How to use UB-LED02 LED stick substrate (3-serial series connection type)

This is what it looks like when a constant-current diode is mounted on the back side.
*Patterns are also available for chip product types.

The following explains how to use LEDs in series connection using UB-LED02.
The brightness of LEDs is determined by the amount of current flowing through them.
In Sanhayato's LED boards (UB-LED01 and UB-LED02), "current limiting resistors" and "constant current diodes" can be used.
Current-limiting resistors" and "constant-current diodes" have their own merits and demerits.
Using a current-limiting resistor
Advantage: Easy, LEDs continue to glow even if the power supply voltage drops to some extent (but they become dimmer)
Demerit: LED brightness changes with changes in supply voltage
■Use constant-current diodes
Advantages: LEDs can be lit at a constant brightness. No flickering even in environments where the power supply voltage tends to fluctuate, such as in cars.
Demerit: It is a little difficult. If the power supply voltage falls below the pinch-off voltage of the constant-current diode, the brightness drops rapidly.

and so on.

In this article, we will explain how to use LEDs with "constant-current diodes.
(For how to use LEDs with "current limiting resistors", please refer to the UB-LED01 article)
First of all, a constant-current diode (CRD: Current Regulative Diode) is a semiconductor component that can easily apply a constant current.
In this case, we will use a type that can flow 10 mA since it is for LEDs.
Like other diodes, CRDs have polarity.
As you can see in the circuit diagram and photo below, there is a line on the cathode mark. Be careful not to use the wrong polarity, as it can be easily broken.
Circuit symbols for constant-current diodes:.

Appearance of the constant-current diode:.

The constant-current diode in the photo is E-103 (10mA) manufactured by Ishizuka Electronics Co.
It is glass-sealed and very clean.

For a detailed explanation of the constant-current diode, please refer to the manufacturer's page.
→Product Information｜LED Stabilization Devices｜SEMITEC Corporation
When using actual constant-current diodes, check the following three characteristics.

1. (1) Pinch-off current: This is the value at which a constant current is generated by the constant-current diode. This value of current also flows to the LED.
2. (2) Shoulder characteristic voltage: Think of this as the lower limit of the voltage at which the constant-current diode can no longer provide constant current. If this voltage or higher is not applied to the constant-current diode, the LED will dim. The total forward voltage of the LEDs plus the shoulder characteristic voltage of the constant-current diode should be equal to or greater than the power supply voltage.
3. (3) Maximum operating voltage: This is the upper limit of the voltage value that the constant-current diode can withstand. Although it depends on the operating environment, it should be 2 to 4 times the supply voltage. If extremely high voltage is applied due to a surge (instantaneous voltage fluctuation), etc., separate measures are required.

The following is a circuit using a constant-current diode.
The following is a basic circuit that connects a constant-current diode and an LED in series.
LED (forward voltage VF = 3.0 V) 1 LED
Constant current diode (pinch-off current = 10mA, shoulder characteristic voltage = 3.5V, maximum working voltage = 30V)
Power supply (9V dry cell battery)

In this circuit, even if the power supply voltage changes from 9V, if the voltage of the constant-current diode is within the range of "shoulder characteristic voltage to maximum operating voltage," the LED brightness is maintained at the brightness when the current is flowing at 10mA.
Below is a circuit diagram of the UB-LED02 board circuit actually using a constant-current diode.
LED (forward voltage VF = 2.0 V) × 3 pcs.
Constant current diode (pinch-off current = 10mA, shoulder characteristic voltage = 3.5V, maximum working voltage = 30V) × 1
Power supply (12V)

Mounting example of constant-current diode.
The following is a board with a constant-current diode mounted on it.

One constant-current diode (E-103 (10mA)) is mounted on the board. 10mA current flows.

The board with two constant-current diodes (E-103(10mA)) mounted. 20mA of current flows.
Since the constant-current diodes are connected in parallel, the shoulder characteristic voltage is the same as when one is used.