| Feature | SN51DP | ULN2003A | ULN2803A | |-----------------------|-----------------|-----------------|-----------------| | Number of channels | 7 | 7 | 8 | | Output voltage max | 50V (or 100V) | 50V | 50V | | Output current (cont.)| 500 mA | 500 mA | 500 mA | | Input compatibility | TTL/CMOS (3-24V)| TTL/CMOS (3-5V) | TTL/CMOS (3-5V) | | Internal base resistor| Yes (2.7k) | Yes (2.7k) | Yes (2.7k) | | Package | 16-pin DIP | 16-pin DIP/SOIC | 18-pin DIP | | Clamp diodes | Yes | Yes | Yes |
| Pin No. | Name | Description | |---------|-------------|----------------------------------------------| | 1 | IN 1 | Input channel 1 | | 2 | IN 2 | Input channel 2 | | 3 | IN 3 | Input channel 3 | | 4 | IN 4 | Input channel 4 | | 5 | IN 5 | Input channel 5 | | 6 | IN 6 | Input channel 6 | | 7 | IN 7 | Input channel 7 | | 8 | GND | Ground (common for inputs and logic) | | 9 | COM | Common free-wheeling diode cathode (VCC for inductive loads) | | 10 | OUT 7 | Output channel 7 (open collector) | | 11 | OUT 6 | Output channel 6 | | 12 | OUT 5 | Output channel 5 | | 13 | OUT 4 | Output channel 4 | | 14 | OUT 3 | Output channel 3 | | 15 | OUT 2 | Output channel 2 | | 16 | OUT 1 | Output channel 1 | sn51dp datasheet pdf
The Darlington pair configuration multiplies the current gain, meaning you can drive heavy loads without needing additional driver transistors or MOSFETs. How to Use the SN51DP: Typical Application Circuits The SN51DP datasheet PDF includes several reference circuits. Let’s explore the most common ones. 1. Driving DC Relays and Solenoids This is the most popular application. Connect the relay coil between V+ (e.g., 24V) and the output pin. Connect the COM pin to the same V+. The internal diode will clamp inductive kickback. | Feature | SN51DP | ULN2003A | ULN2803A
| Symptom | Likely Cause | Solution | |----------------------------------|-----------------------------------------------|----------------------------------------------| | Output not switching | Input voltage too low (<3V) | Increase logic high level or use a pull-up | | IC gets extremely hot | Too much current (>500mA) or no COM connection| Add heatsink; connect COM to load supply | | Relay chatters | Insufficient holding current | Increase load supply voltage | | Output stays on when input low | Damaged output transistor | Replace IC; check for load shorts | | Intermittent operation | Loose ground connection | Ensure pin 8 is solidly grounded | The SN51DP remains a go-to component for interfacing low-voltage logic with high-power loads. Its seven channels, built-in clamping diodes, and high gain make it ideal for relays, solenoids, LEDs, and small motors. However, no matter how experienced you are, you must consult the official SN51DP datasheet PDF before finalizing any design. Let’s explore the most common ones
Whether you are designing a relay driver board, an LED matrix, a stepper motor controller, or an industrial solenoid driver, the is your essential roadmap. This article serves as an extended technical annotation of that datasheet, walking you through every critical parameter and helping you integrate this IC successfully into your projects.