Tl494 Ltspice May 2026

TL494 in LTSpice — A Practical Guide

The TL494 is a classic PWM controller widely used for switch-mode power supplies, battery chargers, and motor drives. This post shows how to simulate the TL494 in LTSpice, explains a basic application (a simple buck converter), and gives tips for accurate results.

Setting up PWM regulation:

  • Error amp 1: IN1+ (pin 1) = voltage reference (e.g., 2.5V from divider), IN1- (pin 2) = feedback from output.
  • Feedback pin (3) is internally connected to error amp outputs (open collector). Add a small pull-up (10k to VREF) if not already in model.

Recommended source:

  • TI TL494 Spice model (unencrypted) – available on TI’s product page under “Tools & Software” → “SLVJ002.ZIP”
  • GitHub / LTspice groups – search for TL494.sub and TL494.asy

2.4 Output Control (Pin 13)

This pin dictates the output topology:

  • Grounded: Parallel output mode (Outputs A and B switch in unison). Used for single-ended topologies like buck or flyback.
  • Tied to Vref: Push-pull mode. Outputs A and B alternate. The effective frequency seen at the output is half the oscillator frequency.

Varying Dead-Time:

Sweep the voltage at pin 4 from 0V to 3V using .step param V_DT 0 3 0.5. Watch the maximum duty cycle drop from 96% to 0%. This is invaluable for transformer-based designs like push-pull or forward converters. tl494 ltspice

Introduction

The TL494 is a legendary integrated circuit in the world of power electronics. Introduced in the late 1970s by Texas Instruments, this fixed-frequency pulse-width modulation (PWM) controller has become a staple in switch-mode power supplies (SMPS), DC-DC converters, UPS systems, and battery chargers. Its longevity is a testament to its robustness: dual error amplifiers, a flexible output stage, dead-time control, and a wide operating voltage range (7V to 40V).

However, designing a power supply on paper is not enough. Modern engineering demands verification. Enter LTSpice—the powerful, free simulation tool from Analog Devices. Combining the TL494 with LTSpice allows you to debug feedback loops, analyze switching waveforms, and optimize component selection without risking blown MOSFETs or burning resistors. TL494 in LTSpice — A Practical Guide The

In this guide, we will explore everything you need to know about using the TL494 in LTSpice, from finding accurate models to simulating a complete buck converter.

Chapter 3: Running the Simulation

  1. Save the subcircuit as TL494.sub
  2. Save the circuit as TL494_buck.asc
  3. Add .include TL494.sub as a SPICE directive on the schematic
  4. Run simulation

Expected waveforms:

  • CT pin: Sawtooth ~10kHz
  • COMP pin: DC level ~2-3V after startup
  • OUT1: PWM pulses, duty cycle adjusts to regulate output to 5V
  • V(OUT_FB): Regulated ~5V after ~1-2ms

Components needed:

  • TL494 (with .lib directive)
  • VCC = 15V DC
  • RT = 10k, CT = 10nF → frequency ≈ 48 kHz
  • DTC pin = 0V (min dead time) or 0.1V for small dead time
  • OUT CTRL pin = VREF for push-pull, GND for single-ended
  • Load resistors on outputs (e.g., 1k pull-up to VCC if open-collector used)

Part 5: Debugging Common TL494 LTspice Simulation Errors

Even with a good model, you will encounter issues. Here is a debugging checklist:

| Error Message | Likely Cause | Solution | |---------------|--------------|----------| | "Time step too small" | Fast switching + floating node | Add 1MEG resistors from each output to GND. Reduce maxstep in .tran. | | "Singular matrix" | Missing DC path to GND | Check the voltage feedback divider; ensure error amp inputs are not floating. | | Output always high or always low | Dead-time pin too high (>3V) or wrong oscillator | Set DTC <0.6V for max duty cycle. Verify RT/CT values. | | No oscillation at pin 5 | Missing ic initial condition | Add .ic V(osc_pin)=0.3V or use startup flag. | Error amp 1: IN1+ (pin 1) = voltage reference (e

Pro tip: Run a DC operating point (.op) before the transient analysis. Check that the error amplifiers are biased correctly (pins 1, 2, 15, 16 between 0 and VCC).