Is cap an only-AC Device?

So, did you think capacitors find applications only on AC systems, as it does not let DC current to pass through it? Well, caps are everywhere.

One, whenever DC is generated from AC mains, the output is never pure DC (The perfect straight line in the voltage-time curve of DC is hardly seen in reality). So, there comes it – Capacitor Filters to smoothen out the voltage variations in the signal.

Two, EMI/ESD capacitors. At the input lines of the system, even if they are DC lines, EMI/ESD capacitors are used to filter out spurious spikes in input voltage occurring due to EMI/ESD. EMI suppression capacitor is shown below.

You might frequently run into situations where you need 10V from a 5V power source or the like. The obvious solution is voltage doublers or charge pumps. Charge pumps mainly employ capactors. Though they use a clock, it is essentially a DC application.

If you observe a typical DC motor, a capacitor is usually soldered across its terminals. A DC motor generates back emf, and this back emf could damage the circuitry at its output if not handled properly. Providing a capacitor alleviates this problem. (Bypass Capacitor). It is shown below.

Capacitors are momentarily used as DC power supplies in DC circuits, to power microcontroller, to provide smoother voltage drops, handle brownouts etc

Also caps are used in Pulsed Power applications. Steady accumulation of energy followed by its rapid release can result in the delivery of a larger amount of instantaneous power over a shorter period of time (although the total energy is the same). For example, if one joule of energy is stored within a capacitor and then evenly released to a load over one second, the peak power delivered to the load would only be 1 watt. However, if all of the stored energy was released within one microsecond, the peak power would be one megawatt, a million times greater. Examples where pulsed power technology is commonly used include radar, particle accelerators, ultrastrong magnetic fields, fusion research, electromagnetic pulses, and high power pulsed lasers.

And, be cautious. Capacitors, when mishandled, can explode. See below.

Want something more? Heard of Exploding-bridgewire detonator? Its used to detonate a wide range of explosives used in mines and quarries. It has evolved to be adopted in Nuclear weapons. It requires high current surges. To achieve this, high-capacity, high-voltage capacitors with 5 kilovolt and 1 microfarad rating and the peak current ranging between 500 and 1000 amperes are used. It is these devices that trigger the sleeping nuclear bombs to explode. Remember the Fat Man bomb dropped over Nagasaki? It used these detonators. Shown below is the Fat Man bomb and its explosion.

The former explosion was far better, wasn’t it?

Well, we cant argue if the applications mentioned above are DC or AC. But I guess it does give an insight into some flaky applications of capacitors other than conventional fixed frequency AC applications.