Computing stuff tied to the physical world

Extremely slow ramps

As a litmus test of the proper switch-on operation of the latest MPS circuit design, we can add an extra 6,800 µF capacitor between Vres and GND and see how things behave:


Obviously, the ramp-up will now be extremely slow. In this case, the horizontal scale is at 20 seconds per division, so it takes over 2 minutes to reach the trigger point.

But as you can see, switch on is still very sharply defined and working fine.

Note the increasing noise on the collector as the switch-over point comes nearer. The NPN transistor has a very high gain which in essence amplifies the noise coming in on the base junction. No matter how large or how many capacitors, there is always some noise.

But again, that’s where the positive feedback kicks in: the moment the Vdd output level starts rising, it reinforces the switching action. Hence the snap action, even in this case.

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