Understanding The Purpose Of Some Electronic Components In Electronic Circuits.

An electronic circuit consist of few or lots of electronic components for it to function properly. The electronic circuits such as the power supply, vertical, horizontal, high voltage, scanner, audio, color, memory, inverter, converter, feedback and etc are the circuits that forms the purpose of electronic equipment. In other words, different electronic equipment have different task because it has different types of electronic circuits in it. This month article is about to reveal the purpose of some electronic components in those electronic circuits. Let’s begin and analyse those components.

Relay

If you have repair electronic equipment before, I believe you have definitely seen a relay in electronic circuits. Sometimes in a circuit can have more than few relays. A relay is basically a switch operated by magnetic force. This magnetic force is generated by flow of current through a coil in the relay. The function of a relay is to open or close a circuit, when current through the coil is started or stopped. Now, the question is why there is a diode located parallel to the coil in the relay as seen from the schematic below?

The diagram shows how a signal diode (eg 1N4148) is connected across the relay coil to provide this protection.

Current flowing through a relay coil creates a magnetic field which collapses suddenly when the current is switched off. The sudden collapse of the magnetic field induces a brief high voltage ‘spikes’ across the relay coil which is very likely to damage ICs and Transistors. The diode which is also called as protection diode allows the induced voltage to drive a brief current through the coil (and diode) so the magnetic field dies away quickly rather than instantly. This prevents the induced voltage becoming high enough to cause damage to ICs and transistors.

Damper Diode

Whenever I draw the diagram of the high voltage circuit of a Monitor, many times my students asked what was the function of the damper diode connected across collector and emitter pin of  horizontal output transistor (HOT). For your information the damper diode can be found built into the HOT or in the circuit. Because of the high inductance and interwinding capacitance of the yoke and flyback transformer, the circuit must be damped out during retrace to prevent ringing. In other word, the damper is used to prevent oscillation in electronic circuit.

Note: Ringing means unwanted oscillation of a signal.

Zener Diode In FET

You may wonder why there is a zener diode connected internally between the drain and the source pin. Mosfets are really sensitive to overvoltage (large voltage spikes) conditions so, to prevent reactive load spikes from destroying your MOSFET (when it switched off) a zener diode is commonly added across the source to drain.

Note: For your information, in some electronic circuit, the zener diode can be connected externally.

RCD Clamp Network

RCD means resistor, capacitor and diode. If you have seen a power supply schematic before, I’m sure you had came across such components that are located besides the primary winding as seen from the schematic diagram below. The function of these circuit (or components) is more or less the same like the damper diode. Whenever the power FET turns off, the leakage inductance of the transformer induces a voltage spike on the drain node. In order to protect the power FET against (inductive) spikes from the transformer primary and to reduce ringing, components R1, C3 and D1 are placed in the circuit. The amplitude of the spike can now be limited by this circuit. 

Conclusion- Of course there are lots more of electronic circuits in the market and there is no way I can reveal all of them. May be you can take this article as a guide to help you to find out the purpose of those electronic components that found in your type of electronic equipment that you are working on.

The advantage of knowing such components in those circuits is that when you want to design electronic circuits, at least you will know what type of components you should put in that circuit. Even if you are not designing any electronic circuits, at least you know the function of those components in the electronic circuits. All right, that’s all for this month and see you again next month.

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