365Chapter 13
Heatsinks and Relays
by Glen Ballou and Henry Villaume
13.1 Heatsinks.............................................................................. 367
13.1.1 Thermal Management of Today’s Audio Systems........................................... 367
13.1.1.1 Convection...................................................................... 367
13.1.1.2 Conduction...................................................................... 367
13.1.1.3 Radiation....................................................................... 368
13.1.1.4 Summary....................................................................... 368
13.1.2 New Technologies to Make Things Fit More Easily.......................................... 368
13.1.3 How Heatsinks Work................................................................. 369
13.1.3.1 Thermal Resistance.............................................................. 370
13.1.3.2 Heatsink Materials and Design...................................................... 370
13.2 Relays................................................................................ 373
13.2.1 Glossary of Terms.................................................................... 374
13.2.2 Contact Characteristics6,7,8............................................................ 377
13.2.3 Relay Loads8......................................................................................................... 378
13.2.3.1 The Effects of Various Loads....................................................... 379
13.2.4 Electromechanical Relays.............................................................. 379
13.2.4.1 Dc Relays....................................................................... 380
13.2.4.2 Ac Relays....................................................................... 380
13.2.5 Reed Relays6,7,8,11................................................................................................... 381
13.2.5.1 Contact Resistance and Dynamics.................................................... 381
13.2.5.2 Magnetic Interaction.............................................................. 381
13.2.5.3 Environmental Temperature Effects.................................................. 382
13.2.5.4 Dry Reed Relays................................................................. 382
13.2.5.5 Mercury-Wetted Contact Relays..................................................... 384
13.2.5.6 RF Relays...................................................................... 384
13.2.5.7 Dry Reed Switches............................................................... 387
13.2.6 Solid-State Relays9.................................................................. 388
13.2.6.1 Advantages..................................................................... 388
13.2.6.2 Disadvantages and Protection4...................................................... 388
13.2.6.3 High-Peak-Transient-Voltage Protection.............................................. 389
13.2.6.4 Low Load Current Protection....................................................... 390
13.2.6.5 Optically Coupled Solid-State Relays................................................. 390
13.2.6.6 Transformer-Coupled Solid-State Relays.............................................. 390
13.2.6.7 Direct-Coupled Solid-State Relays................................................... 390
13.2.6.8 Solid-State Time-Delay Relays10.................................................... 391
References................................................................................. 392