Industrial Electronics

How to select a voltage regulator

16 July 2020

A voltage regulator is a device that is simple and cost-effective. Input voltage can be changed to another level at the output by using this device. It is also useful in varying load conditions as it can maintain a constant voltage at the output. The usage of voltage regulators ranges from small electronic devices like a smartphone charger to complex electromechanical devices that provide different DC voltages per device requirement. Voltage regulator chips are also used in all power supply circuits.

Types of voltage regulators

There are two types of regulators that are worth considering:

1. Linear regulators: This type of regulator is relatively simple, cheap and noise-free; however, they may exhibit low power efficiency. They can only be used for stepping down the voltage.

2. Switching regulators: This type of regulator is more complex, relatively expensive and nosier. However, have high power efficiency. They can be used for both stepping down and stepping up the voltage.Source: AdobestockSource: Adobestock

Important factors for voltage regulator selection

Take the example of a smartphone: A voltage regulator is used in smartphones to step-up or step-down the voltages of the battery for the components per their requirements. By choosing the inappropriate voltage regulator, you can risk the reliability of the product or it may result in higher power consumption or burnt components.

To avoid such a situation, the following are the parameters to remember when you are choosing a voltage regulator.

1. Input voltage and output voltage

The very first step in selecting a regulator is to know about the input voltage and the required output voltage for your project. If you want to use a linear regulator, then the input voltage must be higher than the required output voltage. If the required output voltage isn't less than that of input, it will cause a condition of insufficient voltage that results in dropping out of the regulator and end up providing unregulated output.

For instance, for having a regulated voltage by using a 5 V regulator with 2 V dropout voltage, the input voltage must be equal to at least 7 V, otherwise, it will result in unregulated voltage at the output.

2. Dropout voltage

The dropout voltage of the regulator can be defined as the difference of the input and output voltage. For instance, the minimum input voltage for a regulator (7805) is 7 V and the output is 5 V, so the dropout voltage for 7805 is 2 V. If the input voltage is less than 7 V, the output (5 V) plus dropout (2 V) will cause an unregulated output that is dangerous for your device.

Different regulators may have different dropout voltage; say a rand of 5 V regulators can be found with different dropout voltage. Linear regulators with very low dropout voltage can be very efficient. So, a low dropout regulator can be used for better efficiency if a battery is used as a power source.

3. Power dissipation

Linear regulators are relatively cheap and easy to use but a drawback is they tend to waste a lot of power. And this waste can result in excessive battery drain, product damage or overheating. If you use a battery product that wastes power as heat, it will cause your battery to drain out quickly. If it is not a battery product however it is still producing a lot of heat and it will result in other issues with your project. A lot of heat can be produced by a linear regulator, under specific circumstances, that can destroy the device itself.

While using a linear regulator, begin with finding out how much power will be dissipated by the regulator.

For linear regulators, use this equation:

Power = (input voltages - output voltages) * current

As is clear from the above equation, if the voltage differential is large across the regulator (Vin-Vout) and has a high current load, then a lot of power will be dissipated by the regulator. Let's say the differential is 8.7 V with 12 V as input and 3.3 V as output, and the current load is of 1 A, then 8.7 W of power will be dissipated by the regulator. A lot of power is wasted and is more than any linear regulator can handle.

On the other hand, if the voltage differential is high but the current load is only of a few milli-amperes then the dissipated power will be small. Take the above example but this time the current load is only a 100 mA instead of 1 A; then power dissipation will be dropped down to 0.87 W that can be managed easily by most voltage regulators.

Power dissipation can also be avoided by using a switching voltage regulator as compared to a linear regulator.

4. Efficiency

The ratio of output to input power is the efficiency that has direct proportional relation to the ratio of the output voltage to input. Therefore, the efficiency of regulators is limited by the quiescent current and the dropout voltage of the regulator as the higher dropout voltage will result in lower efficiency.

The dropout voltage of the regulator and quiescent current need to be minimized as well as the difference of input and output also needs to be minimized in order to have higher efficiency.

5. Voltage accuracy

The accuracy of the voltage regulator depends on the following:

· Line regulation

· Load regulation

· Reference voltage drift

· Error amplifier voltage drift

· Temperature coefficient

The output voltage specification of a typical linear voltage regulator ensures that regulated voltage will be within 5% of nominal voltage. Thus, if a regulator is being used to power the digital ICs then the tolerance of 5% is not a big deal.

6. Load regulation

The ability of the circuit to maintain a certain output voltage under changing load conditions is known as load regulation. It can be expressed as:

7. Line regulation

The ability of the circuit to maintain a certain output voltage under changing input voltage conditions is known as line regulation. It can be expressed as:

Conclusion

One must consider all the above-mentioned factors while selecting an appropriate voltage regulator for any application. It will not only increase the reliability of the voltage regulator, it will increase the lifetime of all the components powered by the voltage regulator.

To contact the author of this article, email engineering360editors@globalspec.com


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