Skip to main content

महाराणा प्रताप ट्रेल सज्जनगढ़ उदयपुर

महाराणा प्रताप ट्रेल सज्जनगढ़ उदयपुर में इको ट्रेल 30 नवम्बर को राजस्थान वन विभाग उदयपुर डिविजन तथा WWF-India उदयपुर डिविजन के सानिध्य में महाराणा प्रताप ट्रेल सज्जनगढ़ उदयपुर में इको ट्रेल की गई, जिसमें WWF-India के स्टेट काॅर्डिनेटर श्रीमान अरूण सोनी तथा वन विभाग कीे ओर से डाॅ. सतीश कुमार शर्मा, सेवानिवृत्त अधिकारी मौजूद थे। मुझे भी इस इको ट्रेल में जाने का सुअवसर प्राप्त हुआ, जो गोरीला व्यू पाॅइंट से बड़ी-लेक व्यू पाॅइंट तक की गई इसमें मुझे विज्ञान की एक नई शाखा के बारे में पता चला, जिसे टट्टी विज्ञान कहा जाता है। सुनने में आपको थोड़ा अजीब लगेगा, मुझे भी सुनकर हैरानी हुई, परन्तु वास्तव में एक ऐसा भी विज्ञान है, जिसके बारे में डाॅ. सतीश शर्मा ने बड़े ही विस्तार पूर्वक बताया कि किस प्रकार वनों में जानवरों की टट्टी देखकर यह पता लगाया जा सकता है कि यहां कौनसा जानवर आया था। जानवरों की टट्टी कितनी पुरानी है, वह गीली है या सूखी है। इसी के आधार पर उस विशेष जंगल में कौन-कौनसे जानवर विचरण करते हैं, उसके बारे में वन विज्ञान के कर्मचारी पता लगा लेते हैं। जानवरों की टट्टी का विश्लेषण करके यह पता लगा...
Post a Comment

Power diodes | Power electronics

Power diodes

Introduction of power diode

  • Power diode is a two layer, two terminal, p-n semiconductor diode.
  • The two terminal of diode are called anode and cathode.

Characteristic of power diodes

Circuit diagram for characteristic curve of power diode
  • When diode is positive with respect to cathode, diode is said to be forward biased.
  • With increase of Vs from zero value, initially diode current I is zero.
  • From Vs = 0 to cut-in voltage (threshold voltage or truth-on voltage), the forward diode current is very small.
  • After cut in voltage, the forward diode current increases rapidly and the diode is said to conduct.
  • For Si diode, the value of cut-in voltage is 0.7V
  • When diode conduct, there is a forward voltage drop of the order of 0.8 to 1V.
Characteristic curve of power diode
  • When cathode is positive with respect to anode, the diode is said to be reverse biased.
  • In reverse bias condition, a small reverse current, known as leakage current flow in the circuit and this current is of the order of µA or mA.
  • The value of leakage current increases slowly with the increase in reverse voltage up to breakdown or avalanche voltage.
  • At breakdown voltage, the diode is turned on in the reverse direction.
  • The reverse avalanche breakdown of a diode is avoided by operating the diode below specified peak repetitive reverse voltage VRRM.
  • PIV = peak inverse voltage of a diode.
  • The PIV of a diode is the maximum reverse voltage to which a diode may be subjected during its working. It is same as VRRM.

Diode reverse recovery characteristics

  • After the forward diode current decays to zero, the diode continuous to conduct in the reverse direction, due to the presence of stored charges in the two layers.
  • The reverse current flows for a time called reverse recovery time trr.
Reverse recovery characteristic of power diode

Reverse recovery time (trr)

  • Reverse recovery time is defined as the time between the instant forward diode current becomes zero and the instant reverse recovery current decays to 25% of its reverse peak value IRM.
  • trr = ta + tb
  • ta : The time between zero crossing of forward current and peak reverse current IRM. During this time the charge stored in depletion region is removed.
  • tb : It is measured from the instant of IRM to the instant where 0.25 (or 25%) IRM is reached. During this time the charge from the semiconductor layers is removed.
  • During trr, the stored or reverse recovery charge QR must be removed.

Softness factor or S factor

  • The ratio of  tb and ta is known as softness factor or S-factor.
  • The S factor is a measure of the voltage transient that occur during the time, diode recovers.
  • Usually the value of softness factor is found to be unity, which indicates low oscillatory reverse recovery process.
  • If softness factor is small, then diode has large oscillatory over voltages.
  • If S-factor is 1, the diode is called soft-recovery diode.
  • If S-factor is less than 1, the diode is called or fast recovery diode. or snappy recovery diode.
  • If vf is forward voltage drop across diode, and if is forward current
  • vf x if is power loss in diode
  • Fig (c) shows that major power loss in a diode occurs during tb
  • From fig (a), IRM = ta (di/dt)
  • Here IRM = Peak inverse current, and di/dt = Rate of change of reverse current
  • If we assume that reverse recovery characteristic of fig. (a) is triangular, then
  • QR = ½ IRM x trr ⇒ IRM = 2 (QR / trr)
  • ∵  IRM = ta (di/dt)  and  ta = trr 

  • Thus trr (reverse recovery time) and IRM (peak inverse current) depends on QR (storage charge) and di/dt (rate of change of current)
  • Since QR depends on if (forward diode current)
  • So trr and IRM also depends on if.
  • So a power electronics engineer must know the value of IRM, QR, S-factor and PIV to design the circuit in which power diodes are used.
To know more about this topic please click on https://youtu.be/TjZ4fGWCOZI
Labels:

Comments

Post a Comment

Popular posts from this blog

Electric field due to circular loop of charge | Electromagnetics

Electric field due to circular loop of charge Electric field The space around a charged particle in which another charge experience a force is known as electric field. The source of electric field is either a charge or a time varying magnetic field. If the value of electric field does not change with time, then it will be uniform electric field, otherwise it will be non-uniform electric field. Electric field due to circular loop of charge If λ is linear charge density, then the charge on d l dq = λ d l      ⇒     dq = (q / 2πa) d l Electric field at P due to charge dq Special cases When P lies at the centre of the loop i. e., r = 0, then E = 0 When P lies very far from the centre of the loop i. e., r >> a, then E = kq / r 2 In this case circular loop behaves as a point charge. To know more about this topic please click on the link  https://youtu.be/54MIe0Ow43w   or...
Post a Comment
Read more

Advanced Calculus | Mathematics | BSc

Advanced Calculus Advanced Differential Calculus, Integral Calculus and Vector Calculus Authors: Dr. Vimal Saraswat, Dr. Anil Kumar Menaria ISBN : 978-81-7906-950-9 Price: Rs. 375.00 Publisher: Himanshu Publications, Hiran Magri Udaipur; Himanshu Publications Prakash House, Ansari Road, New Delhi E-mail :  info@sacademy.co.in Phone:  +91 9664392614 To buy this book click on the link Advanced Calculus by Saraswat This book includes the following topics  Continuity Introduction Limit Left and right limit To find the R.H.L. and L.H.L. of a function Existence of limit)/li> Distinction between the value and limit of a function Some theorems based on limits Methods of finding the limit of functions Some standard limits Cauchy’s definition of continuity Continuity from left and right Continuity of a function in an interval Continuity in the open interval); Continuity in the closed in...
Post a Comment
Read more

Cardinal points of a lens system | Optics | General theory of image formation

Cardinal points of a lens system There are total six cardinal points of a lens system, which are first and second focal points, first and second principal points, and first and second nodal points. First and second focal points (First and second focal planes) A pair of points lying on the principal axis and conjugate to points at infinity are known as focal points. First and Second focal points A point on the principal axis in the object space so that the rays starting (or appear to start) from it become parallel to the principal axis after refraction from the lens system is known as first focal point (F 1 ). A point on the principal axis in the image space so that the rays parallel to the principal axis in the image space focus (or appear to focus) at this point after refraction from the lens system is known as second focal point (F 2 ). First and Second focal planes The plane passing through the first focal point, and perpendicular to the optic axis is first f...
Post a Comment
Read more