Handbook for Sound Engineers

Heatsinks and Relays 391

many solid-state systems to achieve very high power
gain—1000 to 10,000 or more. Now marketed in
single-transistor cases, it can be obtained as what
appears to be a single transistor with high operating
voltage ratings that control high amperage loads with
only a few volts at the base connection and draw only a
few milliamperes from the control circuit. It can be used
for relay purposes in a dc circuit the same way, either by
direct control signal coupling or with intermediate isola-
tion devices like those described. It is not usable in ac
power circuits.

13.2.6.8 Solid-State Time-Delay Relays^10

Solid-state time-delay relays, Fig. 13-26, can operate in
many different modes since they do not rely on heaters
or pneumatics. Simple ICs allow the relays to do stan-
dard functions plus totaling, intervals, and momentary
action as described in the following.

On-Delay. Upon application of control power, the
time-delay period begins. At the end of time delay, the
output switch operates. When control power is
removed, the output switch returns to normal,
Fig. 13-26A.

Nontotalizer. Upon the opening of the control switch,
the time-delay period begins. However, any control
switch closure prior to the end of the time delay will
immediately recycle the timer. At the end of the
time-delay period, the output switch operates and
remains operated until the required continuous power is
interrupted, as shown in Fig. 13-26B.

Totalizer/Preset Counter. The output switch will
operate when the sum of the individual control switch
closure durations equal the preset time-delay period.
There may be interruptions between the control switch
closures without substantially altering the cumulative
timing accuracy. The output switch returns to normal
when the continuous power is interrupted, as shown in
Fig. 13-26C.

Off-Delay. Upon closure of the control switch, the
output switch operates. Upon opening of the control

switch, the time-delay period begins. However, any

control switch closure prior to the end of the time-delay

period will immediately recycle the timer. At the end of

the time-delay period, the output switch returns to

Figure 13-25. Darlington direct-coupled solid-state relay.

Control

signal Load

+

Figure 13-26. Types of time-delay relays.

Control

power

Output

switching

Delay

A. On delay.

Continuous

power

Control

switch

Output

switching

Delay

B. Nontotalizer.

Continuous

power

Control

switch

Output

switching

C. Totalizer/preset counter.

Continuous

power

Control

switch

Output

switching

D. Off delay.

Control

power

Output

switching

Delay

E. Interval.

Continuous

power

Control

switch

Output

switching

Delay

F. Momentary actuation.

Delay

D D D D