10/9/2016

Dear Friends and Fellow Americans,

I am not prone to writing public letters. However the current state of affairs in our country has moved me to write. I will be direct and to the point.

Problem

In the Bible, at 2 Chronicles 7:13-14, God says, “¹³When I shut up the heavens so that there is no rain, or command the locust to devour the land, or send pestilence among My people, ¹⁴if My people who are called by My name humble themselves, and pray and seek My face and turn from their wicked ways, then I will hear from heaven and will forgive their sin and heal their land.”

I believe that we as a country have completely lost our moral compass. This belief is substantiated by our current political predicament where we have two very clearly and very corrupt and morally bankrupt candidates as the front runners for President of the United States. As a country we have not figured out how to elect a decent person for the most important leadership position in the world.

I am a big believer in the importance of historical lessons. Consider the Roman Empire. Rome was arguably the vastest empire this world has ever known. But it was when Rome became morally bankrupt that she diminished and was ultimately conquered.

Today, the United States, after having experienced the blessings of the Lord for two centuries, is experiencing the same moral decline. But the Lord, in His Word, has graciously and mercifully provided a path back to His blessings as described in the above quoted verse of 2 Chronicles 7:14.

Solution

Our actions need to be to,

1. Humble ourselves,
2. Pray and seek God’s face,
3. Turn from our wicked ways.

Then God says that He will hear us from heaven, forgive our sin, and heal our land.

Application

Humble ourselves – Acknowledge that we are God’s creation, needing the salvation of the Lord Jesus Christ from our sin, and made to be His servants in the work of glorifying Him and loving and respecting others in His Name.

Pray and seek God’s face – Get a Bible, read it as it is God speaking to you about His plan for you, and pray to the Lord that He will guide and direct your steps for His Glory.

Turn from our wicked ways – Know what the Bible says about right from wrong. Do right and turn away wrong while loving God and your fellow man.

Immediate Application — November Election

In less than a month, we will be casting lots, or voting, for candidates for office including President of the United States.

In Proverbs 1:14, the wicked says, “Thrown in your lot with us. We shall all have one purse.”  But God says in the next verse, “My son, do not walk in the way with them. Keep your feet from their path, for their feet run to evil and they hasten to shed blood.”

No doubt, you have by now heard in the news media that we must choose the lesser of two evils regarding Hillary Clinton and Donald Trump. But the Bible says in Romans 3:9, “And why not say…”Let us do evil that good may come”?  Their condemnation is just”

In light of the apparent quandary in choice for President of the United States, I would like to highlight two alternative candidates that I believe would be solid, conservative, and pro-life.  These candidates may not be on the ballot in all fifty states and territories, but you can always write them in.

Dan Castle – Constitution Party   http://castle2016.com/platform/

Evan McMullin – Independent     https://www.evanmcmullin.com/

While these candidates may not have the charisma of the leading candidates, we have to ask ourselves, “What do we want in a president?”  Remember that when God chose David to be king, David was the least of his brothers. But David was a man after God’s own heart.

I urge you to consider your vote. Do not cast your lot in with the wicked. Do not settle for the lesser of two evils. Instead, vote for a person who you know would honor the office of President of the United States. Trust in the Lord to resolve all of the attendant issues such as Supreme Court Judge of the United States.

Yes it would seem that it would take a miracle at this point for anybody else than Hillary Clinton or Donald Trump to be elected as President.  But then – a miracle is a small thing for the Creator of the universe.

To God Alone Be Glory.

Robert W. Stowe
Marion, IA

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This tutorial installment is: Power Supply Efficiency. This topic answers the following questions:

• What is power supply efficiency and how is it defined?
• How is power supply efficiency defined?
• What are the effects of efficiency on power converter design?

To view a different topic, go to the Power Supply Tutorial table of contents.
Last topic: Linear Supplies
Next topic: Power Supply Capacitors and Inductors

Power Supply Efficiency: Introduction

Efficiency is typically thought of as a measure of how well a product performs its task without waste. When waste is reduced through improved efficiency, there is typically less cost. In the case of a converter, efficiency is a measure of how much power at the input appears at the output, and therefore less waste. Obviously, it is important, and considered technologically “green”, to conserve energy, especially in the case where a battery is the source of energy. However, efficiency, as applied to electronic power supplies, has a far more important aspect than just conserving energy. Power supply efficiency has a direct effect upon the upper limit of output power given a package size and mode of cooling. This consideration often dominates the design of a converter, especially since there is almost always a drive toward size reduction and miniaturization of electronics products.

Power Supply Efficiency: Definition

Very simply put, power supply efficiency is the output power divided by the input power:

Effects of Efficiency in Power Converter Design

The Law of Conservation of Energy is always observed. Therefore the energy that goes into a power converter must equal the energy that comes out plus some waste energy. This waste energy normally is in the form of heat. Power in and out of a power converter obeys the following relationship:

In terms of efficiency, the waste heat can be expressed as:

Poor efficiency means greater waste heat to manage. To illustrate the importance of efficiency, consider the following example. Two DC/DC converters are operated at room temperature, each processing 200W at the output. Each converter is in the same size package which has a thermal resistance to heat transfer of 2 deg C per watt. Converter A operates at a state of the art efficiency of 95%. Converter B operates at an efficiency of 80%. The waste power for converter A operating at 95% efficiency would be about 200W * (1 / 0.95 – 1)=10.53W. At room temperature, with a case to ambient thermal resistance of 2C/W, the case temperature would be about 46C, cool enough to hold in the palm of your hand while processing 200W. The waste power for converter B operating at 80% efficiency would be about 200W * ( 1 / 0.80 – 1) = 50W. At the same room temperature and the same case to ambient thermal resistance, the case temperature would be about 125C, hotter than boiling water and hotter than many electronic components are rated for! To solve the problem of excessive temperature rise, one or more of the following actions must happen:

• The efficiency must to increased to lessen the waste energy which is dissipated as heat,
• The package size must be increased to provide more surface area for heat transfer which reduces the case to ambient thermal resistance,
• Active and/or conduction cooling techniques must be employed,
• The processed power must be reduced.

The first choice would be to improve efficiency as the other choices are usually not desirable. Thus efficiency is a vital measure to converter performance. Any generated waste heat must be removed by a heat transfer method which keeps the component temperatures within a range for acceptable reliability. If efficiency can be kept high, then the burden of waste heat transfer methods to keep the component temperatures in an acceptable temperature range is much less. Linear supplies with low efficiency must have larger package sizes, or forced cooling, or lower power output. Whereas, switching supplies which typically have efficiencies starting at around 80% can enjoy smaller package sizes, perhaps no forced cooling, and higher power outputs.

Next Topic

The next tutorial installment is: Power Supply Capacitors and Inductors. This next topic will answer the following questions:

• What is the purpose of capacitors and inductors in power electronics?
• What are the energy storage and terminal time properties of capacitors and inductors?
• What are the power supply applications of capacitors and inductors?

If you need assistance with power electronics design, call or email us today for help with your requirements. You can also go to our power electronics consultant website for more information about our services for business clients. Thank you for reading this tutorial article entitled “Power Supply Efficiency”

Next topic: Power Supply Capacitors and Inductors

Back to Power Supply Tutorial table of contents.

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