Auto Cut for Manual Stabilisers using 741 IC

Engineeering Projects

Many circuits have been published about the auto-cut arrangement in manual stabilisers. These circuits generally use transistors with zener diodes as the only sensing device. However, these circuits have two main drawbacks.

  1. Spurious triggering of the transistor
  2. Fluctuation in zener diode

Circuit Description of Auto cut for manual Stabilisers

The circuit of auto cut for manual stabilisers described here overcomes spurious triggering of transistor and fluctuation in zener diode drawbacks. It uses the most versatile op-amp IC741 a schmitt trigger. The reference voltage is given by a combination of 4.6V, 400mW zener diode D1 and a 1.6V LED. The negative temperature coefficient of forward biased LED cancels the positive temperature coefficient of reverse biased zener diode, thereby eliminating the error due to temperature etc. Resistor R1 and the output transistor T1 eliminate any false triggering. Diode D1  is used to save the transistor from the back emf of the relay coil RL1.

The preset is adjusted such that the transistor turns on at the highest possible voltage on mains. Point A and B are connected to the references transformer. The reference transformer is connected to the sliding contact of the 7-way switch.

The N/O point of the relay goes to the high voltage cutoff indicator which is an ordinary neon bulb. Output is obtained from the N/C point of the relay.

Other Auto Cut circuit posted in bestengineeringprojects.com

  1. Auto Cut Circuit for Over and Under Voltage
  2. Versatile Auto Cut -Off Unit
  3. Automatic Cut off Power Supply
  4. Single Phase Preventer with Under/Over Voltage Cutout

PARTS LIST OF AUTO CUT FOR MANUAL STABILISERS

Resistor (all ¼-watt, ± 5% Carbon)
R1 = 1 KΩ

R2 = 2.2 KΩ

R3, R4 = 4.7 KΩ

R5 = 3.3 KΩ

R6 = 10 KΩ

VR1 = 470 KΩ
Capacitor
C1 = 0.1 µF (Ceramic Disc)
Semiconductors
IC1 = LM741 (General purpose operational amplifier)

T1 = SL100B (general purpose medium power NPN transistor)

D1 = 1N4001 (Rectifier Diode)

ZD1 = 4.6V, 400Mw

LED1 = 5mm any color LED
Miscellaneous
RL1 = 12V, 200Ω SPST Relay

 

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