Charging

Question 1

What do most diodes need?

Answer 1

Most diodes need a voltage of about 0.6 V before they start to work.

Question 2

Diode Bias

Answer 2

• When a diode is connected so that a current passes, it is forward biased.
• When a diode is connected so that no current passes, it is reverse biased.

Question 3

Half wave rectification

Answer 3

• An AC supply to a single diode produces a half-wave rectified output.
• A resistor is always used in series with a diode to protect the diodes.

Question 4

What does a diode consist of?

Answer 4

• A diode consists of a piece of n-type and a piece of p-type semi-conductor join together
• N-type semi-conductor has a excess of electrons.
• P-type semi-conductor has a shortage of electrons - the gaps are called holes.
• The space between either side of the junction has no electrons or holes.

Question 5

Connecting the positive terminals into the p/n type semiconductor.

Answer 5

• If the positive terminal of the supply voltage is connected to the n-type semiconductor, the space widens and no current passes.
• If the positive terminal of the supply voltage is connected to the p-type semiconductor, the space narrows, eventually disappears and a current passes.

Question 6

Rectifier circuits

Answer 6

• Four diodes can be arranged to make a bridge circuit.
• The addition of a large capacitor makes the output smoother.

Question 7

Capacitor Action

Answer 7

• When a DC supply is connected to a capacitor, the capacitor becomes charged. The voltage across the capacitor increases until it is equal to the supply voltage.
• When the capacitor is connected to a resistor, for example, the voltage decreases as the capacitor discharges.

Question 8

What happens in a bridge circuit?

Answer 8

• During the positive half cycle, the current passes from A to B, to the external circuit to the external circuit, to D then C and back to the AC supply.
• During the negative half cycle, the current passes from C to B, to the external circuit, to D then then A and back to the AC supply.
• This means that the DC output is always positive at B and negative at D

Question 9

Storing Charge

Question 10

Smoothing

Answer 10

A capacitor acts as a reservoir. When DC voltage from the rectifier circuit falls, the capacitor supplies current to the output. The capacitor charges near the peak value of the varying DC.