Based on a IRS2540 the Buck converter uses a unique high-side driver can continuously monitor the load current and time delay hysteretic control method to precisely adjust the current, the method has been patented.
Figure 2 IRS2540 LED converters
From the DC bus or directly from the rectified AC line power LED flashlight, LED so the whole system is very simple and flexible. Regardless of the Buck regulator switch is in the ON or OFF state, the suspension of the high-side drivers can ensure that the The IRS2540 the probe LED load current, thereby providing obvious advantages of the average current control function. In contrast, other systems can only be detected in the ON period current, only uses peak current control. Since the average current controller not only in the ON period, but can also be in the OFF period to adjust, so as to be able to work in a wider range of line and load which does not exceed the design limits, and therefore has its own stable adjustment features.
Figure 3 IRS2540 average current control LED Flashlight
Advantages: simple design concept will be able to achieve very precise current control, and has its own stability, does not require complex circuit analysis.
LED load requiring minimum ripple DC current, peak current mode control or average current mode control, are used in the continuous conduction mode constant current LED Flashlight drive.
The IRS2540 example, must be taken to limit the stress in the hard handover procedure, i.e. the defined delay between the times included in the time of the load current exceeds or falls below the reference level and the Buck switching state change. This delay and the load current (IFB) dI / dt combined section determines the frequency and duty cycle when the system is running, the frequency and duty cycle further decisions taken at the Buck inductor, output capacitor value and the input of the converter output LED flashlight voltage value.
Since the output current is constant and the open-circuit protection easy to implement, so the structure itself provides overload and short circuit protection.
As we all know, the switching power supply design using peak current control in continuous mode operation, thereby running the risk of instability due to sub-harmonic oscillation.
LED Flashlight with slope compensation (slope compensation) can solve this problem, but currently on the market the LED controller does not support the oscillator capacitor connected, it is difficult to implement. In addition, the slope compensation can also cause an error between the current to be detected and the actual LED load current.
Others have tried to solve this problem using fixed OFF time (instead of a fixed frequency). Can alleviate the problem of sub-harmonic oscillations and duty cycle greater than 50%, however, in order to increase the duty cycle frequency must be reduced, resulting in large fluctuations of the frequency of the duty cycle range.