Power Good Comparator:
A power good comparator produces a logic high
referenced to VOUT on the PGOOD pin the first time the
converter reaches the sleep threshold of the programmed
VOUT, signalling that the output is in regulation. The
PGOOD pin will remain high until VOUT falls to 92% of the
desired regulation voltage.
IV. DISCRETE CIRCUIT
Fig. 4 Discrete Circuit
A. Design of Discrete Circuit:
1.) Piezoelectric Transducer:
Output Voltage: 0-15 V
Output Current: 15-20uA
2.) Bridge Rectifier (Diodes):
1N4148: Fast switching diodes are used since the
Frequency of operation of piezoelectric transducer is
high.
Repetitive peak reverse voltage: 100V (max)
3.) Transistor: 2N3906 (PNP Switching Transistor)
hFE = 300(max)
Biasing of Transistor:
Resistors:
R1= RE = 1MΩ
R2= RC = 510KΩ
This is a DC biasing since there is no input signal. The
coordinates of operating point (VCEQ, ICQ) selected as (9V,
2uA).
Applying KVL to above circuit:
VCC – VCEQ – ICQ *(RC +RE) = 0
12V - 9V- 2uA * (RC +RE) = 0
(RC +RE) = 1.5 x 106
Let RC = 1MΩ
Therefore RE = 500K
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 (