74147 (BCD to 10-line decimal decoder/driver)

Description

The 74147 is a BCD to 10-line decimal decoder/driver with priority encoding. This IC is part of the 7400 series and is used to convert Binary Coded Decimal (BCD) input into a decimal output, but with a special feature: priority encoding.

74147 IC Description:

The 74147 is a BCD to decimal decoder that provides an active-low output for the decimal digits 0 through 9. It has a priority encoding function, meaning it can select the lowest (priority) active input if multiple inputs are active at the same time. This feature makes it suitable for applications where a priority-based encoding or decoding is required.

Key Features:

• BCD to 10-line Decimal Decoder: The IC converts BCD (binary coded decimal) inputs into one of 10 decimal outputs (0 to 9).
• Priority Encoding: The IC includes priority encoding, meaning if multiple BCD inputs are active at the same time, the IC will select the lowest active input.
• Active-Low Outputs: The outputs are active-low, meaning the output corresponding to the BCD input is pulled low (0), and all other outputs remain high (1).
• Input Range: It accepts a 4-bit BCD input (A, B, C, D), which represents a decimal value between 0 and 9.
• Unused Input Handling: If the BCD input is greater than 9 (i.e., 1010 to 1111 in binary), none of the outputs will be active.

Pin Configuration (16-pin package):

Here’s the pinout for the 74147 BCD to 10-line decimal decoder/driver:

1. Pin 1 (A): BCD input bit 1 (Least Significant Bit).
2. Pin 2 (B): BCD input bit 2.
3. Pin 3 (C): BCD input bit 3.
4. Pin 4 (D): BCD input bit 4 (Most Significant Bit).
5. Pin 5 (9): Active-low output for decimal digit 9.
6. Pin 6 (8): Active-low output for decimal digit 8.
7. Pin 7 (7): Active-low output for decimal digit 7.
8. Pin 8 (GND): Ground connection (GND).
9. Pin 9 (6): Active-low output for decimal digit 6.
10. Pin 10 (5): Active-low output for decimal digit 5.
11. Pin 11 (4): Active-low output for decimal digit 4.
12. Pin 12 (3): Active-low output for decimal digit 3.
13. Pin 13 (2): Active-low output for decimal digit 2.
14. Pin 14 (1): Active-low output for decimal digit 1.
15. Pin 15 (Enable): Active-low enable input.
16. Pin 16 (Vcc): Supply voltage (typically 5V).

How It Works:

• BCD Input: The 74147 accepts a 4-bit BCD input (pins A, B, C, D). This input represents a decimal value between 0 and 9.
• Priority Encoding: The IC is designed to give priority to the lowest active input when multiple inputs are active. For example, if A = 1 and B = 1, the output corresponding to A will be selected as the lowest active input. This makes the IC suitable for applications where multiple inputs may be active, but the lowest value is required.
• Active-Low Outputs: The IC decodes the BCD input into one of the 10 decimal outputs (pins 5-14). The output corresponding to the input value will be low (0), while all other outputs will remain high (1).
• Invalid Inputs: For BCD inputs greater than 9 (inputs 1010 to 1111), no outputs will be activated, meaning all outputs will remain high.
• Enable Pin: The Enable pin (pin 15) is active-low, which means that if this pin is low, the IC is enabled and will decode the BCD input. If the Enable pin is high, the outputs will be high regardless of the input.

Truth Table:

Applications:

1. Decimal Display Driver: The 74147 can be used to drive seven-segment displays or other types of decimal display devices in applications where a BCD input needs to be decoded into decimal output.
2. Priority Encoding: In systems where multiple inputs might be active simultaneously, the 74147 can be used to select the lowest priority active input, which is particularly useful in systems like priority encoders and data selectors.
3. BCD to Decimal Conversion: The IC is often used in systems where BCD data needs to be converted into decimal outputs, which is common in digital clocks, counters, and displays.
4. Data Decoding: It is used in systems where specific outputs need to be selected based on a 4-bit BCD input, such as in control systems and logic decoding circuits.
5. Timer and Counter Circuits: The IC can also be part of timing and counting circuits that require a BCD to decimal conversion for output.

Electrical Characteristics:

• Supply Voltage (Vcc): Typically 5V, but can range from 3V to 15V.
• Current Consumption: The IC operates with low power consumption typical of TTL logic devices.
• Output Drive: The IC can drive TTL-compatible logic levels directly.

Example Circuit:

Imagine a BCD counter that generates a 4-bit BCD output, and you want to convert this output into a decimal output for display. By using the 74147 IC, the BCD values will be converted to the corresponding decimal outputs, where each decimal digit (0–9) will be represented by an active-low output. This active-low output can then be used to drive seven-segment displays or LEDs to represent the decimal value.