This voltage now needs to be referenced with respect to one of the two other terminals and we will use terminal Y for our purposes here. The voltage on terminal Z now controls the amount of current in terminals X and Y. The ratio of IX to IY which is always less than unity, is also a measure of the device gain and is most often represented by the Greek letter α (alpha).įor the voltage controlled device let's assume, as we did before, that the current flows into terminal X and out terminal Y. The ratio of IX to IZ is the gain of the device and the Greek letter β (beta) is used to represent this gain. To make the device useful it would be desirable to have the control current IZ very small relative to the much larger controlled current IX. Conservation of charge tells us that the sum of the currents flowing into a box must equal the sum of the currents flowing out. In the case of a current controlled device, let's assume that the control current IZ, flows into terminal Z and back out terminal Y. The same can be said for the voltage seen at terminal Z with respect to terminal Y and voltage VZY is a positive number. Because current flows into terminal X, we generally assume the voltage seen at X is greater than terminal Y and voltage VXY is a positive number. To describe the function of this block we first need to define the terminal currents IX, IY and IZ, and the terminal voltages VXY and VZY as shown in the figure. The third terminal, Z, is the control terminal. Let's also assume that the controlled current flows into terminal X and back out terminal Y. It has three terminals we will call them X, Y and Z for the moment. It is sometimes incorrectly attributed to a contraction of transresistance.Ī simple and general form of such a device is shown in figure 8.1.1. The first type of transistor successfully demonstrated was a current-controlled device.Īs a side note: The origin of the term transistor is a contraction of “transconductance varistor”, as Devices working on the principle of one current controlling another current are known as current-controlled devices. ![]() ![]() Devices utilizing a voltage as the controlling signal are, not surprisingly, called voltage-controlled devices. ![]() One type of active device uses a voltage to control the current while another type of active devices uses another current to be the controlling signal. All active devices control the flow of current through them. For a circuit to be called electronic, it must contain at least one active device. An active device is any type of component with the ability to electrically control the flow of current (controlling one electric signal with another electric signal).
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![]() ![]() Recommended salt intake for Australian childrenĪustralian children are eating too much salt External Link too. Sodium intake above 2,000mg per day is associated with high blood pressure, which is a risk factor for kidney disease and cardiovascular disease (such as heart disease and stroke). An adult body only needs around 1 to 2g of salt (460 to 920mg sodium) per day to function. The National Health and Medical Research Council (NHMRC) advises that Australian adults should aim to consume no more than one teaspoon (5 grams) of salt a day (or 2,000mg of sodium a day) in order to prevent chronic disease.Īiming for less than this is perfectly okay too. The average Australian consumes almost double the amount of sodium they need for good health. On the other hand, if sodium levels drop too low, the hormone aldosterone is released, and this increases the amount of sodium held in the body by reducing the amount lost in urine.Įxcessive sodium loss is very rare, but low sodium levels in the body can be dangerous if not treated. Too much sodium can cause high blood pressure and many other health conditions. The kidneys are the main regulators of sodium levels in the body. However, most people consume much more sodium than they need. It is commonly used to preserve and flavour foods and is the main source of sodium in our diet.Ī small amount of sodium is important for good health as it helps to maintain the correct volume of circulating blood and tissue fluids in the body. Salt is a chemical compound (electrolyte) made up of sodium and chloride. |
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