17. Simple electronic devices.

    17.14 Led lamp, from "Dollar Store", in the middle and schematic diagram

  In life, I have to parse different electronic devices and use them for other purposes. At this time I needed a powerful white LEDs for underwater flashlight, and better source than an inexpensive 120 Volts lamp, I have not found. Led's "donor" in the picture below.

LED light from Dollar Store.

  Top parts of the lamp are glued together, so open it without destroying - very hard.

LED lamp inside.

  Under the hood an aluminum heat sink with 12 LEDs connected in series. We can assume that power capacity of each one is less than 0.75 W (9W / 12V = 0.75 W). The total voltage across the group of 12 LEDs is 36 Volts, DC.

 Converter (from 120V AC to 36V DC) is simple and interesting.

AC-DC converet 120V-36V for 12 Hi power LEDs.

  And the bottom side of the board with CMD components.

AC-DC converter for LED, board.

Since the number of components is limited and each properly labeled, the drawing of schematic diagramm does not take a lot of time.

Converter to power LEDs from AC. Schematic diagram. Dollar Store.

  Schematic works in the following way.

  When a voltage is applied, the current through the resistor R7, pre-opens transistor Q1. Additional voltage across the primary winding of transformer T1, even more opens the transistor. When the voltage on the primary winding exceeds ~ 7 Volts, transistor Q2 opens, and it closes transistor Q1. The voltage at the collector of Q1 (secondary T1) starts to increase (due to stored energy in the core of transformer T1). Upon reaching 36V open diode D4 and all stored power discharged into the LEDs. When the current through the transformer ceases, the cycle repeats again. Delay circuit, resistors R3-R5 and capacitor C4 allows you to delay moment of turning off the transistor Q1 to set the output power to the desired level.
  In addition to simplicity, in schematic it is interesting that the current through the LEDs flows two times per cycle.

  For example, the schematic of 'led bulb' from GE does not do that. By the way, on the diagram there may be
inaccuracies, but the idea does not suffer.

Converter to power LEDs from AC. Schematic diagram. GE.

  Plain design, nothing interesting.

  A simple calculations and a simple test remains. 12 LEDs, along 830 lumens or 70 lumens per LED. It remains to check the power consumption at different voltages. At 36V DC it consumes about 200 mA, which changes slightly depending on the temperature.
LEDs power consumption at 36V DC..

  In General, that's all I need to know to use this lamp for my purposes,

  Here's the plan. LEDs with heat sinks, two of such lamps, moving into the light for underwater photography. Agree, it is very tempting to make an underwater flashlight that can supply up to 1600 Lum, almost for free.

  Now that the innards of led lamps we understood, another question arises: why do I need underwater light? Everything is simple. Because to photograph underwater without additional lighting - it is a very, very difficult.

For illustration, two photo from a depth of 10 meters.

Ocean Grass and Horseshoe Crab under water.

  Both done with natural light. On one of the local vegetation, on the other, though in this hard to believe -
crab (Horseshoe Crab).

  Perhaps with a new light, my underwater pictures will turn out much better.

16.06.2016  SKootS

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