ULN2803APG

Ahh yes 😄 — the ULN2803APG is basically the bigger, slightly beefier sibling of the ULN2003, perfect when you want more channels or higher-voltage switching ⚡🤖.

It’s extremely popular in industrial and hobby electronics for driving loads from TTL/CMOS logic.

📦 ULN2803APG – Product Description

The ULN2803APG is a high-voltage, high-current Darlington transistor array IC.

Contains 8 Darlington pairs (instead of 7 in ULN2003)

Each channel can sink up to 500 mA

Maximum voltage per channel: 50 V

Designed to interface low-voltage logic (3.3 V / 5 V) with relays, motors, solenoids, LEDs, and other inductive or resistive loads.

It also includes internal flyback diodes for switching inductive loads safely.

The APG suffix usually indicates PDIP-18 package (through-hole).

✨ Key Features

✅ 8-channel Darlington array
✅ High voltage: 50 V max
✅ High current: 500 mA per channel
✅ Open-collector outputs
✅ TTL / CMOS logic compatible
✅ Internal flyback diodes for inductive load protection
✅ Easy microcontroller interface
✅ Low input current (~1.35 mA at 5 V logic)

📊 Electrical Specifications
Parameter Typical / Max Value
Output voltage 50 V max
Output current 500 mA per channel
Input voltage TTL / CMOS compatible (~3–5 V)
Input current ~1.35 mA @ 5 V
Total package dissipation 2 W
Saturation voltage ~1 V @ 350 mA
Package 18-pin PDIP (ULN2803APG)
Operating temp 0 °C – 70 °C
🔌 Pin Configuration (PDIP-18)
ULN2803APG
┌─────────────────┐
1 IN1 COM 18
2 IN2 OUT8 17
3 IN3 OUT7 16
4 IN4 OUT6 15
5 IN5 OUT5 14
6 IN6 OUT4 13
7 IN7 OUT3 12
8 IN8 OUT2 11
GND OUT1 10
└─────────────────┘

Pin functions:

IN1–IN8 → logic inputs (from MCU or logic circuit)

OUT1–OUT8 → outputs to load (relay, motor, LED, etc.)

COM (18) → common for flyback diodes (connect to +V if switching inductive loads)

GND (9/10) → ground

⚙️ How It Works

Logic input HIGH → corresponding Darlington pair conducts

Output sinks current from load to ground

Internal flyback diodes protect IC from inductive spikes (relays, solenoids)

Each channel handles up to 500 mA

Perfect for microcontroller → high-voltage load interface.

🛠️ Typical Applications

Stepper motor control

Relay arrays / relay boards

LED displays / matrices

Solenoid control

Microcontroller-controlled high-current devices

Arduino / Raspberry Pi interfacing

💡 Design Tips
✅ Flyback protection

Connect COM pin to +V when switching relays/inductive loads.

✅ Paralleling channels

You can parallel outputs for higher current (watch thermal limits).

✅ Low current logic input

Only ~1 mA per input, ideal for 3.3 V/5 V MCUs.

✅ Heat management

If driving many channels simultaneously at high current, consider airflow or heatsinking.

✅ Quick Summary

ULN2803APG = 8-channel Darlington driver IC

Use it when you need:
✔ Drive multiple relays, motors, or LEDs
✔ Interface microcontrollers to high-voltage loads
✔ Handle inductive spikes safely
✔ Simple, reliable, multi-channel solution