X
Advertisement

992 questions

1,172 answers

201 comments

723 users

Why two 1N5401 diodes in the "Auto 12V Bulb Failure Warning" circuit?

304 views
+1 vote
Why two 1N5401 diodes in the "Auto 12V Bulb Failure Warning" circuit?

Assuming that the Light Bulb has a resistance of 4 ohms (36W under 12V):

1) which would the current intensity through diodes D1 and D2 be?

2) which is the internal resistance of each of diodes D1 and D2 under such current intensity?

3) which would the effective tension applied to the Light Bulb be?
asked Jan 10 by manuel-aparicio-alonsogmail-com (130 points)

1 Answer

0 votes

1. Diode current = bulb current = slightly less than 3A in  this case

2.  The internal resistance of each diode is about 1V /3A = 0.33Ω

3.  The voltage applied to the light bulb = approx 10V

At rated current, silicon diodes drop approx 1V each--rather than consider the elusive resistance (that changes with load), it is far easer to estimate voltage drop as the silicon diode tends to have a fixed voltage drop.  At light loads, this voltage drop is about 0.65V.

Two series diodes are required in order to obtain sufficient voltage to forward bias the LED inside the opto-coupler.

I can envision a superior circuit that would use a TL080 op amp and a low value series resistor that would drop perhaps 0.1V and apply 11.9V to the bulb thus making it much brighter.  Dim light bulbs bother me...
answered Jan 29 by j-keith (12,780 points)

Related questions

  • 0 votes
  • 1 answer
  • 263 views
  • 0 votes
answered Jan 3, 2013 by j-keith (12,780 points)
  • 0 votes
  • 1 answer
  • 142 views
asked Sep 6, 2015 by deepita (120 points)
  • 0 votes
answered Feb 18, 2013 by j-keith (12,780 points)

992 questions

1,172 answers

201 comments

723 users

Latest Article Comments

Control a Relay with Arduino - Tutorial...
"hello. im new here. may i know is it the coding for this relay is also can be used with arduino"
Infrared Model Train...
"Hi TravisC About 12 months ago I published a circuit that has none of the problems mentioned and"
Infrared Model Train...
"You statement below about noise and stuff is all a foriegn to me. Way over my head. So I guess I"
Infrared Model Train...
"Hi Perhaps I should have been a bit clearer in my statement. The output noise is not a function"
Automatic Water Tap (Faucet/Valve)...
"hi can run that circuit with 5 V"
Infrared Model Train...
"jeffmonoptusnet-com-au : Noted your suggestions.Thanks! I've re-tested my prototype and observed"
Infrared Model Train...
"Hi TravisC. The circuit of the IR sensors as shown is a good general purpose sensor. However as"
Infrared Model Train...
"I am looking for an easy detection unit for N scale trains, that will detect a train, then will"
Infrared Model Train...
"I am like you Vivek, I can not read scematics and would like a more of a digram how you would put"
Infrared Model Train...
"I am like you Vivek, I can not read scematics and you like a more of a digram how you would put"
electroschematics group on facebook
...
  Search 4 million + Products
Browse Products