Question

3. Consider the following rectifiers a. While constructing a full-wave rectifier, a student mistakenly has swapped the terminals of D3 as depicted in Fig. 3.82. Explain what happens to Vin, Vout, and lin D24 Vour + e RL 0.8 AD. Figure 3.82

Answer 1

Anode Cathode (-)

Basic concept: Diode is an unidirectional current device and it allows current to flow from anode to cathode only. Diode will conduct when forward biased i.e., anode voltage > (greater than) cathode voltage.

+ D3 Ion D2 X"? ) - T R Vout . I diodes. Lett us analyse the circust first then we will draw wave forms. Assuming ideal Let us consider a sinusoidal wave form as input bol u volle - Vinf um aume Te Tz - Considering period T1 forst [o ton.]. Drode Da and Drode, D3, are reverse biased because VK3 & Vk2 are experiencing

positive voltage freig earthocle voltage areater than anode voltage. so, Do& P₂ are off. state. Le Igno vin cutie 22 Dat Voiming The above circuit clearly states the current Comput) will not find a closed path to flow. So, Vout=0

On the onset of negative voltage, in input. voltage wane form, the circuit becomes some what like displayed below. Consider - period Tala to 2n) .. . kz V . LA Vout T AL & zt Latitjen e The 'Drode Pi has anode Aj forward braved , which means D1 is on. But in Drode Dy, ky cathode is experiencing positive voltage, so, De is off & the caruit becomes as shown below.

Dz x 2 XP AL Voutt St It seeme lake both drodes are turned on as the their anode voltages seems positive. But, since, the source is directly connected across Diode Az & A node A, experiencing positive woltage, the drode offers zero resistance, hence, entire current flows through Dzonly L vout gt v TI

Since cloode D3 is ON, it short-circuits source. as VA2K2 zo drode Dz.is off. The net, circuit becomes; - Tana Part 1 i Voul + I Sa Hence, output Voltage is O. zeroll zino output voltage. current & very high cument (input) due to short circuiting Output Zero L source.

Let us summarise - . Vout is zero always. 20 ) none Vin is srnusordal Supply - Zero current is drown at positive half of input voltage & very high cument drawn at negative half, due to Short-circuiting of source by Diode 3 . . .