4.) Zener Diode: A zener Diode (D2) of 12V is
clamped between the base of the transistor and ground.
Therefore the transistor will come into conduction only
when the supply voltage reaches 12.6V. (The Z1 breakdown
voltage plus the drop across the base-emitter junction of
Q1).
5.) MOSFET : VN2222L (N channel Enhancement
type switching MOSFET)
VGS(th): 2V (min)
The drop across the Collector resistor is given as VGS to the
MOSFET. Therefore when the drop across this resistor
reaches 2V the MOSFET turns on.
Drop across RC is calculated as:
VRC = ICQ x RC
VRC = 2uA x 1MΩ
VRC = 2V
6.) MAX 666 Voltage Regulator:
Operating Range: 2V -16.5V
Output Current: 40mA
Dual Mode Operation: Fixed 5V or Adjustable
from
1.3V- 16 V
Here we have designed this regulator to provide
fixed
5V output. Therefore the VSET pin is grounded.
Since the current limiting is not used the SENSE
pin
is connected to VOUT .
MAX666 contains on chip circuitry for low battery
or
low power supply detection. If the voltage at LBI
(pin3) falls below the regulators internal reference
(1.3V), then LBO (pin7) is grounded momentarily.
The Threshold can be set to any level above the reference
voltage by connecting a resistive divider to LBI.
Design Equation:
R5= R6 x (