Ac To Dc Converter (rectifiers): Dirangkum Oleh: I Nyoman Wahyu Satiawan, St, M.sc, Ph.d

AC to DC Converter (Rectifiers) Dirangkum Oleh : I Nyoman Wahyu Satiawan, ST, M.Sc, Ph.D

Jurusan Teknik Elektro Fakultas Teknik Universitas Mataram

Scope of discussion 

Penyearah tak terkendali (Uncontrolled Rectifiers)

◦ Penyearah setengah gelombang (Half Wafe Rectifiers) ◦ Penyearah gelombang penuh (Full Wave Rectifiers) ◦ Penyearah Jembatan (Bridge Rectifiers) Controllable Rectifiers

Multi-phase Rectifiers Three phases

Single phase Rectifiers

Contoh Aplikasi Peralatan elektronika kedokteran  Telekomunikasi  Charger HP  UPS  Electric Vehicles  PC/Laptop  etc 

introduction 

Penyearah adalah peralatan yang fungsinya merubah alternating current (AC), yang secara periodik nilainya berubah, menjadi direct current (DC) / arus searah.

Half wave rectifier 

In half wave rectification, either the positive or negative half of the AC wave is passed, while the other half is blocked.



Because only one half of the input waveform reaches the output, it is very inefficient if used for power transfer.

Half-wave Rectifiers 

Half-wave rectifier – A diode placed in series between a transformer (or ac line input) and its load.

Positive Half-wave Rectifiers This circuit converts an ac input to a series of positive pulses.

Average Load Voltage and Current 

Average voltage (Vave) – The dc equivalent of a voltage waveform.



Average current (Iave) – The dc equivalent of a current waveform. For the output from a half-wave rectifier: I pk Vpk I ave  Vave 





Negative Half-wave Rectifiers

This circuit converts an ac input to a series of negative pulses.

Peak Inverse Voltage (PIV) Peak inverse voltage (PIV) – The maximum diode reverse bias produced by a given circuit.

For the diode in a half-wave rectifier:

PIV  VS (pk)

Full-wave Rectifier

Full-wave Rectifier Operation Diodes

conduct during alternate half cycles of the input signal.

VL(pk)

is approximately half the value of VS(pk).

The

circuit produces two positive half-cycles for each input cycle.

Average Load Voltage and Current 

Average voltage (Vave) – The dc equivalent of a voltage waveform.



Average current (Iave) – The dc equivalent of a current waveform. For the output from a full-wave rectifier: Vave 

2Vpk



I ave 

2I pk



Peak Inverse Voltage (PIV) 

Peak inverse voltage (PIV) – The maximum diode reverse bias produced by a given circuit.

For the diode in a full-wave rectifier:

PIV  VS (pk) PIV  2VL (pk)

Negative Full-wave Rectifiers 

The negative full-wave rectifier converts an ac input to a series of negative pulses.

Full-Wave Bridge Rectifiers 



Single phase rectifier uses four individual rectifying diodes connected in a closed loop "bridge" configuration to produce the desired output The four diodes labelled D1 to D4 are arranged in "series pairs" with only two diodes conducting current during each half cycle.

Main Advantages Full-Wave Bridge Rectifiers It does not require the use of a center-tapped transformer. thereby reducing its size and cost. It can be coupled directly to the ac power line. It produces a higher dc output than a comparable full-wave center-tapped rectifier.

Bridge Rectifier Operation The Positive Half-cycle  During the positive half cycle of the supply, diodes D1 and D2 conduct in series while diodes D3 and D4 are reverse biased and the current flows through the load as shown below.

Bridge Rectifier Operation The Negative Half-cycle  During the negative half cycle of the supply, diodes D3 and D4 conduct in series, but diodes D1 and D2 switch "OFF" as they are now reverse biased. The current flowing through the load is the same direction as before.

Bridge Rectifier Operation 

Conduction alternates between two diode pairs.

Voltage Output 

As the current flowing through the load is unidirectional, so the voltage developed across the load is also unidirectional the same as for the previous two diode full-wave rectifier, therefore the average DC voltage across the load is 0.637Vmax. However in reality, during each half cycle the current flows through two diodes instead of just one so the amplitude of the output voltage is two voltage drops ( 2 x 0.7 = 1.4V ) less than the input VMAX amplitude. The ripple frequency is now twice the supply frequency (e.g. 100Hz for a 50Hz supply)

Calculating load voltage and current relationships VL (pk )  VS (pk)  1.4 V Vave  I ave

2VL (pk ) π

Vave  RL

PIV  VS(pk)  0.7 V

Working with Rectifiers 

Rectifiers are high current circuits, so IFRB can have a significant impact on diode forward voltage (VF ).



Cooling is often used to minimize the effects of high power rectifier reverse current. Components may be cooled using a fan and/or a heat sink.



High transformer tolerances can introduce significant discrepancies between calculated and measured current and voltage values.

Integrated Rectifiers 

Integrated Rectifier – A rectifier circuit that is etched on a single piece of silicon (housed in a single case). IC rectifiers are: ◦ Cheaper to produce ◦ Easier to troubleshoot

The diodes in an IC rectifier operate at the same temperature, so they have equal values of forward voltage and leakage current.  IC rectifier cases are designed to be attached easily to a heat sink. 

Filters 

A filter reduces the voltage and current variations in the output from a rectifier.

Full-wave Rectifier with Smoothing Capacitor 

To increase its average DC output level even higher by connecting a suitable smoothing capacitor across the output of the bridge circuit as shown below.

Bridge Rectifier Ripple Voltage 

The maximum ripple voltage present for a Full Wave Rectifier circuit is not only determined by the value of the smoothing capacitor but by the frequency and load current, and is calculated as:

Where: I is the DC load current in amps, ƒ is the frequency of the ripple or twice the input frequency in Hertz, and C is the capacitance in Farads.

Another Advantage of Bridge Rectifier 

The main advantages of a full-wave bridge rectifier is that it has a smaller AC ripple value for a given load and a smaller reservoir or smoothing capacitor than an equivalent half-wave rectifier. Therefore, the fundamental frequency of the ripple voltage is twice that of the AC supply frequency (100Hz) where for the half-wave rectifier it is exactly equal to the supply frequency (50Hz).

Ripple Voltage (Vr) 

Ripple voltage (Vr) – The variation in the filter output voltage.

The Basic Capacitive Filter TC  5 RD1C1 TD  5 RL C1



The capacitor:

◦ charges through the rectifier diode. ◦ discharges through the load.

Surge Current  

The high initial current through a power supply. Surge current lasts only long enough for the filter capacitor to charge.

I surge 

VS ( pk ) RW  RB

Limiting Surge Current Surge current can be limited by:  Inserting a current limiting resistor between the filter capacitor and the rectifier.  Using a low-value filter capacitor (which shortens the duration of the surge).  Using an inductive filter.

Filter output voltages

Vr Vdc  Vpk  2 I Lt Vr  C

Filtering and Half-wave Rectifier PIV

PIV  2VS ( pk)

LC Filters

Voltage Regulators 

Voltage regulator – The final circuit in the dc power supply.

End of meeting 1

Thank you for your kind attention!