How can IC 74190 will give output freq as 50Hz?

Answer 1

The 74190 is an up/down decade counter. Counters use frequency division to achieve a counting sequence.

To answer your question, it depends on the input frequency. The Qa output will divide the clock input by 2 so if the input is 100Hz, Qa's output is 50Hz.

Since this is a decade (0 to 9, or truncated sequence) counter and not a binary (0 to 15, or full sequence) counter, the outputs Qb, Qc and Qd divide the input but their outputs are not symmetrical (equal time high and time low). Qb and Qc produce 2 pulses for every 10 input pulses, therefore divide the input clock by 5. Qd produces one output pulse for every 10 input pulses, therefore divides the input by 10.

The easiest way to visualize this is to write out the binary count in column format, starting at 0000 and ending at 1001, and looking at each of the output patterns.

To produce the 50Hz output, assuming you are not concerned over symmetry:

-input clock 100Hz for 50 Hz on Qa

-input clock 250Hz for Qb or Qc output of 50Hz

-input clock 500Hz for Qd output of 50Hz