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mission:resources:picouvx [2016-03-18 08:17] – [BOM] chronomission:resources:picouvx [2023-04-19 13:26] (current) – [Constant current source chains] chrono
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 ** Shunt resistor calculation ** ** Shunt resistor calculation **
  
-<x 14>+<m 20>
 I_{out} = {1.25}/{R_{shunt}} = {1.25}/{62} = 0.020A I_{out} = {1.25}/{R_{shunt}} = {1.25}/{62} = 0.020A
-</x>+</m>
  
 Combining an LM317 and a 62 Ohm shunt resistor regulates the current flow to 20mA per chain, running the LED's at their typical recommended operational forward current to maximize the lifespan but leaves room to increase the current if exposure times need to be shorter. If you don't have 62 ohm resistors on site, just use 68 ohm (18mA per chain). The input voltage must be at least 3,5V + sum(Uf,LED) (Uf=Forward Voltage,LED). Combining an LM317 and a 62 Ohm shunt resistor regulates the current flow to 20mA per chain, running the LED's at their typical recommended operational forward current to maximize the lifespan but leaves room to increase the current if exposure times need to be shorter. If you don't have 62 ohm resistors on site, just use 68 ohm (18mA per chain). The input voltage must be at least 3,5V + sum(Uf,LED) (Uf=Forward Voltage,LED).
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 Using this many LED's in a current controlled environment and a 12V power supply usually tends to result in a higher BOM count since a serial configuration will only power 3-4 LED's per chain. One alternative would be to use a parallel configuration, which is strongly discouraged, as there is no control over the LED's internal resistance and therefore the current flowing through it. Using this many LED's in a current controlled environment and a 12V power supply usually tends to result in a higher BOM count since a serial configuration will only power 3-4 LED's per chain. One alternative would be to use a parallel configuration, which is strongly discouraged, as there is no control over the LED's internal resistance and therefore the current flowing through it.
  
-The most efficient solution seemed to be a switch-mode step-up voltage converter, transforming 12V DC up to 42V DC, which makes a serial configuration of up to 11 LED's per chain possible. This design is based on the widely available MC34063 switch-mode controller IC you can even rip off at electronic trash sites, since it's cheap and a very popular controller in chinese electronics.+The most efficient solution seemed to be a switch-mode step-up (boost) voltage converter, transforming 12V DC up to 42V DC, which makes a serial configuration of up to 11 LED's per chain possible. This design is based on the widely available MC34063 switch-mode controller IC you can even rip off at electronic trash sites, since it's cheap and a very popular controller in chinese electronics.
 ==== Specs ==== ==== Specs ====
  
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 **Increasing Efficiency** **Increasing Efficiency**
  
-The trick to get more than 90% efficiency out of the MC34063 seems to be a very high Q inductor. The first test-conductor was wound on a yellow/white toroid which came out of a broken ATX supply and achieved only about 78% efficiency. After acquiring and winding a new inductor onto one of these  [[http://www.vacuumschmelze.com/en/products/cores-inductive-components/applications/cores/vitroperm-standard-types-encapsulated.html|VITROPERM cores from VAC]] it increased to 93%, which is more than just considerable. There are likely to be other high-efficiency SMPS projects to come in the future where VITROPERM cores may offer substantial benefits compared to others. Time and testing will show.+The trick to get more than 90% efficiency out of the MC34063 seems to be a very high Q inductor (L1). At first L1 was wound on a yellow/white core came out of a broken ATX supply and achieved only about 78% efficiency. After winding a new inductor onto one of these  [[http://www.vacuumschmelze.com/en/products/cores-inductive-components/applications/cores/vitroperm-standard-types-encapsulated.html|VITROPERM cores from VAC]], it increased to 93%, which is more than just considerable. There are likely to be other high-efficiency SMPS projects to come in the future where VITROPERM cores may offer substantial benefits compared to others. Time and testing will show.
 ===== Controller ===== ===== Controller =====
  
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