Tl494 Ltspice -
Here’s a solid, practical guide to using the TL494 PWM controller in LTspice.
Exporting and Sharing Your TL494 LTSpice Work
One of LTSpice’s weaknesses is schematic aesthetics. When you publish your TL494 design: tl494 ltspice
- Include the
.asc file AND the .lib file and .asy symbol.
- Avoid absolute paths in the
.include statement. Use .\tl494.lib instead of C:\Users\....
- Add a text box in the schematic explaining the simulation parameters (frequency, expected output voltage).
Example 1 — Single‑switch buck converter (switch‑level TL494)
Purpose: verify startup, soft‑start and current‑limit. Here’s a solid, practical guide to using the
Schematic summary:
- 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
Simulation steps:
- Insert tl494.subckt and instantiate with VCC=24V.
- Hook OUTC to MOSFET gate through 100Ω, tie OUTE to MOSFET gate complement if using half‑bridge.
- Set feedback divider R1 (to FB) and R2 (to GND) so V(FB)=V(REF) at desired Vout.
- Run transient: .tran 0 100ms startup. Observe soft‑start shape, duty ramp, and Vout regulation.
- Introduce a load step (e.g., switch from 1 A to 5 A at t=30ms) and inspect overshoot and recovery.
What to watch:
- Oscillator frequency and duty ceiling.
- Current limiter behavior: add a sense resistor to switch and feed its voltage to ILIM pin.
- Switching node ringing — add MOSFET Cgd/Cgs and parasitic L.
Step 5: Analyzing Results
- Line Regulation: Apply a stepped input voltage (24V to 30V at 2ms) using a PWL source. Observe output overshoot.
- Load Regulation: The
.step parameter shows voltage dip during load transient.
- Efficiency: Use LTSpice’s power measurement:
ALT + Left Click on the inductor input node and MOSFET drain.
Setting up PWM regulation:
- Error amp 1: IN1+ (pin 1) = voltage reference (e.g., 2.5V from divider), IN1- (pin 2) = feedback from output.
- Feedback pin (3) is internally connected to error amp outputs (open collector). Add a small pull-up (10k to VREF) if not already in model.