378 Chapter 13
(13-15)When using a rectifier, the rectifier is an open circuit
to the power source because it is reverse biased;
however, when the circuit breaks, the diode conducts.
This technique depends on a reverse path for the diode
to conduct; otherwise, it will flow through some other
part of the circuit. It is important that the rectifier have a
voltage rating equal to the transient voltage.
Contact bounce occurs in all mechanical-type relays
except the mercury-wetted types that, because of the
thin film of mercury on the contacts, do not break
during make. Bounce creates noise in the circuit, partic-
ularly when switching audio where it acts as a dropout.13.2.3 Relay Loads^8Never assume that a relay contact can switch its rated
current no matter what type of load it sees. High in-rush
currents or high induced back electromotive force (emf)
like those of Fig. 13-11 can quickly erode or weld elec-Figure 13-9. Various contact arrangements of relays. (From American National Standard Definitions and Terminology for
Relays for Electronics Equipment C83.16-1971.)
O. Double-break, double-
make, contact on arm
(Form W).A. Make, single-pole, single-throw, normally
open (Form A).B. Break, single-pole,
single-throw, normally closed (Form B).C. Break, make (transfer)
(Form C).D. Make, break
(continuity transfer).E. Break, make, break.F. Make, make.G. Break, break.H. Break, break, make.I. Make, break, make.J. Make, make, break.K. Single-pole, double-
throw, center off.L. Break, make, make.M. Double-make, contact
on arm (Form U).N. Double-break, contact
on arm (Form V).R. Double-break, double-
make (Form Z).Q. Double-break (Form Y).P. Double-make (Form X).R 0.01 VI©¹§·^150 ----- -+V=-----------------