Overview
The Allen-Bradley 1771-OGD TTL Output Module is a legacy PLC-5 series discrete output module designed to control TTL-compatible external devices. This 16-point output module interfaces directly with TTL devices, providing reliable signal transmission for industrial automation and process control systems. The 1771-OGD is installed in a single slot within Allen-Bradley Universal I/O Chassis (Series B: 1771-A1B, 1771-A2B, 1771-A3B, 1771-A4B) and includes factory-installed fuse protection and output diode clamping.
Key Features
- 16 TTL-compatible discrete outputs per module
- Output diode protection to +5V and ground (protects against accidental overvoltage)
- Integrated 0.5A @ 250V fuse for circuit protection
- Configurable logic selection: High=True or Low=True via DIP switches
- Less than 1 millisecond output signal delay
- Single-slot installation in 1771 I/O chassis
Technical Specifications
- Output Voltage (High Logic): 2.0–5.25V DC
- Output Voltage (Low Logic): −0.2–+0.8V DC
- Maximum Output Current (Source): 1 mA
- Maximum Output Current (Sink): 20 mA
- External Supply Voltage: 5V DC (±0.25V), less than 50 mV peak-to-peak ripple
- External Supply Current (Max): 310 mA
- Backplane Power (5V DC): 230 mA
- Output Signal Delay: <1 ms
- Power Dissipation: 2.8 W (max)
- Heat Dissipation: 9.5 BTU/hr (max)
- Operating Temperature: 0–60 °C (32–140 °F)
- Humidity: 5–95% non-condensing
- Certifications: CSA, CE, UL
- Part Number: 1771-OGD; OEM Code: 96042471
Typical Applications
The 1771-OGD is used in legacy PLC-5 automation systems where TTL output signals drive external devices such as:
- TTL logic gates and microprocessor circuits
- LED indicators and display drivers
- TTL-input sensor interfaces and measurement equipment
- Laboratory and test automation systems
- Retrofit and maintenance of existing PLC-5 installations
Compatibility & Replacements
The 1771-OGD is a 16-output TTL module and differs from the 1771-OG, which provides only 8 outputs. Both modules mount in Allen-Bradley Universal I/O Chassis Series B. The 1771-OGD requires two power sources: the I/O chassis backplane (240 mA @ 5V DC) and an external 5V DC supply (310 mA max) for TTL signal transmission. When installing the 1771-OGD in systems using two-slot addressing, the module must be placed in an odd-numbered slot (right side of a module group). No direct modern replacement exists; equivalent new TTL output functionality is available through current CompactLogix or ControlLogix systems with appropriate I/O modules. This module is suitable for repair and long-term maintenance of original PLC-5 installations.
