Tuesday, January 12, 2010

Autotronics - Sensor

Introductions


- A technical component which can detect a special physical condition or chemical characteristic (e.g. light, temperature, pressure, humidity) and change it to electrical signal

- Input -> physical or chemical effects

- Output -> electrical signal.

- Biological term -> receptor

- Sensors can be divided into 2 groups which can be differentiated by the applications and the form of creations.

- Active sensor

         o Created base on the measurement principal of electrical energy i.e. electro dynamic or piezo electric.

         o It doesn’t need any electrical energy.

- Passive sensor

         o Consists of passive components
   
         o The act of the sensor is depend on the changing of the parameter value of the passive components.

        o E.g. resistor thermometer



Applications

- Light ray -> light, X ray.

- Sounds -> the changing of the sound.

- Temporal -> time between 2 recordings

- Spectral -> width of band , number of bands

- Used in medicine and biology -> CCD Sensors

- Automation -> provide signals



Virtual sensor

- Realised by software.

- Measure the calculated values which can be collected by the real sensors.

- Used by applications where the real sensor is very expensive.



Digital Sensor

- Used in automation field.

- E.g. AC converter

- Get the digital signal directly.

- High linearity

Monday, January 11, 2010

Autotronics - Relays

Introductions


- Electrically operated switch

- Use electromagnet to operate switching mechanism.

- Necessary to control a circuit by a low-power signal.

- Help to control several circuits using one signal.


Basic Design and Operation

- It works using the principal of electromagnet.

- Consist of :-

          o A coil of wire surrounding a soft iron core

          o Iron yoke provides a low reluctance for magnetic flux

          o A movable iron armature.

          o Sets of contacts

- When the electric current passed through the coil, magnetic field attracts the armature.

- Movement of movable contacts makes or breaks a connection with a fixed contact.

- When current is off the armature will return back to its original position by a force.

- The force is normally provided by spring or gravity.

- In low voltage application -> relays operate quickly to reduce noise.

- In high voltage application -> relays operate quickly to reduce arcing.



Types of Relays

- Latching relay

          o Has 2 relaxed states

          o Also called as impulse, keep, stay

          o When the current is switched off, the relay remains in its last state.

           o It consumes power only for an instant while is being switched, and it retains its last setting across a power outage.

           o A current pulse in opposite polarity will change the state.


- Reed relay

          o Set of contacts inside a vacuum or inert gas filled glass tube.

          o It protects against atmospheric corrosion.

          o Capable of faster switching speeds than larger types of relays.

          o Have low switch current and voltage ratings.


- Mercury-wetted relay

          o Contacts are wetted with mercury.

          o Used to switch low voltage signals due to low contact resistance.

          o Used for high-speed counting and timing applications.

          o Position sensitive and must be mounted vertically.


- Polarized relay

        o Placed the armature between the poles of a permanent magnet to increase sensitivity.

         o Used to detect faint pulses and correct telegraphic distortion.



Applications

 to switch on many circuits using only one control circuit at the same time.

 To switch on a high voltage circuit using a low voltage circuit.

 To separate 2 conductors with different characteristics in a circuit.



Advantages

 high switching load.

 don't need any coolant

 can be shorted without losing its function.

 It can switch from small signals until high frequency power.



Disadvantages

 high delay time

 sensitive to vibration.

 Life span is depend on the mechanical components.

 It can create noise during switching.
Autotronics - Notes

Friday, January 08, 2010

Autotronics - Transistor

Introductions


- Active electronic devices used as switches and amplifier for electrical signal.

- Can usually be found as part of electronic switches in the application of communication technique, power electronics and computer system.

- Nowadays transistors are widely applied in integrated circuit especially in microelectronic industries.

- Made of silicon material with at least 3 terminals for connection to an external circuit.

- A voltage or current applied to one pair of transistor’s terminals changes the current flowing through another pair of terminals.

- There are 2 types of transistors which are bipolar transistor and field effect transistor.

- Both of them can be differentiated by the way signal is controlled.

- Bipolar transistor :-

      o The most commonly used transistor

      o Become the transistor of choice for many analogue circuits due to their great linearity and ease of manufacture.

- MOSFET

      o Widely used in digital circuits because of their utility in low-power devices

      o Usually in CMOS configuration.



Simple Operation

- The common usage as amplifier by controlling its output in proportion to the input signal.

- This action is due to its gain properties which enable it to use a small signal applied between one pair of its terminal to control a much larger signal at another pair of terminals.

- Another common application of transistor is as switch.

- Used to turn current on or off in a circuit as an electrically controlled switch.



a) Bipolar transistor

- Control electron (negative charge carrier) and hole (positive charge carrier) by manipulating the principal of generation and recombination of electron in a crystal.

- The principal is basically same as diode whereby electron and hole play a big role.

- A bipolar transistor has terminals labelled as base, collector and emitter.

- A small current at the base terminal(that is flowing from the base to the emitter) can control or switch a much larger current between the collector and the emitter terminals.

- Controlled by manipulating the electrical current.

- The contacts are Base, Emitter and Collector.

- Small control current is applied at the Base-Emitter path.

- The characteristic of NPN-transistor and PNP-transistor can be differentiated by the structure of the transistor.

- Bipolar transistor is basically a self block whereby without control from the small current at the Base-Emitter path, current can’t flow through the Collector-Emitter path.





Field Effect Transistor

- Field Effect Transistor (FET)

- Also known as uni polar transistor is controlled by manipulating voltage across it.

- The contacts are known as Gate, Drain and Source.

- In metal oxide semiconductor FET (MOSFET) there is an extra contact which is called as Bulk, where it is connected to Source.

- The resistance and also the current across the Drain-Source path are controlled by the voltage and also electric field at gate.

- The controlled current in the Drain-Source Canal can flow in both position rather than Collector current in bipolar transistor which can flow only in one direction.



Junction Field Effect Transistor (JFET)

- Normally JFET is a self conductive transistor.

- When there is no voltage at gate, the path between Source and Drain become conductive.

- But if voltage is applied at the Gate the conductivity between Source and Drain will reduce.

- There are 2 types of JFET i.e. N-Canal and P-Canal.

- N-Canal transistor can be recognized by referring to the arrow symbol which direction is showing into the transistor.

- For P-Canal the arrow will point in the opposite direction.

- JFET is normally used in special application such as microphone amplifier due to the complexity of the control.



Metal-Oxide Semiconductor – Field-Effect-Transistor

- This transistor is known as MOSFET due to the structure of semiconductor layer at the Gate.

- But nowadays poly silicon is used as the material at gate.

- MOSFET is normally used for charge transport which is suitable for use at very high frequencies e.g. microwave frequencies.



Special Type of Transistor

- Beside the normal type of transistors there are other types of transistors for special usage such as Bipolar transistor with isolated Gate electrode.

- This type of transistor is widely used in power electronic area where by it is actually a combination of MOS- and bipolar technology in a same package.

- Due to its capability it has been used in power electronic area to replace thyristor.

- Fototransistor is actually an optically sensitive bipolar transistor which has same application as other opto-coupler devices.

- The control of the transistor is not by the Base-emitter current but it is controlled by light.

- Light act similar as the Base current at the PN-junction.

- In some of the LCD display monitor, thin film transistors are used to control every pixel on the monitor.

- These FET is actually transparent. They are used to control the contrast, colour and the brightness of the monitor for each pixel.

- Therefore for each monitor more than million thin film transistors are used for this purpose.

- In programmable storage disk such as EPROMs and EEPROMs special MOSFET (floating gate) are used as prime storage element.

- By manipulating the electrical charge which are stored in the floating gate, the transistor can be switched on and off and also information of one bit can also be stored.



Applications


Digital Circuit

- Here transistors are used mainly in the making of integrated circuit in the RAM-Storage, Flash-Storage, microcontroller, microprocessor and logic gate.

- Normally there are about 1 billion of transistors on a substrat which are made of silicon.


Analogue Circuit

- In the analogue circuit transistors are used as operational amplifier, signal generator and also as reference voltage source.

- To convert between analogue to digital or vice versa Analogue-digital converter and digital-analogue converter are used frequently.

- The number of transistors used are about 100 to 10000.
Autotronics - Diodes

Introduction


- electronic component which let current flow through a conductor in one direction and act as an insulator in the opposite direction.

- can be thought as an electronic version of check valve.

- act as a rectifier to convert AC current to DC current and remove modulation from radio signals in radio receivers.

- The term of diode related to the semiconductor characteristics of PN junction .



The Construction of Semiconductor Diode

- made of impurities P-N semiconductor material (mostly Silicon, Germanium, Galliumarsenide and Sillicon carbide).

- The conductivity of a conductor is depend on the polarity of potential difference i.e. Anode (p-type semiconductor) and Cathode (n – type semiconductor) or the direction of the current flowing across it.

- The PN junction is an area where the action of diode takes place.

- Here the positive charge carriers (holes) from the P-type semiconductor and the negative charge carriers (electron) from the n-type semiconductor combine together.

- The crystal conducts current in a direction from p-type (anode) to the n-type side(cathode) but not in opposite direction.



Mechanical Model of Diode

- The function of diode can be represented as a simple check valve.

- When the pressure( potential difference) of the check valve (diode) is given in the opposite direction the current flow will be blocked.

- Enough pressure must be given in this direction until the spring of the check valve spoil to let the current flow.

- The voltage which is needed to let current flow is called threshold voltage or forward voltage drop.

- To reach this situation voltage at such value must be put in the direction of forward voltage so that diode will become conductive at certain position.


Semiconductor Diode

- made of semiconductor material such as silicon which has been added with impurities in it.

- The impurities is very important to create region on one side which contains negative charge carriers (electrons) i.e. n-type semiconductor.

- On another side it is a region which contains positive charge carriers (holes), called p-type semiconductor.

- Each of these regions are attached by diodes terminals

- between them there is a border which is called PN junction where here all actions of diode takes place.

- Currents flow in a direction from p-type side (anode) to the n-type side (cathode) but not in the opposite direction.

- Another type of semiconductor diode is the Schottky Diode which is formed from the contact between a metal and a semiconductor rather than by p-n junction.





Current – voltage Characteristic

- The behaviour of a semiconductor diode can be observed by the current-voltage characteristic.

- The shape of the curve in the graph is influenced by the transport of charge carriers through the depletion layer in the p-n junction.

- At first when the p-n junction is created the electrons from the N-type region diffuse into the p-type region where there are more holes (places for electron in which no electron is present).

- When an electron from the n-type region combines together with a hole, both electron and hole disappear.

- Now on the N-side, there is a static positively charged donor and on the P-side there is a negatively charged acceptor.

- Therefore right now the area around the P-N junction becomes depleted of charge carriers and thus behaves as an insulator.

- However the width of the depletion region can grow with limit.

- Each time the electron-hole recombines, a positively-charged ion is left behind in N-type region and negatively charged ion is left in the P-type region.

- This process happens continuously and more ions are created.

- After some time an increasing electric field develops in the depletion region and make the process slower and finally stop the recombination process.

- Now there is a built-in potential across the depletion area.

- Now let say if we put an external voltage across the diode with the same polarity as the built-in potential

- the depletion area will act as an insulator to prevent any electric current flow.

- This phenomenon is called reverse bias.

- However if the polarity of the external voltage is put in the opposite direction of the built in potential, the recombination process happen again to create a current flow through the p-n junction.

- For silicon diodes the built-in potential is approximately 0.6V.

- Thus if an external current passed through the diode about 0.6V will be developed across the diode such that the P-doped region is positive with respect to the N-typed region.

- Therefore the diode is said to be turned on as it has forward bias.



Types of Semiconductor Diode

- There are several types of diode

- differentiated by geometric scaling, doping level, choosing the right electrodes and the application of diodes.

- Normally these diodes are made of doped silicon

- rarely germanium.


a) Avalanche Diodes

- It conducts in the reverse direction when the reverse bias voltage exceeds the breakdown voltage.

- Normally they are mistakenly called Zener diodes due to electrical similarity.

- Avalanche diode break down by different mechanism, the avalanche effect.

- It is designed to break down at a well defined reverse voltage without being destroyed.

- The only practical difference is that the two types have temperature coefficients of opposite polarities.


b) Crystal diode

- It is a type of point-contact diode.

- It consists of a thin or sharpened metal wire pressed against a semiconducting crystal, typically galena or a piece of a coal.

- The wire forms the anode and the crystal forms the cathode.

- This type of diode is used normally as a crystal radio receivers.

- But nowadays crystal diode are generally obsolete, but may be available from a few manufacturers.


c) Constant current diode

- It is actually a JFET with the gate shorted to the source and function like a two-terminal current limiter analogue to the Zener diode, which is limiting voltage.

- Current is allowed to pass through then to rise to a certain value, and then level off at a specific value.

- It is also called CLDs, constant-current diode, diode-connected transistors or current-regulating diodes.


d) Esaki or tunnel diode

- It has a region of operation showing negative resistance caused by quantum tunnelling, thus allowing amplification of signals and very simple bistable circuits.

- This diode is also the type most resistant to nuclear radiation.


e) Gunn diode

- It is similar to tunnel diode in that it is made of materials such GaAs or InP that exhibit a region of negative differential resistance.

- With appropriate biasing, dipole domains form and travel across the diode, allowing high frequency microwave oscillators to be built.


f) Light emitting diode (LED)

- In a diode formed from a direct band-gap semiconductor, such as gallium arsenide, carriers that cross the junction emit photons when they recombine with the majority carrier on the other side.

- Depending on the material, wavelengths (or colors) from the infrared to the near ultraviolet may be produced.

- The forward potential of these diodes depends on the wavelength of the emitted photons: 1.2 V corresponds to red, 2.4 V to violet.

- The first LEDs were red and yellow, and higher-frequency diodes have been developed over time.

- All LEDs produce incoherent, narrow-spectrum light; “white” LEDs are actually combinations of three LEDs of a different color, or a blue LED with a yellow scintillator coating.

- LEDs can also be used as low-efficiency photodiodes in signal applications. An LED may be paired with a photodiode or phototransistor in the same package, to form an opto-isolator.


Laser diodes

- When an LED-like structure is contained in a resonant cavity formed by polishing the parallel end faces, a laser can be formed.

- Laser diodes are commonly used in optical storage devices and for high speed optical communication.


Peltier diodes

- These diodes are used as sensors, heat engines for thermoelectric cooling.

- Charge carriers absorb and emit their band gap energies as heat.


Photodiodes

- All semiconductors are subject to optical charge carrier generation.

- This is typically an undesired effect, so most semiconductors are packaged in light blocking material.

- Photodiodes are intended to sense light(photodetector), so they are packaged in materials that allow light to pass, and are usually PIN (the kind of diode most sensitive to light).

- A photodiode can be used in solar cells, in photometry, or in optical communications.

- Multiple photodiodes may be packaged in a single device, either as a linear array or as a two-dimensional array.

- These arrays should not be confused with charge-coupled devices.


Point-contact diodes

- These work the same as the junction semiconductor diodes described above, but their construction is simpler.

- A block of n-type semiconductor is built, and a conducting sharp-point contact made with some group-3 metal is placed in contact with the semiconductor.

- Some metal migrates into the semiconductor to make a small region of p-type semiconductor near the contact.

- The long-popular 1N34 germanium version is still used in radio receivers as a detector and occasionally in specialized analog electronics.


PIN diodes

- A PIN diode has a central un-doped, or intrinsic, layer, forming a p-type/intrinsic/n-type structure.

- They are used as radio frequency switches and attenuators.

- They are also used as large volume ionizing radiation detectors and as photodetectors.

- PIN diodes are also used in power electronics, as their central layer can withstand high voltages.

- Furthermore, the PIN structure can be found in many power semiconductor devices, such as IGBTs, power MOSFETs, and thyristors.



Schottky diodes

- Schottky diodes are constructed from a metal to semiconductor contact.

- They have a lower forward voltage drop than p-n junction diodes.

- Their forward voltage drop at forward currents of about 1 mA is in the range 0.15 V to 0.45 V, which makes them useful in voltage clamping applications and prevention of transistor saturation.

- They can also be used as low loss rectifiers although their reverse leakage current is generally higher than that of other diodes.

- Schottky diodes are majority carrier devices and so do not suffer from minority carrier storage problems that slow down many other diodes — so they have a faster “reverse recovery” than p-n junction diodes.

- They also tend to have much lower junction capacitance than p-n diodes which provides for high switching speeds and their use in high-speed circuitry and RF devices such as switched-mode power supply, mixers and detectors.


Super Barrier Diodes

- Super barrier diodes are rectifier diodes that incorporate the low forward voltage drop of the Schottky diode with the surge-handling capability and low reverse leakage current of a normal p-n junction diode.


Gold-doped diodes

- As a dopant, gold (or platinum) acts as recombination centers, which help a fast recombination of minority carriers.

- This allows the diode to operate at signal frequencies, at the expense of a higher forward voltage drop.

- Gold doped diodes are faster than other p-n diodes (but not as fast as Schottky diodes).


Snap-off or Step recovery diodes

- The term step recovery relates to the form of the reverse recovery characteristic of these devices.

- After a forward current has been passing in an SRD and the current is interrupted or reversed, the reverse conduction will cease very abruptly (as in a step waveform).

- SRDs can therefore provide very fast voltage transitions by the very sudden disappearance of the charge carriers.


Transient voltage suppression diode (TVS)

- These are avalanche diodes designed specifically to protect other semiconductor devices from high-voltage transients.

- Their p-n junctions have a much larger cross-sectional area than those of a normal diode, allowing them to conduct large currents to ground without sustaining damage.


Varicap or varactor diodes

- These are used as voltage-controlled capacitors.

- These are important in PLL (phase-locked loop) and FLL (frequency-locked loop) circuits, allowing tuning circuits, such as those in television receivers, to lock quickly, replacing older designs that took a long time to warm up and lock.

- A PLL is faster than an FLL, but prone to integer harmonic locking (if one attempts to lock to a broadband signal).

- They also enabled tuneable oscillators in early discrete tuning of radios, where a cheap and stable, but fixed-frequency, crystal oscillator provided the reference frequency for a voltage-controlled oscillator.


Zener diodes

- Diodes that can be made to conduct backwards.

- This effect, called Zener breakdown, occurs at a precisely defined voltage, allowing the diode to be used as a precision voltage reference.

- In practical voltage reference circuits Zener and switching diodes are connected in series and opposite directions to balance the temperature coefficient to near zero.

- Some devices labeled as high-voltage Zener diodes are actually avalanche diodes (see above).

- Two (equivalent) Zeners in series and in reverse order, in the same package, constitute a transient absorber (or Transorb, a registered trademark).

Thursday, January 07, 2010

Autotronics - Electrical Switches

Introduction


   - Electrical component which can break an electrical circuit.

   - Interrupting the current or diverting it from one conductor to another.

   - A manually operated electro mechanical device with one or more sets of electrical contacts.

   - Closed – contacts are touching and electricity can flow.

   - Open – contacts are separated and non conducting.


Contacts

   - The simplest -> 2 pieces of metal called contacts to make a circuit when they touch and separate to break the circuit.

   - Material of contacts are chosen base on its resistance to corrosion.

   - This is due to the problem of insulating oxides form at the metal which prevents the switch from working.

   - Materials of contacts are chosen base on the electrical conductivity, hardness (resistance to abrasive wear), mechanical strength, low cost and low toxicity.



Actuator

   - Moving part which applies the operating force to the contacts.

   - E.g. toggle , dolly, push-button.



Arcs and Quenching

   - When the wattage or voltage are large-> electron flow across opening switch contacts is sufficient to ionize the air molecules as the switch opened.

   - Gas plasma / electric arc is formed.

   - The disadvantage of gas plasma :

      o Low resistance

      o Able to sustain power flow.

      o Very hot and capable to erode the metal surfaces.

   - To minimize arc formation and preventing contact damage :

      o Use fast-moving switch mechanism. e.g. a spring operated tipping point mechanism.

      o Use a series of nonconductive blades spanning between switch contacts.

     o Use a puffer to blow a sudden high velocity burst of gas across the switch contacts.



Contact Arrangements

   - SPST -> Single Pole Single Throw

   - SPDT -> Single Pole Double Throw

   - SPCO -> Single Pole Change Over

   - DPST -> Double Pole Single Throw

   - DPCO -> Double Pole Change Over



Biased Switches

   - Switch that contain a spring to return the actuator to a certain point.

   - E.g. momentary push-button

     o Push-to-make (Normally Open)

     o Push-to-break (Normally Close)



Special Types

   - Designed to respond to any type of mechanical stimulus :

      o Vibration

      o Tilt

      o Air pressure

      o Fluid level

     o The turning of a key

     o Linear or rotary movement

     o Presence of a magnetic field

   - Mercury tilt switch

     o Consists of a drop of mercury inside a glass bulb with 2 or more contacts

     o When the bulb tilt contacts will be connected by mercury.

     o Better than ball tilt switch.-> unaffected by dirt, debris and oxidation.

     o Used when arcing is dangerous e.g. presence of explosive vapour.

   - Knife switch

     o Consist of flat metal plate hinged at one end and a fixed contact.

     o Usually it is not enclosed.

     o Used in electrical transmission and distribution, gang-operated switches which us used in circuits up to the highest voltages.

     o Disadvantages :- slow opening speed

 

Monday, January 04, 2010

Autotronics - Power Source


Introduction


- Source of electrical power.

- Device or system that supplies electrical or other types of energy to an output load or group of loads

- It is called a power supply unit or PSU.


Primary or Secondary Power Supplies

There are a lot of types of power supplies which may include a power distribution system as well as primary or secondary of energy such as:

- A converter which converts one form of electrical power to other desired form like converting AC voltage to a well regulated lower voltage DC for electronic devices. Low voltage or low power DC power supply units are normally integrated into electronic devices such as computers and household electronics.

- Batteries

- Fuel cells

- Solar power

- Generators or alternators.


There are some factors that should be considered when using a power supply:

- The amount of the power that can be supplied

- The duration of supply without needing some kind of recharging or refuelling

- The stability of the output voltage or current under varying load conditions

- Whether they provide continuous power or pulses.


Power Supply types

A) Linear Power Supply

- Simple design which becomes bulky and heavy for high current devices.

- Voltage regulation in a linear supply can result in low efficiency.

Battery Power Supply

- linear power supply which is mobile, portable and reliable.

- Constructed using multiple electrochemical cells connected to get the voltage desired


(i) Dry-Cell Battery

- The most commonly used dry-cell battery is the carbon-zinc dry cell battery.

- Made of carbon plate, electrolyte paste and a zinc plate which are stacked together.

- The chemical process which happened inside the battery produce voltage desired.

- The voltage is produced during the discharge of a carbon-zinc battery

- The zinc metal is converted to a zinc salt in the electrolyte

- Magnesium dioxide is reduced at the carbon electrode.

- It produces a voltage at about 1.5V.


(ii) Lead –acid battery

- Rechargeable

- Consists of lead and lead/dioxide electrodes which are immersed in sulphuric acid

- When fully charged it can produce about 2.06-2.14V voltage

- During discharge process, the lead is converted to lead sulphate and the sulphuric acid is converted to water

- But during charging process, the lead sulphate is converted back to lead and lead dioxide.


(iii) Nickel-cadmium battery

- become more popular.

- Completely sealed and rechargeable.

- Has longer life span because electrolyte is not involved in the electrode reaction

- During the charging process nickel oxide is oxidized to its higher oxidization state and cadmium oxide is reduced.

- It can be stored both charged and uncharged

- Has a long service life, high current availabilities, constant voltage and ability to be recharged.



AC Linear Power Supply

- Uses transformer to convert the voltage from the socket outlet (mains) to lower voltage.

- If it used to produce DC voltage so a rectifier will be used.

- A capacitor is used to smooth the pulsating current from the rectifier.

- The voltage produced by unregulated power supply will vary depending on the load and the variations in the AC power supply.

- Linear regulator is normally used by critical electronics applications to stabilize and adjust the voltage.

- It normally provides current limiting, protecting the power supply and attached circuit from the over current.

- The simplest dc power supply circuit consists of a single diode and resistor in series with the AC supply.

- The circuit is common in rechargeable flashlights.


AC/DC Supply

- Formerly mains electricity was supplied as DC and AC separately.

- A simple power supply would run directly from the either AC or DC mains often without using transformer.

- Consisted of a rectifier and a capacitor filter.



B) Switching power supply.
- A switched mode supply of the same rating as a linear supply will be smaller
- Usually more efficient but will be more complex.



Switch Mode power supply (SMPS)

- A SMPS work differently.

- AC, mains input is directly rectified without the use of a transformer, to obtain DC voltage.

- This voltage is then sliced into small pieces by a high-speed electronic switch.

- The size of these slices grows larger as power output requirement increase.

- The input power slicing occurs at a very high speed.

- High frequency and high voltages in this first stage permit much smaller step down transformers than are in a linear power supply.

- After transformer secondary, the AC is again rectified to DC.

- To keep output voltage constant the power supply needs a sophisticated feedback controller to monitor current draw by the load.

- Nowadays it is equipped by the crowbar circuit as the safety features to help protect the device form the harm.

- When the abnormal high current power is detected, it can assume this is a direct short and will shut down before it is damaged.

- Normally used in PC to provide a power good signal to the motherboard which prevents operation when abnormal supply voltages are present.


Programmable power supply

- Can supply output which can be varied remotely.

- Can be controlled digitally using a computer interface.

- Composed of a processor, voltage/current programming circuits, current shunt, and voltage/current read-back circuits.

- Used in many applications such as automated equipment testing, crystal growth monitoring, and differential thermal analysis.


Uninterruptable power supply (UPS)

- It takes its power from two or more sources simultaneously.

- Usually powered by AC (mains), while simultaneously charge the storage battery.

- Should there be a dropout or failure of the mains, the battery will take over so that the load never experiences an interruption.

- Such a scheme can supply power as long as the battery charge suffices, e.g., in a computer installation, giving the operator sufficient time to effect an orderly system shutdown without loss of data.

- Other UPS schemes may use an internal combustion engine or turbine to continuously supply power to a system in parallel with power coming from the AC mains.

- The engine-driven generators would normally be idling, but could come to full power in a matter of a few seconds in order to keep vital equipment running without interruption.

- Such a scheme might be found in hospitals or telephone central offices.


High-voltage power supply

- It refers to an output on the order of hundreds or thousands.

- High voltage supplies use a linear setup to produce voltage in this range.

- It is able to reverse the output polarity along with the use of circuit breakers and special connectors to minimize arcing and accidental contact with human hands.


Voltage multipliers

- It is actually a circuit designed to multiply the input voltage.

- The input voltage may be doubled (voltage doubler), quadrupled (voltage quadrupled).

- It is also actually a power converter.

- An AC input inside converted to a higher DC output.

- It allows high voltages to be obtained using a much lower voltage AC source.

- It can be found in televisions, photocopier, cathode ray tubes, and oscilloscopes.


Applications


Computer power supply

A modern power supply is a switched mode supply designed to convert 110-240V AC power from mains supply to several output both positive DC voltages.


Welding power supply

Arc welding uses electricity to melt the surfaces of the metals in order to join them together. The electricity is provided by a welding power supply and can be either AC or DC. It requires high current between 100 and 350 amps.


AC Adapter

A linear or switched mode power supply that is built in the top of the plug is known as power adapter. They are actually either the same kind of DC plug offering different voltage or polarity or different plug offering the same voltage.

The least expensive AC units consists of a small transformer while DC adapters include a few additional diodes. Whether or not a load is connected to the power adapter, the transformer has a magnetic field continuously present and normally cannot be completely turned off unless unplugged.