The simplest of design, one OP-AMP driving 3 MOSFETs. All fine until I made a mistake: with the signal generator connected and turned ON, i connected a 24V 5A supply that was already on, while the signal generator was providing a square wave for 5A current. This caused one of the MOSFETs to blow up (shorting) due to an avalanche event. Finally the power supply went into hiccup mode.

Have you ever seen a fuse pulsating? With the output of the supply shorted and the fuse quite at the limit of the current, it is almost melting each time the power supply tries to restart