frequency division by 5 using only JK flip flops
The answer to this question is in "Gateless Scalers with J-K Flipflops", written in 1968 by P A Neeteson of Philips. This document shows seven configurations of 3 J-K flipflops which all divide by 5. The best is attached; this is synchronous and has an output which is negative-going on the 5th clock.







simulate this circuit &ndash; Schematic created using CircuitLab