[Reprinted] switch power supply Parts

In the past, when purchasing computer accessories, the power supply was one of the most easily overlooked components. However, its various voltage output specifications, voltage stability, and protection in case of exceptions were very important, because the power required for all the accessories in the host must be supplied by the power supply, and the output load is adjusted with the power consumption of each hardware in different states, the stability of long operation and Full output must be taken into account, when the power supply is faulty or the load is abnormal, the protection system must be immediately involved to avoid device damage due to Overvoltage/current. For global energy shortage, the new power supply, in addition to the above features, also began to improve the conversion efficiency, for example, 80 plus is one of the marks that represent the power supply through high efficiency authentication.

The common power supply function of computer is to convert the input AC Mains (ac110v/220 V) into various low-voltage direct current required by each hardware through an isolated exchange Buck circuit: 3.3 V, 5 V, 12 V,-12 V, and 5 V standby (5vsb) for standby when the computer is shut down ). Therefore, the power supply also has high-voltage and high-power components, as well as small-power components that process low voltage and control signals.

The power conversion process is AC input → EMI filtering circuit → rectification circuit → Power Factor Correction Circuit (active or passive PFC) → power level primary side (High Voltage Side) switching circuit to pulse flow → Main Transformer → power level secondary side (Low Voltage Side) rectification circuit → voltage adjustment circuit (such as Magnetic amplification circuit or DC-DC conversion circuit) → filter (smooth Output Ripple, consists of inductance and capacitance) circuit → power management circuit monitoring output.

The following describes the common components of the EMI filter circuit at the AC input end.

AC input Outlet

This is the first level of the AC power supply from the external input, in order to block online interference from the power supply, and to prevent the switching noise generated by the power supply operation from spreading out through the power line to interfere with other power devices, the first-to second-order EMI (electromagnetic interference) filter (filter) will be installed on the AC input end. Its function is a low-pass filter that bypasses high-frequency noise contained in the AC or guides the ground, only the pattern of 60Hz is passed.

In the above picture, the central part is an integrated EMI filter power outlet, and the filter circuit is fully enclosed in an iron case, which can effectively avoid noise leakage. The right side is a small circuit board used to create an EMI filter circuit, it is usually used in power supplies without enough depth to install an integrated EMI filter. When the case of a tin case is missing, there will be noise leakage; however, only CX and Cy capacitors are added to the socket on the left (which will be introduced later). When this type of power supply is used, the EMI filter circuit is usually used on the main circuit board, if the EMI circuit area on the main circuit board is empty, the components in the area are omitted.

At present, the internal space of the power supply using a 12-centimeter fan is not able to plug in the integrated EMI filter, so most of the practices of both sides of the photo are used.

■ X capacitor (CX, also known as cross-wiring filter capacitor)

This is a capacitor used in the EMI filter circuit to interwork between the wire (l) and the Neutral Line (N). It is used to eliminate low-pass Normal Noise from power lines.

The appearance is shown in square shape. The top is marked with X or X2.

■Y capacitor (CY, also known as line Bypass capacitor)

The y capacitor is located between the floating ground (FG) and the FireWire (L)/Neutral Line (n) to eliminate normal and common state noise of Qualcomm.

The appearance of the Y capacitor is like a pie in the photo.

The FG points in the computer power supply are connected with the metal shell, Ground Wire (E), and the output end 0 V/Gnd. Therefore, when the ground wire is not connected, two Cy capacitors in series are used to extract the half potential difference of the input power supply (VIN/2). When the human body is touched, it may generate electric sensing.

Co-state throttling (Ac-connected inductor)

In the filter circuit, the common mode Throttling is connected in series on the FireWire (L) and Neutral Line (n) to eliminate online low-pass common state and RF noise of power supply. Some power supply input lines will be wound around the core design, can also be considered as a simple co-state throttling.

Its appearance is a square shape like a transformer, And the exposed coils can be seen in some parts.

The so-called common noise represents the noise between the L/N line and the ground line E, while the normal noise is the noise between the L and n lines, emi filters are used to eliminate and block these two types of noise. The EMI filtering circuit is followed by the instantaneous protection circuit and the rectification circuit. The common components are as follows.

■ Fuses

The fuse is used to protect the connection to the backend circuit in the mode of fusing when the current value flowing through it exceeds the rated value. It is generally used in the power supply, it is better to use explosion-proof fuses. The biggest difference between the fuses and general fuses is that the external tubes are beige ceramic tubes, which are filled with fireproof materials to avoid Sparks During fusing.

It is installed on the circuit board by means of fixed above the chip (the two ends are directly mounted to the wire seat and welded to the circuit board) and detachable in the center of the picture (fixed with metal clips ). The square component below is a temperature Fuse, which is fixed on the high-power cement resistor or the heat sink of the power component. It is mainly used for over-temperature protection to avoid component overheating and damage or fire, this type of fuse is also available in combination with current fuses for dual protection of current and temperature.

■ Negative temperature coefficient resistance (NTC)

When the power supply is switched on to the power supply, the high-voltage electrolytic capacitor is in a non-electric state. When the power supply is switched on, large current surges and line pressure drop will be generated. This may cause components such as the bridge-type rectifier to burn out when the current is exceeded. When NTC is used in series on line L or line N, its internal impedance value can limit the current value at the moment of charging at startup, while the negative temperature coefficient is defined as its resistance will decrease as its temperature increases, so as the current flow through the body gradually increases the temperature, the resistance will decrease to avoid unnecessary power consumption.

Most of the products are black and dark green.

However, the disadvantage is that when the power supply is started in a heat engine, its protection effect will be discounted, and even if the impedance can decrease with the temperature, it will still consume some power, currently, most high-efficiency power supplies use more advanced transient protection circuits.

Gold oxygen rheostat (mov)

The varistor is connected to the FireWire and ground wire at the backend of the fuse. The working principle is that when the voltage difference between the two ends is lower than the rated voltage value, the body presents a high impedance. When the voltage difference exceeds the rated value, the body resistance will rapidly decline, the L-N shows an approximate short-circuit state, the front-end fuse due to short-circuit and the rising current will make it fuse, to protect the back-end circuit, sometimes the body withstand power is too large, the user is also warned in self-destruction mode that the device has encountered problems.

It is usually used at the AC input end of the power supply. When the input AC voltage occurs, the fuse can be melted in time to avoid damage to internal components. Its color and appearance are very similar to cy capacitor, but they can be different from the words and models on the component.

■ Bridge rectifier

It is a bridge rectifier consisting of four diode interactive connections. It is used to perform full-wave rectification of input and exchange for the back-end switching circuit.

Its appearance and size may vary with the rated voltage and current of the component. Some power supplies will fix it on the heat sink to help it heat dissipation, so as to facilitate stable and long-term operation. After rectification, it enters the switching circuit at the power level. The components here determine the maximum output capacity of the power supply, which is a very important part of the power supply.

■ Switch Crystal

As a non-contact fast electronic switch in the switching circuit, the current flow is determined based on the control signal conduction and cutoff. It plays an important role in Active Power Factor Correction Circuit and Power Level One-side circuit.

In the photo, the N-mos (n-type gold-oxygen semiconductor field-Effect Transistor) are common in the power supply, and the lower part is the BJT (two-sided transistor of the type)

With the circuit composition of the switch component, it can form different power-level extensions such as dual-crystal shunted, semi-bridge, full bridge, and push-pull. in highly efficient power supply, there are also the use of switching crystal to form a Synchronous rectification circuit and the application of DC-DC Buck circuit.

Transformer

It is called an isolated exchange type buck power supply because transformers are used as the separation of high voltage and low voltage, and magnetic energy is used for energy exchange, which not only avoids the risk of leakage in the case of high voltage and low voltage circuit faults, it can also generate a variety of voltage outputs. Because of its high operation frequency, the transformer volume is smaller than the general ac transformer.

Because the transformer is one of the power transmission paths, the current large output power supply has a multi-transformer design, to avoid a single transformer saturation phenomenon and limit the power output. In the photo, the smaller transformer is the auxiliary power circuit and the pulse transformer used for signal transmission. The larger transformer is the main power transformer and the second side transformer used for Annular adjustment.

Using transformer as the isolation demarcation, the output voltage on the secondary side is much lower than that on the primary side. However, it still needs to be rectified, adjusted, filtered, and smoothed, it will become the various voltage DC required for computer parts.

■ Diode

In the power supply, different types and specifications are used with various circuit requirements and output sizes. In addition to the general silicon diodes, there are also Shaw barrier diode (SBD) and fast recovery diode (FRD) ZD.

Typical encapsulation of diodes in the image

FRD is mainly used for active power factor correction and Power Level One-side circuit. SBD is used for power level secondary side, and transformer output is rectified. ZD is used for voltage reference.

■ Inductor

The inductor can be used as an energy storage component in the exchange circuit, a voltage adjustment component of the Magnetic amplification circuit, and an output filter after secondary rectification as the core structure, inductance value, and the position where the circuit is installed, it is widely used in power supplies.

The inductance is in a ring and a cylindrical shape. The inductance varies with the number of rings and the thickness of the paint wire as the sensing value and current bearing capacity.

Capacitor

Like an inductor, capacitors are also used as energy storage components and ripple for smooth use. To withstand the high-voltage DC after rectification, the high voltage electrolytic capacitor is used in the one-side circuit of the power supply. To reduce the losses caused by the continuous discharge of the electrolytic capacitor under the output, the secondary circuit uses high temperature, long life, and low impedance electrolytic capacitor.

The larger lower part of the figure is the high voltage electrolytic capacitor used for one side, and the lower voltage is used for the secondary side and peripheral control circuit.

Due to the relationship of chemicals (electrolyte) in the capacitor, the operating temperature has a considerable impact on the life of the electrolytic capacitor. Therefore, in addition to maintaining the good heat dissipation of the power supply, the electrolytic capacitor brands and series also determine the reliability and service life of the stable operation of the power supply.

■ Resistor

The resistor is used to limit the current flowing through the circuit and release the charge stored in the capacitor after the power supply is closed to avoid electric shock.

In the picture, the left side is the high-power cement resistance, which can withstand high-power excess. The right side is the common resistance, and the color code on it indicates its resistance value and error.

If the circuit composed of the above components is not equipped with a control circuit, it will not be able to play its functions, and all outputs need to be monitored and managed at any time. In case of any exceptions, the output should be cut off immediately, to protect the security of computer components.

■ Various control IC

The Control IC in the power supply depends on its installation position and usage, it is used as a PFC circuit, a power-Level One-side PWM circuit, a PFC/PWM integrated control, an integrated component for auxiliary power circuit, and a power monitoring management IC.

PFC circuit is used as an active power factor correction circuit control, so that the power supply can maintain a certain power factor and reduce the generation of higher harmonic.

Power-Level One-side PWM circuit: Used as the power-Level One-side switching crystal Drive Using PWM (Pulse Width Adjustment) signal generation, with the power output state of its task cycle (Duty Cycle) control. Generally, PWM control ICS such as UC3842/3843 are commonly used.

PFC/PWM Integrated Control: combining the two controllers in a single IC can simplify the circuit, reduce the number of components, and reduce the failure rate. For example, the common cm680x series is the PFC/PWM Integrated Control IC.

Auxiliary power supply circuit integrated components: because after the power is off, the auxiliary power supply circuit still needs to be output continuously, so it must be self-contained in an independent system, because the output of the wattage is not too high, therefore, the industry's small power integration component is used as its core, such as Pi's TOPSwitch series.

Power supply monitoring management IC: UVP (Low Voltage Protection), OVP (Over Voltage Protection), OCP (over current protection), SCP (short circuit protection), OTP (over temperature protection) monitoring and Protection: When the threshold is exceeded, the control circuit is closed and locked. The power supply output is stopped and can be restarted after the fault is rectified.

In addition to the above components, other vendors also need to add their own IC, such as the fan control IC.

■ Optical coupler

Optical coupler is mainly used for signal transmission between high voltage circuit and low voltage circuit, and maintains its circuit isolation to avoid abnormal current flow between high and low voltage circuits in the case of a fault, so that the low voltage components are damaged. The principle is to use light emitting diodes and phototransistor to transmit signals. Because there is no link between the two wires, the circuit isolation between the two ends can be maintained.

The internal components of the power supply are generally introduced here. Next time, the actual photos of the power supply will be taken to describe the circuits of each part.