Computer Interfacing and Peripheral Equipment Laboratory Report (Rick L. Swenson)

Laboratory exercise number:

Practice 14.

Laboratory exercise name: Thyristors and solid state interfacing.

Name: Roll Number Date

Martn Santiago Francisco 01202208 April- 10-2013

Giovanni De la Vega Huerta 01204102

Israel Pimentel Bermdez 01204459

Material:

LM339 Quad Voltage Comparator (for single power supply)

Unijunction Transistors (UJT): 2N2646

Silicon Controlled Rectifiers (SCR): TIC106B or C106D

TRIACs: 2N6073 or Q4010

OptoIsolators: MOC3010

Light Bulb (Resistive Load)

Hair Dryer (Inductive Load)

Several Resistors of different values (see schematics)

1 NPN transistor 2N2222A

Monostable multivibrators: 74LS221

Report description:

Thyristors are typically used for power electronics interfacing and control. During

this laboratory experiment you will be using three of these devices, namely: SCRs, UJTs

and TRIACs.

Obtained results with schematic, block diagrams and timing diagrams:

Stage 1. SCR applications

Assemble the following two circuits shown in Figure 1. If you cant find a 6V light bulb, use a 330 Ohms resistor with a LED connected in series. For RL, also use a LED.

Figure 1: SCR application examples

Figure 2: Figure 3: Circuit implemented on

breadboard

Stage 2. TRIAC applications

The following circuit (Figure 4) is for switching resistive loads (e.g. light bulb, heater

element, etc.) connected to an AC source using digital circuitry. It uses a MOC3010 to

provide optical isolation between the digital circuitry and the AC source. For the resistive

load, RL, use a 60 Watt light bulb.

Figure 4: Digital circuitry interfaced to an AC resistive load

Figure 5: Figure 6:

The following circuit (Figure 7) is for switching inductive loads (e.g. motors) connected

to an AC source using digital circuitry. It uses a MOC3010 to provide optical isolation

between the digital circuitry and the AC source. For the resistive load, ZL, use a hair dryer

motor.

Figure 7: Digital circuitry interfaced to an AC inductive load

Figure 7: Digital circuitry interfaced to an AC inductive load on protoboard.

Stage 3. UJT applications

Figure 8 shows two oscillators using and UJT. Assemble both circuits and verify that the

LED flashes for the circuit on the left. Then check that a varying tone is heard on the

speaker when you turn R2.

Figure 8: UJT oscillator circuit

Figure 8: Time base implemented on

protoboard.

Figure 9: Tone generator implemented

on protoboard.

A ramp generator based on an UJT is depicted in Figure 10. Verify the functionality of

the circuit by putting it together. Connect an oscilloscope to the output OUT.

Figure 10: UJT ramp generator circuit

Figure 11: UJT ramp generator circuit

implemented on protoboard.

Figure 12: Output of the circuit.

Stage 4. Challenge

In this section, we decided to solve the challenge 1 that is the next:

Challenge 1: Modify the digital side of Figure 2, to convert the circuit into a light dimmer. In order to achieve this, you will have to use a monostable multivibrator

(74LS221) and a zero-crossing circuit to detect when the AC voltage crosses 0V.

The zero-crossing circuit is shown in Figure 13.

Figure 13: zero-crossing circuit used to detect when a 120VAC phase crosses 0V

generating square wave pulses.

This circuit is directly coupled to the AC line and it is only recommended as a temporary way of checking zero-crossing. Be very CAUTIOS with the top circuit and dont use it a permanent solution.

Next we present the circuit results.

In these images we can observe how the light intensity changes according to the value of

resistor, implemented with a potentiometer, so we can assume that the triack its working

according to the requirements of the challenge.

In these images we compare the output signal from the monostable multivibrator with the

voltage level that receives the load, in order to observe how the alternate voltage input its cut by

the tirack, and how this action modulate the intensity light of the bulb.

Conclusions:

1. We learned that an input gate signal causes the SCR to turn on, allowing forward current conduction. SCRs are true rectifiers: they only allow current through them

in one direction. This means they cannot be used alone for full-wave AC power

control.

2. Also we learned that the unijunction transistor are used for a wide range of applications such as sawtooth generators, trigger circuits, timing controls and

other related circuits.

Problems encountered:

1. We did not find an AC motor to test the proper operation of the digital circuitry interfaced to an AC inductive load.