Understanding of Power Conversion Blocks

In any electronics products the power section is one of the vital part and it plays a major role in quality functioning of a board. For most of the electronics product the power source is the AC supply which we have in our house power sockets. So it is necessary to convert this AC power into DC voltage levels which is applicable for the components in the board. Hence it is important to understand about power conversion and the quality it shall have.

Power conversion blocks:

The high AC voltage (230V/110V) is given to a step down transformer and it is reduced to lower level depending upon the desired DC output level. The step down transformer shall have appropriate turns ratio - to convert 240VAC into 12VAC, turns ratio of 240/12 = 20:1 shall be used. But if the desired DC level is 12V then the reduced AC voltage shall be chosen as 15V, this slightly higher level is required to compensate losses which will occur in subsequent steps.  

The stepped down AC voltage is given to rectifier to convert AC into DC voltage. The diode based rectifiers are normally used, the popular one is wheatstone bridge full wave rectifier. The resultant DC voltage is unsmoothed one which means the output level is not a constant one and it will vary within a certain limits.

The unsmoothed output is converted into smoothed DC voltage by filtering stage. The resultant output DC voltage is similar to straight line with certain level and with very low variation.

The resultant filtered DC voltage is used to power the electronic boards with the use of regulators or DC DC converter based on the requirements.         

Understanding of AC Signal

AC (Alternating Current) signal is commonly used format in most of the electrical systems. But when it comes to electronics, DC (Direct Current) plays major role. However it is necessary to understand about AC signal.

AC Signal components:

Frequency (f):
AC signal propagates in cyclic form with positive cycle and negative cycle. The measure of how fast this cycle repeats is called as frequency, and it is the inverse of time required to complete a cycle.

Frequency (f) = 1/Time required to complete a cycle

The unit for frequency is Hertz (Hz).

If an AC signal frequency is 50 Hz. Then time required to complete one cycle is T = 1/f =>0.02 Sec.

Average Value:

Average value of an AC signal is zero, because it has both positive and negative peaks.

RMS Voltage (Vrms):

RMS (Root Mean Square) value is the effective value of a varying voltage or current. It can be considered as the equivalent DC value which gives same effect. Multimeter measures the RMS value of AC signal.

Vrms = (1/√2)*Vp = 0.707*Vp

How to draw a 230V AC Signal:

Vrms = 230V

So, Vp = √2*Vrms = √2*230 = 325 V

Inverting Amplifier Gain Analysis

This is a constant gain amplifier with negative feedback where the input signal is applied to the inverting terminal of the opamp.  The resultant output is inverted.

As per Kirchoff’s Current Law,

I + If = Ii

Opamp input current is Zero i.e Ii = 0

I + If = 0

If Vi is the voltage at the inverting input terminal,

(Vs - Vi)/Ri + (Vo - Vi)/Rf = 0

Opamp input voltages are always equal, ∴ Vi = 0, because non inverting input terminal is connected to ground.

Vs/Ri + Vo/Rf = 0

Vo/Vi = -Rf/Ri

∴ The gain of inverting amplifier is A = -Rf/Ri

OPAMP Basics

OPAMP (Operational Amplifier) is an Integrated Circuit (IC) designed for Linear Amplification.

Ideal OPAMP Characteristics:

1. Infinite Input Impedance

2. Zero Output Impedance

3. Differential Mode Gain is infinite

4. Common Mode Gain is zero

5. Bandwidth is infinite

6. Slew rate is infinite

Understand the benefits of Ideal OPAMP Characteristics:

• Infinite Gain because of Infinite input impedance and Zero output impedance
• No noise amplification as the Common mode gain is zero
• Amplification of all the frequency ranges from DC to infinite frequency of AC signal as the Bandwidth is infinite

OPAMP Golden Rules:

1. Inputs draw no current

2. Output does whatever is necessary to maintain the two inputs at equal voltages

In every Opamp analysis the above rules are applicable.

OPAMP Circuits:

1. Inverting Amplifier

2. Non-Inverting Amplifier

3. Voltage Follower

4. Comparator

5. Differential Amplifier

6. Integrator

7. Differentiator

8. Summation Amplifier

9. Instrumentation Amplifier

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