Functional principle of switching power supplies:
(And common mistakes made in China)
Considering that people who have been studying electronics often look like a calf when they talk about
Switch-mode power supply; I write the main operating principles.
(I do not want to divide the principle of "sharing the Estonian" with anyone, but at most "repetition on the mother of knowledge")
Some common questions:
· Why is it used?
- Because it fits in a much smaller place than a conventional transformer power supply
- Because it has a good efficiency (a transformer with rectifier, buffer condition and stabilizer much worse)
- Because it is much
cheaper than the transformer itself, because it is more powerful (over 20W)
How can this be small compared to performance?
- Since the frequency of the transformer is in the formula (the higher the frequency, the smaller the iron cross section is required)
So we change this to the appropriate value (20-50kHz).
Smooth transformer iron is not suitable for transmitting frequencies above 100-200Hz, therefore ferrite core is used.
Ferrite is a powder metallurgy product. Its essence is that it consists of elemental particles, so it is not possible to form an eddy current, and
It is able to magnetize much faster (up to 100,000 times per second) much faster.
The operation is as follows:
The mains voltage is rectified and buffered (stored / "dimmed" in the condenser).
This DC voltage (230V x 1, 41 = 324V) is discharged by a transistor at about 30kHz and then
To the pulse-powered transformer. The voltage from the secondary winding of the transformer is rectified (only switched / Schottky
Diode can be used), then filtered and buffered. The output voltage rises to the control electronics (usually a TL494 pulse width is the IC of the soul),
Which continuously changes the fill factor of the pulses. (The higher the power, the wider the impulses are placed on the transformer).
The power shown in the next drawing also has a separate standby part, which is also switchable.
The diagram shows a circuit diagram of a decently built ATX computer power supply (with interference filter, output
filter, surge protection).
Note that all computers power up to 5Volt voltage. (If you load 5 volts, go up, for example, 12Voltos).
Unfortunately, today, in the world of cheap bulk goods, very poor quality computer power supplies are produced.
Here are some tips to learn about the power of the computer:
- 230Volt inputs lack interference suppression and surge arresters (C1, R1, Z1, C4, C2, C3, T1, T5, T, Z2).
- Out of the output filter coils (L1, L2, L3, L4, L6 this will reduce the efficiency and damage the buffer capacitors or the Schottky diodes at the output).
- Buffer capacitors with too little capacity at output (over two to three years - for the previous reason too!)
- NTC (NTCR1) is excluded from the input
- Insufficient Schottky diodes are output to the output. If it is short, it will kill the buffer capacitor behind it.
If this occurs at regulated 5V, then the power supply will be disconnected and ALL of it will be lost even
when the computer is connected. (TL494, Q1, Q2, C30, C26, C27, C29, C28, STB ...)
- Voltage feedback is provided by an optocoupler or a small transformer. If this circuit is interrupted, the power supply
will also be discharged.
Leaving the 230V input is also dangerous because the two network buffer capacitors are switched on when the
power is switched on, so the diodes at them will suddenly cause an electric shock (Power current).
If the rectifier bridge is short-circuited, the buffer condition may explode (the transistors afterwards are endangered).
If your computer often freezes, it is also worth checking the power supply. If the top of any condenser is
hollow, it is a sign of overheating. Such a capacitor may smoke over at any moment, so it needs to be replaced immediately (a common
mistake on motherboards too!).
A capacitor (C7, which is for 1uF and 250V) is connected in series with the transformer. This is the role of separating the DC parts per transformer;
In addition, the Q1 or Q2 shortcut would not cause the transformer to be rectified 230V!). It is warmed up because of the high loads and after a while
it is so dry that the capacity of the power supply can not yield its nominal capacity. In such cases, the output voltages become unstable.
Since a slimmer computer power supply is only designed for 2-3 years (or the output buffer capacitors from the cheapest type to 1 to 10,000 hours), so
if you want it for a long time we have to use spare parts every two years to use. In the absence of the input
filter, it is good if the first larger near lightning is survived by the power supply, so when not in use pull the computer out of the
socket, so it will not work unnecessarily.
(Saved a computer that was not plugged in, it was just plugged in ...)
Adrián Sarok 2006.