TL494

The TL494 is a widely-used and versatile integrated circuit (IC) primarily designed for controlling switch-mode power supplies (SMPS) using pulse-width modulation (PWM). It incorporates all necessary functions for switch-mode power supply control, offering flexibility while reducing the number of required external components.

1. Key Features

The TL494 is a fixed-frequency PWM control circuit that includes the following functional blocks:

• Internal oscillator: An integrated oscillator whose frequency can be adjusted with external components (a resistor RT and capacitor CT). It can also be synchronized with an external oscillator for multi-power supply applications.
• Two error amplifiers: High-gain operational amplifiers that can be used for voltage and/or current regulation by comparing a feedback voltage with an internal reference.
• Precise 5V reference voltage: A stable 5V reference voltage source with typical tolerance of ±5%. This reference can be used for error comparators and other circuits.
• Dead-time control comparator (DTC): A comparator that introduces adjustable dead time in the PWM output signals. Dead time is a period when both output transistors in a push-pull configuration are turned off, preventing short circuits. A fixed offset of about 5% dead time is built-in.
• Pulse-steering flip-flop: Directs PWM pulses to appropriate outputs for push-pull operation.
• Uncommitted output transistors: Two open-collector output transistors that can be configured as common-collector or common-emitter and capable of sourcing or sinking up to 200mA (some versions up to 500mA).
• Output control logic: Allows selection of output operation mode: either push-pull (both outputs operate out-of-phase to drive a transformer or two transistors) or single-ended (outputs operate in parallel or independently for single-ended configurations).
• Undervoltage lockout (UVLO): A circuit that disables outputs when the supply voltage (VCC) is below a predefined threshold, protecting the system during insufficient power supply.

2. Pin Configuration (Typical DIP-16 Package)

While pin count may vary slightly by package, a typical DIP-16 configuration is:

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1. COMP (Compensation): Compensation pin for error amplifiers, used to stabilize the feedback loop.
2. -IN1 (Error Amp 1 Inverting Input): Inverting input of the first error amplifier.
3. +IN1 (Error Amp 1 Non-Inverting Input): Non-inverting input of the first error amplifier.
4. DTC (Dead-Time Control): Input to control dead-time duration. Higher voltage on this pin increases dead time.
5. CT (Timing Capacitor): Connection for the oscillator timing capacitor.
6. RT (Timing Resistor): Connection for the oscillator timing resistor.
7. GND (Ground): Circuit ground connection.
8. Output 1: First transistor output.
9. VCC (Supply Voltage): IC supply voltage (typically 7V to 40V).
10. VREF (Reference): 5V internal reference voltage output.
11. Output Control: Used to select output operation mode (single-ended or push-pull). Connect to VREF for push-pull mode and GND for single-ended mode.
12. -IN2 (Error Amp 2 Inverting Input): Inverting input of the second error amplifier.
13. +IN2 (Error Amp 2 Non-Inverting Input): Non-inverting input of the second error amplifier.
14. Feedback: Used to introduce output voltage feedback signal to one of the error amplifiers.
15. Emitter Output: Common emitter point for output transistors (if configured as common-emitter). Can be connected to ground or VCC depending on configuration.
16. Collector Output: Common collector point for output transistors (if configured as common-collector). Connected to the load.

3. Typical Applications

The TL494 is widely used in various power conversion applications, including:

• Switch-mode power supplies (SMPS): Output voltage control in AC-DC and DC-DC power supplies.
• DC-DC converters: Voltage regulation in boost, buck, and inverting converters.
• Battery chargers: Control of battery charging current and voltage.
• Motor control: Using PWM to control DC motor speed.
• Solar inverters: Converting DC power from solar panels to AC.
• PC and server power supplies.
• Electronic ballasts for lamps.
• Uninterruptible power supplies (UPS).

4. TL494 Advantages

• High integration: Combines many power control functions on a single chip, reducing external components.
• Flexibility: Can be configured for various power supply topologies and operation modes (single-ended or push-pull).
• Precision: Stable internal voltage reference enables accurate output regulation.
• Built-in protection: Undervoltage lockout (UVLO) protects the system from low-voltage operation.
• Adjustable dead time: Allows optimization of efficiency and prevents issues in push-pull configurations.
• Synchronization capability: Internal oscillator can be synchronized with an external source to reduce noise and facilitate multi-power supply system design.
• Low cost and wide availability.

Summary

The TL494 is a powerful and versatile PWM control IC essential for designing efficient and reliable switch-mode power supplies. Its integration of multiple functions and configuration flexibility make it a preferred choice for many power supply designers.

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