Probe the output pin (Pin 9 or 10) and the switching node. You should see a PWM square wave
To use the TL494 PWM controller in LTspice, you must use a third-party subcircuit because there is no native, official model provided by Linear Technology (Analog Devices) [2]. 1. The TL494 Subcircuit Code
You can save the following code as a text file named TL494.sub and place it in your LTspice library folder (typically C:\Users\[User]\Documents\LTspiceXVII\lib\sub) [1, 3].
* TL494.sub * Connections: 1IN+ 1IN- FB DTC CT RT GND C1 E1 E2 C2 VCC OC REF 2IN- 2IN+ .subckt tl494 1IN+ 1IN- FB DTC CT RT GND C1 E1 E2 C2 VCC OC REF 2IN- 2IN+ [SPICE model code omitted for brevity; see references [1, 3] for full listing] .ends tl494 Use code with caution. Copied to clipboard 2. Implementation Steps tl494 ltspice
Symbol Creation: Create a 16-pin symbol (.asy) that matches the subcircuit's pin order: 1IN+, 1IN-, FB, DTC, CT, RT, GND, C1, E1, E2, C2, VCC, OC, REF, 2IN-, 2IN+ [1, 3].
Directive: Add the SPICE directive .lib TL494.sub to your schematic if the file is not in the default library directory. Oscillator Setup: Connect your timing resistor ( RTcap R sub cap T ) to the RT pin and timing capacitor ( CTcap C sub cap T ) to the CT pin. The frequency is approximately for single-ended use [2].
Output Configuration: Use the OC (Output Control) pin to switch between single-ended (grounded) or push-pull (connected to REF) modes [1]. 3. Quick Tips for LTspice Simulation Probe the output pin (Pin 9 or 10) and the switching node
Adding Text: Press T on your keyboard to add comments or SPICE directives [6].
Editing Values: Right-click on any component to modify its parameters [8]. Micro Units: Use u for micro (e.g., 10u for ) [9].
Use this when you want cycle‑by‑cycle PWM behavior, deadtime, soft‑start and current limit. Save as tl494.subckt. Use this when you want cycle‑by‑cycle PWM behavior,
* TL494 behavioral subckt (switch-level)
* Pins: VCC GND FB COMP RT CT DTC SS OUTC OUTE ILIM
.SUBCKT TL494 VCC GND FB COMP RT CT DTC SS OUTC OUTE ILIM
* Internal nodes
.node 1 2 3 4 5
* Reference 5V (approx)
BREF REF GND V=V(VCC)*0.08 ; simple reference scaled from VCC (adjust as needed)
* Oscillator: ramp from C
RRT RT REF 100k
CCT CT REF 10n
* Use behavioral current to form saw; simplistic: I = k/RT
BIOSC SAW REF I=V(VCC)/(100k) ; replace with better oscillator if needed
* Error amplifiers (inverting inputs: FB, ILIM; non-inv to reference)
* EA1: drives COMP node
EEA1 COMP GND VALUE = clamp( (V(REF)-V(FB))*10, -5, 5 )
* PWM comparator with deadtime (DTC pin sets min-off)
BPD CMP_OUT GND V= if( V(COMP) > V(SAW)*(1 - V(DTC)/5), 1, 0 )
* Outputs: open-collector to drive gate driver resistor network
* OUTC and OUTE are complementary PWM outputs (simple)
EOUTC OUTC GND VALUE= V(CMP_OUT) ? 0.1 : 0 ; low impedance sink when active
EOUTE OUTE GND VALUE= !V(CMP_OUT) ? 0.1 : 0
* Soft-start: clamp COMP by SS voltage
BSS COMP LIMIT GND V= min(V(COMP), V(SS))
* Current limit sense: if ILIM > threshold reduce duty
BLICM COMP GND V= if( V(ILIM) > 0.5, V(COMP)*0.5, V(COMP))
.ENDS
Notes: This is a condensed, pragmatic starting point — refine slopes, gains, and the oscillator to match TL494 datasheet values (osc frequency set by RT/CT, deadtime control range, internal reference ≈5V, EA gains, output transistor drive limits).
[
f_osc = \frac1R_T \cdot C_T
]
(For RT in ohms, CT in farads, f in Hz)
Actual output frequency = ( f_osc ) in single-ended mode, ( f_osc/2 ) in push-pull.