5. Power Supply Units

Definitions

• Half wave rectification will allow current flow through the load during the positive half cycles
• Full wave rectification will allow current flow through the load during both positive and negative cycles
• Diode bridge configuration circuit allows for full wave rectification of an input AC souce
• Voltage Regulators are circuits that help to maintain a constant voltage output

Diagrams

Power Supply Unit

Image credit: Electronics Area

Circuit diagrams

• Half-wave rectification

  

  Image credit: Electronics Tutorial

• Full-wave rectification

  

  Image credit: Electronics Tutorial

  

  Image credit: Play hookey

• Voltage regulators

Image credit: Fairchild Semiconductor

Graphs

• Zener diode graph

  

  Image credit: Electronics Tutorial

Notes

Most modern Amateur Radio equipment operates:

• 13.8 V DC low voltage supply
• 20 A high current

Power supply from:

• outdoors: car battery
• indoors: convert the 230 Volt AC “mains” to 12 Volt DC

Power Supply Unit	Components	Description
Mains	230V AC
Transformer	step-down Transformer	(1) capable of handling the required power (2) primary winding of the transformer usually has a few “taps” so that various mains voltages can be used
Rectifier	1 or more diodes	(1) very simple circuit will produce a great deal of hum at the supply frequency 50 Hz (2) A full wave rectifier circuit gives an output that contains hum at twice the supply frequency 100 Hz
Smoothing (filtering)	large capacitor	In order to further reduce the hum an inductor and a another large capacitor are added
Stabilizer (Voltage regulator)	zener diode	(1) If a zener diode is reversed biased there is a critical voltage at which the current flow increases dramatically (2) Beyond this “knee” in the characteristic, a very small change in voltage will result in a large change in the current passed
Output	load