13-04-2013, 04:29 PM
STUDY OF OP AMPS - IC 741, IC 555, IC 565, IC 566, FUNCTIONING, PARAMETERS AND SPECIFICATIONS
IC 741
General Description:
The IC 741 is a high performance monolithic operational amplifier constructed using the planer epitaxial process. High common mode voltage range and absence of latch-up tendencies make the IC 741 ideal for use as voltage follower. The high gain and wide range of operating voltage provide superior performance in integrator, summing amplifier and general feed back applications.
Features:
1. No frequency compensation required.
2. Short circuit protection
3. Offset voltage null capability
4. Large common mode and differential voltage ranges
5. Low power consumption
6. No latch-up
IC 555:
Description:
The operation of SE/NE 555 timer directly depends on its internal function. The three equal resistors R1, R2, R3 serve as internal voltage divider for the source voltage. Thus one-third of the source voltage VCC appears across each resistor.
Comparator is basically an Op amp which changes state when one of its inputs exceeds the reference voltage. The reference voltage for the lower comparator is +1/3 VCC. If a trigger pulse applied at the negative input of this comparator drops below +1/3 VCC, it causes a change in state. The upper comparator is referenced at voltage +2/3 VCC. The output of each comparator is fed to the input terminals of a flip flop.
The flip-flop used in the SE/NE 555 timer IC is a bistable multivibrator. This flip flop changes states according to the voltage value of its input. Thus if the voltage at the threshold terminal rises above +2/3 VCC, it causes upper comparator to cause flip-flop to change its states. On the other hand, if the trigger voltage falls below +1/3 VCC, it causes lower comparator to change its states. Thus the output of the flip flop is controlled by the voltages of the two comparators. A change in state occurs when the threshold voltage rises above +2/3 VCC or when the trigger voltage drops below +1/3 Vcc.
The output of the flip-flop is used to drive the discharge transistor and the output stage. A high or positive flip-flop output turns on both the discharge transistor and the output stage. The discharge transistor becomes conductive and behaves as a low resistance short circuit to ground. The output stage behaves similarly. When the flip-flop output assumes the low or zero states reverse action takes place i.e., the discharge transistor behaves as an open circuit or positive VCC state. Thus the operational state of the discharge transistor and the output stage depends on the voltage applied to the threshold and the trigger input terminals.