Tl494 Ltspice May 2026

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).

When simulating SMPS in LTspice, "Timestep too small" errors are common.

Purpose: simulate PWM balancing and deadtime effects for transformer drive.

Key additions:

Simulation tips:

LTSpice doesn’t include a built-in TL494 device, so you have three realistic options:

Below is a step-by-step walkthrough for option 1 (using a vendor model) and a compact alternative using a behavioral subcircuit for quick tests. tl494 ltspice

| Parameter | Change | Effect | |-----------|--------|--------| | Frequency | C_CT or R_RT | f ≈ 1.1/(R_RT * C_CT) | | Duty cycle | Modify DTC voltage on pin 4 | Max duty ~96% if pin 4 grounded | | Feedback | Change R1/R2 divider | Sets output voltage | | Compensation | Adjust R_COMP, C_COMP | Loop stability |

If you need to create your own symbol, map these pins:

| Pin | Name | Function | |-----|---------|------------------------------| | 1 | IN1+ | Non-inverting input of error amp 1 | | 2 | IN1- | Inverting input of error amp 1 | | 3 | FEEDBACK| PWM comparator input (usually from amps) | | 4 | DTC | Dead-time control (0–3V) | | 5 | CT | Timing capacitor | | 6 | RT | Timing resistor | | 7 | GND | Ground | | 8 | C1 | Output transistor 1 collector | | 9 | E1 | Output transistor 1 emitter | | 10 | E2 | Output transistor 2 emitter | | 11 | C2 | Output transistor 2 collector | | 12 | VCC | Supply (7V–40V) | | 13 | OUT CTRL| Output control (GND=parallel, Vref=push-pull) | | 14 | VREF | 5V reference output | | 15 | IN2- | Inverting input of error amp 2 | | 16 | IN2+ | Non-inverting input of error amp 2 | Simulation tips:

You can save the following code as TL494.sub and include it in your schematic.

* TL494 Behavioral Model for LTspice
.SUBCKT TL494 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
* Pins: 1(IN1+) 2(IN1-) 3(FB) 4(DT) 5(CT) 6(RT) 7(GND) 8(C1) 9(E1) 10(C2) 11(E2) 12(VCC) 13(OUT_CTRL) 14(VREF) 15(IN2+) 16(IN2-)
* VREF Generator (Pin 14)
B1 14 7 V=5
* Oscillator (Pins 5, 6)
* Note: Frequency depends on Rt/Ct. Simplified behavioral ramp here.
* We generate a 0-3V sawtooth.
A1 5 7 OSC RAMP=3 FREQ=100k
* Note: Real implementation uses current source I=V(14)/Rt into Ct.
* Dead Time & PWM Logic (Pin 4)
* Dead time voltage effectively offsets the sawtooth floor or clamps the comparator.
* If V(4) > Sawtooth, Output is OFF.
* Effective PWM comparator: Duty Cycle = (V_saw - V_dead) / V_saw_amp.
* Error Amplifiers (Simplified)
* EAMP1 (Pins 1, 2, 3)
E1 3 7 TABLE  V(1,2)  = (0 0) (1m 5) 
* EAMP2 (Pins 15, 16)
E2 3 7 TABLE  V(15,16)  = (0 0) (1m 5)
* PWM Comparator Logic
* Sawtooth internal node (assume node 100)
B2 100 0 V=IDTMOD(I=10m, MODE=1) ; Simplified ramp generator for logic
B3 101 0 V=IF(V(100) > (V(3)+V(4)), 0, 1)
* Output Stage Control (Pin 13)
B4 102 0 V=V(13) ; Output Mode
* Output Transistors (Pins 8,9,10,11)
* Q1 (Pins 8 Coll, 9 Emit)
* Q2 (Pins 10 Coll, 11 Emit)
S1 8 9 101 0 SW
S2 10 11 101 0 SW
.MODEL SW SW(RON=0.1 ROFF=1Meg VT=0.5 VH=0.1)
.ENDS TL494

(Note: The code above is a high-level abstraction. For precise engineering, utilize the official Texas Instruments PSpice model.)

Let's verify the model by building a simple open-loop Buck converter. LTSpice doesn’t include a built-in TL494 device, so

Components needed:

Schematic Netlist Example: If you were to textually describe the connections for the simulation command:

X1 IN1 IN2 FB DTC CT RT GND C1 E1 C2 E2 VCC OC VREF IN2_NEG IN1_NEG TL494
V1 VCC GND 15
R_RT RT GND 15k
C_CT CT GND 10n
R_pullup VCC C1 1k
R_load Out 0 10
L1 C1 Out 100u
C1 Out 0 47u