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Simulating the TL494 in LTspice: A Practical Guide
The TL494 is a industry-standard pulse-width-modulation (PWM) control circuit. It is ubiquitous in PC power supplies, motor controllers, and DC-DC converters. While LTspice is renowned for its simulation of Linear Technology (Analog Devices) parts, it does not include the TL494 in its standard library by default.
.tran 0 5m 0 1u startup
.options method=gear
.lib TL494.sub
Part 4: Advanced TL494 Topologies in LTspice
4.1 Push-Pull Converter (Ideal for High Power)
The TL494 shines in push-pull because of its alternating output stages. tl494 ltspice
Example: Simulating a Simple Buck Converter with TL494
- Build a buck: N-channel MOSFET (or switching transistor) on the high side, diode or synchronous MOSFET on the low side, inductor, capacitor, and load.
- Use the TL494 subcircuit (real model or behavioral) to drive the gate via a gate driver or a level-shifting transistor stage.
- Set RT and CT per TL494 datasheet for desired switching frequency (e.g., 50–200 kHz).
- Close the feedback loop: sense the output voltage via a resistor divider into the TL494 error amp input; set the other error amp as a current limit if needed.
- Run transient simulation:
Feedback Loop: Connect pin 3 (Feedback) to the output of an error amplifier. Simulating the TL494 in LTspice: A Practical Guide
Internal Reference (5V) R_ref 14 0 1k E_ref 14 0 VALUE=5.0 Part 4: Advanced TL494 Topologies in LTspice 4
- Input: 24 V
- Switch: N‑MOSFET driven by OUTC via 100Ω gate resistor
- Diode: fast Schottky
- Inductor: 33 µH, Capacitor: 220 µF
- Feedback: resistive divider to FB targeting 12 V output
- RT/CT set for 50 kHz oscillator
- SS ramp of ~5 ms
Troubleshooting common problems
- Oscillator too fast/slow: adjust RT/CT; verify ramp amplitude.
- No PWM: check COMP driven below ramp (error amp), SS clamp may be active.
- Shoot‑through in push‑pull: increase DTC or add gate deadtime.
- Unstable loop: reduce error‑amp gain, move crossover lower, add feedforward.