Vin (120V AC) --> Bridge Rectifier --> Vcc (170V DC) Vcc --> R1 --> TL494 (Pin 1) TL494 (Pin 2) --> R2 --> Q1 (MOSFET) TL494 (Pin 3) --> R3 --> Q2 (MOSFET) Q1 --> L1 --> Vout (12V DC) Q2 --> Vout
Once you have a functional simulation, the next step is applying it to a real circuit.
: Most available models are "idealized." They may not perfectly capture thermal drift or the exact propagation delays found in the physical silicon. Rating: 4.5/5
LTspice needs a graphical symbol to represent the text model. tl494 ltspice
The approximate frequency is given by: $$f_osc \approx \frac1.1R_T \cdot C_T$$ In LTspice, this is modeled using a current source charging a capacitor, with a Schmitt trigger to reset the capacitor once the voltage threshold is reached.
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
In LTspice, the transformer leakage and magnetizing inductance must be realistic. Add Rser=0.01 to inductors to avoid unrealistic ringing. Vin (120V AC) --> Bridge Rectifier --> Vcc
| 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. |
: These are linear nodes used for voltage or current feedback. Dead-Time Control (Pin 4)
Double-check your .include path directive. Ensure the filename matches perfectly (e.g., .sub vs .lib ). The approximate frequency is given by: $$f_osc \approx
integrates all essential SMPS control functions into a single 16-pin package.
In LTspice, go to and type .include tl494.sub to link the model.