Greetings, homemade radio amateurs!
Taking photography, even at an amateur level, requires considerable financial investments, because good photographic equipment is not cheap, and in addition to it, many accessories are required – covers, interchangeable optics, tripods, lighting, etc. Alternatively, you can make a small lantern for illumination with self-powered battery power, small in size, but with sufficient power with your own hands. The manufacture of various kinds of lighting devices is just the case when you can make a device cheaper with your own hands, but at the same time no less quality than branded ones, if you approach the manufacture with your heart. How well the lantern will meet the set requirements will also depend on the choice of a successful scheme. In the simplest case, you can do without any circuits at all and connect the LEDs directly to the battery through a resistor, but the efficiency in this case will be lost due to unnecessary heating of the resistor, and the brightness of the lighting will noticeably decrease with the discharge of the batteries.
The above circuit is both a boost converter and a current stabilizer. As you know, LEDs are powered by current, and the voltage drop across them is always the same. Therefore, it is important that the supply circuit provides exactly the stabilization of the current, so the brightness will not depend on the degree of battery discharge, and the risk of burning the LEDs due to exceeding the permissible current will be reduced to zero. A supply voltage is applied to the input of the circuit, it can be in the range of 5-10V. 6 LEDs connected in series are connected to the output. The circuit has two modes of operation – powerful and weak, in the first case a current of 200 mA flows through the LEDs, in the second case 60 mA. Switching is done by pressing the SW button. Weak mode saves batteries (power 1 W), powerful mode provides a good luminous flux (power 4 W) and is useful when shooting in especially dark places. The advantage of the circuit is its high efficiency; a PWM signal from the ATTINY13 microcontroller is used to increase the voltage and stabilize the current, the switching frequency is 19 kHz. The high switching frequency is also an advantage of the circuit, because at lower frequencies, due to the flickering of light, eyes can get tired, or, even worse, ripples can be seen when recording video under such lighting.
A few words about the details of the circuit. Inductance L1 is an important part of the step-up inverter, its rating should be approximately equal to 100 μH, while it should be rated for a current of 1-2A. It is advisable to choose copies with the smallest possible dimensions, because the inductance, in this case, comes out as the largest element of the circuit. The PWM signal from the microcontroller goes to the gate of the field-effect transistor, any sufficiently powerful field-effect transistor with a logic level can be used here; to minimize the size of the board, the transistor in the SMD case will ideally fit. Diode D2, to increase the efficiency of the converter, is used by Schottky, while it must be designed for a current of at least 1 ampere. Zener diode D1, together with resistor R2, stabilizes the input voltage at 4.7V to power the microcontroller, any 4.7-5.1V zener diode is suitable for people. Moreover, if the input voltage for the circuit is already 5V, then stabilization is not required and the resistor with a zener diode can be excluded by connecting the 8th pin of the microcircuit directly to the power supply. Any non-latching button is suitable as a SW button. All resistors in the diagram are low-power (0.125 or 0.25 W) except for R3 – it must be designed for 1 W of dissipated power.
The entire circuit is assembled on a small printed circuit board with dimensions of 25×30 mm, while a separate printed circuit board is etched for the LEDs, which will become the front for the flashlight. Please note that the LED board is almost entirely “flooded” with a large polygon – it goes under the LEDs and takes away their heat, acting as a small heat sink. Both boards involve surface mounting, so after assembly they can be connected to each other – on one surface of the “sandwich” there will be LEDs, and on the other there will be tracks with circuit details. High-quality and accurate assembly of parts on the board is the key to a good and long service life of the device.
After assembling both boards, they need to be connected with flexible wires. Now you can supply power and check the operation of the device – the LEDs should light up immediately after power is applied, their brightness should be switched with a button. It will also not be superfluous to include in the break of one of the wires to the multimeter LEDs in ammeter mode and control the flowing current: it should be about 200 mA for a powerful mode and about 60 mA for a weak one. During operation, no part of the circuit should heat up – neither the transistor, nor the inductance, if there is heating, you should put more powerful parts and check the correct installation. It is desirable to use LEDs for this circuit with maximum efficiency in order to achieve the maximum luminous flux with this circuit. In order to have a power reserve, it is advisable to use 3-watt ones.
After checking the operability for the lamp, a light and durable case is made, as well as a mount for installation on a regular place of the camera. As a power source, you can use, for example, two series-connected lithium-ion batteries, for example, size 18650. Their capacity (usually 2000-3000 mAh) will be enough for a whole day of shooting even in a powerful mode. Below are examples of photographs taken in a dark room using the assembled backlight. Happy assembly!
Greetings, homemade radio amateurs!