Q14
4.7k
R16
to P-CON terminal
from SP-P-CON
D8
R44
100k
10u
35
3.3k
Q13
A
Q2
power control
D11
7.5v
KAC-859
3
CIRCUIT DESCRIPTION
When the SP output from the head unit is con-
nected to SP IN, the power can be switched
ON/OFF based on the DC voltage of the SP out-
put.
However, As certain head unit models output DC
permanently or generate a click during switching
OFF, it is required to provide the capability of pre-
vious P-CON switching.
A circuit which can perform the switching without
using a switch is described below.
This circuit performs switching by inhibiting the
operation of the S-P-CON circuit when a voltage
is applied to the P-CON pin.
Circuit operation description When the head unit
is connected to SP-INN, the DC component in the
SP output turns Q2 ON through D8 and R16.
When a voltage is applied to the P-CON pin under
this condition, Q13 is turned ON via R44, positive
feedback is applied by combination of Q13 and
Q14, Q13 and Q14 are held at ON, so the voltage
at point (A) is almost 0V and the SP-P-CON cir-
cuit is not activated.
This circuit holds the ON status while the DC volt-
age from SP is present.
Therefore, in this condition, the P-CON circuit
continues functioning.
To cancel the functioning, the voltage at the SP-IN
pin should go 0V.
SP P-CON Switching Circuit
