source:Industry News Popular:adapter release time:2021-06-26 09:15:02 Article author:sznbone
Thermal shutdown is a unique feature of the TOP Switch design. Since the switch tube and the control circuit are on the same chip, the overheat protection of the switch tube is easy to achieve. With an external switch tube, it is more difficult to directly measure the core temperature of the switch tube, so it is difficult to measure the temperature of the switch tube directly. The temperature rise cannot be detected, causing the switch tube to be overheated and damaged.
Under normal conditions, the maximum duty cycle of the switch tube of the flyback GS power adapter is set to 0.5 or less. If the power supply voltage range is very wide, such as the international general power supply voltage of AC85-265V, the corresponding DC bus voltage change will reach 3.5 times or even higher. At this time, the duty cycle of 0.5 is selected at the lowest DC bus voltage. Under the same output conditions at the highest input voltage, the duty cycle will be lower than 0.15. In this way, under medium load conditions, the working state of the power adapter Will be very poor, mainly due to inefficiency.
In order to solve this problem, someone proposed to make the flyback power adapter work in the current continuous state at the 110V voltage level, and the idea of working in the current discontinuous state at the 220V voltage level, so that the duty cycle when the input voltage is high can be solved well. Too small a problem.
So what is the maximum duty cycle? By calculation, the duty cycle corresponding to the critical state of the excitation inductor current on the primary side of the transformer under AC176V input voltage is 04, and the maximum duty cycle under AC85V input voltage state is 0.67. This is the basis for the maximum duty cycle of TOP Switch.
In the schematic block diagram of the TOP Switch in Figure 15-1, the maximum duty cycle has a built-in oscillator to provide a rectangular wave with a duty cycle of 0.67. During the period when the maximum duty cycle is outputting a low potential, the output of the sugar driver is low, and the switch tube It is off state. The switch tube is only allowed to be turned on during the period when the maximum duty cycle is at a high potential, but it needs to be powered on to start and output high potential (that is, start normally), and thermally shut down to output high potential (that is, the chip is not overheated), PWM link output High potential.
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