LED 5 Technology Barriers and Their Solutions

  • 2022-06-08

This technical article introduces 5 technology barriers and relevant solutions, including chip fever, operating frequency, and so on.

1. Chip fever

If the consumption current of chips is 2mA, with 300v voltage and 0.6W power consumption, it will absolutely cause the fever of chips. The biggest current of driving chips come from the consumption of MOS tube, whose calculating formula is I = CVF (consider charging resistance performance, actually, I=2 CVF, in which c is CGS capacitance of the power MOS tube, v tube is the gate voltage during the power turn-on, and in order to reduce the power consumption of the chip, you have to think of some way to reduce the c, v and f. If they can't be changed, you can think of some way to move chip power consumption outside to the device, but be careful to not to introduce extra power consumption.)

 

2. Power tube fever

Power consumption of the power tube is divided into two parts: switch losses and conduction losses. Note that on most of the occasions, especially the LED drive electric applications, switch damage is larger than conduction loss. Switch loss is relevant with the CGD and CGS of power switch tube and driving ability of the chip and working frequency, so you can solve the power tube heat problem from the following aspects:

 

A. Don't choose MOS power tube according to the size of resistance, because the smaller resistance, the bigger the CGS and CGD capacitance is. For example, 1N60 CGS is about 250pF, 2N60 CGS about 350pF, 5N60 CGS is about 1200pF.

 

B. Here we only talk about the influence of frequency. Frequency is proportional to the conduction loss also, therefore, when the power tube heating, the first thing to consider is that if the frequency is a little high. Find a way to reduce the frequency, but note that when the frequency decrease, in order to get the same load capacity, peak current or inductance must be larger, which is likely to lead inductance into saturation area. If the inductor saturation current is enough, you can consider changing CCM (continuous current mode) to DCM (discontinuous current mode), so you need to add a load capacitance.

 

3. Reduced operating frequency

This is also a common phenomenon in the process of debugging, which is mainly caused by two aspects: the proportion of input voltage and the load voltage is small, and system interference is large. For the former problem, the load voltage should not be set too high, although it will increase the efficiency. In the latter case, you can try the following several ways:

e. Set a smaller minimum current;

f. Install a clean wiring especially the key way sense;

g. Select a small inductance or closed magnetic circuit inductance;

h. Add RC Lowpass filtering.

 

Anyway, frequency reduction does no good to the product, so you have to fix it.

 

4. Inductance and transformer selection

Many users said that with the same drive circuit, the inductance produced by a have no problem, while another one with b the inductance current becomes small. In this case, you can check the inductor current waveform. Some engineers didn't pay attention to this phenomenon and directly adjust current sense resistance or working frequency to required current, which could seriously affect the service life of the LED. So, before the design, a reasonable calculation is needed. If the theoretical calculation of parameters and debugging are a little bit different, you need to consider whether the frequency reduction and transformer is saturated. Under saturation situation, L will become smaller, which may lead to a sharp rise in the peak current, then the peak current of the LED will increase too. On the premise of constant average current, you can only look at light wane.

 

5. Electricity value of LED

It is well known that too big LEDripple will influence the life of LED, as to how, no one has said. The best advice is to control it as small as possible. If the cooling solution is not good, the LED must be derating used. It is also hoped that experts can give a specific indicators; otherwise the LED promotion will be affected.

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