Master Guide to Simulating the TL494 PWM Controller in LTspice
The circuit is a half-bridge power supply that converts a 120V AC input to a 12V DC output. The circuit uses a TL494 PWM controller IC to drive two power MOSFETs, which are connected in a half-bridge configuration. The output filter consists of an inductor and capacitor.
The is one of the most resilient and widely manufactured Pulse Width Modulation (PWM) control chips in the history of power electronics. Designed by Texas Instruments and multi-sourced by numerous chipmakers, it serves as the foundational controller for ATX computer power supplies, DC-DC buck/boost converters, and high-frequency inverters.
Place both tl494.asy and tl494.sub into the exact same folder as your current project file ( .asc ). Open your schematic in LTspice. tl494 ltspice
Databases like the open-source GitHub repositories or old Linear Technology forums host optimized TL494 subcircuits specifically rewritten for LTspice performance. File Components A complete model requires two distinct files:
| Pin | Name | Function | |-----|---------|------------------------------| | 1 | IN1+ | Non-inverting input of error amp 1 | | 2 | IN1- | Inverting input of error amp 1 | | 3 | FEEDBACK| PWM comparator input (usually from amps) | | 4 | DTC | Dead-time control (0–3V) | | 5 | CT | Timing capacitor | | 6 | RT | Timing resistor | | 7 | GND | Ground | | 8 | C1 | Output transistor 1 collector | | 9 | E1 | Output transistor 1 emitter | | 10 | E2 | Output transistor 2 emitter | | 11 | C2 | Output transistor 2 collector | | 12 | VCC | Supply (7V–40V) | | 13 | OUT CTRL| Output control (GND=parallel, Vref=push-pull) | | 14 | VREF | 5V reference output | | 15 | IN2- | Inverting input of error amp 2 | | 16 | IN2+ | Non-inverting input of error amp 2 |
is a versatile Pulse-Width Modulation (PWM) control circuit widely used in switch-mode power supplies (SMPS) for its fixed-frequency operation and dual output capability. Integrating it into Master Guide to Simulating the TL494 PWM Controller
The combination of Texas Instruments’ TL494 Pulse-Width Modulation (PWM) controller with Analog Devices’ LTspice simulation tool is a potent, albeit often tricky, pairing for power electronics engineers and hobbyists. However, this is not an officially supported configuration, leading to frequent challenges, from sourcing the right files to debugging elusive simulation errors.
Use .ic directives to set initial voltages (e.g., .ic V(out)=0 ) to simulate the turn-on phase.
: You forgot to include the library file. Add the spice directive .include tl494.lib directly onto your schematic screen using the S hotkey. Error: "Time step too small" or Simulation Freezes The is one of the most resilient and
Probe the output pin (Pin 9 or 10) and the switching node. You should see a PWM square wave
| File | Purpose | |------|---------| | TL494.sub | Subcircuit definition (Spice netlist) | | TL494.asy | LTspice schematic symbol | | TL494_test.asc | Example test circuit |
This is where simulation shines.
: Achieving high-frequency PWM (e.g., 120kHz) can sometimes result in waveform overlap or unexpected offsets in the simulated output [12]. Common Troubleshooting Tips Driver Stage
The simulation results show that the TL494-based half-bridge power supply circuit operates as expected, with a regulated output voltage and a high efficiency. The output ripple voltage is within acceptable limits.