source:Industry News Popular:adapter release time:2021-06-11 10:04:49 Article author:sznbone
In-line power adapter foldback current limiting!It can be seen from the figure that the load current flows to point D through the current detection resistor R1, so the voltage of R1 is proportional to the load current. R1 and Q2 provide overload current limit. The output voltage of point D relative to point C decreases as the load current increases. When the voltage of the base of Q2 relative to point C via R4 remains constant at -2.2V, this reduced voltage is directly applied to the emitter of Q2. When the base voltage of Q2 is 0.6V greater than the emitter voltage, Q2 gradually turns on; when the load resistance decreases, the shed current of Q1 shifts to prevent the current from increasing further, resulting in a lower output voltage. Resistors R3, R4 and R generate a negative bias voltage at point F, so that the voltage of R1 must exceed 2. 8V (resistance 220, current 130mA) before Q: starts to conduct. During current limiting, as the output voltage decreases, the negative bias voltage at point F also decreases, so Q2 is turned on under harder conditions, and the current limiting effect is weakened, forming a foldback current limiting characteristic. This foldback process reduces the stress of Q1 in the case of a short circuit.
The figure shows the good voltage regulation characteristics of the output voltage within the normal load range of current from 0 to 100mA, and the current limiting process when the current exceeds 130mA (load resistance is 16000). For an overload situation with a current greater than 13mA, the figure shows the foldback current-limiting characteristic during the process of reducing the load resistance from 1600 to 0 (short circuit). 130mA is the current limit point, providing a working margin; the current under normal conditions cannot exceed 100mA.
Although the design of the switching regulator is relatively simple, it can be seen from the figure that the regulator has good starting characteristics and provides satisfactory performance for this application.
Since the input voltage of the sine wave inverter is stable at 215V, the 50kHz output of the converter is semi-stable and fluctuates within an acceptable range, so it can be used in a variety of auxiliary systems without any additional adjustment systems.
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