output current and output voltage (without the Load), of different values of X-rated capacitors are given in the below table
Capacitor Code |
Capacitor value |
Voltage |
Current |
104k |
0.1 uF |
4 v |
8 mA |
334k |
0.33 uF |
10 v |
22 mA |
474k |
0.47 uF |
12 v |
25 mA |
684k |
0.68 uF |
18 v |
100 mA |
105k |
1 uF |
24 v |
40 mA |
225k |
2.2 uF |
24 v |
100 mA |
Selection of voltage dropping capacitor is important, it is based on Reactance of Capacitor and the amount of current to be withdrawn. The Reactance of the capacitor is given by below formula:
- X = 1 / 2¶fC
- X = Reactance of Capacitor
- f = frequency of AC
- C = Capacitance of X rated capacitor
We have used 474k means 0.47uF capacitor and frequency of AV mains is 50 Hz so the Reactance X is:
- X = 1 / 2*3.14*50*0.47*10^{-6} = 6776 ohm (approx.)
Now we can calculate the current (I) in the circuit:
- I = V/X = 230/6775 = 34mA
So that’s how the Reactance and Current is calculated.
Circuit Diagram with controlled Voltages
Caution
- Its extremely dangerous to work with AC mains without proper experience and precaution. So, be very careful while building this circuit.
- Replace X-Rated capacitor with normal capacitor.
- You can increase the value of capacitor if more output voltages needed as given in the table.
- Zener diode must be 1w or more than 1watts Zener diode is only controller of output in this circuit.
- If you use fuse it will be more suitable.
- Never touch the circuit while it is on.
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