Two LED constant current drive power control decomposition

Said first principle. The first to present constant-current LED dedicated IC represented, mainly, such as 9910 series, AMC7150, all now playing the brand of LED constant current driver IC are basically this, and told him to constant current IC type it. But I think to do this so-called constant-current constant current IC, the effect is not how good. The control principle is relatively simple, is the primary power supply circuit, setting a current threshold, when the primary MOS turns on, then the inductor current is linearly increasing, up to a certain value when the time to achieve this threshold, the turn-off current, the next cycle is triggered by the trigger circuit conduction. In fact, this constant should be a limit, we know that when the inductance of a different time, primary current shape is different, although the same peak, but different from the current average. Therefore, as this power is generally mass-produced, the constant size of the consistency of very good control. There is a feature of this power, the output current is generally trapezoidal, that is, volatility-type current, electrolytic output is generally not smooth, this is a problem, if the current peak is too large, will have an impact on LED. If the power supply and output stage is not the kind of electrolysis current to smooth power, basically fall into this category. That is, to determine whether this is the control, to see there and on the output of electrolytic filter. I had this constant has been called the false constant, because its essence is a limit, not through op amp comparison, the obtained constant value.

The second constant current mode, switching power supply should be called a style. This control mode and constant voltage control mode switching power supply is similar. We all know that constant pressure to do it with a TL431, because it has an internal 2.5 V reference, and then use the resistor divider mode. When the output voltage is higher when, or low point, when you generate a comparison voltage, after amplification, to control the PWM signal, so this control can be very precise control of voltage. This control method requires a reference, but also an operational amplifier, if the base enough to accurately op amp magnification is large enough, then be very accurate. Similarly, do the constant is the need for a constant reference, an op amp, resistor overcurrent detection, as the signal, then the signal amplification, to control PWM, unfortunately now is not very good to find a very accurate reference signal, commonly used transistor, the base drift to do big, there is that you can take the diode conduction value of about 1V to do the benchmark, this may be not high, the best is when the TL431 op amp plus basis, but circuit complexity. However, this constant-current power supply, constant current control accuracy is better than. And this constant current mode control, the output will have to add electrolytic filter, so the DC output power is smooth, not pulsating, pulse, then it can not sample the. So to determine what kind as long as there is to see whether the output electrolytic on the line.

Two kinds of constant current control mode determines the use of two different types of devices, one to determine the two devices use different circuit, different performance, cost is also different. The 9910 series, represented by constant-current LED power supply control IC to do, but the actual limit, control is relatively simple, strictly speaking, it does not belong to the mainstream switch mode power supply control, switching power supply control of the mainstream model is required benchmarks and op amp. However, this IC can only be used out of LED, it is difficult for other things, just because the LED on the requirements of very low ripple. But because it is only used for LED, so now the price is higher. 9910 plus is the use of basic MOS pipe production, the output without electrolysis, in general I see a lot of people do is labor power conversion word inductance inductance. This power, the general information on the chip manufacturers have a map, are basically buck. I do not say, good at this much more than me.

Second, I represented, that is, the constant current control mode switching power supply drive. This is an ordinary switching power supply chip as the core conversion device, the chip a lot, such as the PI TNY series, TOP series, ST's VIPER12, VIPER22, Fairchild's FSD200, and even with only MOS transistor or tube RCC, etc., can be done. Advantage of low cost, reliability is good. Because the average price of switching power supply chip is not only good, but after extensive use are the classic products. In fact, as this IC is generally integrated MOS, MOS than the 9910 plus convenient, but control more complex, require the addition of constant current control device, you can use transistors or operational amplifier. Magnetic components can be inductive character of labor, can also be used with a gap of high-frequency transformer.

I love transformers, because the inductor while the cost is very low, but I do not think its load capacity, a sense of the amount of addition is not flexible adjustment. So I think a better device selection, the common integrated MOS chip plus high-frequency switching power supply transformer, from the performance, cost, and are the best choice, no need to use any constant current IC, the kind of thing, but difficult to use, and expensive.