Capacitive power supply with bridge rectifier

Question 4. (a) A full-wave bridge rectifier power supply is powered from the secondary of a transformer which has a rms secondary voltage of 15.6V. The primary of the transformer is connected to a 50Hz, 230VRMS power supply. A 2700uF filter capacitor is used. A current of 1.5 Amp is drawn from the supply. (i) Sketch a schematic diagram of the setup. (ii) Calculate the mean de output voltage. Assume each power diode has a forward voltage drop of 1 volt. (iii) Assume that each diode conducts for one-twelfth (1/12th) of a cycle. What is the mean diode current while each is conducting? (iv) What would happen to the mean diode current you calculated in (iii) if a larger filter capacitance was used in your circuit? Give a reason for your answer. You design a half-wave power supply using the same transformer and filter capacitor as above. What is the minimum rating you should choose for the diode's maximum inverse voltage (peak inverse voltage)? Give a reason for your answer. (vi) Why are 3-terminal regulators often added to the output of a full wave power supply- i.e. what advantages are there to using a 3-terminal regulator over just using a big filter capacitor in a full wave supply? (vii) In electronic circuits, the voltage drop across a signal diode is taken as approximately 0.7 volts for all the usual range of currents that go through the diode. Explain why this is a good approximation using a diode characteristics graph. (b) A crude battery backup circuit is to be created from a diode and a 13-volt battery for a burglar alarm that requires a power supply with a voltage from 12 - 14 volts. When the 14-volt mains powered power supply is switched off the battery will take over powering the alarm. It is important that no current passes through the battery when the 14-volt mains powered power supply is powering the circuit. In your answer book complete the below circuit and explain how it works:(i) when the mains powered power supply is connected, and (ii) when the mains powered power supply is turned off. 13V battery Alarm 14V mains powered power supply (c) One green led (forward voltage drop of 3.8V) and two orange leds (each with a forward voltage drop of 2.2V) are connected in series along with a 330 2 resistor. A 12-volt battery is used to light the leds. (i) Sketch a schematic diagram of the setup. (ii) What is the current through the leds? (iii) What power is dissipated in the green led? (iv) What is the purpose of the resistor?' +15 V (d) The circuit at right shows a modified form of the simple common-emitter RL C amplifier, where the base bias current is supplied from the collector instead of the positive power supply terminal. The transistor has B = 130, and it is TH required to set the operating point such that VCE = 8 volt, and Ic = 1 mA. Find the values of Rb and Ru required. Rb c v2 v1