Power supplies literally keep devices running. Even when devices have internal batteries, these need periodic recharging with a power supply. It’s therefore obvious that power supplies are essential for technology to function. It’s becoming increasingly appreciated that choosing the right power supply can make a significant difference to an item’s functionality.
The basics of power supplies
All power supplies have to conform to the standards of the mains power supply. This varies from place to place. For example, the UK mains power supply delivers a current of 240 volts and 50 Hertz. In the USA, by contrast, the mains power supply delivers a current of 120 volts and 60 Hertz.
This is why power supplies are produced and tested with a particular region in mind. It’s also why just using a basic adapter on a power supply will not necessarily make it suitable for use in a different region. Generally, the shape of the plug is not the main issue. The main issue is the nature of the current.
Bespoke power supplies need to be capable of delivering a suitable level of watts within a suitable time. In other words, they need to deliver enough power for the device to function and/or enough power for it to charge reasonably quickly. What this means in practice, of course, depends on the item. For example, a power supply that was perfectly suitable for a phone would not be at all suitable for an electric car (and vice versa).
The mechanics of power supplies
Local electrical standards and the needs of the device give power supply manufacturers a basic idea of what is required. It’s then up to them to work out how best to implement this. Their first decision is whether the power supply should be unregulated or regulated.
Unregulated power supplies have only three components. These are a transformer, a rectifier and a low-pass filter. Unregulated power supplies only really work with fixed output current or voltage because the voltage changes with the load-current draw. As a result, they tend to create a lot of AC noise such as ripple voltage.
With that said, unregulated power supplies are affordable, simple, robust and efficient. This is why they are also known as “brute-force power supplies”. They may become obsolete eventually. For now, however, they still have their uses.
Regulated power supplies, as their name suggests, are designed to regulate the electrical current. This means that they can deliver a consistent voltage that can be precision-tuned if required. They also reduce or eliminate noise. The disadvantage of regulated power supplies is that they are more complex than unregulated power supplies. This not only makes them more expensive but more vulnerable to failure.
Linear power supplies
A linear-regulated power supply is an unregulated power supply plus a transistor circuit that operates in its linear (active) mode. A linear regulated power supply essentially takes the standard input voltage and reduces it as necessary until it meets the maximum output voltage for the load.
This means linear power supplies have two main shortcomings. Firstly, they cannot increase voltage. Secondly, the voltage they discard is converted into heat. This means that heat-management can become a major issue. The need for cooling also tends to create noise.
Switched power supplies
Switched power supplies take their name from the fact that they can turn any current into any other type of current by a process of switching it between AC and DC. This is why they are also known as "universal" power supplies. Switching power supplies are the power supplies you need to make an electrical device work in a different region.
The main shortcoming of switched power supplies is that they are extremely complex to manufacture. This makes them more expensive. Switched power supplies also generate more mains pollution and higher noise.
Ripple power supplies
Ripple power supplies consist of an unregulated front-end and a linear-regulated back-end. This means that, effectively, they are brute-force power supplies with the rougher edges smoothed off.
Luke Timmins is the Sales Controller at PSU Designs, industry leading power supply designers who offer bespoke solutions across a wide range of industry applications.
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