Houston Radar PD420 User Manual
Page 42 of 46
Note 1: Connecting a RS232 cable to the radar or forcing the RS232 interface to ON does not
affect the sleep power usage.
Note 2: The radar power usage is approximately constant regardless of the input supply voltage
in the sleep region. This is different when the radar is in the operational region where is behaves
as a constant power device (current goes down with increasing voltage).
Method 1
to provide clock backup power (Wired OR with two supplies):
Method 2
to provide clock backup power (main supply switched off but not removed):
Note 1: The zenner value should be “X” and satisfy the following two equations:
Eq1 fully charged battery: Bmax – X = 6.5 to 4.5
Eq2 fully discharged battery: Bmin – X = 6.5 to 4.5
PD420
+VCC
GND
Clock Backup Battery (4.7V
to 6.7V assuming 0.2v diode
drop).
Ensure it cannot be
removed or disconnected.
Main Battery (8.6V to
18 V.
May be removed.
Backup battery will
provide power to
maintain clock.
Low Drop voltage diodes
to Wire OR the batteries.
+
+
PD420
+VCC
GND
Main Battery (8.6V to 18
V.
May NOT be removed
if
time is to be maintained
when switch is in OFF
position.
Zener diode to drop enough voltage
from main battery to supply
between 4.5V and 6.5V to PD420
+
Main power ON/OFF switch puts
PD420/PNL10 into low power sleep mode
when turned OFF. Zenner still provides
enough voltage and current to allow PD420 to
keep time with minimal power usage.
* See Note 1
Note: Please use low forward voltage drop diodes to maintain efficiency. Also carefully
consider the reverse leakage currents if using a lithium backup battery which is very
intolerant of such currents. D1 could be a signal diode that has very low reverse
currents. D2 needs to be rated for >=1A.
D1
D2
