Led Flash for Macro photography

[gvi70000]

Hello,
I want to build my own flash for macro photography and i have some questions.

1. Do you think is better to have each led controlled by a transistor (2N2222A ?)and with a capacitor attached (470uF tantal)?

2. How can i have a visual indicator(LED) that the capacitors are charged?

Any idea or guidance on this matter is welcomed.

Thank you.

 

[srizbf]

for macro shots , LEDs may be a choice but you should select pure white LED . otherwise your leds may give its own color to the object being photographed.

if you use LEDs , need not have 470uf for each one.

just use appropriate DC supply and turn on LED by a transistor with a pulse.
the pulse for base of transistor should be triggered by the shutter contact.

and you have a choice of varying the pulse duration , if you wish .

 

[KJ6EAD]

You can use an LED photoflash driver such as this: **broken link removed**. You will probably find similar devices at the other analog houses such as Maxim IC, Linear Technology, Analog Devices and Texas Instruments.

 

[gvi70000]

Hi,

I've made the flash using 3 rows of leds (24 led's on each row) to control the amount of power - using DIP Switch.
The device can be used as a flash or as a lamp by setting S2.
If used as a flash the trigger command is receive from the camera through the optocoupler
Here are the schematics, what do you think?

 

[betwixt]

You wont get much of a flash from your circuit, the current through the LEDs is going to be quite low, probably in the region of 15mA. If you want a bright flash, use white LEDs as suggested and a driver transistor, preferably a power MOSFET to discharge the capacitor into them.

If you have 3 x 24 LEDs at the moment, are you saying you have a 470 Ohm resistor in series with each LED (72 resistors)? If so, you can dramaticaly reduce component count by using fewer (maybe only one) LED and the transistor driver I suggested.

Brian.

 

[gvi70000]

I have 3 cells with 8 rows, each row with 3 led's in series with 1 ohm resistor (only 24 resistors, one at three led's)
Each cell (A, B and C) is connected in parallel with a 3mm led and 470Ohm resistor.

The transistor was replaced by the optocoupler when the device is used as a flash (S2 upper position) and when used as a lamp S2 is in the lower position

 

[betwixt]

That means the LED cuirrent is only about 8mA so they must be quite dim. The opto-coupler is also running at higer current than the manufacturer recommends.
For a flash, running the LEDs at maximum currrent or even a little beyond would be a better solution. You should consider using the opto-isolator to drive a transistor, peferably a MOSFET but a high current bipolar one will work. Remove the 1 Ohm resisotrs as they have no effect and drop all the 470 Ohm resistors down to a lower value so the LED current is at the maximum their manufacturer suggests.

Brian.

 

[gvi70000]

With the removal of 1 Ohm resistor i agree but with those of 470..they serve the led indicator.