| Error | Likely cause | Fix |
|-------|--------------|-----|
| Unknown subcircuit | Missing .lib directive or wrong filename | Add .lib TL494.sub |
| Floating node | Unconnected input pins | Tie unused inputs to GND or VREF via 10k |
| No oscillation | CT/RT missing or DTC > 3V | Set DTC ≤ 0.5V, check CT/RT values |
| Output always high/low | Feedback pin (3) not driven | Connect to error amp output or voltage source |
| Convergence error | Steep edges, missing cap | Add 1nF from outputs to GND, use uic or startup |
Add this as text on your schematic for a 50 kHz push-pull converter: tl494 ltspice
.lib TL494.sub
Vcc Vcc 0 15
Rrt N005 0 10k
Cct N004 0 10n
XU1 Vcc 0 0 Vcc N004 N005 0 out1 0 out2 Vcc Vref Vcc 0 0 TL494
* Pin order: VCC, GND, DTC, FEEDBACK, CT, RT, IN1-, IN1+, IN2-, IN2+, OUT CTRL, C1, E1, C2, E2, VREF
(Note: pin order depends on your specific symbol/subcircuit – always check the .sub file’s .SUBCKT line.) Mastering Power Supply Design: A Complete Guide to
The TL494 oscillation frequency ($f_osc$) is determined by two external components: a timing capacitor ($C_T$) and a timing resistor ($R_T$). The oscillator charges $C_T$ with a constant current determined by $R_T$. (Note: pin order depends on your specific symbol/subcircuit
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.
Let’s simulate a simple buck converter stepping down 20V to 5V at 100 kHz. We’ll use a community model called TL494_TR.lib.