74155 (BCD to 1-of-16 line decoders)

74155 IC Description:

The 74155 IC contains two independent BCD to 1-of-16 line decoders, each of which accepts a 4-bit BCD input (ranging from 0000 to 1001 in binary, which corresponds to decimal 0 to 9) and decodes it into one of 16 output lines. This type of IC is useful in applications such as driving 7-segment displays, memory address decoding, and multiplexing.

Key Features:

• Dual BCD to 1-of-16 Decoder/Driver: The IC contains two separate decoders that each convert a 4-bit BCD input into one of 16 outputs.
• Active-low Outputs: The IC’s outputs are active-low (i.e., the selected output will be LOW while all other outputs are HIGH).
• Binary Coded Decimal (BCD) Input: The IC accepts a 4-bit BCD input, which can represent decimal numbers 0 to 9.
• Output Drive Capability: The IC can drive TTL-compatible loads, which makes it suitable for driving displays, relays, or other components in digital circuits.
• Simple Control: The outputs are controlled by the BCD inputs, and the IC automatically selects the appropriate output based on the binary value of the BCD input.

Applications:

1. 7-Segment Display Drivers: The 74155 IC is commonly used to drive 7-segment displays in digital clocks, meters, or other display applications where a 4-bit BCD input must be converted into a signal that activates the appropriate segments of the display.
2. Memory Address Decoding: It can be used for memory address decoding where a 4-bit address needs to select one of several memory locations or devices.
3. Multiplexing: The IC can be used in multiplexing circuits where multiple outputs are needed, and only one output is activated at a time.
4. LED Driver: The 74155 can drive LEDs or other indicators, where each of the 16 outputs can control a separate LED.
5. Switching Applications: It can be used in digital switching applications where one of several output lines must be activated based on a BCD input.

Electrical Characteristics:

• Supply Voltage (Vcc): Typically 5V (with a range of 4.5V to 5.5V).
• Output Drive Capability: The 74155 IC can drive TTL-compatible loads.
• Power Consumption: As a CMOS device, it consumes very little power when operating.

Example Application:

In a digital clock application, the 74155 can be used to decode the BCD input from the hours and minutes counter into signals that drive the 7-segment displays for each digit. The BCD inputs could come from a counter IC like the 74160, and the 74155 would decode the value and activate the correct output to drive each segment of the display.