Presume you have two whispers, one a little louder than the other.
An op amp is like a super listener that can focus on the difference between those whispers.
It ignores the quiet background noise electrical noise and boosts just the part you want to hear the voltage difference.
Because it is so precise and powerful, op amps are used in many electronics to fine tune weak signals.
Circuit Working:
Parts List:
| Category | Item | Quantity | Additional Specifications |
|---|---|---|---|
| Resistors | 6.8k | 1 | All resistors are 1/4 watt unless specified |
| 4.7k | 1 | ||
| 1k | 1 | ||
| 100k | 1 | ||
| 68k | 1 | ||
| 1M | 1 | ||
| Capacitors | Ceramic 33nF | 1 | |
| Ceramic 4.7nF | 1 | ||
| Electrolytic 4.7µF | 1 | ||
| Semiconductors | Transistor BC547 | 2 | |
| Transistor BC557 | 1 | ||
| LEDs | Red 5mm 20mA | 2 |
This circuit demonstrates how three transistors can be used to create a simple operational amplifier.
Essentially, it functions as an AC coupled single ended class A amplifier with an open loop gain of approximately 5,000.
However, for practical purposes, it can be treated as a basic op amp.
The output is biased to around half the supply voltage by utilizing the combined voltage drops across two LEDs the emitter base voltage of the input transistor and the 1V drop across a 1M feedback resistor.
Additionally, a 68k resistor and a 4.7nF capacitor form a compensation network that prevents the circuit from oscillating.
This op amp configuration can be employed as an active filter or an oscillator driving a 1k load.
It exhibits a good square wave response at 10kHz with the output decreasing by 3dB at 50kHz.
Electrical Characteristic for transistor BC547
| Symbol | Parameter | Conditions | Min. | Typ. | Max. | Unit |
|---|---|---|---|---|---|---|
| ICBO | Collector Cut-Off Current | VCB = 30V, IE = 0 | 15 | nA | ||
| hFE | DC Current Gain | IC = 2mA, VCE = 5V | 110 | 800 | – | |
| VCE(sat) | Collector-Emitter Saturation Voltage | IC = 10mA, IB= 0.5mA | 90 | 250 | ||
| IC = 100mA, IB = 5mA | 250 | 600 | ||||
| VBE(sat) | Base-Emitter Saturation Voltage | IC = 10mA, IB = 0.5mA | 700 | |||
| IC = 100mA, IB = 5mA | 900 | |||||
| VBE(on) | Base-Emitter on voltage | IC = 2mA, VCE = 5V | 580 | 660 | 700 | |
| IC= 10mA, VCE = 5V | 720 | |||||
| fT | Current Gain Bandwidth Product | IC= 10mA, VCE = 5V, f = 100MHz | 300 | MHz | ||
| Cob | Output Capacitance | VCB= 10V, IE = 0, f = 1MHz | 3.5 | 6.0 | pF | |
| Cib | Input Capacitance | VEB= 0.5V, IC = 0, f = 1MHz | 9 | pF | ||
| NF | Noise Figure | BC547 | IC = 200µA, VCE = 5V | 2.0 | 10 | dB |
How to Build:
To build a simple Op Amp Circuit follow the below mentioned steps for connections:
- Connect the input of the op amp to the base of the input side BC547 transistor through a series 33nF capacitor and 100k resistor.
- Connect the emitter of above BC547 to junctions of 4.7k resistor and 2 series connected LEDs.
- Connect 4.7k resistor to the positive and LEDs to the negative.
- Connect the base of BC557 transistor to the collector of the above BC547 transistor through a 68k resistor.
- Connect a resistor 6.8k between the collector of the above BC547 and positive.
- Connect the emitter of the BC557 to the positive.
- Connect a 4.7nF capacitor between the base of BC557 and ground.
- Connect the collector of the BC557 with the base of the output side of BC547 transistor.
- Connect the emitter of the above BC547 to ground.
- Connect the collector of the above BC547 to the positive through a 1k resistor.
- Connect the collector of above BC547 to the output through a 4.7uF capacitor.
- Connect a 1M feedback resistor between the collector of the output side BC547 and the base of the input side BC547.
Note:
- You can adjust component values based on the specific requirements of your circuit.
- Remember to use proper safety measures when working with electronics.
Conclusion:
Building a simple operational amplifier op amp circuit is a great way to learn about the basics of op amp functionality and applications in electronics.
By understanding how op amps amplify signals and control voltages, you can create a variety of useful circuits for amplification, filtering and signal processing.
Experimenting with different circuit configurations and component values will deepen your understanding and enhance your skills in electronics design.