**First, TL494 Introduction**
The TL494 is a fixed-frequency pulse width modulation (PWM) integrated circuit that contains all the necessary functions for controlling switching power supplies. It is commonly used in various topologies such as single-ended, forward, half-bridge, and full-bridge configurations. Its versatility makes it a popular choice for designing efficient and stable power supply systems.
**1. Internal Structure of TL494**
The internal structure of the TL494 includes an oscillator, error amplifier, voltage reference, and output stage. The chip is designed to handle both push-pull and single-ended operations, making it adaptable for different applications. Below is a simplified diagram showing its internal layout:
**2. Key Features of TL494**
- Integrated PWM control circuit
- Built-in linear sawtooth oscillator with only two external components (a resistor and a capacitor)
- On-chip error amplifier for feedback control
- 5V precision voltage reference
- Adjustable dead time for preventing shoot-through in switching circuits
- Output drivers capable of providing up to 500mA of drive current
- Push-pull or open-collector output options
**3. Pin Configuration**
Here’s a visual representation of the TL494 pinout:
**Second, Classic TL494 Inverter Applications**
**1. Application One: Simple Inverter Circuit**
This is one of the most straightforward applications of the TL494. It uses the chip’s built-in features like soft-start and dead-time control while disabling the two error amplifiers. The circuit is highly efficient and stable.
Key points:
- Pins 1 and 16 are grounded through a 1kΩ resistor, effectively disabling the first error amplifier.
- Pins 2 and 15 are connected to the 5V reference (pin 14), ensuring the second error amplifier remains inactive.
- Pin 4 controls the dead time; connecting it to a capacitor and resistor allows for a soft-start function.
- Oscillation frequency is determined by R and C on pins 5 and 6, with the formula F = 1.1/(R×C).
- Pin 13 sets the operating mode (single-ended or push-pull).
- The output transistors (pins 8–11) can drive high-current MOSFETs for power applications.
**2. Application Two: Voltage Regulation and Current Limiting**
This application adds functionality by using both error amplifiers. One is used for voltage regulation, and the other for overcurrent protection.
- For voltage regulation, the error amplifier compares a divided portion of the output voltage with the 5V reference.
- For current limiting, a shunt resistor (R10) is used to sense the output current. When the current exceeds a threshold, the error amplifier reduces the duty cycle.
- This setup ensures safe operation and protects against overloads.
**3. 400W Inverter Circuit Using TL494**
A practical example of a high-power inverter using the TL494 is shown below. It features a transformer rated at 400VA and uses N-channel MOSFETs for switching. The circuit is easy to build and requires minimal tuning.
Key components include:
- Primary winding with 1.2mm diameter enameled wire
- Secondary winding with 0.8mm wire, center-tapped
- MOSFETs such as 2SK564 or parallel 2SK906 for higher current capacity
- Diodes like 1N400X for rectification
- Filtering capacitors for clean output waveform
**Additional Tips**
- Ensure proper filtering on the power supply to reduce noise.
- Keep the ground traces short and separate from signal lines for better stability.
- Use a 0.1µF capacitor on pin 3 for improved waveform quality.
- If you encounter asymmetry in push-pull outputs, double-check the transformer windings.
By leveraging the TL494's robust features, you can design efficient and reliable power conversion circuits suitable for a wide range of applications, from small inverters to high-power systems.
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