Regulated Power Supply Lecture Notes PDF

Ministry of Higher Education & Scientific Research Al-kunooze University College Medical Instrumentation Technical engineering Department Lecture – 1 – Regulated Power Supply Electronic medical systems 3th Year Class...

Ministry of Higher Education & Scientific Research Al-kunooze University College Medical Instrumentation Technical engineering Department Lecture – 1 – Regulated Power Supply Electronic medical systems 3th Year Class 1 Syllabus : Week Syllabus 1st Regulated power supplied. 2nd Monolithic regulators. 3rd Switching regulators. 4th , 5th Additional switching regulator to pologies. 6th Active filters. 7th , 8th Butter worth filter, practical realization. 9th , 10th Band pass filter, band – reject filter. 11th , 12th Active resonant and band pass filter. 13th Active RC band pass filter. 14th Digital to analogue converters (DAC). 15th A lodder – type DAC, multiplying DAC. 16th Analogue to digital converters (ADC). 17th , 18th The counting ADC, successive approximation ADC. 19th , 20th The parallel – comparator ADC, dual – slope or radiometric ADC. 21st , 22nd ,23rd Medical data acquisition system. 24th Microcomputer based system. 25th Monitoring. 26th , 27th Control. 28th , 29th , 30th Other medical electronic systems. 2  Regulated Power Supply A regulated power supply converts unregulated AC (Alternating Current) to a constant DC (Direct Current). A regulated power supply is used to ensure that the output remains constant even if the input changes. A regulated DC power supply is also known as a linear power supply, it is an embedded circuit and consists of various blocks. The regulated power supply will accept an AC input and give a constant DC output. The figure below shows the block diagram of a typical regulated DC power supply. The basic building blocks of a regulated DC power supply are as follows: 1. A step-down transformer 2. A rectifier 3. A DC filter 4. A regulator 3  Operation of Regulated Power Supply Step Down Transformer A step down transformer will step down the voltage from the ac mains to the required voltage level. The turn’s ratio of the transformer is so adjusted such as to obtain the required voltage value. The output of the transformer is given as an input to the rectifier circuit. 𝑉𝑠1 𝑚𝑎𝑥 𝑛1 ∴ = 𝑉𝑠2 𝑚𝑎𝑥 𝑛2 4  Operation of Regulated Power Supply Rectification Rectifier is an electronic circuit consisting of diodes which carries out the rectification process. Rectification is the process of converting an alternating voltage or current into corresponding direct (DC) quantity. The input to a rectifier is AC whereas its output is unidirectional pulsating DC. There are a number of ways in which the amplitude of a sinewave is referenced, usually as peak voltage (Vpk, Vp or Vmax) peak-to-peak voltage (Vp.p ), average voltage (Vavg), and root-mean-square voltage (Vrms). Peak voltage and peak-to-peak voltage are apparent by looking at the above plot. Root- mean-square and average voltage are not so apparent. 5  Operation of Regulated Power Supply As the name implies, Vrms is calculated by taking the square root of the mean average of the square of the voltage in an appropriately chosen interval. In the case of symmetrical waveforms like the sinewave, a quarter cycle faithfully represents all four quarter cycles of the waveform. Therefore, it is acceptable to choose the first quarter cycle, which goes from 0 radians (0°) through p/2 radians (90°). Vrms is the value indicated by the vast majority of AC voltmeters. It is the value that, when applied across a resistance, produces that same amount of heat that a direct current (DC) voltage of the same magnitude would produce. For example, 1 V applied across a 1 Ω resistor produces 1 W of heat. A 1 Vrms sinewave applied across a 1 Ω resistor also produces 1 W of heat. That 1 Vrms sinewave has a peak voltage of √2 V (≈1.414 V), and a peak-to- peak voltage of 2√2 V (≈2.828 V). Average voltage or mean voltage (Vmean) is calculated by taking the average of the voltage in an appropriately chosen interval. Therefore, it is acceptable to choose the first quarter cycle, which goes from 0 radians (0°) through p/2 radians (90°). As with the Vrms formula, a full derivation for the Vmean formula is given here as well. 6  Operation of Regulated Power Supply Although a half wave rectifier could technically be used, its power losses are significant compared to a full wave rectifier. The output DC voltage of a half wave rectifier, given a sinusoidal input, can be calculated with the following ideal equations: 𝑉𝑠𝑚𝑎𝑥 𝑣𝑠 𝑟𝑚𝑠 = √2 7 Operation of Regulated Power Supply 8 Operation of Regulated Power Supply 9  Operation of Regulated Power Supply The form factor (FF) is the ratio between RMS value and average value and is given by the formula: Ripple factor (RF) determines how well a halfwave rectifier can convert AC voltage to DC voltage. Ripple factor can be quantified using the following formula: The efficiency of a halfwave rectifier (Rectification efficiency) (η) is the ratio of output DC power to the input AC power. The efficiency formula for halfwave rectifier is given as follows; η 10 Ex1: For the 1-𝜑 half wave rectifier circuit shown in Figure below, 𝑅 = 1.3𝐾Ω, 𝑉𝑠 = 150 𝑠𝑖𝑛𝑤𝑡. Calculate 𝑉𝐿𝑚𝑒𝑎𝑛, 𝐼𝐿𝑚𝑒𝑎𝑛 ,𝑣𝑠𝑟.𝑚.𝑠 , 𝑣𝑜𝑟.𝑚.𝑠 , 𝑖𝑜𝑟.𝑚.𝑠 , 𝑓𝑜𝑟𝑚 𝑓𝑎𝑐𝑡𝑜𝑟 (𝐹𝐹), 𝑟𝑖𝑝𝑝𝑙𝑒 𝑓𝑎𝑐𝑡𝑜𝑟 (𝑅𝐹) and Rectification efficiency (η). Solution: The Answer with MULTISIM 11 Ex2: (H.W) For the 1-𝜑 half wave rectifier circuit shown in Figure below, 𝑅 = 10Ω, 𝑉𝑠 = 200 volt. Determine 𝑉𝐿𝑚𝑒𝑎𝑛, 𝐼𝐿𝑚𝑒𝑎𝑛, 𝑣𝑠𝑟.𝑚.𝑠 , 𝑣𝑜𝑟.𝑚.𝑠 , 𝑖𝑜𝑟.𝑚.𝑠 , 𝐹𝐹, 𝑅𝐹 𝑎𝑛𝑑 η. 12 Ex3 (H.W): For the 1-𝜑 half wave rectifier circuit shown in Figure below, has a purely resistor load of 𝑅=1K, determine 1. Efficiency. 2. FF. 3. RF. 13 A full wave rectifier or a bridge rectifier is used to rectify both the half cycles of the ac supply (full wave rectification). The figure below shows a full wave bridge rectifier. A bridge rectifier consists of four p-n junction diodes connected in the manner shown above. In the positive half cycle of the supply, the voltage induced across the secondary of the electrical transformer i.e. VMN is positive. Therefore point E is positive with respect to F. Hence, diodes D3 and D2 are reversed biased and diodes D1 and D2 are forward biased. The diode D3 and D4 will act as open switches (practically there is some voltage drop) and diodes D1 andD2 will act as closed switches and will start conducting. 14 Hence a rectified waveform appears at the output of the rectifier as shown in the first figure. When voltage induced in secondary i.e. VMN is negative than D3 and D4 are forward biased with the other two reversed biased and a positive voltage appears at the input of the filter. 15 Ex4: For the 1-𝜑 full wave rectifier circuit shown in Figure below, 𝑅 = 10𝑘Ω, 𝑉𝑠𝑚𝑎𝑥 = 200 volt. Determine 𝑉𝐿𝑚𝑒𝑎𝑛, 𝐼𝐿𝑚𝑒𝑎𝑛, , 𝑣𝑜𝑟.𝑚.𝑠 , 𝑖𝑜𝑟.𝑚.𝑠 , RF and rectifier efficiency. 16  The Answer with MULTISIM Ex5 (H.W): For the 1-𝜑 full wave rectifier circuit, 𝑅 = 1𝑘Ω, 𝑉𝑠 = 100 sin 𝑤𝑡. Determine 𝑉𝐿𝑚𝑒𝑎𝑛 , 𝐼𝐿𝑚𝑒𝑎𝑛 , , 𝑣𝑜𝑟.𝑚.𝑠 𝑎𝑛𝑑 𝑖𝑜𝑟.𝑚.𝑠 17 Ex5 (H.W): For the 1-𝜑 full wave rectifier circuit, 𝑅 = 1𝑘Ω, 𝑉𝑠 = 100 sin 𝑤𝑡. Determine 𝑉𝐿𝑚𝑒𝑎𝑛 , 𝐼𝐿𝑚𝑒𝑎𝑛 , , 𝑣𝑜𝑟.𝑚.𝑠 𝑎𝑛𝑑 𝑖𝑜𝑟.𝑚.𝑠 18 A center-tapped rectifier is a type of full-wave rectifier that uses two diodes connected to the secondary of a center-tapped transformer, as shown in Below Figure. The input voltage is coupled through the transformer to the center-tapped secondary. Half of the total secondary voltage appears between the center tap and each end of the secondary winding as shown. For a positive half-cycle of the input voltage, the polarities of the secondary voltages are as shown in Figure (a). This condition forward-biases diode D1 and reverse-biases diode D2. The current path is through D1 and the load resistor RL, as indicated. For a negative half-cycle of the input voltage, the voltage polarities on the secondary are as shown in Figure (b). This condition reverse-biases D1 and forward-biases D2. The current path is through D2 and RL, as indicated. Because the output current during both the positive and negative portions of the input cycle is in the same direction through the load, the output voltage developed across the load resistor is a full-wave rectified dc voltage, as shown. 19  (A) (B) (b) During negative half-cycles, D2 is forward-biased and D1 is reverse- biased. 20 21 Thanks 25