External Control Logic Output Connection Examples
Page 35
Peavey Electronics Corporation
Using Logic Ports with High-Current Devices
As mentioned on page 33, the TTL Logic Output has a limited source/sink capability of 7mA per port. To properly interface
high-current devices, an intermediate switching stage must be constructed using the TTL out logic from the MM
™
-8802 as a
control voltage or triggering logic. One of the most efficient, reliable and cost effective methods may be to use a simple transis-
tor logic circuit. The transistor is gated using the low-current TTL Logic Output of the MM-8802. The transistor, in turn, trig-
gers a larger power supply and relay providing a higher current contact output. These contacts can then be used to trigger
motors, lights, or other high-current devices. The example below is typical of such a circuit, shown with a single N.O. output.
The circuit examples
shown on this page are
intended to illustrate the
use of the TTL Logic Output port with
simple transistor circuits. This is NOT
a circuit design. The values, parts and
configuration of this circuit are an
approximation of what would actually
be required in real-world audio systems
installations. Any circuit constructed
for this purpose should be designed
specifically for the application in which
they are intended. Peavey Electronics
Corp. assumes no responsibility for the
accuracy of such circuits, their design,
construction or installation. These
types of circuits should be implement-
ed ONLY by qualified electronics per-
sonnel.
Euro connector block
Rear panel
Two-wire termination at
connector block
From external power
supply. This supply
powers the simple tran-
sistor circuit only.
Contractor fabricated
PCB with simple tran-
sistor logic circuit and
wiring harness for
external connections
Normally open relay w/dry
contacts rated at 3A
Equivalent DC Circuit
5 V Logic at “OUT” terminal
Ground terminal
R1
R2
D1
K1
Q1
+V
N.O.
