RF Transformers
RF transformers are widely ud in low-power electronic circuits for impedance matching to achieve maximum power transfer, for voltage step-up or step-down, and for isolating dc from two circuits while maintaining ac continuity. They are also ud for common mode rejection and as baluns. Esntially, an RF transformer consists of two windings linked by a mutual magnetic field. When one winding, the primary has an ac voltage applied to it, a varying flux is developed; the amplitude of the flux is dependent on the applied voltage and number of turns in the winding. Mutual flux linked to the condary winding induces a voltage who amplitude depends on the number of turns in the condary winding. By designing the number of turns in the primary and condary windings, any desired step-up or step-down voltage ratio can be realized. Mutual coupling is accomplished simply with an air core but considerably more effective flux linkage is obtained with the u of a core of iron or ferromagnetic material with higher permeability than air.
The relationship between voltage, current, and impedance between the primary and condary windings of the transformer may be calculated using the following relationships. With reference to Figure 1,
As an example, if Z equals 50 ohms and the turns ratio equals 2, the condary impedance equals 200 ohms. In this ca, the condary voltage is twice the primary voltage and the condary current is one-half the primary current.
The basic pha relationship between the RF signals at the transformer input and output ports may be in-pha, 0 degrees, or out-of-pha, 180 degrees. Conventionally, the ports that are in-pha 1, and 3, are marked by dot notation as shown in Figure 2. Ports 1, 4 and 2, 3 are out-of-pha, 180 degrees.
Mini-Circuits' transformers are physically asmbled by winding a pair of twisted wires around a ferrit
e toroidal core. The ends of the primary and condary wires which leave the same side of the toroid are in
the in-pha ports. See Figure 3.
For transformers that have a condary winding with a center-tap, the schematic reprentation and dot locations are shown in Figure 4.
In this ca ports 1 and 3 are in-pha, 0 degrees, and ports 1 and 6 are out-of-pha, 180 degrees. The transformers may be operated as low as 12.5 ohms at the primary with esntially the same impedance matching ratio and only a slight change in frequency respon. For convenience, all Mini-Circuits transformers are specified as a step-up.
For each RF transformer model, the minimum and maximum frequency is given for the inrtion loss at the 3 dB, 2 dB and 1 dB points, as shown in Figure 5 and listed in the data chart. For example, the T1-1 inrtion loss is 1 dB from 2 to 50 MHz and 3 dB from 0.15 to 400 MHz.
Mini-Circuits offers various transformer package styles for asmbly on a printed circuit board. Thes
新生儿母乳喂养e include:
(1) plastic-ca T ries, style X65, plug-in leads
(2) plastic-ca T ries, style W38, flat-pack leads
(3) plastic-ca T ries, style KK81, surface-mount gull wing leads
(4) metal-ca TMO ries, plug-in leads
(5) open construction TC ries, surface-mount leadless
For the various types, the electrical configurations that are available are:
(A) DC isolated primary and condary, center-tap condary
(B) DC isolated primary and condary, center-tap primary and condary
(C) DC isolated primary and condary
(D) unbalanced primary and condary
(E) DC isolated primary and condary, balanced primary and unbalanced condary
(F) DC isolated, three open windings
Coaxial connector models are available from 5 KHz to 500 MHZ and are offered with 50 ohm and 75 ohm impedances; 75 ohm connectors are ud at 75 ohm ports. The FT1.5-1, with unbalanced input and output is especially uful for 50 ohm to 75 ohm matching applications. The FTB ries with unbalanced output and balanced input as shown in Figure 6 (connector ground insulated from the ca) helps eliminate ground loop problems, especially when long cable runs are involved.
In some applications there is a need to pass a relatively high DC current through the primary winding. In this ca, the transformer core may saturate resulting in reduced transformer bandwidth and power handling capability. Mini-Circuits TH ries of transformers are designed to handle up to 100 mA in the primary winding without appreciable saturation and change in RF characteristics.
Transformer core saturation is influenced by (1) DC current through the winding, (2) RF input power, and (3) frequency of operation. The three variables interact to affect the point at which saturation occurs. See Figures 7 and 8 in which conventional transformer saturation is compared to the TH ries. Mini-Circuits has developed many special transformer impedance ratios and configurations where high DC current is pasd through one winding of the transformer. Many of the designs have been for open package surface-mount requirements. Consult our Applications Department for your particular needs.悲惨的近义词
Modern Definition of Terms
amplitude balance
is a measure of the absolute difference in signal amplitude between each output of a center-tapped transformer relative to the center-tap.
pha balance
is a measure of the difference in signal pha between each output of a center-tapped transformer relative to the center-tap.
inrtion loss
is the amount of power lost through the transformer under matched conditions.
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balun
is a transformer that has a balanced input, where both ports are isolated from ground, to an unbalanced output where one side is connected to ground.
autotransformer
is a transformer where the condary winding also compris a portion of the primary winding.
1 dB bandwidth
is the frequency range over which inrtion loss is less than 1dB referenced to the midband inrtion loss.
Most Often Asked Questions About
中国人寿意外险价格表Transformers
Q: Explain the difference between DC-isolated and non-isolated transformers.
A:A DC-isolated transformer is one that does not allow a DC current to pass between the primary and condary windings.
Q: Mini-Circuits transformers are tested with 50-ohm systems. How do they perform at other impedance?
A:Mini-Circuits' transformers can be ud over a wide range of impedance ranges with an impedance as low as 12.5 ohms with a only small change in the bandwidth.
Q: Are Mini-Circuits' transformers step-up or step-down?
A:All Mini-Circuits transformers are specified as step-up transformers. However, they are tested both ways and may be ud as a step-up or a step-down.
Q: Can I just u one side of a center-tapped transformer ?
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A:Yes. You may u one side of the transformer but you should remember you will obtain only one-fourth of the impedance ratio.
Q: Can Mini-Circuits supply MIL-tested transformers?
A:Yes, Mini-Circuits' hermetically-aled TMO transformers meet military needs. Plea submit your environmental requirements to Mini-Circuits for review.
Q: What are the effects of temperature extremes on Mini-Circuits transformers?
A:The permeability of the core is influenced by temperature. As the temperature decreas, there is a change in the permeability causing an increa in the inrtion loss at low frequency.
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As temperature increas, the permeability increas thereby slightly decreasing inrtion loss at low frequency. This is true, however, as long as the temperature does not increa above the Curie temperature of the core. Mini-Circuits' designs u cores that have a Curie temperature much higher than the highest specified operating temperature.
Q: Explain the reasons for low-end and high-end loss of a transformer.
A:The general curve for a transformer vs. inrtion loss is shown below.
The low-end loss is heavily influenced by the primary inductance while the high-end loss is attributed to the interwinding capacitance and ries inductance.
Q: How do I measure the inrtion loss of a transformer?
A:The inrtion loss is measured on two transformers connected back-to-back (impedance matched) and dividing the resulting inrtion loss by two.
Q: Can I build a power splitter with Mini-Circuits' transformers?
A:You can u the Mini-Circuits' T2-1T, to create a 50- ohm, 180 degree power splitter.
学校故事The isolation between output ports and the output return loss of each port will not be as good as a Mini-Circuits' standard power splitter.
Q: What are the breakdown voltage ratings of Mini-Circuits' transformers?数字化摄影
A:Mini-Circuits does not typically specify a break down voltage. However, many of our transformers are able to handle up to 1000 VRMS. Plea contact the factory about the transformer of your choice.
Last Updated: 09/08/1999
