Hub Switching Power Supply Circuit Diagram
As shown in the figure, the utility power by C1, NF1 and other components of the filter network to filter out high-frequency clutter, added to the full-bridge circuit composed of D1 a D4. Rectified DC pulsating voltage filtered by c2, about 300V DC voltage at both ends of c2, the voltage all the way through the switching transformer T1 (1)-(2) winding added to the switching tube Q1 D-pole, the other way through the starter resistor R2 added to the U1 (KA3842AN) of the (7) feet, while charging the C7, when the charging voltage of the C7 on the ≥ 12V, the U1 internal 5V reference voltage is established and the oscillator starts to work.
R6, c4 for the oscillator external Rc timing elements, its parameters determine the oscillation frequency of U1. (4) feet of the sawtooth wave amplified by the internal shaping, from the (6) feet of U1 output duty cycle adjustable excitation pulse, coupled by R4, D6, added to the G-pole of Q1. Q1 drain current ID ~ s through the T1 (1) a (2) winding electromagnetic induction, coupled by T1, from the T1 (3) a (4) winding induced pulse voltage, rectified by D9, R13 current limiting, c7 filtering is also added to the (7) foot of u1, to provide u1 with the operating voltage required for normal operation, u1 into normal operation. state.
Voltage regulator circuit
The voltage regulator circuit is mainly composed of U2 (PC817), U3 (KA431) and u1 (2) foot part of the circuit. Because the main power consumption of the hub is 3.3v power supply.
Therefore, the regulated voltage sampling is obtained from the 3.3V output of the switching power supply. When the utility power rises or when the load becomes lighter, the output voltage is bound to rise. 3.3V by R16 to U2's (1) a (2) feet of the voltage also rises, u3's (3) feet of the potential rises, due to the precision regulator u3's (1) feet of the voltage is constant, so this change ultimately makes the flow through the u2's (1) a (2) feet of the current increases, the internal light-emitting diodes within the u2 brightness enhancement, so that the (4) a (3) feet of the internal resistance decreases, u1 (4) a (3) feet of the internal resistance decreases, u1 (4) a (3) feet of the internal resistance increases, u1 (3) feet of the internal resistance decreases, u1 (3) feet of the internal resistance decreases, u1 (3) feet of the internal resistance decreases, u1 (4) feet of the internal resistance decreases, u1 (3) feet of the internal resistance increases. Internal resistance decreases, u1's (8) feet 5v reference voltage by u2's (4) a (3) feet to u1's (2) feet of the voltage rises, when the voltage ≥ 2.5v internal trigger flip-flop in advance. After internal control, the duty cycle of the output pulse of the (6) foot of u1 decreases, the Q1 on-time is shortened, and the T1 energy storage decreases. The output voltage of the switching power supply decreases; conversely, the control process is the opposite of the above. Thus, the whole switching power supply works in a controllable voltage regulation state.
Protection circuit
NT1 is a negative temperature coefficient thermistor, which can effectively choke the inrush current of the utility rectifier circuit of the switching power supply at the moment of powering up, and protect D1-D1 from the inrush current.
VR2 is an over-voltage protection varistor. VR2 is an over-voltage protection varistor, which can effectively absorb the instantaneous pulse of high voltage in the utility power supply, and R3, c3 and D7 are spike pulse absorption networks. R12 is the limit current resistor of Q1, when the switching power supply is overloaded, the drain current Id-s of Q1 is bound to increase, and the voltage drop on R12 increases, and the voltage added to the (3) foot of u1 by R7 also rises. When the voltage of this foot ≥ 1v, U1 internal current comparator trigger flip-flop. Forcibly shut down its (6) feet of the pulse output, Q1 quickly cut off, thus avoiding Q1 from overcurrent breakdown damage.
In the switching power supply there is an overvoltage protection circuit by ZD1, Q2, Q3 and other components. When the switching power supply output voltage transient abnormally high, ZD1 pole shorted to ground, Q3 positively biased conduction due to the B-pole potential pull-down. This positive feedback. And make 02 further saturation conduction. Therefore, 02, Q3 circuit is equivalent to unidirectional silicon controlled circuit. Once triggered conduction will be in a locked state, until the power failure to recharge. q2 conduction, R201 will u2 (2) foot voltage directly shorted to ground, controlled by u2, u1, so that the switching power supply quickly cut off.
