In remote villages, there is often power outages. Some universities will also have power outages at night, and those who like to stay up late will not have electricity. But that’s okay, you can solve this problem.
This is very easy to make an inverter that can turn the 12V supply voltage to be 220V. The circuit is driven by a multivibrator consisting of BG2 and BG3, and then driven by BG1 and BG2 to control BG6 and BG7 operation.
The oscillating circuit is powered by the regulated power supply of the BG5 and DW groups, which makes the output frequency relatively stable. At the time of production, we can choose the commonly used AC transformers with dual 12V output. A 12V battery can be selected as needed.
This schematic diagram can also be used for small generator for home use.
Introduction
A transistor inverter circuit converts a digital input signal to its opposite logic level at the output. For example, when the input is HIGH the output will be LOW and vice versa. Inverters play a key role in digital logic systems by providing signal inversion, buffering, logic level shifting, clock generation and other functions.
Inverters form the fundamental building block for more complex digital logic gates and functions. This article provides an overview of transistor-based inverter circuits, their operation, key parameters, types and applications.
Inverter Basics
An inverter uses an amplifying device like a transistor connected in a switching configuration to generate the inverted output:
- When the input is LOW, the amplifying device turns ON pulling the output HIGH.
- When the input is HIGH, the device is OFF and the output is pulled LOW through the load resistor.
This functionally inverts the logic level between input and output. The amplifying element provides gain to ensure solid logic HIGH and LOW voltage levels.
Basic Inverter Functional Diagram
Some key characteristics of inverters:
- Gain should be higher than 1 for unambiguous logic levels
- Provide high input impedance and low output impedance
- Capable of high speed operation with fast switching
- Output inverted copy of input waveform
- Support fan-out to drive multiple gate inputs
Properly designed inverters are critical building blocks for reliable digital systems.
BJT Inverter
Here is a simple inverter circuit using a bipolar junction transistor:
When the input is LOW (< 0.7V), the transistor is OFF. Output is pulled HIGH through Rc.
When input is HIGH (>0.7V), transistor turns ON and pulls output LOW via collector-emitter path.
Resistor RB provides biasing to keep transistor OFF when input is LOW. Capacitor CE helps speed up switching by providing current bursts.
Key characteristics:
- Slow compared to MOSFET circuits due to minority carrier charge storage
- Input HIGH level must exceed 0.7V (base-emitter diode drop)
- Output swing typically 0.2V to (Vcc – 0.2V)
- Low input impedance, moderate output impedance
Simple and inexpensive but performance limited. Better for lower speed applications.
MOSFET Inverter
Here is an inverter using a MOSFET transistor:
When input is LOW (<threshold voltage), MOSFET is OFF, output pulled HIGH.
When input is HIGH (>threshold voltage), MOSFET turns ON discharging output to ground.
No biasing network needed compared to BJT version.
Key characteristics:
- Very high speed since no minority carrier storage
- Low input threshold voltage (~1-2V)
- Rail-to-rail output swing potential
- High input impedance, low output impedance
- Draws no current when OFF
Much faster switching speeds than possible with BJTs. Widely used for high performance digital logic.
CMOS Inverter
CMOS inverters use complementary NMOS and PMOS transistors:
When input is LOW, PMOS is ON pulling output HIGH. NMOS is OFF.
When input is HIGH, NMOS turns ON and discharges output LOW. PMOS is OFF.
No current flows from supply to ground when in static state. Very low quiescent power.
Provides excellent noise immunity and high gain. Standard for modern digital ICs.
Key Inverter Characteristics
Some key performance parameters for inverters:
- Propagation Delay: Time taken to switch output state after input change. Need very low (ns range) for high speed operation.
- Rise/Fall Time: Time taken for output voltage to transition between logic levels. Lower is better for high speed.
- Gain: Ratio of output to input voltage. Should exceed one for robust noise margin.
- Fan-out: Number of standard input gates that can be reliably driven by the output. Higher is better.
- Power Consumption: Quiescent and dynamic power. CMOS is most efficient topology.
- Noise Immunity: Ability to reject noise coupling and avoid false triggering. VIL and VIH levels determine immunity.
Optimizing these parameters through careful transistor sizing and biasing is key to designing robust high performance inverters.
Types of Inverters
Some common types of inverters used in digital systems include:
- Buffer Inverters – Provide isolation between circuits while inverting logic level. Used to prevent loading effects.
- Logic Level Shifters – Convert between voltage levels like TTL and CMOS. Provides compatibility.
- Clock Inverters – Special fast inverters designed to provide inverted clock signals with precision timing.
- Schmitt Trigger Inverters – Provides hysteresis for noisy inputs. Cleans up waveforms.
- Rail-to-Rail Output Inverters – Swings output from supply rail to ground. Improves high/low logic levels.
- Open Drain Output Inverters – Used when wired-AND logic is needed. Pulls output low but does not drive high.
Selecting the right inverter type enhances performance for the target application.
Inverter Circuits Examples
Here are some example inverter circuit implementations:
Buffer Inverter
Isolates loading on upstream gate/source. Boosts current drive for higher fan-out.
Level Shifter
Converts 1.8V CMOS logic to 5V TTL input requirements. Provides inter-logic family translation.
Schmitt Trigger Inverter
Provides hysteresis for noisy waveforms. Cleans up slow rise/fall times.
Inverter Applications
Inverters play a vital role in many digital logic systems:
- Oscillator and clock generation circuits
- Driving logic signals across long PCB traces
- Interfacing logic families with incompatible voltages
- Buffering high fan-out signals to prevent overloading
- Inversion of control and timing signals
- Waveform shaping of noisy digital signals
- Logic level translation between circuits
Any design needing signal inversion, buffering, gating, or logic level shifting will require inverters as fundamental building blocks.
Summary
- Inverters use transistor amplifiers to invert the logic level between input and output.
- BJT, MOSFET and CMOS are common transistor types used to build inverters.
- Key performance factors include propagation delay, speed, gain, fan-out, noise immunity.
- Many circuit variations exist optimized for functions like buffering, level shifting, noise reduction.
- Inverters are core components in digital logic, timing generation, signal conditioning, and translation applications.
Understanding inverter circuits provides the foundation for designing more complex digital logic functions.
FAQ
What is the difference between inverter and NOT gate?
Inverters and NOT gates perform the same logic function of inverting the input signal. Inverter tends to refer to transistor circuit implementations while NOT gate can be used when discussing abstract boolean logic functions.
Why use an inverter vs direct connection?
Inverters provide gain, isolation, and logic level shifting. This prevents distortion of the original signal. A direct connection can load down source circuits and potentially cause malfunction.
What is the basic structure of all inverter circuits?
A switching element (transistor) with load configured to invert input to output. BJT, JFET, MOSFET switching devices with resistors as loads are common. The active device provides amplification.
How does an inverter provide logic level shifting?
The inverter can operate between higher and lower supply voltages. The input threshold and output swing adapt to the inverter’s own supply levels allowing translation.
Why use Schmitt Trigger inverters?
Schmitt Trigger inverters incorporate positive feedback to provide hysteresis in the switching thresholds. This makes them less sensitive to noisy input signals and improves waveform shaping.
