Tl494 Ltspice ~repack~

: A constant current charges the external timing capacitor ( CTcap C sub cap T ), producing a linear sawtooth wave profile.

Simulating the TL494 in LTspice is a valuable skill for any power electronics engineer. While the path is fraught with initial obstacles—finding an uncorrupted model, understanding the syntax quirks, and mastering the common errors—the payoff is significant. Being able to iterate a power supply design virtually before touching a soldering iron accelerates development, reduces cost, and deepens your understanding of control theory.

If you’re trying to use the LTspice TL494 model in KiCad (which uses ngspice), you’ll face fundamental syntax differences. LTspice uses “A-devices” (AND, OR, DFLOP, SCHMITT) that ngspice does not directly support. To port the TL494 to ngspice, you’d need to replace these A-devices with equivalent behavioral models or hand-crafted subcircuits. This is a significant undertaking and beyond the scope of this article. tl494 ltspice

| 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 |

Connect Pin 13 directly to GND . Both output transistors switch simultaneously, permitting a maximum duty cycle near : A constant current charges the external timing

To start, let's build a basic using the TL494 in LTspice. Schematic Setup: Supply: VCCcap V sub cap C cap C end-sub (12V) connected to VCCcap V sub cap C cap C end-sub pin and Output Collector (OC) pin. Oscillator: Connect RTcap R sub cap T (e.g., 10k) from RT to GND, and CTcap C sub cap T

* 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) Being able to iterate a power supply design

Once you have the corrected model files, the installation is straightforward. The TL494.sub file must be placed in your LTspice library’s sub directory. The typical path on Windows is Documents\LTspiceXVII\lib\sub . The TL494.asy symbol file should be placed in the sym directory, or better yet, in a sym\Misc or sym\MyParts subfolder for easy organization.

If the simulation fails to converge, try changing the Level parameter in the simulation settings or using Gear integration method.

On-chip operational amplifiers configuration used for voltage or current loop feedback control.

The TL494 remains a popular choice for educational projects and legacy designs due to its low cost, availability, and versatility in topologies like buck, boost, push-pull, and flyback converters. Simulating it in LTspice allows you to validate your control loop, observe switching behavior, and optimize component values without the risk of burning out hardware.