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Sometimes We Don’t Need All of that Energy by Britt Storkson Owner, P2FlowLLC The average automobile has considerable power available to climb hills and accelerate quickly from a stop. Often, we don’t need all of the power at one time. Many times, we are slowly making our way through traffic or traveling down the highway at moderate speeds. We need to be able to adjust the speed and power of the vehicle so we have it when we need it, yet conserve it when we don’t. DC (direct current) electric motors and electronic components have the same need for speed/power control. We need power (voltage x amperage) available to use, but also must be able to limit the power when we don’t need it. We limit the power by limiting (regulating) the voltage, and there are basically two ways to do this: 1. Dissipate the unneeded power away as heat. 2. Shut off the power periodically to limit the energy flow to the load. The first method is called linear voltage regulation. A transistor, essentially, acts as an adjustable resistor that becomes a higher resistance when the current load is lower, and becomes a lower resistance when the current load is higher using an internal voltage- sensing feedback circuit. These voltage regulators are cheap, reliable, and used in many electronic items all over the world. There is one disadvantage here, and it’s a big one. Whatever energy we don’t use is dissipated as heat, and this heat can be considerable. Say we want to reduce the voltage from 24 volts to 12 volts at 1 amp. We have 12 volts at 1 amp “unused” so to speak that doesn’t go through the load. The energy must go somewhere, so it is dissipated as heat. In this case, 12 volts x 1 amp = 12 watts. We have to “get rid of” 12 watts of heat/energy if we want to maintain 12 volts at 1 amp on the output. This heat dissipation can be considerable, so cooling fins and cooling fans must be used to remove the heat. This is undesirable for a number of reasons. It can be a big waste of energy, and the electronic enclosures must be vented with the heat routed to someplace where it isn’t going to hurt anything. This is why linear voltage regulators are used only for low power applications where power dissipation isn’t a big issue. The second method is called switching regulation. We implement voltage regulation by switching the voltage off and on rapidly using one or more transistors so the load “sees” the correct voltage. This is done using a technique called Pulse Width Modulation (PWM). A microprocessor (typically) switches the higher input voltage off and on rapidly so it limits the amount of energy getting to the load. See the illustration: So, the only energy losses are the voltage losses sustained as the current flows through the transistor, which are very small relative to the amount of current (amperage) switched. We get a higher average voltage by turning the transistor(s) “on” for longer periods of time relative to the “off” time. Conversely, we get lower average voltages by keeping the switching transistors off for longer periods relative to the on time. This is also how variable frequency drives work, but different in that the PWM pulses generated are tailored to service an AC (alternating current) three-phase induction motor. While it’s more complicated to implement, the idea is the same. The microprocessor also monitors the output voltage and adjusts the PWM pulse width to maintain the proper voltage, even under widely varying current loads. This is called a switching regulator. The advantage is much less power dissipation for a given current load. The only energy losses are through the switching transistor(s) when current (amperage) is flowing through the transistor when the transistor is fully switched on. Of course, there is very little power dissipation when the transistors are fully switched off. The disadvantage is there are more components, which add to the size and cost of the device, but like most things electronic, as more and more of these devices are used the reliability goes up and the costs go down. So switching power suppl ies are replacing l inear power supplies in just about every application. Britt Britt Storkson may be contacted via e-mail to michele@ worldwidedrillingresource.com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orldWide Drilling Resource ®