TL494 Pulse-Width Modulation (PWM) Control Circuit

Overview

The TL494 is a highly integrated pulse-width modulation (PWM) control circuit designed for power supply and power conversion applications. It incorporates all the essential building blocks required for PWM control in a single IC, making it a versatile choice for a wide range of power management tasks. The device is widely used in both consumer and industrial applications due to its reliability, flexibility, and robust feature set.

The TL494 provides a stable 5V reference supply, adjustable dead-time control, and uncommitted output transistors that can be configured for either single-ended or push-pull operation. Its internal architecture ensures protection against double-pulse generation, enhancing system reliability. The device is particularly well-suited for switch-mode power supplies (SMPS), inverters, and motor control applications.

Features

• Complete PWM Power-Control Circuitry: Integrates all necessary functions for PWM generation and control in a single package.
• High-Current Output Drivers: Uncommitted outputs capable of sinking or sourcing up to 200mA, suitable for driving power MOSFETs or bipolar transistors.
• Flexible Output Configuration: Output control selects between single-ended or push-pull operation modes.
• Double-Pulse Suppression: Internal circuitry prevents double-pulse generation at either output, ensuring reliable operation.
• Adjustable Dead-Time Control: Variable dead time provides precise control over the total range of pulse width modulation.
• Stable Voltage Reference: Internal regulator provides a stable 5V reference supply with ±5% tolerance.
• Synchronization Capability: Circuit architecture allows for easy synchronization with external clock signals.
• Wide Operating Voltage Range: Typically operates from 7V to 40V, making it suitable for various power supply designs.

Applications

The TL494's versatile feature set makes it suitable for numerous applications across multiple industries:

Consumer Electronics

• Desktop PCs and computer peripherals
• Microwave ovens
• Washing machines (both low-end and high-end models)

Power Supply Systems

• AC/DC power supplies (both isolated and non-isolated)
• Power supplies with Power Factor Correction (PFC) > 90W
• Power supplies without PFC < 90W
• Server power supply units (PSUs)
• Telecom power supplies

Renewable Energy and Transportation

• Solar micro-inverters
• E-bike motor controllers and power systems

Electrical Characteristics

Absolute Maximum Ratings

• Supply Voltage (V_CC): 42V
• Collector Output Voltage: 42V
• Collector Output Current: 250mA
• Amplifier Input Voltage: V_CC + 0.3V
• Power Dissipation: 1000mW
• Operating Junction Temperature: 125°C
• Storage Temperature Range: -65°C to +150°C

Recommended Operating Conditions

• Supply Voltage (V_CC): 7V to 40V
• Output Voltage: 40V max
• Output Current (sink or source): 200mA
• Oscillator Frequency Range: 1kHz to 300kHz
• Operating Ambient Temperature: -20°C to +85°C (TL494C), -40°C to +85°C (TL494I)

Key Electrical Parameters

• Reference Output Voltage: 4.75V to 5.25V (at 10mA load)
• Reference Voltage Tolerance: ±5% over temperature
• Oscillator Frequency Deviation: ±10% max
• Output Saturation Voltage: 1.3V max (at 200mA)
• Standby Supply Current: 10mA max
• Error Amplifier Input Offset Voltage: 2mV to 10mV
• Error Amplifier Gain Bandwidth Product: 1MHz typical

Package Information

Available Packages

• 16-pin Plastic Dual In-line Package (PDIP)
  • Package code: N
  • Dimensions: 19.30mm x 6.35mm
  • Lead pitch: 2.54mm
• 16-pin Small Outline Package (SOIC)
  • Package code: D
  • Dimensions: 9.90mm x 3.91mm
  • Lead pitch: 1.27mm
• 20-pin Plastic Shrink Small Outline Package (SSOP)
  • Package code: PW
  • Dimensions: 7.20mm x 5.30mm
  • Lead pitch: 0.65mm

Thermal Characteristics

• PDIP Package:
  • Thermal Resistance, Junction-to-Air (θ_JA): 80°C/W
  • Thermal Resistance, Junction-to-Case (θ_JC): 25°C/W
• SOIC Package:
  • Thermal Resistance, Junction-to-Air (θ_JA): 120°C/W
  • Thermal Resistance, Junction-to-Case (θ_JC): 40°C/W

Functional Description

The TL494 integrates several key functional blocks that work together to provide comprehensive PWM control:

Reference Voltage Regulator

The internal 5V regulator provides a stable reference voltage for all internal circuitry and can also be used to power external components. This reference maintains ±5% accuracy over the full operating temperature range.

Oscillator

The sawtooth oscillator generates the basic timing signal for PWM operation. The frequency is determined by an external resistor (R_T) and capacitor (C_T), with a typical range from 1kHz to 300kHz. The oscillator can be synchronized to an external clock signal.

Dead-Time Control

The dead-time control comparator prevents both outputs from being active simultaneously, which is crucial for push-pull configurations. The dead time can be adjusted from 0% to 100% of the oscillator period.

Error Amplifiers

The device includes two high-gain error amplifiers with typical bandwidth of 1MHz. These can be used for feedback control in voltage regulation or current limiting applications. The amplifiers have a common-mode input range that includes the reference voltage.

Output Control

The output stage features two NPN transistors that can be configured for either single-ended or push-pull operation through the output control pin. Each transistor can sink or source up to 200mA, with typical saturation voltage of 1.1V at 200mA.