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TL494 PWM Controller: Pinout, Circuit, Datasheet [Video]

  • Contents

Description

TL494 was designed in the early 1980s. It was widely accepted by the market immediately after it was launched, especially on the ATX half-bridge power supply of PCs. Until today, a considerable proportion of PC power supplies are still based on the TL494 chip.

How to Test TL494N

Catalog

Description

Component Datasheet

TL494 Pinout

TL494 Parameter

Features

Advantages

Applications

TL494 Simplified Block Diagram

TL494 Package and Pins

Functional Block Diagram

Where to use TL494

How to use TL494

TL494 Typical Application

FAQ

Ordering & Quantity

Component Datasheet

Datasheet

TL494 Pulse-Width-Modulation Control Circuits datasheet (Rev. H)

Application notes1

Isolated Multiple Output Flyback Converter Design Using TL494

Application notes2

Designing Switching Voltage Regulators With the TL494 (Rev. E)


TL494 Pinout

tl494 pinout

Pin

Description

Name

NO.

1IN+

1

Noninverting input to error amplifier 1

1IN

2

Inverting input to error amplifier 1

2IN+

16

Noninverting input to error amplifier 2

2IN-

15

Inverting input to error amplifier 2

C1

8

Collector terminal of BJT output 1

C2

11

Collector terminal of BJT output 2

CT

5

Capacitor terminal used to set oscillator frequency

DTC

4

Dead-time control comparator input

E1

9

Emitter terminal of BJT output 1

E2

10

Emitter terminal of BJT output 2

FEEDBACK

3

Input pin for feedback

GND

7

Ground

OUTPUT CTRL

13

Selects single-ended/parallel output or push-pull operation

REF

14

5-V reference regulator output

RT

6

Resistor terminal used to set oscillator frequency

VCC

12

Positive Supply


TL494 Parameter

Topology

Boost, Buck, Flyback, Forward, Full-Bridge, Half-Bridge, Push-Pull

Control method

Voltage

VCC (Min) (V)

7

VCC (Max) (V)

40

Duty cycle (Max) (%)

45

UVLO thresholds on/off (V)

Frequency (Max) (kHz)

300

Operating temperature range (C)

-40 to 85, 0 to 70

Gate drive (Typ) (A)

0.2

Features

Adjustable Switching Frequency, Dead Time Control, Error Amplifier, Multi-topology

Rating

Catalog


Features

  • Complete PWM Power-Control Circuitry
  • Uncommitted Outputs for 200-mA Sink or Source Current
  • Output Control Selects Single-Ended or Push-Pull Operation
  • Internal Circuitry Prohibits Double Pulse at Either Output
  • Variable Dead Time Provides Control Over Total Range
  • Internal Regulator Provides a Stable 5-V Reference Supply With 5% Tolerance
  • Circuit Architecture Allows Easy Synchronization

Advantages

The TL494 device incorporates all the functions required in the construction of a pulse-width-modulation (PWM) control circuit on a single chip. Designed primarily for power-supply control, this device offers the flexibility to tailor the power-supply control circuitry to a specific application.

The TL494 device contains two error amplifiers, an on-chip adjustable oscillator, a dead-time control (DTC) comparator, a pulse-steering control flip-flop, a 5-V, 5%-precision regulator, and output-control circuits.

The error amplifiers exhibit a common-mode voltage range from –0.3 V to VCC – 2 V. The dead-time control comparator has a fixed offset that provides approximately 5% dead time. The on-chip oscillator can be bypassed by terminating RT to the reference output and providing a sawtooth input to CT, or it can drive the common circuits in synchronous multiple-rail power supplies.

The uncommitted output transistors provide either common-emitter or emitter-follower output capability. The TL494 device provides for push-pull or single-ended output operation, which can be selected through the output-control function. The architecture of this device prohibits the possibility of either output being pulsed twice during push-pull operation.

The TL494C device is characterized for operation from 0°C to 70°C. The TL494I device is characterized for operation from –40°C to 85°C.


Applications

  • Desktop PCs
  • Microwave Ovens
  • Power Supplies: AC/DC, Isolated, With PFC, > 90 W
  • Server PSUs
  • Solar Micro-Inverters
  • Washing Machines: Low-End and High-End
  • E-Bikes
  • Power Supplies: AC/DC, Isolated, No PFC, < 90 W
  • Power: Telecom/Server AC/DC Supplies: Dual Controller: Analog
  • Smoke Detectors
  • Solar Power Inverters

TL494 Simplified Block Diagram

 tl494 block diagram


TL494 Package and Pins

Package

Pins

Size

PDIP (N)

16

181 mm² 19.3 x 9.4

SOIC (D)

16

59 mm² 9.9 x 6

SOP (NS)

16

80 mm² 10.2 x 7.8

TSSOP (PW)

16

22 mm² 4.4 x 5


Functional Block Diagram

tl494 funtional block diagram


Where to use TL494

The TL494 fixed frequency PWM Controller can be used for DC to DC conversion regardless of buck or boost topology. TL494 can be used to provide a constant current by varying the output voltage to the load. This IC feature an output control circuit, a flip flop, a dead time comparator, two different error amplifiers, a 5V reference voltage, an oscillator, and a PWM comparator.

So if you are looking for an IC to produce PWM signals for controlling a power switch based on the current flowing through the circuit, then this IC might be the right choice for you.


How to use TL494

A test circuit from the TL494 datasheet is shown below.

tl494 circuit

Non inverting pins are connected to the Ref pin while inverting pins are connected to the ground. Test inputs are given to DTC and FEEDBACK pins. External capacitor and resistor are connected to pin 5 & 6 to control the oscillator frequency. The error amplifier compares a sample of the 5-V output to the reference and adjusts the PWM to maintain a constant output current


TL494 Typical Application

  • Switching and Control Sections

tl494 circuit

  • Input Power Source

tl494 circuit

  • Error-Amplifier Section

tl494 circuit

  • Current-Limiting Circuit

tl494 circuit

  • Soft-Start Circuit

tl494 circuit

  • Switching Circuit

tl494 circuit

  • Power-Switch Section

tl494 circuit


FAQ

  • What is TL494?

TL494 is a PWM controller IC used for power electronics circuits. It comprises of on-chip two error amplifiers an oscillator with adjustable frequency feature, an output flip-flop having pulse steering control, and an output control circuit with feedback.

  • What is the detailed description of TL494?

The TL494 device incorporates all the functions required in the construction of a pulse-width-modulation (PWM) control circuit on a single chip. Designed primarily for power-supply control, this device offers the flexibility to tailor the power-supply control circuitry to a specific application. The TL494 device contains two error amplifiers, an on-chip adjustable oscillator, a dead-time control (DTC) comparator, a pulse-steering control flip-flop, a 5-V, 5%-precision regulator, and output-control circuits. The error amplifiers exhibit a common-mode voltage range from –0.3 V to VCC – 2 V. The dead-time control comparator has a fixed offset that provides approximately 5% dead time. The on-chip oscillator can be bypassed by terminating RT to the reference output and providing a sawtooth input to CT, or it can drive the common circuits in synchronous multiple-rail power supplies. The uncommitted output transistors provide either common-emitter or emitter-follower output capability. The TL494 device provides for push-pull or single-ended output operation, which can be selected through the output-control function. The architecture of this device prohibits the possibility of either output being pulsed twice during push-pull operation.

  • What are TL494 product features?
    • Complete PWM Power-Control Circuitry
    • Uncommitted Outputs for 200-mA Sink or Source Current
    • Output Control Selects Single-Ended or Push-Pull Operation
    • Internal Circuitry Prohibits Double Pulse at Either Output
    • Variable Dead Time Provides Control Over Total Range
  • What is PWM IC?

The TL494 fixed frequency PWM Controller can be used for DC to DC conversion regardless of buck or boost topology. ... This IC feature an output control circuit, a flip flop, a dead time comparator, two different error amplifiers, a 5V reference voltage, an oscillator, and a PWM comparator.

  • How does PWM IC work?

As its name suggests, pulse width modulation speed control works by driving the motor with a series of “ON-OFF” pulses and varying the duty cycle, the fraction of time that the output voltage is “ON” compared to when it is “OFF”, of the pulses while keeping the frequency constant.

  • Which IC is better for a buck converter, TL494 or UC3843?

They mainly differ in type of control…
TL494 => voltage mode control (One loop control) ….
while UC3843 uses current mode control (Nested loop control, with a inner/fast current loop and another outer/slower voltage loop)…
Typically voltage mode are used in multiple output converters with good cross-regulation. Current mode when you want to parallel multiple converters to make a single converter with higher current rating…
TL494 is a very popular IC. If you have simple requirements… TL494 is recommended…

  • How do I properly set the feedback pin on a TL494 SMPS IC?

The feedback pin is the output of both error amplifiers, used in comparing and adjusting the output pulse width to the DC control voltage.
On various circuits I have looked up, the op-amp connected to pins 2 & 3 are used to set the gain of the feedback loop, using 2 resistors with one resistor connecting to 2.5V potential divider on 5V reference voltage. With the other connecting to the output (via suitable isolation)
The gain appears to be set at 101, using a 51k feedback with 510 ohms to the 2.5V reference. It is used to control the gain of the feedback voltage. No literature I have yet found, gives an indication on how this gain be set, except a graph showing an open loop gain of 1000, presumably the gain is set for the best stability, although there will also be a time constant.

  • Why is there no frequency compensation required in TI's TL494 example buck regulator design (operational amplifier, buck phase, shift phase, margin, TL494, electronics)?

It's a fixed frequency PWM controller with internal dead time timer. Frequency compensation is not required. Take a look at the datasheet.

  • How to use TL494?

 

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