Ltspice: Tl494

Place a standard independent DC voltage source ( voltage ) configured to and wire it to VCCcap V sub cap C cap C end-sub (Pin 12) and GND (Pin 7). Establish the Reference: Connect a decoupling capacitor to the VREFcap V sub cap R cap E cap F end-sub output (Pin 14) to ground. Verify it produces a stable Oscillator Setup: Wire a resistor from RTcap R sub cap T to GND, and a capacitor from CTcap C sub cap T

Tie unused error amplifiers by putting their non-inverting inputs to GND and inverting inputs to VREFcap V sub cap R cap E cap F end-sub . Ensure Pin 4 sits below Limitations of SPICE-Based Power Supply Simulation

: Provides a dead-time adjustment to prevent switch overlap.

| 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. |

: Ensure this pin is tied to GND for maximum duty cycle or biased with a voltage to set a specific dead-time, otherwise, the PWM may not start [8, 15]. Wait for Stabilization tl494 ltspice

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Search for a reliable TL494 SPICE .subckt file (often found in community forums or Github repositories like sunnyiisc/Spice-Model-Collections ). Create a New Component: Save the model as tl494.sub .

Some TL494 models reference external files like universalOpamps2 or level.2 opamp models. If these are missing, you’ll get errors like universalOpamps2 file library is included in the TL494 file, but there is no ltspice software in the library itself . Place a standard independent DC voltage source (

The TL494 has a second error amplifier—perfect for cycle-by-cycle current limiting.

: Connect Pin 13 ( OUTPUT CTRL ) to Pin 14 ( REF ) to enable push-pull mode . Tie it to ground for single-ended parallel mode . 4. Designing the Oscillator Frequency The internal oscillator frequency ( foscf sub o s c end-sub

because the steering flip-flop divides the frequency by two:

: Complex IC models can slow down simulations significantly. It is often recommended to first simulate your circuit with an ideal voltage-controlled switch before introducing the full TL494 model to troubleshoot stability. Where to Find the Model Ensure Pin 4 sits below Limitations of SPICE-Based

: A widely cited model can be found on this forum thread . 2. Import the Model into LTspice

The TL494 model typically includes several functional blocks that must be correctly biased for simulation: Error Amplifiers (Pins 1, 2 and 15, 16)

Websites like DIYstompboxes or EEVblog forums have user-created TL494 subcircuits. These models are behavioral rather than transistor-level, meaning they run faster but may ignore some second-order effects (like temperature drift).

: Pin 4 sets the minimum allowable off-time between pulses. It features a built-in 0.12V offset ensuring an absolute minimum of 5% dead time.