Why Do Electronic Circuits Use DC Current instead of AC?

Why Electronic Devices Use DC Supply instead of AC Supply ? 

One thing should be cleared that not all the electronic devices, components and circuits are using only DC supply, but AC as well. If it comes to Logic circuits and ICs (Integrated Circuits), yes, they use DC only. In short, it depends on the electronic circuit needs and purpose, whether we use AC or DC. Let’s see how.

Below are the scenarios where we use both AC and DC in electronics circuits and why most of the electronic circuits use a DC supply only.

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AC in Electronic Circuits

• In case of LC (resonant circuit tank circuit or tuning circuit), DC signal converted to an AC signal using capacitor and an inductor (where we know that a capacitor blocks DC but passes AC) which may further supply to the clipping circuit or amplifier to amplify or modify the shape of the signal according to the circuit needs.
• In filters, capacitors and inductors are used to remove the ripples from the AC or pulsating DC supply to convert it to the pure DC supply.
• Rectifiers (which contains on Diodes) are used to convert the input AC supply to the pulsating DC supply and the process is known as rectification.
• In amplification, a biased transistor can be used as an amplifier with input AC signals.

The above discussion clearly shows that electronic circuit uses AC as well, not only the DC.

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Why Most of Electronic Circuits Uses DC Only?

Below are the reasons we use a DC supply in electronic circuits instead of AC.

• Digital Logic Gates:

We know that the basic working principle of logic gates is based on “Binary” states which is “1” (ON) and “0” (OFF).

In ICs, Microprocessors and digital computers, they need ripple free and pure DC as input signal to generate a digital binary signal (High or Low) for ON/OFF operation which is only possible with DC Supply.

This would be difficult in case of AC as it changes its direction and value multiple times in every second due to frequency. (50Hz in UK and 60Hz in US). It means, the AC input signal having the ability to changes 50 or 60 times in every second will generates lots of “ON” and “OFF” signals which is harmful for the circuit operation. In addition, the processor won’t be able to decide which is the OFF and ON signal in case of noisy AC signals.

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• Unidirectional Components:

You can’t imagine electronic engineering without the backbone which is transistor. A transistor needs a DC bias, i.e. for normal operation a positive signal is applied to the base of a transistor. In case of AC supply to the transistor or a diode, it may not work properly as constant for normal operation, but provide a continues switching operation due to multiple positive and negative signals of AC (due to frequency) and even explode if the input voltage are high.

For specific purposes like amplification and rectification, a biased transistor and diode can be used as an amplifier and a half wave rectifier respectively, but is it not always the case in circuit design. In short, AC does not maintain a unidirectional current flow where we need constant and steady state voltage for most of the electronic components.

• Batteries:

Almost all Modern electronic devices (mobile, laptops, digital watches, etc) use batteries for storage and backup operations, where we know that batteries can’t store AC, but DC only.

These are the exact reasons why most of the modern electronic circuits, devices and components use DC instead of AC.

Good to know: The amount of power is same for both AC and DC signals i.e. 5V AC will generate the same amount of heat as 5V DC when connected to the same heating element (RMS Value).

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Other reasons:

DC is much more easy to control, accurate and easier to propagate than DC signal.

If we use AC in most of electronic circuits instead of DC,

• It will create extra work for just handling the phase-shift between signals.
• It will be harder to supply them by batteries.
• You lose a part of the power when the voltage cross 0.
• If you have single phase, you have pulsating power.
• You need to adapt the frequencies, if you expect them to work together.
• And to design a good grounding would be a pure nightmare.

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