Secondary turns

To illustrate the important features of a VT, let us analyse its equivalent circuit diagram. Refer to a simple diagram as in Figure 15.1 which is drawn along similar lines to those for a motor (Section I.IO, Figure I.I.5). For ease of analysis, the ratio of primary and secondary turns has been considered as l l. Then from the circuit diagram, the following can be derived ... 

Knee point voltage (kpv) at the maximum secondary turns,... 

The number of secondary turns on the lowest voltage (-1-5 V) output (assuming a Schottky rectifier) is... 

In calculating the number of secondary turns needed, one needs to consider that the resonant transition period is approximately 0.5qSec within a 2.5qSec maximum period per MOSFET at 200 kHz. That corresponds to an 84 percent duty cycle. So,... 

Suppose 10,000 V, j (e.g., from an electrical power plant generator) is input to a transformer where the number of secondary turns is 75 times more than the number of primary turns. Then the voltage from the secondary will be 75 X 10,000 = 750,000... 

This means that if you increase the number of secondary turns you will increase the output voltage. Tfiis has an application in power distribution. 

Alternatively, reducing the number of secondary turns will reduce the output voltage. This is useful for low-voltage supplies such as domestic bell transformers. Because it has no moving parts, a transformer can have a very high efficiency. Large power transformers, used on electrical distribution systems, can have an efficiency of better than 90%. 

Vp = the primary voltage /s = the secondary voltage Np = the number of primary turns Ns = the number of secondary turns... 

A 230V to 12V emergency lighting transformer is constructed with 800 primary turns. Calculate the number of secondary turns required. Collecting the information given in the question into a usable form, we have ... 

FIGURE 7.52 The graphical solution to the push pull Class B amphfier configuration is shown. The quiescent point is midway between the ends of the loadline as in Class A, but unlike Class A, the quiescent current is zero. Each transistor output sees Ri at the collector since the center tapped primary transformer has a 1 1 turns ratio from Ri to each transistor even though it has a 2 1 primary (end to end) to secondary turns ratio. 

For simplicity, assume that the output transformer primary to secondary turns ratio is 2 1 so that either active-half has a 1 1 turns ratio with the secondary. For a load at the secondary winding Ri, the primary end-to-end load is but each transistor works into Ri for each half-cycle. The load presented to each transistor is, therefore, Ri. It follows that... 

Secondary turns Secondary volts Rectifier cells... 

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