What is Diode Valve? Explain it.

A diode valve is a type of electronic component used to control the flow of electrical current. It allows current to flow in only one direction, effectively acting like a one-way gate. In simple terms, it helps to manage and direct electrical signals, making it essential in various electronic devices and circuits.

Explanation

A diode valve consists of a cathode which can be heated to a high temperature to emit electrons and an anode which can collect these electrons. The cathode and the anode are sealed in an evacuated glass bulb. The cathode is also called filament and the anode is also called plate. In one design, a pure tungsten wire or a thorium-coated tungsten wire is used as the cathode. This wire can be directly connected to an external circuit driving current through it and hence increasing its temperature. In another design, a hollow nickel tube coated with barium oxide is used as the cathode. The tube surrounds a heater coil. When the external circuit drives a current through the heater coil, the nickel tube gets heated by radiation. The anode is in the form of a hollow nickel cylinder which surrounds the cathode. Potential difference may be applied between the cathode and the anode by connecting a battery through the leads coming out of the sealed valve. The positive terminal of the battery is connected to the anode and the negative terminal to the cathode.

(Figure (41.9) shows the symbolic representation of a diode valve and the circuit to study the current through the valve. When the cathode is heated, it emits electrons. These electrons are attracted towards the anode when a positive potential V, (with respect to the cathode) is applied to it. This potential V, is called the plate voltage. The electrons pass through the battery and then return to the cathode. Thus, an electric current ip is established in the circuit which can be measured by the ammeter connected in the circuit. This current is called the plate current. If the plate voltage V_p is changed, the plate current i, is also changed. A set of plots between the plate current and the plate voltage is called diode characteristics.