i have the 240V AC to 12V AC step down transformerwhen i connecting directly to 240V line the output is higher at about 16Vi need only 12V for my circuithow to get the exact amount of output voltage?
you have a 1/20 step down transformer that is broken,you should try another trans and see what happens or try 220 witch is the reel voltage/20 maybe you get 10v if your lucky at the end
Put a load on its output to reduce the peak voltage. Try 60 ohm resistor rated 5W. If not lower down into 12V, then try 24 ohm rated 10W.
You could get a second transformer with 120 VAC to 4 VAC output. If you connect the low voltage terminals in series and out of phase from one another (in a subtractive configuration), you will subtract the 4 V ac of one transformer from the 16 V ac of the other transformer, and reduce the combined voltage to 12 Vac. Alternatively, you can use a variac, which is similar to a variable, unity ratio transformer coupled to the 120 VAC side of the transformer. This will allow you to adjust the input voltage, thereby varying the output. Variacs are relatively expensive however. First, check the requirements of the load to make certain that 16 V ac is definitely too high. Some devices have a fairly wide range of tolerance.
This is typical of smaller transformers. They are not very efficient, and so the output voltage changes with changes in load. They are specified for voltage at the full load, so with a light load the voltage is higher. Of course the output voltage also depends on the input voltage with a transformer, and there can be measurement issues with non sinusoidal waveforms. Usually a DC supply in an appliance or device (if that is your purpose) is designed so it can accommodate the full expected range of input AC voltages. This often involves a DC regulator applied to the unregulated DC output. This leads to a DC supply with a specified range of AC input voltages. You will need to consider the range of voltages your appliance can use. This is not always specified, but it may be shown as a maximum and minimum AC voltage allowed. With more information about your circuit it should be possible to determine the maximum and minimum input voltages required. There are ways to change this to suit your transformer if the appliance circuit is known. Ways to reduce the AC voltage: Increase the load on the transformer, perhaps with a suitable lamp or heater. The total load (watts) must be less than the transformer power ratings. Near full load the voltage will be more like the specified voltage for the transformer. This assumes the normal load is much less than the transformer power rating, which is when the voltage is high. If the load varies, this method is not ideal and it wastes power. Use a second transformer or variac to adjust the AC input to the transformer. This only works if the transformer is used with a small load. This will work best with a fixed load current, and is bulky and expensive. Get a different transformer specified to supply the correct voltage at the current you are using. If the current varies widely this is not a suitable method.
