1 POWER SUPPLIES Unit 18 Best viewed with PowerPoint XP®

2 References 1. NEETS Mod 7 – Introduction to Solid State Devices and Power Supplies.

3 Enabling Objectives 1.RECOGNIZE the major sections of a solid state power supply. 2.RECOGNIZE the operating characteristics of power supplies. 3.CONSTRUCT a power supply circuit and OBSERVE normal operation. 4.APPLY the safety precautions associated with the use of test equipment on solid state power supplies in accordance with NAVY SAFETY PRECAUTIONS FOR AFLOAT FORCES.

4 INTRODUCTION All electronic equipment requires some form of a power supply. Power supplies are a source of electrical energy, used to furnish proper voltages and currents to electronic circuits for their proper operation. FOUR (4) BASIC SECTIONS OF A POWER SUPPLY a. Transformer b. Rectifier c. Filter d. Regulator

5 POWER SUPPLIES 1.Transformer – Used for circuit isolation. Prevents grounds on the main distribution system, and provides for the stepping up or stepping down of the input voltage. Common Types of Transformers: a. Step-Up

6 b. Step-Down

7 c.Center-tapped A center-tapped transformer provides 2 equal voltages, 180 o out of phase which are needed for the full-wave rectifier.

8 2.Rectifiers - changes AC voltage to a pulsating DC voltage. Common Types of Rectifiers a. Half-Wave rectifiers - uses a single diode in the circuit. + _ INPUT OUTPUT

9 2.Rectifiers - changes AC voltage to a pulsating DC voltage. Common Types of Rectifiers a. Half-Wave rectifiers - uses a single diode in the circuit. + _ INPUT OUTPUT Reverse Bias – No current flow

10 b. Full-Wave rectifier – a device that has 2 or more diodes arranged so that load current flows in the same direction during each half cycle of the AC supply

11 b. Full-Wave rectifier – a device that has 2 or more diodes arranged so that load current flows in the same direction during each half cycle of the AC supply

12 b. Full-Wave Bridge rectifier – a device that uses 4 diode, configured such that the input to the circuit is applied to the diagonally opposite corners of the network and the output is taken from the remaining two corners. + -

13 b. Full-Wave Bridge rectifier – a device that uses 4 diode, configured such that the input to the circuit is applied to the diagonally opposite corners of the network and the output is taken from the remaining two corners. + -

14 FULL-WAVE RECTIFIERFULL-WAVE BRIDGE RECTIFIER INPUT OUTPUT FULL-WAVE RECTIFICATION COMPARISON 500V 1000V

15 3.Filters FOUR BASIC TYPES OF FILTERS a.Shunt Capacitor filter b.LC Choke-Input filter c.RC Capacitor-Input filter (pi-type) d.LC Capacitor-Input filter (pi-type)

16 c. RC Capacitor-Input filter – consists of two shunt capacitors with a series resistor, resembling the Greek letter “Pi”. 1.Used where load current is constant and voltage regulation is not important. 2.Capacitor C1 functions to reduce pulsations of DC voltage out of the rectifier to a low ripple voltage. 3.Capacitor C2 blocks DC, resulting in maximum DC voltage supplied to the load.

17 4. The major drawback of this type of filter is the amount of voltage being dropped across R1 is wasted in the form of heat, and as the load resistance changes, voltage across the load also changes.

18 d. LC Capacitor-Input filter – most commonly used filter where output is low with a relatively constant load current. 1.Output voltage is greater than the choke input filter but with a smaller output current. 2.Composed of an input shunt capacitor C1, a series inductor or choke L1, and an output shunt capacitor C2. 3.The capacitor, C1, exhibits the same filtering action as the capacitor in the shunt capacitor filter.

19 4. Regulators a. There are 2 factors which can cause output voltage of a basic power supply to change: 1. Variation in AC line voltage 2. Load resistance.

20 d. Modern series voltage regulator has a transistor (Q1) replacing the variable resistor which required manual assistance.

21 e. In the shunt type regulator, output voltage is determined by current through the parallel resistance of the regulating device (RV), the load resistance (RL), and the series resistor (RS).

22 SUMMARY AND REVIEW Enabling Objectives 1.RECOGNIZE the major sections of a solid state power supply. 2.RECOGNIZE the operating characteristics of power supplies. 3.CONSTRUCT a power supply circuit and OBSERVE normal operation. 4.APPLY the safety precautions associated with the use of test equipment on solid state power supplies in accordance with NAVY SAFETY PRECAUTIONS FOR AFLOAT FORCES.