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Basic AC-DC Power Supplies
31 questions By Tony R. Kuphaldt
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Question 10 of 31
What parameters determine the frequency of a power supply’s ripple voltage?
Reveal answerFor linear power supplies (those designs having a transformer-rectifier-filter topology), the parameters determining ripple frequency are line frequency and rectification pulses.
Notes:Note that I did not simply say the ripple frequency is equal to line frequency for half-wave rectification and double the line frequency for full-wave. Such an answer is misleading, since it completely ignores polyphase AC rectification!
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Question 11 of 31
Suppose a power supply is energized by an AC source of 119 V RMS. The transformer step-down ratio is 8:1, it uses a full-wave bridge rectifier circuit with silicon diodes, and the filter is nothing but a single electrolytic capacitor. Calculate the unloaded DC output voltage for this supply (assume 0.7 volts drop across each diode). Also, write an equation solving for DC output voltage (Vout), given all these parameters.
Reveal answerVout = 19.6 volts
Vout = Vin r0.707
− 2 Vf
Where,
Vout = DC output voltage, in volts
Vin = AC input voltage, in volts RMS
r = Transformer step-down ratio
Vf = Forward voltage drop of each diode, in volts
Follow-up question: algebraically manipulate this equation to solve for Vin.
Notes:It is important for students to understand where this equation comes from. Ask your students to explain, step by step, the process of calculating output voltage for a simple power supply circuit. It is helpful in this process to calculate the voltage at each “stage” of the power supply (transformer primary, transformer secondary, etc.), as though we were building the circuit one component at a time.
Incidentally, the method of building a project (such as a power supply) in a step-by-step fashion rather than all at once, saves a lot of time and effort when things go wrong. The same “step-by-step” strategy works well for mathematical analysis, and other problem-solving tasks as well: try to analyze the circuit one “block” at a time instead of the whole thing at once.
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Question 12 of 31
What does it mean if a power supply exhibits 2% voltage regulation?
Reveal answerThis means the difference between no-load output voltage and full-load output voltage is 2% of the full-load output voltage.
Notes:The purpose of this question is to get students to look up the formula for calculating voltage regulation percentage. Notice how I did not simply ask them to regurgitate a formula; rather, I presented a realistic figure for them to interpret. When at all possible, try to format your questions in this sort of practical context!
i m using power supply for CCTV PTZ Camera with his adaptor rating of 230v AC input & 24V AC Output ,2A load current. what would be the power consumption is their from the main supply line? means is it taking 2 amp from main line of it would be from the adaptor itself?