Transformer turns ratio

Example What is the DM noise spectrum measured at the LISN for a 5 V 15 A flyback at an input of265 VAC, with a transformer turns ratio of 20 We are using an aluminum electrolytic bulk capacitor whose datasheet states that it has a capacitance of270 p,F, a dissipation factor (tangent of loss angle) of tan S = 0.15 as measured at 120 Hz, and a frequency multiplier factor of 1.5 at 100 kHz. 

The gate drive transformer is a very simple 1 1 turns ratio forward-mode transformer. There are not extraordinary demands being plaeed on the transformer sinee it is a very low power, ae-eoupled (bipolar flux), 300 kHz transformer. 

Figure B-10. Figure B-10 shows the presence of a transformer. For the buck converter, the designer can assume that the turns ratio is 1 1.

Classic transformer action implies that the voltages across the windings of the transformer, and the currents through each of them, scale according to the turns ratio, as described in Figure 3-1. But it is perhaps not immediately apparent why the flyback inductor exhibits transformer action. 

Summarizing, transformer action works as follows — when reflecting a voltage from primary to secondary side, we need to divide by the turns ratio. When going from the secondary to the primary side, we need to multiply by the turns ratio. The rule reverses for currents — so we multiply by the turns ratio when going from primary to secondary, and divide in the opposite direction. 

The magnetization current component is not coupled by transformer action to the secondary. In that sense, it is like a parallel leakage inductance. We need to subtract this component from the total switch current, and only then will we find that the primary and secondary currents scale according to the turns ratio. In other words, the magnetization current does not scale — it stays confined to the primary side. 

The known load characteristics and the desirability of the lowest possible turn ratio for the pulse transformer suggest the lumped element Blumlein-pulse forming network (PFN) configuration (Fig. 5.1). Ordinarily, a Blumlein-pulse forming... 

As you might guess, there are several problems with using quarter wave lines, even though they work very well under many circumstances and, as already implied, are widely used. One is that they are not broadband devices, that is, a particular quarter wave line is just that for about a 10% variation of the frequency. A second and related problem is that the characteristic impedance Z which governs the transformation property (or the "turns ratio") through the relation ZjZQ = Z is also an inherent property of the cable. Therefore, you have to have a set of quarter wave lines for each frequency as well as for each characteristic impedance which may be acceptable for single frequency operation but not for multi-nuclear operation. The third problem is that quarter wave lines are very cumbersome and inefficient at low frequencies. With a 50 Q coax, a quarter wave line is about 3 meters (10 feet) at 15 MHz, which is not bad. At 3 MHz, however, it is 15 meters and that is bad. 

It is therefore necessary to provide a sensitive method for detecting earth fault currents. The most common method is to provide a core balance current transformer at the circuit breaker or contactor. This current transformer has a current or turns ratio, which is independent of the ratios used by the transformers connected in the three-phase conductors. This is because a particular level of current is to be detected rather than a fraction or multiple of the stator load current. The switchgear manufactnrer will normally recommend the ratio of the core balance transformer and the matching relay. The relay will be either instantaneous 50 N or an inverse time 51 N type depending upon whether the motor is controlled by a circuit breaker or a contactor. 

Tesla coll A device for producing a high-frequency high-voltage current. It consists of a transformer with a high turns ratio, the primary circuit of which includes a spark gap and a fixed capacitor the secondary circuit is tuned by means of a variable capacitor to resonate with the primary. It was devised by Nikola Tesla. Tesla coils are commonly used to excite luminous discharges in glass vacuum apparatus, in order to detect leaks. 

Step down transformers are used to reduce the output voltage, often for safety reasons. Figure 2.57 shows a step down transformer where the primary winding has twice as many turns as the secondary winding. The turns ratio is 2 1 and, therefore, the secondary voltage is halved. 

A current transformer (CT) has the large load currents connected to the primary winding of the transformer and the ammeter connected to the secondary winding. The ammeter is calibrated to take account of the turns ratio of the transformer, so that the ammeter displays the actual current being taken by the load when the ammeter is actually only taking a small proportion of the load current. 

This allows the natural incorporation of the purely electrical aspects of the loudspeaker system, as shown in Fig. 1.26(c). In Fig. 1.26(c) the voltage generator of emfE supplies the normal actualvoice coil current. The electrical impedance as viewed from the vantage point of this generator is the series combination of the voice coil impedance, R + jcoLg, with the impedance presented by the primary of the ideal transformer. This latter impedance is the square of the turns ratio multiplied by the impedance connected to the secondary of the transformer. This product is... 

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