SMPS电源技术.docx

1、SMPS电源技术Switch Mode Power Supply Basics Tutorial- summary or tutorial about the basics of switch mode power supplies, their design, operation and advantages and disadvantages.SMPS TUTORIAL INCLUDES Switch mode power supply Switch mode regulator fundamentals Step down Buck converter Step up Boost con

2、verter Buck-Boost converterSwitch mode power supplies are widely used because of the advantages they offer in terms of size, weight, cost, efficiency and overall performance.As a result of their performance, switch mode power supplies are used in all but the most exacting applications to provide an

3、efficient and effective source of power for most forms of electronic systems.Switch mode power supplies have become an accepted part of the electronics scene and are often referred to as switch mode power converters, or just switchers.Switch mode power supply terminologySwitch mode power supply, SMP

4、S, technology may be referred to by a number of similar terms. While they all look at the same basic technology, they refer to different elements of the overall technology: Switch mode power supply, SMPS: The term switch mode power supply is generally used to indicate an item that can be connected t

5、o the mains, or other external supply and used to generate the source power. In other words it is a complete power supply. Switch mode regulator: This typically refers just to the electronic circuit that provides the regulation. A switch mode regulator will be part of the overall switch mode power s

6、upply. Switch mode regulator controller: Many switch mode regulator integrated circuits do not contain he series switching element. This will be true if the current or voltage levels are high, because an external series switching element would be able to better handle the higher current and voltage

7、levels, as well as the resultant power dissipation.Switch mode power supply basicsThe basic concept behind a switch mode power supply or SMPS is the fact that the regulation is undertaken by using a switching regulator. This uses a series switching element that turns the current supply to a smoothin

8、g capacitor on an off.Switching regulator concept used in switch mode power supplyThe time the series element is turned on is controlled by the voltage on the capacitor. If it is higher than required, the series switching element is turned off, if it is lower than required, it is turned on. In this

9、way the voltage on the smoothing or reservoir capacitor is maintained at the required level.Switch mode power supply advantages / disadvantagesThe use of any technology is often a careful balance of several advantages and disadvantages. This is true for switch mode power supplies which offer some di

10、stinct advantages, but also have their drawbacks.SMPS advantages High efficiency: The switching action means the series regulator element is either on or off and therefore little energy is dissipated as heat and very high efficiency levels can be achieved. Compact: As a result of the high efficiency

11、 and low levels of heat dissipation, the switch mode power supplies can be made more compact. Flexible technology: Switch mode power supply technology can be sued to provide high efficiency voltage conversions in voltage step up or Boost applications or step down Buck applications.SMPS Disadvantages

12、 Noise: The transient spikes that occur from the switching action on switch mode power supplies are one of the largest problems. The spikes can migrate into all areas of the circuits that the SMPSs power if the spikes are not properly filtered. Additionally the spikes or transients can cause electro

13、magnetic or RF interference which can affect other nearby items of electronic equipment, particularly if they receive radio signals. External components: While it is possible to design a switch mode regulator using a single integrated circuit, external components are typically required. The most obv

14、ious is the reservoir capacitor, but filter components are also needed. In some designs the series switch element may be incorporated within the integrated circuit, but where any current is consumed, the series switch will be an external component. These components all require space, and add to the

15、cost. Expert design required: It is often possible to put together a switch mode power supply that works. To ensure that it performs to the required specification can be more difficult. Ensuring the ripple and interference levels are maintained can be particularly tricky. Costs: Careful consideratio

16、n of the costs of a switch mode power supply must be made before designing or using one. Beyond the basic power supply, additional filtering may be required and this can add to the cost.Despite the disadvantages, switch mode power supply technology is the major form of power supply technology used f

17、or a whole variety of applications especially those included in computers. For applications where very low noise are required, linear regulator technology is still widely used.Switch Mode Regulator Fundamentals- summary of the fundamentals of how a switch mode regulator works and the fundamentals of

18、 its operation.SMPS TUTORIAL INCLUDES Switch mode power supply Switch mode regulator fundamentals Step down Buck converter Step up Boost converter Buck-Boost converterA switch mode regulator is at the heart of any switch mode power supply.The switch mode regulator is the circuit that provides the vo

19、ltage regulation. It can be used on its own or as part of a complete power supply.Switch mode regulators come in a variety of forms, but each one will be able to provide voltage regulation by using a series switching element that charges up a reservoir capacitor when the voltage falls below a predet

20、ermined level.Switching regulator basicsThe basis of switch mode regulator revolves around the ability of inductors and capacitors to store energy. The capacitors and inductors are integral elements of the switch mode regulator technology. Capacitance If a current is applied to a capacitor, the capa

21、citor gradually charges up and the voltage across it rises linearly at a rate equal to I/C where is the applied current and C is the capacitance. In this case the voltage across the capacitor cannot change instantly.When an instantaneous change in current occurs, the voltage changes linearly. This a

22、ssumes a current source with an infinite voltage capability is used. Inductor: For an inductor, it is not possible for there to be an instantaneous change in current. Instead, when a voltage is applied, the current builds up linearly over time at a rate equal to V/L where V is the applied voltage an

23、d L is the inductance.Using the standard equations it is possible to determine the current and voltage profiles:The energy from the rising current is stored in the magnetic field associated with the inductor. If the current flowing through the inductor is suddenly interrupted, the magnetic field rea

24、cts against this and produces a very high back emf to counteract the change.Having seen the fundamental or basic concepts behind switching voltages and currents to capacitors and inductors, these basic concepts can be applied to switch mode regulator solutions to provide a variety scenarios for volt

25、age step up and step down circuits.As the technology uses switching techniques where the series element is on or off, this approach provides much better levels of efficiency than a linear where power is dissipated.Capacitor based switch mode regulationThe basic concept of the capacitor switched mode

26、 regulator is shown in the diagram. When the switch is closed, current is able to flow into the reservoir capacitor and provide charge. When the voltage on the capacitor is at is required level, the switch opens and the load will draw current from the capacitor.As the voltage falls, this will be sen

27、sed by the control circuitry and the series switch will be turned on again to bring the capacitor voltage up to the required level.This circuit is not as effective as may be thought at first sight. Although the only resistive element in the theoretical circuit is the load, this is not the only way i

28、n which energy is lost because charging a capacitor directly from a voltage source or a capacitor dissipates as much energy as is transferred to the capacitor. As a result of this, switching mode regulators cannot use capacitor switching techniques alone.Inductor based switch mode regulationIt is al

29、so possible to use inductors as an element in switch mode regulators.The inductor can be used to transfer energy from one voltage source to another. While a simple resistor can be used as a dropper to drop voltage when transferring from one voltage source at a higher voltage to one at a lower voltag

30、e, this is very wasteful in terms of power. If an inductor is used, then all the energy is transferred, assuming a perfect inductor.The use of an inductor has the advantages that energy can be transferred from one source to another regardless of the respective values of voltage and their polarities.

31、 To achieve this the proper configuration is obviously required.When the switches are in the positions shown above, the voltage V1 is applied across the inductor and the current i1 builds up at a rate equal to V1/L. Therefore the peak value obtained will be proportional to the time the switches are

32、in this position, i.e. (V1/L) x tWhen the switches are reversed, the current will continue to flow at a rate i2 which is equal to -V2/L.As an ideal inductor dissipates no energy, there is no power loss in an ideal system using an inductor in this fashion. As a result, it is this method of energy transfer that forms the basis for all switching regulators.Step Down Buck Regulator / Converter- summary or tutorial about the circuit and o