Switching power supply
The internal structure of switch power supply
Introduced here is the DC switching power supply, its function is to make the original ecological supply poor quality of power (coarse power, or storage) such as power supply Battery Power supply, DC voltage is converted to meet the high quality requirements of the equipment (precision). The core of DC switching power supply is DC/DC Converter . Therefore, the classification of DC switching power supply is dependent on the DC/DC Converter classification. That is to say, the classification and the DC/DC converter DC switching power supply is basically the same, DC/DC converter classification basically is the direct current switch power classification.
DC DC/DC converter in between input and output is there Electrical isolation Can be divided into two categories: one category is separate called isolated DC/DC converter; another kind is no separation is called non isolated DC/DC converter.
Isolated DC/DC converter can also be classified according to the number of active power devices. The single DC/DC converter with forward (Forward) and flyback (Flyback) two. Dual DC/DC converter has two transistor forward type (DoubleTransistor Forward Converter), dual switch flyback (Double Transistr Flyback Converter), a push-pull (Push-Pull Converter) and half bridge (Half-Bridge Converter) four. Four tubes of DC/DC converter is a full bridge DC/DC converter (Full-Bridge Converter).
Non isolated DC/DC converter, according to the number of active power devices, can be divided into single, double and four pipe three.
The internal structure of switch power supply
The single DC/DC converter has six kinds, namely buck DC/DC converter (Buck), step-up (Boost) DC/DC converter, boost Buck (Buck Boost) DC/DC converter, Cuk converter, DC/DC Zeta DC/DC converter and SEPIC DC/DC converter. In this six kinds of single DC/DC converter, Buck and Boost type DC/DC converter is basic, Buck-Boost, Cuk, Zeta, SEPIC type DC/DC converter is derived from. Dual DC/DC converter has two series connected boost type DC/DC converter (Buck-Boost). Four tube DC/DC converter is used in full bridge DC/DC converter (Full-Bridge Converter).
Isolated DC/DC converter in the realization of the input and output electrical isolation, usually by Transformer To achieve, because the transformer with transformer function, so that is conducive to expanding the application range of the converter output, also easy to realization of multiple output different voltage, multiple output or the same voltage.
Tube voltage and current switching in the power rating is the same, the output of the power converter is usually proportional to the number of switches. So the switch tube number, DC/DC converter's output power is larger, four tube is twice as large as two tube output power, output power of single tube only four tube type 1/4.
Combination of non isolated converter with isolation converter, some characteristics can be a single converter does not have.
According to the energy transfer to DC/DC converter, a one-way transmission and two-way transmission two. With two-way transmission function of the DC/DC converter, which can load side transmission power from the supply side, which can also be from the load side power supply side transmission power.
The DC/DC converter can also be divided into self and his control. With the help of positive feedback signal converter itself to realize switch self sustained periodic switch converter, called self-excited converter, such as Loel (Royer) converter is a kind of typical push-pull self oscillating converters. He can control the switch control signal in the DC/DC converter, is composed of external special control Circuit Produce.
According to the switching condition of switch, DC/DC converter can be divided into hard switching (Hard Switching)
Switching power supply
And soft switching (Soft Switching) two. Switch the hard switching DC/DC converter is under voltage or current situation, on or off the circuit, so in the on-off process will produce overlapping loss is larger, the so-called switch loss (Switching loss). When the converter's working state The timing switch Loss is certain, and the switch frequency is higher, the greater the switching losses, at the same time during switching will arouse circuit distribution Inductance Oscillation and parasitic capacitance, bring additional loss, therefore, the switching frequency is not the hard switching DC/DC converter is too high. Switch soft switch DC/DC converter tube, in the open or off course, or add to the voltage is zero, zero voltage switching (Zero-Voltage-Switching, ZVS), or through the switch current is zero, zero current switching (Zero-Current · Switching, ZCS). This soft switching method can significantly reduce the switching loss, oscillation and switching process, the switch frequency can be increased greatly, to create the conditions for the miniaturization and modularization converter. Power Field effect transistor ( MOSFET Switching device) is used, it has higher switch speed, but also the large parasitic capacitance. It is turned off, the voltage under the effect of the parasitic capacitance, full of electricity, if the opening is not the partial charge off, will consume in device, which is capacitive turn-on loss. In order to reduce or eliminate such loss, power field effect tube should be zero voltage switching mode (ZVS). Insulated gate bipolar Transistor (Insu1ated Gate Bipo1ar tansistor, IGBT ) is a kind of composite switch, off current off trail leads to large turn off loss, if the current flowing through it in the off before dropping to zero, it can significantly reduce switch loss, so IGBT should use the zero current switching mode (ZCS). IGBT in the zero voltage condition Shimonoseki Broken, can also reduce the turn off loss, but the MOSFET opened in the zero current conditions, and can not reduce the capacitive turn-on loss. Resonant converter (ResonantConverter, RC), quasi resonant converter (Qunsi-Tesonant Converter, QRC), multi resonant converter (Mu1ti-ResonantConverter, MRC), zero voltage switching PWM converter (ZVS PWM Converter), zero current switching PWM converter (ZCS PWM Converter), zero voltage switching (Zero-Vo1tage-Transition, ZVT) and zero current switching (PWM converter Zero- Vo1tage-Transition, ZVT) PWM converter, belong to the soft switching DC converter. Electric power Electronics Development of switching devices and zero switching converter technology, promote the High frequency switching power supply Development.
Switching power supply is composed of a main circuit,
Switching power supply
The control circuit, detection circuit, auxiliary power supply is composed of four parts.
1, the main circuit
The impact of current limiting: limit switch on the power transient inrush current side.
Input filter: its role is to filter network existing clutter and hinder the machine generated clutter feedback to power grid.
Rectifier and filter: the grid AC power supply directly for a smooth DC rectifier.
Inverter: the rectified DC power into high frequency alternating current, which is part of the core of high frequency switching power supply.
The output rectifier and filter: according to the need of load, to provide stable and reliable DC power supply.
2, the control circuit
On the one hand from the output end of the sampling, compared with the settings, and then to control the inverter, change the pulse width and pulse frequency, output stability, on the other hand, provides the circuit under test data, the protection circuit differential, provides the control circuit protection measures for power supply.
3, the detection circuit
The various parameters and various kinds of instrument data is running to provide protection circuit.
4, the auxiliary power supply
Realize the power of software (remote) start, in order to protect the circuit and the control circuit (PWM chip) power supply.
People in the switching power supply technology is related to the development of power electronic devices,
320W single set of switch power supply
Switching frequency edge technology development, promote each other to promote the switch power every year, with more than two digit growth rate toward the light, small, thin, low noise, high reliability, anti interference direction. Switching power supply can be divided into two categories AC/DC and DC/DC.
A miniature low power switching power supply
Switching power supply is becoming popular, miniaturization. Switching power supply will gradually replace the transformer all application in life, low power micro switch power supply to in a first embodiment, a digital display meter, smart meters, mobile phone charger etc.. The present state in promoting the construction of smart grid, the power meter requirements increase, switching power supply will gradually replace the transformer used in electric energy meter.
Inversion type series switching power supply
The difference between reverse series switching power supply with the general series of switch power is, the reverse type series voltage switching power supply output is negative voltage, just positive voltage and general series switching power output of opposite polarity; and as the energy storage inductor L shut off only in the switch K to the output load current, therefore, under the same conditions, reverse current series switching power supply output than the series switching power supply output current small times.
High frequency switching power supply is the direction of its development, so that high-frequency switching power supply miniaturization, and switching power supply into a wider range of applications, especially in the High tech field Application, promoted the development of switch power forward, every year to more than two digit growth rate toward the light, small, thin, low noise, high reliability, anti interference direction. Switching power supply can be divided into AC/DC and DC/DC two kinds, DC/DC converter has been the realization of modularization, and the design and production technology at home and abroad has been mature and standardized, and has been recognized by the user, but the AC/DC module, with its own features in the modular process, encounter technology and the more complex manufacturing process. In addition, the development and application of switching power supply has great significance in saving energy, saving resources and Protect environment.
Power electronic devices used in the switch power supply is mainly Diode , IGBT And MOSFET , Transformer .
SCR There is little used in switching power supply input rectifier circuit and soft start circuit, GTR Driving is difficult, low switching frequency, IGBT and MOSFET were gradually replaced.
Switching power supply is the development direction of high frequency, high reliability, low power, low noise, interference and modular.
Switching power supply
As the key technology for switching power supply light, small, thin is high frequency, so the switching power supply manufacturers are committed to the development of new high intelligent synchronous components, especially the improvement of two rectifier of the loss, and increase scientific and technological innovation in power ferrite materials, in order to improve the high frequency and large flux density (Bs) under high magnetic properties, and the small capacitor is also a key technology. The application of SMT technology makes the switching power supply has made considerable progress, both sides in the circuit board layout components, to ensure that the switching power supply light, small, thin. High frequency switching power supply for innovation is bound to the traditional PWM switching technology, soft switching technology, ZVS ZCS has become the mainstream technology of switching power supply, and greatly improve the work efficiency of the switching power supply. For the high reliability, switching power supply manufacturers USA by lowering the operating current, reduce the junction temperature and other measures to reduce the stress of the devices, greatly improving the reliability of the product.
Modularity is the general trend of the development of switching power supply, can adopt modular power distributed power systems, can be designed into the N+1 Redundant power supply System, and realize the capacity expansion parallel. The switching power supply operation Noise This disadvantage, if the individual pursuit of its high-frequency noise will increase, and use of the resonance conversion circuit technology, high frequency can be realized in theory and can reduce the noise, but the actual application part resonant conversion technology is still a technical problem, so it still need to carry out a lot of work in this field, in order to make the technology to practical.
Power electronic technology Continuous innovation, switching power supply industry has broad prospects for development. China's switch to accelerate the pace of development of power industry, we must take the road of technological innovation, out of joint research development road with the China characteristics, for our country The national economy The contribution of the high speed development.
The working process of switching power supply is quite easy to understand, in the linear power supply, power transistor operating in the linear mode, is different from the linear power supply, PWM switch power supply is to let the power transistor in the turn-on and turn off state, in the two states, plus the power transistor on the volt ampere product is very small (low voltage at turn-on, Electric current High; high voltage, low current shutdown,) / loss generated voltammetry product power device is on the power semiconductor devices.
Compared with linear power supply, PWM switch power supply is working process effectively is through "chopper", namely the input DC voltage is equal to the input voltage amplitude cut into the Pulse voltage To achieve.
Switching power supply Bert diagram
The duty ratio of the pulse by the controller to adjust the switching power supply. Once the input voltage is cut into AC Fang Bo, its amplitude can be increased or decreased by a transformer. The increase in the number of two winding transformer could increase the output voltage value. At the end of the AC waveform after rectifying and filtering after get the DC output voltage.
The main purpose of the controller is to maintain the stable output voltage, the controller and its working process and linear form is very similar. That is to say the function of the controller block, reference voltage and the error amplifier, can be designed into the tank with the same linear regulator. For all their differences, the output of the error amplifier (error) in the drive power tube to go through before a voltage / pulse width conversion unit.
Switching power supply has two main works: the forward converter and boost converter. Although the arrangement of each part of the difference is very small, but the work is great, in specific applications under each have advantages.
1, switch: power electronic devices in the switch state instead of linear state
2, the high frequency: power electronic devices working at high frequency and low frequency is not close to
3: switching power supply, DC output is DC instead of exchange
1, small size, light weight: because there is no industrial frequency transformer, so the volume and weight of only linear power supply 20 ~ 30-.
2, small power consumption, high efficiency: the power transistor in the switch state, so the power transistor on the small, high conversion rate, generally 60 ~ 70-, and the linear power supply only 30 ~ 40-.
As the name implies, switching power supply is the use of electronic devices (such as the transistor, FET, SCR thyristor etc.),
Switching power supply, circuit diagram
Through the control circuit, the electronic switch device does not stop the "on" and "off", let the electronic switch of the input voltage pulse modulation device, so as to achieve the DC/AC, DC/DC voltage, and the output voltage adjustable and automatic voltage regulator.
Switching power supply has three working modes: frequency, pulse width fixed mode, fixed frequency, variable pulse width, frequency, pulse width variable model. Before a working model for DC/AC inverter power supply, or a DC/DC voltage; after two working modes used in switching power supply. In addition, the switching power supply output voltage can work in three ways: the direct output voltage mode, average output voltage mode, the amplitude of the output voltage mode. Similarly, a mode used for DC/AC inverter power supply voltage, or DC/DC transform; mode two work for switching power supply.
According to a switching device is connected in the circuit, switching power supply is widely used at present, generally can be divided into: tandem type switching power supply, switching power supply, transformer parallel switching power supply and other three categories. The switching power supply, transformer (hereinafter referred to as transformer switching power supply) can be further divided into: push-pull, half bridge, full bridge etc; according to the phase excitation and the output voltage of the transformer, and can be divided into: forward, flyback, single excitation type and double excitation type etc; if from the use of up points, can be divided into more types.
Because of the switching power supply with high efficiency, to achieve more than 80-, so the output current of the choice, should be accurately measured or calculated using the maximum absorption current electrical equipment, in order to make the switch power supply is chosen has high cost performance ratio, usually output calculation formula is:
Type: the rated output current of Is switching power supply;
If - the maximum absorption current electrical equipment;
K - margin coefficient, generally 1.5 ~ 1.8;
Switching power supply produces more interference than the linear power supply, the The common mode interference Electrical equipment should be sensitive, grounding and shielding measures, according to ICE1000, EN61000, FCC, EMC, switching power supply using EMC electromagnetic compatibility measures, so the switching power supply should be generally with EMC EMC filter. Such as the HA series switching power supply and Edward Fu technology, its FG terminal connected with earth or the user case, in order to meet the electromagnetic compatibility requirements.
Switching power supply must have a flow, overheating, short circuit protection function in the design of switch power supply module, it should be preferred protection functions in the design, and its protection circuit with the technical parameters of the work of electrical equipment matched, so as to avoid damage to the electrical equipment or switching power supply.
L: connected with 220V AC line
N: connected with 220V AC zero line
FG: the ground
G: DC output.
+5v: output +5V port
ADJ: is a regulated output voltage within a certain range, rated voltage output switching power supply of the original factory is fixed, which is the nominal rated output voltage, set this potentiometer can let users according to the actual use to regulate the output voltage in a smaller range, generally do not need to adjust it.
1, repair of switch power supply, first use the multimeter to detect the power components are short circuit breakdown,
Switch power supply
Such as the power rectifier bridge, a switch tube, high frequency and high power rectifier; power resistors surge current suppression is not blown. To test the output voltage port resistance is abnormal, the components such as damage should be replaced.
2, the first step is completed, after turning on the power can not work normally, then to detect power factor module (PFC) and pulse width modulation component (PWM), access to relevant information, necessary conditions of normal working function and familiar with the PFC module and PWM module of each foot.
3, then, the power supply with PFC circuit is needed to measure the filter capacitor voltage is about 380VDC, such as 380VDC voltage, PFC module is working correctly, then the detection of PWM components work state, measuring the power supply input end reference voltage VC, output VR, start control Vstart/Vcontrol voltage is normal, the 220VAC/220VAC isolation transformer for switching power supply, with an oscilloscope observation PWM module CT end to the waveform is good linearity sawtooth or triangle, such as TL494 CT end sawtooth wave, triangle wave FA5310 CT end. The output V0 waveform is a narrow pulse signal orderly.
4, in the repair practice of switching power supply, there are a lot of switching power supply using UC38 * * series 8 feet PWM components,
Switching power supply adapter
Most of the power can not work because of power starting resistor is damaged, or the chip performance decline. When no VC R circuit, PWM module does not work, need to replace the resistance and the same with the original power resistance. When the starting current increases PWM component, the R value can be reduced to PWM components can work normally. In a GE DR power supply, PWM module of UC3843, detected no abnormal, in R (220K) resistance is connected with a 220K, PWM module, output voltage is normal. Sometimes because of peripheral circuit failure, resulting in VR end of the 5V voltage is 0V, the PWM component is not working, in the repair Kodak 8900 camera power, encounter such a situation, the external circuit and connected with the VR end disconnected, VR from 0V to 5V, the PWM component to work, the output voltage is normal.
5, when the filter capacitor without voltage about 380VDC, PFC circuit does not work,
Schematic diagram of switching power supply circuit
PFC module test pin input pin VC for power, start the foot Vstart/control, CT and RT pin and V0 pin. Fix a Fuji 3000 camera, test plate filter capacitor voltage without 380VDC. VC, Vstart/control, CT and RT wave and V0 wave were normal, measuring field effect power switch tube G without V0 waveform, because FA5331 (PFC) for SMD components, machine later weld between V0 terminal and the board, V0 signal is not sent to the field effect tube G. Will V0 end plate welding good, measured with a multimeter filter capacitor 380VDC voltage. When Vstart/control is low, PFC also does not work, the relevant circuit to detect the endpoint and the peripheral.
In short, the switching power supply circuit is easy to difficult, power is big is small, the output voltage is varied. As long as grasp the core of things, that is fully familiar with the basic structure of the switching power supply and the characteristics of PFC and PWM module, the basic conditions for their work, in accordance with the above steps and methods, were more hands-on switching power supply repair, can quickly eliminate switching power supply failure, to achieve a multiplier effect.
Switching power supply repair can be divided into two steps:
The absence of power, "look, smell, ask, volume"
See: turn the power of the shell, check whether the fuse fuse, then look inside the power supply, if it is found that the PCB board power has scorched or element rupture, should focus on examination of the components and related circuit element. Asset management
Smell smell whether there is an internal power supply: paste flavor, check whether a charred components.
Ask: ask power supply damage after, whether illegal operation to power.
Quantity: no electricity, voltage with a multimeter measure the voltage across the capacitor start. If it is not exciting or switching power supply switch open circuit faults caused by it, in most cases, high voltage filter capacitor is not discharge the mourning, the voltage is 300 volts, be careful. Measuring two AC power line of positive and negative resistor and capacitor million charge, resistance value should not be too low, or else the power possible internal short circuit. Capacitors should be able to charge and discharge. Off load, respectively measured the output to ground resistance, normal, hands should be capacitor charging and discharging swing, final instructions should be the bleeder resistor.
Observe whether the power supply has a fire insurance and individual components of smoke phenomena such as electricity, if you have to cut off the power timely maintenance.
Measurement of high voltage filter capacitor has no 300 volt output, if not should check diode rectifier, filter capacitor.
The measurement of high frequency transformer secondary coil has no output, if not should check the switch tube is damaged, whether the vibration, the protection circuit is action, if any, should focus on checking the output side of the diode rectifier, filter capacitor, three pass voltage regulator tube etc..
If the power supply to start stop, then the power in the protection of the state, the voltage can be measured directly PWM chip protection input pin, if the voltage exceeds the prescribed value, the power supply in the protection of the state, reason should focus on checking the protection.
1, select switch power supply matters needing attention
1) the input voltage specification suitable;
2) select the appropriate power. In order to make the life of the power supply growth, can choose 30- more output power rated model.
3) considering the load characteristics. If the load is the motor, lighting or capacitive load, when the moment of starting when the current is large, should be the appropriate choice of power in order to avoid overload. If the load is the motor should be considered when stopping voltage injection.
4) in addition to still need to consider the environment temperature of power supply, and there is no auxiliary additional cooling equipment, in the loop temperature too high to derating power. The amount of reduction of output power curve of temperature.
5) according to the application need to choose the various functions:
Protection function: over voltage protection (OVP), over temperature protection, over load protection (OTP) (OLP).
Application of functions: signal function (normal power supply, power supply failure), the function of remote control, telemetry functions, parallel function etc..
Special features: power factor correction (PFC), uninterruptible power supplies (UPS)
6) select the required for compliance with the safety and electromagnetic compatibility (EMC) certification.
Note 2, the use of switching power supply
1) the use of power, to determine the input and output voltage and the nominal values are matched with power supply;
2) before power, check the input and output of the lead is connected properly, so as not to damage the user equipment;
3) check for secure fit, install screw and the power supply board device has no contact, measure the insulation resistance of shell and the input, output, so as to avoid the electric shock;
4) to ensure the use safety and reduce interference, ensure that the grounding end reliable grounding;
5) source of multi output generally divided into main, auxiliary output, the main output performance is better than that of main auxiliary output, output current large general. In order to guarantee the output load adjustment rate and output dynamic index, general requirements for load each with at least 10-. If the roads without a main road, the main road must add appropriate dummy load. See the specification of the corresponding model;
6) Note: power frequent switch will affect their life;
7) the working environment and load level also affects its life.
In general, fuse that internal circuit power supply problems. Because the power supply in the high voltage, high current state, wave, surge voltage will cause the power within the current moment increases fuse. The focus should be to check the power input end of the rectifier diode, high-voltage capacitor, inverter power switches, check the components have no breakdown, open, damage etc.. If indeed the fuse, should first check all elements on the circuit board, look at these elements appearance have been burnt, there is no electrolyte overflow, if not found above, with a multimeter measuring switch tubes with and without short circuit breakdown. Special attention is: must not be found in a certain element is damaged, replace directly after the boot, so it is very likely due to other high voltage element still has fault and will replace the damaged element, must all the high-pressure components on the circuit to conduct a comprehensive inspection measurement, fault can be completely ruled out the fuse links.
No output DC voltage or voltage instability
If the fuse is intact, the load cases, the DC voltage no output. This is mainly the following reasons: open circuit, short circuit phenomenon in power supply, over-voltage, over-current protection circuit failure, auxiliary power failure, the oscillation circuit does not work, the power load is overweight, the rectifier diode rectifier filter circuit breakdown, filter capacitor leakage etc.. In the multimeter is used to measure the secondary element, remove the high-frequency rectifying diode breakdown, load short circuit, if the output to zero, it can be sure is out of control circuit of power supply. If some output voltage that the former circuit works normally, the fault in the high-frequency rectifying filter circuit. A high frequency filter circuit is mainly composed of a rectifying diode and a low voltage filter capacitor DC voltage output, the rectifier diode breakdown will make the circuit does not output voltage, filter capacitor leakage will cause the output voltage instability fault. With a multimeter measuring the corresponding static components can check out the damaged elements.
Power load ability
Power load ability is a common fault, are commonly found in the power of old or long working hours, the main reason is the component aging, the switch of the unstable work, heat dissipation, no timely. Should focus on checking whether the heating leakage zener diode, rectifier diode damage, high voltage filter capacitor damage etc..