Pulse and analog power supplies, working principles and main differences

Virtually all modern electronic devices already use for their work switching power supplies and simple (analog) power supplies are quite rare. To understand the reason why it happened, let's examine the algorithms of their operation, as well as strengths and weaknesses.

Power supply with power transformer

For ease of understanding, let us study a simplified diagram of such a power supply unit (PSU)

From the above presented figure shows that the input is a step-down transformer. Thanks to it the incoming voltage transformation is performed, for example 230 volts, the output voltage, for example 12 volts. As is the transformer isolating the high and low side.

Next is a converter unit, wherein the sinusoidal current is converted into a pulse. For this purpose diodes connected in a bridge in this block.

In the third block aligned two functions, namely, the voltage smoothing (using a selected capacitance capacitor) and its stabilization (to avoid failures with increasing load).

I repeat, that the presented scheme is quite simplified, as it does not specify the input filter and protection circuits, but for an understanding of the operating principle of these omissions are permitted.

Drawbacks and advantages of power supplies to the transformer

Minuses

- main weakest element, and hence a disadvantage of such power supplies is a transformer. Its dimensions are just not physically possible to create compact chargers, and its cost is often several times the cost of all other components of the product.

- Also, such low efficiency power units (compared with pulse power supply).

- To stabilize the output voltage necessary to additionally use a stabilizer which further reduces the efficiency (due to additional losses).

pros

In addition to the weaknesses of such products, there are undeniable advantages, namely:

- High reliability of the product.

- Such power units do not generate spurious radio wave interference (as opposed to pulsed power supplies).

- Pretty simple design.

Switching Power Supplies

Let us now consider a simplified block diagram of a switching power supply:

The principle of operation of such power supplies is a significant difference from the transformer power supplies and it is primarily due to the fact that there is no transformer itself. And now let's get acquainted with the algorithm more:

- The network voltage is applied to the surge protector. The main function of the representation of elements - reducing network interference, which arise directly from the power supply and from there in the incoming line voltage.

- is then connected to the converter unit, which transforms the sinusoidal voltage into a DC voltage pulsed character. Then, connect a smoothing filter.

- Next, the inverter generates a high frequency rectangular signal. In this case, the feedback from the inverter is performed through the control unit.

- A further element entering the job is an IT unit (the power transformer). This unit performs galvanic isolation. Just IT is necessary for automatic generator mode and to power protection circuits, control and load. The core member is made from ferromagnetic materials that guarantee the transmission of high frequency signals ranging from 20 kHz to 100 kHz.

- The next element entering into the conversion process is the output rectifier. Since there is an operation with high frequency voltage then applied to this block Schottky diodes.

- and in the final stage at the output there is voltage smoothing filter and issuing the converted voltage to a load.

Here we examined the algorithm of the switching power supply, let's find out what their advantages and disadvantages

Pros and cons of pulse power supplies

pros

As compared with switching power transformer analogs similar power supply have a rather modest size, and therefore rather small and the weight of the unit.

In pulse BP efficiency reaches 98% (the loss caused in the device only during transients key opening).

Due to the very wide distribution of components, finished products have a relatively low cost.

Minuses

- High-frequency interference. Since the principle of operation of such devices is built on the conversion of high-frequency pulses, it is inevitable to develop spurious.

There are power restrictions

Pulsed power supplies feature lies in the fact that they can not be, not only to overload, but underload. In the case, if the current consumption in the circuit falls below the critical limit, the circuit may run simply refuse to work, or the output voltage will have the characteristics are far from working range.

conclusion

Thus, we examined the algorithms of pulse transformer and power supplies. As you can see, despite the very widespread pulsed power supply, transformer power supply still are used in equipment that is sensitive to high-frequency interference.

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