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I have a 120v ac to 5v dc transformer and want to decrease the voltage to 4.5v dc. The device being used is rated 4.5 v 2.28 watts.?
Wiki User
∙ 12y ago
If the device requires 2.28 watts at 4.5 volts, then its current draw is 0.507 amperes. (Watts = volts times amperes) If you want to drop 0.5 volts at 0.507 amperes, you need a resistance of 0.987 ohms. (Volts = amperes times resistance)
One solution is to put a 0.987 ohm resistor in series with the device. That resistor would need to handle 0.253 watts, so a half watt resistor would be minimum.
Problem is, this depends on constant power demand by the device. If the power goes up or down, probably down, then the voltage drop across the resistor will change.
Another problem is that the closest standard resistor value to 0.987 is 1 ohm, and that would deliver slightly less than 4.5 volts to the device.
Another solution would be to place a diode in series with the device. The diode would drop about 0.7 volts, giving the device about 4.3 volts. Of course, the diode would need to be rated for 0.507 amperes and one half watt, but the output voltage would be more stable.
A regulator is probably not going to work, because you don't have enough headroom between 5.0 volts and 4.5 volts to do it without a complex design.
Best solution: Get a 4.5 volt power pack.
Wiki User
∙ 12y ago
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Can a Dy11 vector group transformer be connected to a Yd1 vector group transformer source?
In series, yes. In parallel, nope! Putting a Yd1 transformer in series with a Dy11 transformer would result in the output of the Dy11 transformer being identical to the input of the Yd1 transformer with the exception of the voltage magnitude - this will change depending on the winding ratio's on both transformers. But, in regards to other properties of the voltage, the phases will in be in phase, with the voltage in-between the two transformers lagging by 30 degrees.
How do you work out the secondary voltage in a transformer?
The voltage ratio is the same as the turns ratio for an ideal transformer, and most transformers are close to being ideal. So use the following equation:Vs/Vp = Ns/Np
Difference between potential transformer and current trasnformer?
The difference between current transformer and potential transformer is that the secondary of a current transformer can not be open circuited while under service whereas that of the potential transformer an be open circuited without any damage to the transformer.
How do you know if a transformer is a step up transformer?
You will most likely see a 'step-up' transformer on neon signs. The next time you're at a restaurant or bar, look at their neon sign. You'll see a black box (4" x 4" x 6"w) connected to the sign (usually). This is the transformer, and it takes 120 volts AC and steps it up to 7500 to 10,000 volts AC. This excites the neon gas and causes it to glow.AnswerA step-up transformer transforms voltage to a higher level. Like 120 volts to 277 volts.AnswerIt is type of transformer which is used to step up the voltage from low to high value in order to make it applicable for high rated appliances.Not only for high rated appliances but also for transmission in power distribution systems. It is critical in this role. Power distribution systems depend heavily on step-up transformers to generate the high voltages needed for more efficient long-distance power distribution. (And yes, there are step-down transformers at the other end to make the voltages more "user friendly" and less dangerous.)
What is the output of the control transformer?
Depends on what the voltage is being stepped down in that particular control transformer. Control transformers usually step down a voltage of 480/208v to 120V. The 120Volts can now be used in safer manner to "control" start/stop buttons, and other components that are only built to run on 120V
Why secondary terminal voltage decreases with increase in load?
An increase in load (equivalent to a decrease in resistance*) causes an increase in load current. This increases the internal voltage drop within the transformer, and the terminal voltage reduces accordingly.[*An increase in load means more current is being drawn by that load, so an increase in load is equivalent to a decrease in load resistance]
What a transformer is?
Transformation are nothing but changing the image in to different forms by 1)scaling 2)translation 3)rotation scaling:increasing the size of the actual image translation:moving image from one position to another position rotation:changing the angle of image and yaw
Can a Dy11 vector group transformer be connected to a Yd1 vector group transformer source?
In series, yes. In parallel, nope! Putting a Yd1 transformer in series with a Dy11 transformer would result in the output of the Dy11 transformer being identical to the input of the Yd1 transformer with the exception of the voltage magnitude - this will change depending on the winding ratio's on both transformers. But, in regards to other properties of the voltage, the phases will in be in phase, with the voltage in-between the two transformers lagging by 30 degrees.
What is a curect transformer?
A 'current transformer' is a type of transformer which, together with a 'voltage transformer' (or 'potential transformer' in N America), is classified as being an 'instrument transformer'. It is used to reduce large currents to smaller currents which can be measured safely, and to isolate the primary circuit from the secondary circuit for the purposes of safety. Current transformers are also used to drive protective relays used in high-voltage protection systems.
How voltage transformer can be protected?
by you not being stupid and shooting it with your great-great grand-pappys 22 rifle
In D.C supply the transformer is not connected why?
In a DC power supply a transformer is connected. The only time there would be no transformer used would be if the DC voltage wanted was 120 VDC. The transformer in the power supply is connected to 120 VAC on the primary side and the secondary side of the transformer is connected to either a half wave or a full wave diode bridge. The voltage out of the diode bridge will be the same output voltage potential as the transformer's secondary voltage but it will be a DC (Direct Current) potential.Reading the question in another way, transformers are not connected in a DC circuit. The reason being is that the transformer operates on a collapsing magnetic field. This field induces a voltage into the secondary side of the transformer. Since the DC circuit does not operate on the principle of a collapsing field except when the circuit is opened, the transformer would not operate as a transformer should..
How do you work out the secondary voltage in a transformer?
The voltage ratio is the same as the turns ratio for an ideal transformer, and most transformers are close to being ideal. So use the following equation:Vs/Vp = Ns/Np
Is vacuum tube a voltage controlled device?
yes, effectively a voltage controlled conductance. (conductance being the reciprocal of resistance)
Why isn't the current coming out of a transformer not a sine function?
The voltage of a transformer should be a sine wave but if the transformer is overloaded with excess voltage there could be nonlinear effects in the magnetic core that cause harmonics (i.e. departure from a sine wave) in the voltage. The current is determined by the load. If the load is resistive the current and voltage have the same waveform (by Ohm's law) but if the load is nonlinear, a diode rectifier for example, the current will depart from being a sine wave.
Certain electric devices such as cordless telephones have small transformers that plug into walls.what do the transformers do?
Transformers are relatively simple devices which change both the current and the voltage of an electric source without affecting the total amount of power being given. Power, as the product of current and voltage, is mostly conserved as transformers are used, but the current and voltage changes. If the device needs just half the voltage of what is coming out of your wall (240v in Australia), then it will 'step down' this voltage by half, but will have to 'step up' the current, so your voltage will halve, your current will double, but the total amount of power will remain the same. Essentially the transformer exists to give your device the required input of electricity so your device is not fried!
If the primary winding of the transformer in the power supply opens what will you observe in the rectified output?
There would be no rectified output. The transformer primary has to be closed to induce a current into the secondary winding. At this point of the secondary the voltage is still AC. This voltage is then applied to the rectification bridge to change it to DC. So you can see how no voltage on the primary, the same as the unit being unplugged, affects the output voltage.
How relay used for protection purpose?
Relay are operated by small current /voltage connected to Secondary side of Current Transformer and /or Voltage Transformer. The signal stimulates the magnetic substance nearby with the attracting force. This closes or opens the circuit being used in protection purpose.
