The TL494 is one of the most popular, versatile, and inexpensive pulse-width modulation (PWM) controller ICs. Designed originally by Texas Instruments, it remains a favorite among hobbyists and professionals for building switch-mode power supplies (SMPS), DC-DC converters, battery chargers, and inverters.
If you are looking to understand or design a circuit using the TL494, this guide breaks down its internal architecture, pin configuration, and two essential circuit diagrams.
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| Application | Configuration | |-------------|---------------| | Boost converter | Single-ended, external MOSFET | | Push-pull inverter | Pin 13 to REF, external transformers | | Battery charger | Use second error amp for current limiting | | Solar MPPT controller | Dual-loop control using both error amps | | ATX power supply modification | Replace original PWM controller | tl494 circuit diagram
| Pin | Name | Description | |-----|--------------|-------------| | 1 | 1IN+ | Non‑inverting input of error amp 1 | | 2 | 1IN‑ | Inverting input of error amp 1 | | 3 | FEEDBACK | PWM comparator input (usually from error amp output) | | 4 | DTC | Dead‑time control (0V to 3V, higher = more dead time) | | 5 | CT | Timing capacitor (to GND) | | 6 | RT | Timing resistor (to GND) | | 7 | GND | Ground | | 8 | C1 | Collector of output transistor 1 | | 9 | E1 | Emitter of output transistor 1 | | 10 | E2 | Emitter of output transistor 2 | | 11 | C2 | Collector of output transistor 2 | | 12 | VCC | Supply voltage (7V to 40V) | | 13 | OUTPUT CTRL | Output mode control: to GND = parallel mode; to REF = push‑pull mode | | 14 | REF | 5V reference output (max 10 mA) | | 15 | 2IN‑ | Inverting input of error amp 2 | | 16 | 2IN+ | Non‑inverting input of error amp 2 |
+12V ──┬───┐
│ │
│ C1 ── 0.1µF
│ │
└───┴─── GND
│
┌──┴──┐
│ │
│ TL494│
│ │
└──┬──┘
│
RT ── 47kΩ ──┬──── Pin6 │
│ │
CT ── 10nF ──┴──── Pin5 │
│
DTC ── Pin4 ── 0.01µF ─┴─ GND
│
VCC ── Pin12 ── +12V │
GND ── Pin7 ─── GND │
REF ── Pin14 ── 5V ────┤
│
Output Ctrl ── Pin13 ── GND (parallel mode)
│
C1 ── Pin8 ──┬─── 1N4148 ──┬─── L1 ──┬─── C_out ── GND
│ │ │
E1 ── Pin9 ──┤ │ │
│ │ │
C2 ── Pin11 ─┤ │ │
│ │ │
E2 ── Pin10 ─┴─── 1N4148 ──┘ │
│
Feedback network: │
R1 = 2.2kΩ ──┬─── Pin1 (1IN+) │
│ │
R2 = 10kΩ ──┴─── GND │
│
Pin2 (1IN‑) ──┬─── R3 = 1kΩ ── GND │
│ │
└─── R4 = 10kΩ ────────┘ (to output voltage)
│
Pin3 (FEEDBACK) ── C_comp = 1nF ──┬─── R_comp = 10kΩ ── Pin1
│
└─── GND
(Note: This is a simplified schematic – for a real PCB, include gate drive resistors, bypass caps, and snubbers.)
| Frequency | R_T (pin 6) | C_T (pin 5) | |-----------|-------------|-------------| | 20 kHz | 30 kΩ | 2.2 nF | | 50 kHz | 10 kΩ | 2.2 nF | | 100 kHz | 5.1 kΩ | 2.2 nF | | 200 kHz | 2.7 kΩ | 1 nF | The TL494 is one of the most popular,
If you need 24V from a 12V battery, use this TL494 boost circuit diagram.
Principle: When the MOSFET turns on, current flows through L1 to ground. When it turns off, the magnetic field collapses, forcing current through D1 into the output capacitor at a higher voltage than the input.
Design Notes for Boost Topology:
Warning: Boost converters are dangerous to prototype. If the MOSFET fails shorted, input voltage appears directly at the output, destroying your load. Always add a fuse.
(Reference exact pin numbers/labels to the TL494 datasheet for the package variant you use.)