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 |
The TL494 is a fixed‑frequency pulse‑width modulation (PWM) control IC, designed for switch‑mode power supplies (SMPS). It includes:
Common applications: buck, boost, flyback, forward, and push‑pull converters. tl494 circuit diagram
This buck regulator maintains a stable 5V output regardless of input variations or load changes.
f_osc (kHz) = 1.1 / (R_rt (kΩ) × C_ct (µF))
Example: RT = 47kΩ, CT = 10nF →
f = 1.1 / (47 × 0.01) = 2.34 kHz (or 1.1 / (47e3 × 10e-9) = 2.34 kHz) Example: RT = 47kΩ
Before diving into schematics, understanding why you would choose the TL494 over a simpler chip like the SG3525 or a microcontroller is crucial.
Before diving into circuits, it is crucial to understand the pins. The TL494 is available in DIP-16, SOIC-16, and TSSOP-16 packages. excessive drive current
| Pin No. | Name | Function | |---------|------|----------| | 1 | 1IN+ | Non-inverting input of Error Amplifier 1 | | 2 | 1IN- | Inverting input of Error Amplifier 1 | | 3 | FEEDBACK | PWM comparator input (usually for output voltage control) | | 4 | DTC | Dead-Time Control (sets minimum off-time) | | 5 | CT | Timing Capacitor (sets oscillator frequency) | | 6 | RT | Timing Resistor (sets oscillator frequency) | | 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 | Positive supply voltage (7V to 40V) | | 13 | OUT CTRL | Output control (High = Push-Pull mode, Low = Single-ended) | | 14 | REF | 5V Precision Reference Output | | 15 | 2IN- | Inverting input of Error Amplifier 2 | | 16 | 2IN+ | Non-inverting input of Error Amplifier 2 |
| Problem | Likely Cause | |------------------------|--------------------------------------------| | No switching | Pin12 VCC < 7V; Pin13 floating; CT/RT wrong; no power to outputs | | Full duty cycle always | Pin4 too low; feedback loop open (Pin3 stuck low) | | Output voltage too low | Divider resistors wrong; inductor saturating; load too high | | IC hot | Output transistors shorted; excessive drive current; VCC > 40V | | Instability / noise | Poor compensation; missing bypass caps; ground loops |
