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Switching Power Supply Introduction

Switching power supply is the use of modern power electronics, control the switch turn-on and turn-off time ratio, maintaining a stable output voltage of a power supply, switching power supply generally consists of a pulse width modulation (PWM) control IC and MOSFET constituted. Switching power supplies and linear power compared with the increasing cost of both the output power and growth, but the rate of increase of both different. Linear output power costs on a power point, but higher than the switching power supply, which is called the cost of turning points. With the development of power electronics technology and innovation, making switching power supply technology is constantly innovating, increasing the cost of the reversal point moves to the low output power terminal, which provides a broad space for development switching power supply.

High-frequency switching power supply is the direction of its development, high-frequency switching power supply miniaturization, and switching power supply into a wider range of applications, especially applications in high-tech fields, and promote the miniaturization of high-tech products, lightweight technology. In addition the development and application of switching power supply has an important significance in saving energy, saving resources and protecting the environment.

Application of the switching power supply main power electronic devices as a diode, IGBT and MOSFET.

SCR has a switching power supply input rectifier circuit and soft-start circuitry in a small number of applications, GTR driven hard, low switching frequency, gradually replaced by IGBT and MOSFET.

Three conditions of switching power supply

1, the switch: power electronic devices work in the off state, rather than a linear state

2, high-frequency: power electronic devices operate at high frequencies, rather than close to the power frequency of the low-frequency

3, DC: DC switching power supply output is not AC

Switching Power Supply Classification

People in the field of switching power supply technology is related to the development of power electronics side, while the development of the switching frequency technology, both of which promote each other to promote the switching power supply more than two-digit annual growth rates toward the light, small, thin, low-noise, high reliability, interference direction. Switching power supply can be divided into AC / DC and DC / DC two categories, DC / DC converters are now modular, and the design and production process technology at home and abroad have already matured and standardization, and has been authorized users, but AC / DC modular, makes its own characteristics in the modular process, encountered more complex technology and manufacturing process problems. The following were the two types of switches for the power structure and characteristics in order to elaborate.

2.1 DC / DC conversion

DC / DC converter is a fixed DC voltage into a variable DC voltage, also referred to as the DC chopper. Chopper work in two ways, one pulse width modulation Ts unchanged, change ton (GM), the second is the frequency modulation, ton constant change Ts (prone to interference). Specific circuit by the following categories:

(1) Buck circuit - Buck chopper, the average voltage output

U0 is smaller than the input voltage Ui, the same polarity.

(2) Boost circuit - boost chopper, the average voltage output

U0 is greater than the input voltage Ui, the same polarity.

(3) Buck-Boost circuit - buck or boost chopper, its

The average output voltage U0 is greater than or less than the input voltage Ui, of opposite polarity, the inductor transmission.

(4) Cuk circuit - buck or boost chopper, its average output power

U0 pressure greater or less than the input voltage Ui, opposite polarity, capacitance of the transmission.

There Sepic, Zeta circuit.

These non-isolated circuit, isolated forward converter circuit has flyback circuit, half-bridge circuit, full bridge circuit, push-pull circuit.

Today soft-switching technology allows DC / DC has undergone a qualitative leap, US VICOR ECI design and manufacture a variety of soft-switching DC / DC converter, the maximum output power 300W, 600W, 800W, etc., the corresponding power density (6.2 , 10,17) W / cm3, efficiency (80 to 90)%. Japan's latest NemicLambda a soft switching technology high-frequency switching power supply module RM series, the switching frequency (200 ~ 300) kHz, power density has reached 27W / cm3, using synchronous rectifiers (MOSFET instead Schott yl diode), so that the whole circuit efficiency to 90%.

2.2AC / DC conversion

AC / DC converting AC is converted to DC, which may be bi-directional power flow, power flow from the power source to the load is called a "rectifier", power flow from the load to return the power supply is called the "active inverter." AC / DC converter input for AC 50 / 60Hz, the result must be rectified, filtered, and therefore a relatively large volume of the filter capacitor is essential, at the same time due to meet safety standards (such as UL, CCEE, etc.) and EMC Directive restrictions (such as IEC ,, FCC, CSA), AC input side must be added using the EMC filter and components comply with safety standards, thus limiting the AC / DC power supply volume of miniaturization, in addition, due to the internal high-frequency, high-voltage, large current switching action, making solve EMC problems more difficult, it is installed on the internal high-density circuit design made high demands, for the same reason, high voltage, high current switching power supply makes the loss increases, limiting AC / DC converter modular process, it is necessary to optimize the use of power system design approach to make it work efficiency reaches a certain level of satisfaction.

 AC / DC conversion circuit according to the connection mode can be divided, a half-wave circuit, a full-wave circuit. Power can be divided according to the number of phases, single-phase, three-phase, multi-phase. The circuit can be divided into quadrants by a quadrant, two quadrant, three quadrants, four quadrants.

Choice of switching power supply

Switching power supply input on anti-jamming performance, due to the characteristics (Tandem) its circuit structure, the general input disturbances such as surge voltage is difficult to pass on the output voltage of the technical indicators and linear power compared with the greater advantage, the output voltage stability up (0.5 to 1)%. Switching power supply module as an integrated power electronic devices in the selection should pay attention to the following points:

3.1 the output current selection

Due to the high efficiency switching power supply, and can be up to 80%, so the output current of choice, should be accurately measured or calculated the maximum absorption current electrical equipment, was chosen to make the switching power supply with high performance and low cost, Typically the output is calculated as:

Is = KIf

Where: Is- switching power supply rated output current;

If- current maximum absorption of electrical equipment;

K- margin coefficients, and generally 1.5 to 1.8;

3.2 Ground

Switching power supply will produce more than linear interference, common-mode interference sensitive electrical equipment, grounding and shielding measures should be taken, according to ICE1000, EN61000, FCC and other EMC limit, switching power supply with EMC measures are taken, so the switch Power General EMC EMC filter should have. Leader & Harvest technologies such as HA series switching power supply, which is connected to the earth terminal FG chassis or receiving user, can meet the electromagnetic compatibility requirements.

3.3 Protection Circuit

Switching power supply design must have overcurrent, overheating, short circuit protection, it should be the first choice in the design of complete protection switching power supply module, and its technical parameters of the protection circuit should match the operating characteristics of the electrical equipment to To avoid damaging the electrical equipment or switching power supplies.

Switching power supply technology developments

The development direction of high-frequency switching power supply, high reliability, low consumption, low noise, interference and modular. Because switching power light, small, thin, high-frequency technology is the key, so the major switching power supply manufacturers abroad are committed to the simultaneous development of new high-intelligence components, in particular to improve the loss of secondary rectifiers and power iron increase scientific and technological innovation on the ferrite material (MnZn), in order to improve the high frequency and large magnetic flux density

 Obtained (Bs) at high magnetic properties, the miniaturization of the capacitor is a key technology. SMT technology makes application switching power supply has made considerable progress in the circuit board components are arranged on both sides to ensure that the light switching power supply, small, thin. High-frequency switching power supply is bound to traditional PWM switching technology innovation to achieve ZVS, ZCS soft switching technology has become mainstream technology of switching power supply, and significantly improve the efficiency of the switching power supply. For high reliability, the US manufacturer of switching power supply by reducing operating current, lower junction temperature and other measures to reduce the stress of the device, making the product reliability is greatly increased.

Modularity is the overall trend in the development of the switching power supply can be composed of modular distributed power supply system can be designed to N + 1 redundant power systems, and to achieve parallel capacity expansion. Switching power supply noise for the big run this shortcoming, if the individual pursuit of its high frequency noise will also increase with, and the use of part of the resonant converter circuit technology, you can achieve in theory, but also reduce the high frequency noise, but some the practical application of the resonant converter technology, there are still technical problems, it still needed a lot of work in this area, so that the technology to practical use.

Power electronics technology innovation, so that the switching power supply industry has broad prospects for development. To accelerate the pace of development of the switching power supply industry, we must take the road of technological innovation, out of the joint research with Chinese characteristics, development, for the rapid development of China's national economy to contribute.

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Switching power supply test methods

One. Withstand voltage

(HI.POT, ELECTRIC STRENGTH, DIELECTRIC VOLTAGE WITHSTAND) KV

1.1 Definitions: at designated terminals, such as: between I / PO / P, I / P-FG, O / P-FG, resistant RMS AC, the allowable leakage current is generally 10 mA, for 1 minute.

1.2 Test conditions: Ta: 25 ℃; RH: indoor humidity.

1.3 Test circuit:

1.4 Description:

1.4.1 Pressure test is mainly to prevent electrical damage, via an input string into the high-pressure, affect the safety of users.

1.4.2 Test voltage must begin upped by 0V, and raised to the highest point within one minute.

Must pay attention to the Timer setting Tester 1.4.2 discharge voltage repatriated before OFF 0V.

1.4.3 Safety Certification testing, plus testing to be subject to the transformer, indoor, temperature 25 ℃, RH: 95 ℃, 48HR, beginning after the test transformer / secondary and primary / CORE.

1.4.5 production line testing time is 1 second.

II. Ripple noise (ripple noise voltage)

(Ripple & Noise)%, mv

2.1 Definitions:

Overlap on the DC output voltage of the AC voltage component of the maximum (PP) or RMS.

2.2 Test conditions:

I / P: Nominal

Switching power supply Bert Figure O / P: Full Load

Ta: 25 ℃

2.3 Test circuit:

2.4 Test Waveform:

2.5 Description:

2.5.1 oscilloscope GND line of the shorter the better, the test line was far from PUS.

2.5.2 Use 1: Probe 1's.

2.5.3 Scope of the BW is generally set at 20MHz, but for now the best network product testing ripple noise BW is set to maximum.

2.5.4 Noise and use of equipment, environmental vary greatly, so the test must show that the test sites.

2.5.5 Test ripple noise does not exceed the original specifications for + 1% Vo.

Three. Leakage current (leakage current)

(Leakage Current) mA

3.1 Definitions:

Enter a circulating current between the chassis (chassis must be connected to earth when).

3.2 Test conditions:

I / P:. Vin max × 1.06 (TUV) / 60Hz

Vin max. (UL1012) / 60Hz

O / P: No Load / Full Load

Ta: 25 ℃

3.3 Test circuit:

3.4 Description:

3.4.1 L, N need to be measured.

3.4.2UL1012 R value 1K5.

TUV R value 2K / 0.15uF.

3.4.3 Leakage current specifications TUV: 3.5mA, UL1012: 5mA.

Four. Temperature Test

(Temperature Test)

4.1 Definitions:

PSU temperature test refers to the normal working under its parts or materials shall not exceed the Case temperature regulation

Grid or specifications given value.

4.2 Test conditions:

I / P: Nominal

O / P: Full Load

Ta: 25 ℃

4.3 Test method:

4.3.1 Thermo Coupler (TYPE K) firmly fixed to the measurement of the object

(Quick-drying, Tape or welding).

4.3.2 Thermo Coupler at the end of the skein into a ball three times after welding test.

4.3.3 We generally use point temperature meter.

4.4 Test parts:

Susceptible to heat and heat affected part

For example: input terminals, Fuse, input capacitance, inductance input filter capacitor, the whole bridge, hot

Min, surge absorber, the output capacitor, the output capacitor, the output inductors, transformers, core,

Winding, PCB heat sink, power semiconductor, Case, heat the parts under .......

4.5 parts Temperature limits:

There were marked temperature on the part 4.5.1, to indicate the temperature of the benchmark.

4.5.2 Other temperature of the parts are not marked, the temperature does not exceed the PCB temperature.

4.5.3 inductance display individual applications are safety, temperature limit 65 ℃ Max (UL1012), 75 ℃

Max (TUV).

Five. Input voltage regulation rate

(Line Regulation),%

5.1 Definitions:

When the input voltage changes within the rated range, the output voltage change rate.

Vmax-Vnor

Line Regulation (+) = ------------------

Vnor

Vnor-Vmin

Line Regulation (-) = ------------------

Vnor

Vmax-Vmin

Line Regulation = ----------------

Vnor

Vnor: Input voltage for normal value, the output of the output voltage at full load.

Vmax: maximum output voltage when the input voltage changes.

Vmin: minimum output voltage when the input voltage changes.

5.2 Test conditions:

I / P:. Min / Nominal / Max

O / P: Full Load

Ta: 25 ℃

5.3 Test circuit:

5.4 Description:

Line Regulation or directly Vmax-Vnor and Vmin-Vnor of ± maximum

Value expressed in mV, together with Tolerance% representation.

VI. Load Regulation

(Load Regulation)%

5.1 Definitions:

Output current change (static) within the nominal range, the output voltage change rate.

| Vminl-Vcent |

Line Regulation (+) = ------------------ × 100%

Vcent

| Vcent-VfL |

Line Regulation (-) = ------------------ × 100%

Vcent

| VminL-VfL |

Line Regulation (%) = ---------------- × 100%

Vcent

VmilL: The minimum load of the output voltage

VfL: the output voltage at full load

Vcent: half load when the output voltage

6.2 Test conditions:

I / P: Nominal

O / P: Min / Half / Full Load.

Ta: 25 ℃

6.3 Test circuit:

6.4Load Regulation or directly Vmin.L-Vcent and Vcent-Vmax. The maximum ±

Value expressed in mV, together with Tolerance% representation.

Switching Power Supply

With the rapid development of power electronics technology, power electronics device relationships with people working and living increasingly close, and electronic equipment are inseparable reliable power, into the 1980s, the full realization of the computer power supply switching power supply technology, the first to complete a computer power generation, the 1990s have entered into a variety of switching power electronic and electrical equipment in the field, PBX, communications, electronic testing equipment supply, power supply and other control devices have been widely used switching power supply, but also to promote the rapid development of the switching power supply technology . Switching power supply is the use of modern power electronics, control switching transistor turn-on and turn-off time ratio, maintaining a stable output voltage of the power supply, switching power supply generally consists of a pulse width modulation (PWM) control IC and MOSFET constituted. Switching power supplies and linear power compared with the increasing cost of both the output power and growth, but the rate of increase of both different. Linear output power costs on a power point, but higher than the switching power supply, the cost of turning points. With the development of power electronics technology and innovation, making switching power supply technology in constant innovation, the cost of reversing the growing point moves to the low output power terminal, which provides a broad space for development switching power supply.

 

High-frequency switching power supply is the direction of its development, high-frequency switching power supply miniaturization, and switching power supply into a wider range of applications, especially applications in high-tech fields, and promote the miniaturization of high-tech products, lightweight technology. In addition the development and application of switching power supply has an important significance in saving energy, saving resources and protecting the environment.



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