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Transformerless Power Supplies

No Transformer Power Concept

Without a transformer concept, it works using a high voltage capacitor to reduce the AC voltage of the network to the required lower level required for the connected e circuit or load.
The specification of this capacitor is selected with a margin. An example of a capacitor that is commonly used in circuits without transformer power is shown below:

This capacitor is connected in series with one of the AC input voltage signals.
When mains alternating current enters this capacitor, depending on the size of the capacitor, the reactance of the capacitor comes into effect and limits the alternating current of the network from exceeding the specified level by the indicated value of the capacitor.

However, although the current is limited, the voltage is not limited, therefore, when measuring the rectified output without a transformer power source, we find that the voltage is equal to the peak value of the AC network, it is about 310 V.

But since the current is sufficiently lowered by the capacitor, this high peak voltage is stabilized by a zener diode at the output of the bridge rectifier.

Zener diode power must be selected in accordance with the permissible current level of the capacitor.

Advantages of using without a transformer power circuit

Cheapness and at the same time the efficiency of the circuit for low-power devices.
Without the transformer power circuit described here, it very effectively replaces a conventional transformer for devices with a current power below 100 mA.

Here, a high voltage metallized capacitor is used on the input signal to lower the mains current
The circuit shown above can be used as a DC 12V power supply for most electronic circuits.
However, after discussing the advantages of the above construction, it is worthwhile to dwell on several serious drawbacks that this concept may include.

Disadvantages without a transformer power circuit

Firstly, the circuit is unable to produce high current outputs, which is not critical for most designs.
Another drawback, which certainly requires some consideration, is that the concept does not isolate the circuit from the dangerous potentials of the AC network.

This drawback can have serious consequences for structures associated with metal cabinets, but it will not matter for blocks that are all covered in a non-conductive housing.

And last but not least, the aforementioned circuit allows power surges to penetrate through it, which can lead to serious damage to the power circuit and the power circuit itself.

However, in the proposed simple power supply without a transformer circuit, this drawback was reasonably eliminated by introducing various types of stabilizing steps after the bridge rectifier.

This capacitor makes instantaneous high voltage ripple, thus effectively protecting the associated electronics with it.

How the circuit works
1. When the AC mains input is turned on, capacitor C1 blocks the mains input and limits it to a lower level determined by the reactance value C1. Here we can roughly assume that it is about 50 mA.
2. However, the voltage is not limited, and therefore 220V can be on the input signal, allowing you to reach the next stage of the rectifier.
3. The bridge rectifier rectifies 220V to a higher DC 310V, to peak AC waveform conversion.
4. The DC 310V is quickly reduced to a low-level DC zener diode, which shunts it to a value according to the zener diode rating. If a 12V zener diode is used, then the output will be 12 volts.
5. C2 finally filters the DC 12V with ripples, into a relatively clean DC 12V.


Circuit example

The driver circuit shown below controls a tape of less than 100 LEDs (with an input signal of 220V), each LED is designed for 20mA, 3.3V 5mm:

Here, the input capacitor 0.33 uF / 400V produces about 17 mA, which is approximately correct for the selected LED strip.
If the driver is used for a larger number of similar LED strips 60/70 in parallel, then simply the value of the capacitor is proportionally increased to maintain optimal illumination of the LEDs.

Therefore, for 2 tapes included in parallel, the required value will be 0.68 uF / 400V, for 3 tapes replace with 1uF / 400V. Similarly, for 4 tapes it should be updated to 1.33 uF / 400V, and so on.

Important: although the limiting resistor is not shown in the circuit, it would be nice to include a 33 Ohm 2 W resistor in series with each LED strip, for added security. Can be inserted anywhere sequentially with individual ribbons.

WARNING: ALL CIRCUITS MENTIONED IN THIS ARTICLE ARE NOT ISOLATED FROM THE AC NETWORK, SO ALL SECTION OF THE CIRCUIT IS EXTREMELY DANGEROUS TO TOUCH WHEN CONNECTING TO THE AC NETWORK.

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11 comments
Not just unsuccessful, but worse: a source of information of dubious reliability was taken, translated by an auto-translator, slightly tweaked, cut and spoiled in places, in some places the original absurdities preserved. Moreover, the simple essence of the principle of action of such a source is not explained - what you had to do for the author.
To calculate the quenching capacitor, the voltage drop across the diodes (1.4) can be neglected.
But with the fact that you need to have 15 volts of change I agree completely.After all, the capacitor (at the output of the rectifier) ​​will be charged precisely to an amplitude value of 21 volts.
In any case, the article turned out to be some kind of unsuccessful ...
Yes, he was wrong. But you are also inaccurate: once the output has a constant voltage of 20 V, then the corresponding alternating voltage will be (20 + 1.4) / 1.4 = 15 V. At the rated voltage in the network, it is necessary to repay 230-15 = 215 V. And if it is necessary to guarantee 20 V at the load with the minimum allowable mains voltage (minus 10%), then it is necessary to pay off (230-23) -15 = 192 V.
But what about this:
For example, we need to have 20 volts at a load with a load current of 0.05 A. If the voltage needs to be stabilized, then we select the appropriate zener diode
? From your text it is obvious that we are talking about constant tension.
Quote: Ivan_Pokhmelev
300

Not 300, but 200.
We carry out the calculation in real values, and not in amplitude. Why drag them here at all?
Everything is so, only
Quote: Nruter
So 200 volts should "go out" on the capacitor
not 200 volts, but 300 (230 * 1.41 - 1.4 - 20 - drop on a small resistor).
Especially for Khabibra
The transformerless power supply is calculated easily and simply. For example, we need to have 20 volts at a load with a load current of 0.05 A. If the voltage needs to be stabilized, then we select the appropriate zener diode and remember that the current through it must be no less than the load current. So, the voltage is 20 volts, the current is 100 milliamps. This means that 200 volts should "go out" on the capacitor. At a current of 0.1 A, the reactance of the capacitor will be Xc = 200 / 0.1 = 2000 Ohms. Hence, the capacitance of the capacitor is C = 1 / (2 * 3.15 * 50 * 2000) = 1.6 microns. Choose the closest value or collect a battery of several.
That's how it is easy and simple without abstruse terms.
Mr Khabibra, in vain you try using the auto-translator to convey to the reader a topic that you yourself do not understand. ((
Guest Eugene
"Without transformer ..." - it is written so many times and hurts the eye. In such cases, you need to write together!
When a network variable current enters this capacitor, depending on the capacitor valuesreactive capacitor resistance takes effect and limits the alternating current of the network from exceeding the specified level, the specified value of the capacitor
the voltage is equal to the peak value of the AC network, it is about 310 V
high peak voltage stabilizes using a zener diode at the output of a bridge rectifier
for devices power current below 100 mA.
The bridge rectifier rectifies 220V to a higher DC 310V, to peak AC waveform conversion. 4.DC 310V is quickly reduced to a low-level DC zener diode, which shunts it to a value according to the zener diode rating
Here input capacitor 0.33 uF / 400V gives out about 17 ma
Well, Mr. WARENIC got followers! And for some people it takes a long time to learn! fool
Basil
Author pi3du in bast shoes is trying to put on shoes ...

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