LED Lamp Bead Model And Use Parameters

When using LED lamp beads, we are mainly concerned about some main parameters. We can discuss it. Connecting all LED in series or in parallel not only limits the usage of LED, but also the load current of parallel LED is large, and the cost of the driver will also increase. The solution is to use the hybrid method, most of the current usage is the hybrid form.

First, Lamp bead model

Small patch lamp bead model: 0201 lamp bead, 0402 lamp bead, 0603 lamp bead, 0805 lamp bead, 1206 lamp bead, etc.
Medium power SMD lamp bead model: 3014 lamp bead, 3528 lamp bead, 4014 lamp bead, 2835 lamp bead, 5730 lamp bead, 5050 lamp bead, etc.

High-power SMD lamp bead model: 3030 lamp bead, 3535 lamp bead, 7030 lamp bead, etc.

Second, Main parameters
The parameters of the LED lamp bead model mainly include the voltage, current, power, wavelength, color temperature, etc. of the lamp bead.

1. Led lamp bead voltage
The voltage of red light, yellow light, orange light and green light of led lamp beads is generally around 1.9-2.3V, and the voltage of other colors is around 3.0-3.4V.

2. LED lamp bead current
The working current of led lamp beads is generally 20mA for small lamp beads, 30-150mA for medium-power lamp beads, and 150-300mA for high-power lamp beads.

3. LED lamp bead power
The power of LED lamp beads is generally 0.06W for low-power lamp beads, 0.1-0.5W for medium power lamp beads, and 0.5W for high-power lamp beads, and above 1W.

4. Color temperature of led lamp beads
Mainly refers to the white light series, unit: K, warm white light: 2800-3200K, neutral white light: 4000-4500K, positive white light: 6000-6500K, warm white light: 7000-10000K or more.
5. LED brightness (unit: mcd or lm)

Brightness, different manufacturers, different brands and different chip sizes, the brightness will be different, the specific brightness can refer to the brightness reference value marked by the LED lamp bead manufacturer. High-brightness LED lamp beads are generally customized by LED lamp bead manufacturers.

Third, Commonly used LED lamp working circuit schematic diagram
Now introduce 2 commonly used LED lamp working circuit schematic diagrams for their reference.
1. The schematic diagram of the working circuit of the LED lamp composed of 38 LED light-emitting diodes. As shown in Figure ①

Figure ① control 38 LED lights circuit

The working principle of the circuit: the lamp is powered by 220v power supply, and the 220v alternating current passes through C1 step-down capacitor (polypropylene metal film high-voltage resistant capacitor) as shown in Figure ②
Figure ② Polypropylene metal film high voltage capacitor.

After stepping down, it is rectified by the full bridge to DC, and then filtered by C2, and then the current limiting resistor R3 provides constant current power to the 38 LED lamp beads in series (this is the classic part of this circuit).

The rated current of the LED lamp is 20mA. In the figure, R1 is the protection resistor, R2 is the discharge resistor of capacitor C1, and R3 is the current limiting resistor to prevent the current of the LED from increasing as the voltage and temperature rise. C2 is the filter capacitor, which is used to prevent the damage to the LED caused by the inrush current when the light is turned on. There will be a large charging current due to the existence of C1 at the moment of power-on, and the current flowing through the LED will cause damage to the LED. With C2 The charging current that intervenes in turning on the light is completely absorbed by C2 to protect against impact when turning on the light.

The voltage of each LED lamp bead in this circuit is 3-3.2v, each lamp bead is 0.05w-0.06w, 38 pieces x0.05=2-2.5w (power), and the brightness is equal to the brightness of an incandescent bulb about 15w.

2. The working principle of the LED lamp circuit composed of 60 LED lamp beads. As shown in the picture ③

Figure ③ The working circuit of controlling 60 LED lamp beads

The working principle of the circuit: 220v mains is stepped down by C1 and R2 resistance capacitance (see the picture above for C1 polypropylene high-voltage capacitor), where R2 is the discharge resistor, C1 is the voltage drop capacitor, its withstand voltage is 400v, and then it is passed through w1 rectifier bridge The output direct current is sent to 60 LED connected in series after the current is limited by R4, because the load connected to the LED is not a pure resistance, but approximates the characteristics of a Zener tube. According to this schematic diagram, refer to the selected components, C2 It is a filter capacitor, which can prevent the impact of high current on the LED tube when the light is turned on. R1 is a thermistor (NTC). When an unexpected situation in the circuit causes the current to increase, its limit value becomes larger, which promotes the reduction of the current, thus playing a protective role.

The circuit uses 60 LED lamp beads, and its power is about 3.5w
Fourth. Working principle of RC step-down

The working principle of the RC step-down is to use the capacitive reactance generated by the capacitor at a certain frequency of the AC signal to limit the maximum operating current. At the same time, a resistive element is connected in series with the capacitor, and the voltage obtained at both ends of the resistive element and the power consumption generated by it depend entirely on the characteristics of the resistive element.
Therefore, the capacitive step-down actually uses the capacitive reactance to limit the current, and the capacitor actually plays a role of limiting the current and dynamically distributing the voltage across the capacitor and the load.
For example, under the condition of 50Hz power frequency, the capacitive reactance produced by a 1uF capacitor is about 3180 ohms. When the AC voltage of 220V is applied to both ends of the capacitor, the maximum current flowing through the capacitor is about 70mA. Although the current flowing through the capacitor is 70mA, no power consumption is generated on the capacitor, because if the capacitor is an ideal capacitor, the current flowing through the capacitor is the imaginary part current, and the work it does is reactive power.

According to this feature, if we connect a resistive element in series with a 1uF capacitor, the voltage obtained across the resistive element and the power consumption it generates depend entirely on the characteristics of the resistive element. For example, we connect a 110V/8W light bulb in series with a 1uF capacitor. When it is connected to 220V/50Hz AC voltage, the light bulb is lit and emits normal brightness without being burned. Because the current required by the 110V/8W bulb is 8W/110V=72mA, it is consistent with the current limiting characteristics produced by the 1uF capacitor.
In the same way, we can also connect a 5W/65V bulb and a 1uF capacitor in series to 220V/50Hz AC, and the bulb will also be lit without being burned. Because the working current of a 5W/65V bulb is also about 70mA. Therefore, capacitive step-down actually uses capacitive reactance to limit current. The capacitor actually plays a role of limiting the current and dynamically distributing the voltage across the capacitor and the load.

Figure 1 is a typical application of resistance-capacitance step-down, C1 is the step-down capacitor, R1 is the discharge resistor of C1 when the power is disconnected, D1 is a half-wave rectifier diode; D2 provides a discharge circuit for C1 in the negative half cycle of the mains, otherwise Capacitor C1 will not work when it is fully charged, Z1 is a Zener diode, and C2 is a filter capacitor. The output is the stable voltage value of Zener diode Z1.

In practical applications, Figure 2 can be used instead of Figure 1, where the forward and reverse characteristics of Z1 are used, its reverse characteristic (that is, its voltage stabilization characteristic) is used to stabilize the voltage, and its forward characteristic is used to The negative half cycle provides a discharge circuit for C1.

In larger current applications, full-wave rectification can be used, as shown in Figure 3.

In the case of small voltage full-wave rectification output, the maximum output current is:
Capacitive reactance Xc=1/(2πfC)
Current Ic = U/Xc=2πfCU
Summarize
When using capacitors to step down, pay attention to the following points:
1. Select the appropriate capacitor according to the load current and AC operating frequency, not according to the voltage and power of the load;
2. Current-limiting capacitors must be non-polar capacitors, and electrolytic capacitors are not allowed. The capacitor voltage must be above 400V, and the ideal capacitor is an iron shell oil-immersed capacitor;
3. The capacitive voltage reducer cannot be used under high power conditions because it is not safe;
4. The capacitive voltage reducer is not suitable for dynamic load conditions;
5. The capacitive voltage reducer is not suitable for capacitive and inductive loads;
6. When DC operation is required, half-wave rectification should be used as much as possible. Bridge rectifiers are not recommended. But to meet the conditions of constant load.

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