Three Reasons the Summer is Warmer Than the Winter

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A common misconception is that the Earth is closer to the Sun in summer, but it's actually further away. Diagrams would be better for explaining this. I'll get around to it, but I'll try to do it with words for now. 

Less atmosphere to pass through

Because of the greater elevation of the Sun in summer, the distance light has to travel through the atmosphere is shorter than it would be if the Sun were low in the sky. The Sun feels hotter in summer because of this and also the filtering effect is the reason the Sun looks dimmer and redder when it's low in the sky near sunset as light gets scattered and absorbed. Because of the higher intensity of illumination of the Earth's surface in summer, this makes air temperatures higher as the ground warms up and transfers its heat to the ambient air. This atmospheric filtering effect wouldn't happen on the Moon, irrespective of the Sun's elevation, because there's no atmosphere.

Lower angle of incidence

Because the Sun is higher in the sky, when solar radiation hits the Earth's surface, it's spread out less than in winter (compare the difference between a torch shone perpendicular to a wall and at an acute angle). Greater solar irradiance, measured in watts per square metre (W/m²), warms the ground more, which in turn heats the air above it. This is why solar panels are angled so that the Sun's rays strike them as close as possible to right angles, maximising the irradiance they receive.

Longer days 

Because of the tilt of the Earth, days are longer and nights are shorter. This gives more time for the Sun to warm up the ground, raising the average air temperature higher than in winter. Night-time temperatures remain mild because the ground acts as a thermal reservoir and stores heat. If the Sun mysteriously disappeared, ground and air temperatures would continue to fall over days and months to a level hundreds of degrees below 0 °C.

What Are Voltage Regulators Used For?

78XX series of voltage regulators. E.g. 7805 and 7812 having regulated outputs of plus 5 volts and plus 12 volts respectively. Silverxxx, CC BY SA 3.0 Unported via Wikimedia Commons.

We're surrounded by electronic gadgets and appliances, and even devices that don't appear to be electronic may use electronic circuitry internally. For electronics to work properly, it's imperative that voltage be stable and constant. That's the job of a voltage regulator. In this article, we'll explore voltage regulators in a little more detail.

An L7805 linear voltage regulator on a printed circuit board (PCB). This regulator outputs 5 volts at currents up to 1 amp. © Raimond Spekking / CC BY-SA 4.0 (via Wikimedia Commons)

What Is a Voltage Regulator?

A voltage regulator is an electronic device used to keep the voltage output of a power supply at a constant level, independent of the current drawn by a load and changes in the input voltage supplied to it. In general, these devices are implemented as a single integrated circuit (IC) in a variety of package formats or as separate modules, consisting of several discrete components and possibly integrated circuits. A regulator that reduces voltage is called a buck regulator, and one that increases voltage is called a boost regulator.

What Affects the Output of an Unregulated Voltage Source?

The output voltage of an unregulated voltage source depends on:

• Load current: The output of an unregulated voltage source will drop as the current increases. This is because of internal resistance, which causes a voltage drop as current flows. This voltage drop subtracts from the ideal internal voltage source and causes the output of the supply to be lower than the open circuit voltage without a load. We'll examine this in more detail later and work out the equations for output voltage versus load resistance.
• Battery charge state: If a voltage source is a battery, the output voltage can vary depending on its state of charge or discharge.
• Input voltage to the unregulated voltage source: The output voltage of an unregulated power supply powered by the mains can also change as the mains voltage changes.

For more information on basic electricity and volts, amps and watts, see my guide: How to Understand Electricity: Volts, Amps and Watts Explained on Appliances

Block diagram of a voltage regulator. Vout may be greater or less than Vin. © Eugene Brennan

Why Does Voltage Vary if a Regulator Isn't Used? A Detailed Analysis

All linear electrical networks containing only voltage sources, current sources and resistances (which include power supplies and batteries) can be modeled as a Thévenin equivalent circuit with an ideal voltage and a source resistance in series, as shown in the diagram below. The ideal voltage source produces a voltage that doesn't change no matter what current is drawn from it. So, for instance, if the voltage source is 12 V and one million amps are drawn, it still outputs that voltage. Such devices don't exist in real life, and all voltage supplies have internal resistance that causes a voltage drop as the voltage source is loaded.

As current increases through the internal resistance of the source, R_int in the diagram below, it causes a potential drop across the resistor. The potential drop equals the current through the source resistance, multiplied by the resistance R_int. This potential drop subtracts from the ideal voltage V, so the voltage at the output terminals of the Thévenin equivalent circuit at the load R_L, which we'll call V_L is:

V_L = V - IR_int

Any linear electrical network can be modeled as a Thévenin equivalent circuit (enclosed within the red dotted line) with an ideal voltage source V and a source resistance Rint in series. RL is a connected load. © Eugene Brennan

On open circuit, with no load connected (R_L is infinite) and I is zero, so:

V_L = V - IR_int = V - 0R_int = V

The output voltage on open circuit is the same as the ideal voltage source.

What is the output voltage with a load connected?

To work out the voltage with a load connected, we need to find the current I.

The total resistance of the circuit is the sum of the Thévenin equivalent source resistance R_int and load resistance R_L in series.

The current through both resistors is given by Ohm's law as:

I = V/(R_int + R_L)

The voltage at the load equals the current I flowing through the load, multiplied by the resistance of the load. If the load voltage is V_L, then substituting for I from the equation above gives us:

V_L = IR_L = VR_L/(R_int + R_L)

Dividing the numerator and denominator of the right hand side of the equation by R_L gives:

V_L = V/(R_int/R_L + 1)

We can see that if R_L is infinite, i.e., on open circuit:

V_L = V/(R_int/∞ + 1) = V/(0 + 1) = V

So, the output voltage is the same as that of the ideal voltage source.

When RL = 0, i.e. a short circuit:

V_L = V/(R_int/0 + 1) = V(∞ + 1) = 0

The output voltage is zero when the load resistance is zero.

(Strictly speaking, division by 0 is undefined in math, but we can practically think of division by 0 giving an infinite result and dividing by infinity as giving 0 in the equations above.)

In between these values, as the load resistance falls, the R_int/R_L + 1 term in the denominator of the equation increases, and V_L decreases. This is the crux of the problem. As a supply is loaded and load resistance falls and more current is drawn, the output voltage of a non-regulated supply falls. A regulator solves this problem.

It's important to remember that the Thévenin equivalent circuit is just a model, and there aren't actually an ideal voltage source and series resistor component in, for example, an AA cell, bench power supply, lithium battery or power supply in an appliance or gadget. The model just describes how a supply behaves.

What Are the Two Types of Voltage Regulators?

There are two types of semiconductor regulators: the linear regulator and switching regulator.

Linear Regulator

There are two types:

• Series regulator. This uses a pass transistor such as a bi-junction transistor (BJT) or metal–oxide–semiconductor field-effect transistor (MOSFET) and associated circuitry to control voltage. The pass transistor effectively works as a controlled dropper resistor in series between the input supply and the regulator output. A typical regulator has a 5-volt output. So, if the input voltage is 14 volts, it drops that voltage from 14 to 5 volts.

  The control circuitry in the regulator monitors the regulator output voltage, and if the load tries to take more current and output voltage tries to fall, the control circuit reduces the resistance of the pass element so that it drops less voltage in order to maintain the output at a constant 5 volts. Similarly, if the load takes less current, the resistance is increased. A linear regulator is a classic negative feedback control system (like the governor on an engine, keeping speed constant as the load increases/decreases).

• Shunt regulator. This uses a device such as a Zener diode in parallel with the load. A Zener diode has a characteristic such that the voltage drop across its terminals is relatively constant, independent of the current through it. By placing the diode in parallel with a load, this has the effect of stabilising voltage and keeping it the same as the Zener diode voltage.

Disadvantages of Linear Regulators

Since the pass component in the regulator is in series with the load, the current supply from the source is the same as that supplied to the load. However, since the voltage is dropped by the pass component, power is wasted as heat in the device. The higher the input voltage, the greater the wastage since P = VI, where V is the drop across the regulator, I is the current through the load and P is the power, dissipated as heat. The lower the input voltage, the better, and a small or large heat sink may be needed, depending on the ambient temperature and voltage drop. Basic regulators need about a 2-volt difference between input and output voltages to work, but low-dropout regulators are available, which can work with a smaller difference between IP and OP.

Voltages and Packages

Linear voltage regulators are commonly available in the TO220 package with voltages of ± 5 V, 6 V, 9 V, 12 V, and 15 V. The 780XX series can output a current of up to 1.5A. Regulators with higher current outputs are also available in different packages. Adjustable voltage regulators, such as the LM317, are also available.

Block diagram of a series linear regulator. © Eugene Brennan

A basic regulator made from discrete components can be made using a pass transistor, Zener diode and resistor to bias the diode. The Zener diode acts as a reference voltage, the potential drop across it staying relatively stable as the voltage of the unregulated input to the power supply varies.

Taking KVL about the base circuit:

V_D = V_L + V_be

So V_L = V_D - V_be

If the load increases and V_L tries to fall, V_D remains constant. However, V_be increases, causing an increase in base current. This increases the collector current and decreases the collector-emitter voltage, increasing V_L to compensate.

Schematic of a basic voltage regulator. The Zener diode sets a reference voltage and the transistor keeps the output voltage reasonably stable as current changes. © Eugene Brennan

Switching Regulators

A switching regulator, on the other hand, works differently. Unlike a linear regulator, which can be very inefficient and waste power as heat, switching regulators can be up to 95% efficient. In buck mode (reducing voltage), they work by chopping the input voltage to the regulator into a pulsed waveform and applying this to a capacitor/inductor, which effectively works as a tank, smoothing the chopped waveform (analogous to the way an engine flywheel smooths the pulsed intermittent power from the cylinders). The duty cycle (how long the pulse is on) of the switching waveform is varied depending on the demand of the load in order to keep the op voltage constant.

Disadvantages of Switching Regulators

Since a switching regulator runs at high frequency, switching voltages on and off can generate a lot of electromagnetic interference (EMI). Most countries have regulations for the amount of EMI emitted by products sold, governing the level of both interference radiated through the air and through power cords. Most appliances have EMI filters to reduce this interference, but some still get transmitted. If you turn on a radio and switch it to the AM band and tune away from a channel and hold the radio close to a device such as a computer or a phone, you can hear the interference as noise on the radio.

Another issue with switching regulators is that switching noise can make its way to sensitive electronics in the device. So extra filtering is necessary to reduce this.

References

Boylestad, Robert L. (1968). Introductory Circuit Analysis. (6th ed. 1990) .Merrill Publishing Company, London, England.

Donald G. Fink, H. Wayne Beatty (1978). Standard Handbook for Electrical Engineers Eleventh Edition, Mc Graw Hill.

Millman, J., & Grabel, A. (1987). Microelectronics. McGraw-Hill.

Linear and switching voltage regulator fundamental part 1. Texas Instruments. https://www.ti.com/lit/an/snva558/snva558.pdf

Disclaimer

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualised advice from a qualified professional.

© 2022 Eugene Brennan