HELP16

Question

Answer 1

QUESTION 6

6.1)

There are three methods of switching off the SCR(Silicon-controlled rectifier).

(1) Natural commutation :

When the anode current is reduced be­low the level of the holding current, the SCR turns off.

(2) Reverse bias turn-off :

A reverse anode to cathode voltage (the cathode is positive with respect to the anode) will tend to interrupt the anode current.

(3) Gate turn-off :

In some specially designed SCRs the characteristics are such that a negative gate current increases the holding current so that it exceeds the load current and the device turns-off.

Answer 2

6.3)

Step 1 :

6.3.1)

Traic :

D. TRIAC is a bi-directional trigger used as an AC switch.

6.3.2)

Diac :

A. DIAC is a multilayer three-terminal, bi-directional semi-conductor device.

6.3.3)

SCR :

B. A silicon-controlled rectifier (or semiconductor-controlled rectifier) is a four-layer p-n-p-n device.

6.3.4)

LASCR :

E. A light activated silicon controlled rectifier is a four-layer p-n-p-n device turned on by light.

6.3.5)

QUADRAC :

C. Basically a triac and diac combined together in a single package.

Solution :

6.3.1) Traic : D.

6.3.2) Diac : A.

6.3.3) SCR : B.

6.3.4) LASCR : E.

6.3.5) QUADRAC : C.

Answer 3

5.2)

Step 1:

Output voltage of inphase operational amplifier is .

Feedbak resistance is .

Input resistance is .

Since the output voltage is in phase with input voltage, the op-amp is non inverting amplifier.

Expression for input voltage of non inverting amplifier is

.

Substitute corresponding values in above expression.

V.

Step 2:

Circuit diagram of the amplifier:

Solution:

Input voltage of the operational amplifier is V.

Answer 4

(5.1)

Operational amplifier:

An Operational amplifier is a DC-coupled high-gain electronic voltage amplifier with a differential input and usually, a single-ended output.

Properties of an ideal operational amplifier:

• Infinite input impedance.

• Zero output impedance.

• Infinite open-loop gain.

• Infinite bandwidth.

• Infinite power supply rejection ratio.

Properties of an real operational amplifier:

• Finite input impedance.

• Finite gain.

• Non-zero output impedance.

• Finite bandwidth.

Answer 5

(5.3)

Comparator :

Comparator is a device which compares two voltages or currents, and switches its output to indicate which is larger.

Input and Output wave forms of Comparator :

Comparator is a device which compares two voltages or currents, and switches its output to indicate which is larger.

It has two analog input terminals and and one binary digital output .

The output is ideally .

Answer 6

6.2.1

A quadrac is a three terminal bi-directional semi-conductor component and consist of a Diac and Triac in one package and has the characteristic of each component on its own, but ther is no characteristic curve for the combination Triac and Diac.
So the quadrac has no characteristic curve.

Answer 7

6.2.2

The light-activated SCR (LASCR) is the light sensitive equivalent of the normal SCR.

Its state is controlled by the light falling on depletion layers like in a normal SCR gate current turns on the device.

Just as a normal SCR, the LASCR will continue to conduct even if the light source is removed.

The characteristic curve of SCR :

Diagram for the characteristic curve of the SCR :

The characteristic curve of LASCR like as SCR.