SINGLE PHASE (1Ø ) BRIDGE RECTIFIER WITH INDUCTIVE FILTER ON DC SIDE By Zoran Bilic November, 2011

What is a rectifier ? It is an electrical device that converts alternate voltage and current (AC) into direct voltage and current (DC) 1

Difference between AC and DC Voltage

Basic Circuit Schematic Major circuit components: AC Voltage Source Diodes D1, D2, D3, D4 Inductive Filter Ls Load (consumer) R Major circuit parameters AC voltage E AC current I Unfiltered DC Voltage EKA Filtered DC Voltage Ed Filtered DC Current Id 1

How does it work? Diodes D1 to D4 are “semiconductor valves” that can conduct electric current in one direction only while they block it in the opposite direction Diodes are connected in so called BRIDGE CIRCUIT AC voltage E and rectified (unfiltered) voltage EKA waveforms Voltage EKA is not smooth Dc voltage, it contains strong “ripple” 1

EKA (average) = 0.9 • E (Volts) DC voltage EKA has an average value that is related to AC input voltage E EKA (average) = 0.9 • E (Volts) Also, peak value of EKA EKA peak = √2 • E (Volts) Example: What would be average and peak value of EKA if AC input voltage E=120V? 1

EKA (average) = 0.9 • E = 0.9 • 120 = 108Vdc Solution: EKA (average) = 0.9 • E = 0.9 • 120 = 108Vdc EKA peak = √2 • E = √2 • 120 = 170Vdc 1

Without a filter DC current Id would be rippled Current Id Voltage EKA Since the ripple (fluctuation) of the EKA is too high for many applications, there is a need for smooth ripple-less DC voltage This can be achieved by use of inductive or capacitive filter located between EKA and load. Without a filter DC current Id would be rippled Current Id Voltage EKA It also important to observe that AC current I at the input has sinusoidal shape AC Voltage E AC Current I 1

How does inductive filter work? Inductor’s nature is to always oppose to any change in electrical current , including ripples of DC current Id Installing sufficiently large inductor Ls, current ripples will disappear completely Inductive filter LS installed on DC side of the rectifier 1

Here we can observe waveforms for DC voltage EKA along with smoothed DC current Id Consequently, output voltage at the load will be smooth, ripple- less equal to the average value of DC voltage EKA DC voltage EKA DC voltage Ed

And that is unwanted consequence because creates another problem. As a consequence of use of inductive filter, AC input current I will not be sinusiodail anymore. AC Voltage E AC Current I And that is unwanted consequence because creates another problem. It will be rectangular shaped curve. This phenomenon is due to fact that smooth, flat DC current flows in DC side, and AC input side must provide that. 1

However input current I is still ALTERNATING (AC) current. There is direct correlation between input AC current I and output DC current Id Id(DC) = I (AC) However input current I is still ALTERNATING (AC) current. Example: What would be input ac current value if load on DC demands 10 Amps of DC current? 1

Solution: I d(DC) = I (AC) = 10 Amps 1

Summary Rectifiers are electrical devices or circuits that convert alternating (AC) currents/voltages into direct (DC) currents/voltages Diodes are semiconductor “valves” that provide rectification. They conduct current in one direction and block current flow in opposite direction Rectified DC voltage and current are not smooth and without ripple unless we apply filters Filters can be capacitive or inductive. Inductive filter smoothes rectified current ripple. Consequence of inductive filter use is that input AC current is not sinusoidal any more. It becomes rectangular. 1