LED driver power supplies can generally be divided into three categories
1）Switch constant current LED driver
2）Linear IC drive power supply
3）Resistance-capacitance buck drive power supply
Switching constant current power supply
A transformer is used to convert high voltage into low voltage, and the current is rectified and filtered to output stable low-voltage direct current.
Switching constant current drive power is divided into the isolated power supply and non-isolated power supply.
Isolation power supply means
The output high and low voltage are isolated, and the safety is very high, so the insulation requirements of the casing are not high.
The safety of a non-isolated power supply is slightly worse, but the cost is relatively low. Traditional energy-saving lamps use a non-isolated driving power supply and are protected by insulating plastic shells.
The safety of the switching power supply is relatively high (usually output low voltage) and the performance is stable. The disadvantage is that the circuit is complicated and the price is high. The switching power supply technology is mature and the performance is stable, which is the mainstream of LED lighting at present.
At the same time, when the switching power supply is applied to different lamps, corresponding requirements should also be made. For example outdoor floodlights, and street lights. Due to the harsh application environment, the switching power supply must have anti-corrosion and waterproof performance. Therefore, in the application of outdoor lighting, the switching power supply usually needs to be treated with glue and waterproofing, and the waterproof level of IP66 is the most ideal.
Linear IC Power Supply (DOB for short)
One IC or multiple ICs are used to distribute voltage, and there are few types of electronic components. Power factor and power efficiency are very high, no electrolytic capacitors are required, long life and low cost. The disadvantage is that the output high voltage is non-isolated, and it is stroboscopic, so the shell is required to be protected against electric shock.
The market claims to have no electrolytic capacitors and long life. Most use linear IC drive power.
Linear IC drive power has the advantages of high reliability, high efficiency, and low cost, and is an ideal LED driver power in the future. Ideal for outdoor floodlight applications.
RC Buck Power Supply
A capacitor is used to provide the driving current through its charging and discharging, the circuit is simple and the cost is low, but the performance is poor and the stability is poor.
It is easy to burn out the LED when the voltage fluctuates, and the output high voltage is non-isolated, requiring an insulating protective casing. Low power factor and short life, generally only suitable for economical low-power products (within 5W).
For high-power products, the output current is large, and the capacitor cannot provide a large current, otherwise it is easy to burn out. In addition, some countries have requirements for the power factor of high-power lamps, that is, the power factor of more than 7W is required to be greater than 0.7, but the resistance-capacitance step-down power supply is far from reaching (generally between 0.2-0.3), so high-power products are not suitable. Adopt resistance-capacitance step-down power supply.
On the market, a large part of low-end LED lighting products with low requirements use resistance-capacitance step-down power supplies, such as LED bulbs. There are also some cheap low-end LED lighting products with high power, which also use resistance-capacitance step-down power supply.
The difference between LED switching power supply and LED driver
In a nutshell, an LED driver is also a kind of switching power supply, but it has several special features. It is also the commonality of this type of switching power supply, so it is customary to classify it as an LED driver.
The special features of LED driver power supply are:
1) Its voltage output is a multiple of 3.2
That is to say, the voltage output of the LED driver is in the form of 3.2V, 6.4V, 9.6V, and 12.8V. However, it generally does not exceed 25.6V at most. Because after this number is exceeded, when the LED is turned on, there will be a possibility of instantaneously burning the last LED that is turned on due to poor product consistency. And this voltage is not constant, it changes with the change of the load to achieve the purpose of constant current.
2) Its output current is constant
The ideal circuit is that no matter how the characteristic curve of the LED changes, the current of the LED driver power supply remains unchanged. However, limited by the accuracy of electronic components, there will still be a small change, and this change is also an important parameter for judging whether the drive circuit is excellent. The function of LED conduction and voltage is a nonlinear “three-segment” relationship, so it is very important to maintain a constant current.
3) It belongs to soft start
Since the consistency of the LED is very poor, and the activity of the internal PN junction changes instantaneously when it is turned on, the LED driver is generally designed to be soft-started to avoid this defect.
4) Its circuit requirements are the simplest
Because many times, the circuit is required to be installed in a small space to match the convenience of LED lighting, the circuit should be as simple as possible, which can also save costs and reduce energy consumption.
5) It generally does not require isolation
Because many products are similar in structure to ordinary lighting, the safety aspect is similar to lighting. But this first item is an “option”. Don’t misunderstand when you understand, because some LED driver still needs to be isolated. This feature is only applicable to our current popular circuits, not necessarily suitable for future circuit development needs.
In summary, it can be considered that: soft start, constant current, step voltage, and simple circuit are the characteristics of the LED driver.
One more point here
Many people unilaterally emphasize constant current but do not mention voltage, which is wrong.
Because the concept of constant current has nothing to do with voltage, for example, a power supply, if it is only a constant current output of 30V, then when you open the circuit, its voltage is 30V; then if you connect an LED, then this directly uses a PN junction Components that work, burn out before the most precise circuit can react.
Because any circuit needs a reaction time, and the working components in the circuit are semiconductors. The PN junction can only respond after the sampling signal is given by the power supply, and the PN junction of the LED starts to work directly. So its “reaction” is faster than the “many PN junctions” in the circuit, and it burns out in advance!
Of course, there are also special occasions that use this kind of LED driver, but this kind of LED driver does not allow the output terminal to be open. To be precise, it is “not allowed to open the output and then connect the LED”.
Advice on choosing an LED driver
The LED driver cannot rely solely on the distinction between good and bad. In the case of stable overall performance, factors such as the total cost of the lamp, the use environment, and local use standards should also be considered. Choose the one that suits you best.