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Posted on 01 April 2019

Power Trends in Television

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New Power Solutions for HDTVs

With growing attention on energy conservation around the world, auto companies are not the only ones making the move towards higher efficiency. Every Company in consumer electronics is doing their part in order to adapt to the changing times. As of November 1st, 2008, new Energy Star® program requirements (Version 3.0) for televisions were introduced.

By Brian Huang, John Lee and Cam Jackson, Product Marketing, Micrel, Inc.

 

Prior to Version 3.0, TV manufacturers simply had to limit power consumption during “standby” modes which basically limited power consumption when the TV is off to below one watt. The goal of Version 3.0 is to set new standards to reduce TV power consumption while the TV is on and to further push manufacturers to develop more efficient models. In order to comply with more stringent requirements, manufacturers are eager to find new solutions that will lead to superior products. This article will discuss new technological power solutions for TVs that will improve performance.

Low Dropout (LDO) Linear Regulators

A typical LDO converts a higher input voltage to a lower output voltage. Voltage regulation is achieved by dissipating power across a bipolar junction transistor (BJT) and is controlled by the error amplifier (EA) and feedback resistors (R1, R2), as shown in Figure 1.

Typical LDO Regulator Circuit

LDOs are simple to use, fast, have very low output noise and ripple, and can be relatively inexpensive. One huge drawback inherent to LDOs is efficiency. The power dissipation across the BJT of a typical LDO is equal to the voltage drop (Vdrop) multiplied by the current through the BJT. As current increases, the power dissipation increases. When the input voltage is much higher than the output voltage (Vdrop increases), the power dissipation increases even more. In addition, the combination of a high input voltage with a low output voltage results in a lower efficiency for LDOs. At higher currents, this combination can lead to over heating and poses a problem for electronic designers. This LDO problem is widely known and the reason switching regulators were developed.

Switching Regulators

In today’s electronics industry, it is very common for switching regulators to achieve 90 percent efficiency. A switching regulator converts power by utilizing the electrical properties of inductors, capacitors and some transistors to store and transfer energy. There are three main types of switching regulator configurations — the buck (stepdown), the boost (step-up) and the fly-back (buck and boost) regulator.

Similar to the LDO, the buck regulator converts a higher input voltage to a lower output voltage. Figure 2 shows a typical buck regulator circuit. Two power transistors (Q1, Q2) connect and disconnect the input from the output. By doing so, the transistors alternately deliver energy to the output at a specific frequency.

Typical Synchronous Buck Regulator Circuit

By managing the amount of power delivered from the input to the output using the inductor’s inherent properties and the switching of the transistors, the buck regulator does not need to dissipate as much power, unlike LDOs.

The efficiency comparison between a typical constant frequency, pulse-width-modulated (PWM) buck regulator and a LDO is shown in Figure 3.

Efficiency Comparison

HyperLight LoadTM (HLL) Mode

The Micrel HyperLight LoadTM Buck Regulator Family is one of the most advanced switching regulators available on the market today. “Hyper” refers to the ultra-fast load transient response. “Light Load” refers to high efficiency at light loads. The HLL buck regulator family was developed to fill the need in the electronics market for unconditional high efficiency, ultra-fast transient response, ease-of-use with few external components and a minuscule solution size.

“Hyper”

Just like PWM buck regulators HLL regulators uses the properties of inductors, capacitors and transistors to alternately deliver energy to the output. Unlike PWM buck regulators, the HLL control scheme only needs one error comparator and some feedback resistors to control the output voltage.

The HLL transient response is ultra-fast because any change in the feedback is immediately compared by the control circuitry. The main difference between HLL and other switching regulators is that it does not have an Error Amplifier before the comparator, eliminating the delay to charge the compensation capacitor often used at the output of the Error Amplifier. By design, the lack of an Error Amplifier removes an extra block in the control loop and reduces the amount of time it takes to respond to load changes. As a result, the load transient response of HLL devices is one of the fastest in its class.

“Light Load”

The HyperLight LoadTM has two modes of operation that is internally determined, depending on the load. At low output currents (discontinuous mode) it is governed by pulse frequency modulation (PFM). At higher output currents (continuous mode) it is governed by a constant-on-time, controlled off-time, control scheme. The combined control method is what allows the HLL buck regulators to be efficient under all load conditions.

Typical constant frequency PWM buck regulators have been shown to be less efficient at light loads due to switching losses. In order to improve efficiency at low output currents, HLL buck regulators operate in pulse frequency modulation (PFM). Since the output current is low, the output capacitor can maintain the voltage longer during the Q1 off-time. During the Q1 on-time, the output voltage increases, but is slowly being pulled down by the load. During the Q1 off-time, everything is turned off in the control loop except the band gap and the comparator. This saves power during the off-time. As the output voltage slowly decreases, it is being compared to the band gap voltage. Once it is below the band gap voltage, the comparator immediately tells the control loop to turn the Q1 transistor on again. The switching frequency increases and decreases with the output current in discontinuous mode. This reduces excessive switching and reduces power loss. This makes the HLL buck regulators efficient, even at light loads. At higher output currents the HLL buck regulators behave like other PWM buck regulators and switch at a constant frequency. Figure 4 shows the efficiency comparison between a LDO, a typical switcher and Micrel’s HyperLight LoadTM regulator.

Efficiency Comparison with HyperLight LoadTM

Conclusion

As the globalization of electronics continues to spread throughout the world, the reason for energy conservation will become more and more prominent. Micrel’s HyperLight LoadTM product family represents a technology developed to address the need for unconditional high efficiency, ultra-fast transient response and the smallest possible solution size. In order to preserve the planet for future generations, our generation must continue to think forward, develop ideas and continue the innovations required to surmount the challenges we face. HyperLight LoadTM was developed based upon the awareness in the importance of conservation of energy in modern electronics and is the result of Micrel’s innovation through technology.

HyperLight LoadTM is a trademark of Micrel, Inc.

 

 

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