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:

Pin #	Name	Function
1	COMP	Compensation (regulation loop)
2	-IN1	Inverting input (Error Amp 1)
3	+IN1	Non-inverting input (Error Amp 1)
4	DTC	Dead-time control
5	CT	Timing capacitor
6	RT	Timing resistor
7	GND	Ground (0V)
8	Output 1	Output 1 (open collector)
9	VCC	Power supply (+7V to +40V)
10	VREF	Internal 5V reference
11	Output Ctrl	Push-pull/single mode select
12	-IN2	Inverting input (Error Amp 2)
13	+IN2	Non-inverting input (Error Amp 2)
14	Feedback	Voltage feedback
15	Emitter Out	Common emitter for output transistors
16	Collector Out	Common collector for output transistors

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