Gosbell GRS-2001E digital satellite receiver switching power supply circuit

Gosbell G RS -2001E digital satellite receiver switching power supply circuit

Gosbell GSR-200IE digital satellite receiver switching power supply circuit is mainly composed of AC input circuit, switching oscillation circuit, voltage stabilizing
circuit, reverse peak voltage absorption circuit and output circuit, as shown in the figure.
    (1) The AC input circuit
    Ls, L6, C13, and cl form a double common-mode low-pass filter network. Its function is to suppress electromagnetic interference on the power grid. At the same time, it also
inhibits the electromagnetic interference generated by the switching power supply itself to ensure that the power grid Not stained. This combination has better suppression effect on various high-frequency interference signals.
VD1 ~ VD4 and C2 form a bridge rectifier filter circuit. TH1 in the circle is a thermistor element with a negative temperature coefficient. Its characteristic
is that the resistance value is large when the temperature is low, and the resistance value is reduced when the temperature is high. When the circuit is just turned on, due to the low temperature of the resistor, the resistance value is large,
thus limiting the starting current of the circuit. This is the surge suppression circuit, which has a certain protective effect on the switching power supply itself. After the circuit is connected, there is current on TH1
, its temperature increases, and the resistance value becomes smaller, which has no effect on the circuit.
    (2) Switching oscillation circuit
    When the rectified and filtered DC voltage of 300 V is added to the ④ terminal of the primary winding of the switchable inverter Tl, the starting resistors RI,
Rz and the voltage regulator tube ZD2 provide a gate for Qi. pole voltage, Q. begins to conduct, and the primary winding of the switching transformer begins to have current, so the secondary winding of the switching
transformer generates an induced voltage. The output signal of pin ④ passes through c5. When positive feedback is formed, the switching circuit enters oscillation. state. During the startup process of the rising
and closing tube, the current of this winding increases linearly. When the current reaches the control value of Q], the current in the winding no longer increases. According
to the electromagnetic principle, the voltage on the winding drops. ③The induced voltage on the D winding turns on Q2 through R5, short-circuiting the gate voltage of Qi to ground and
turning off Qt. This completes a switching oscillation cycle.
    (3) Voltage stabilizing circuit
    The voltage stabilizing control circuit is set in the +3.3 V output circuit. When the output voltage rises for some reason,
the voltage value at the sampling resistor Rts, Rl6. RV dividing point will also rise. High, the sampling circuit sends this increased change to the control terminal (i.e. R terminal) of the current comparison amplifier 11431
, and the level of the control terminal R will also increase, causing the current of the K" terminal of TJ A31 to increase, and the photoelectric coupling The brightness of the light-emitting diodes in the UI of the transformer
is also enhanced, causing the phototransistor to turn on, thereby shortening the on-time of driving Q2. The energy obtained from each secondary winding of the transformer will
be reduced , and the output voltage will be reduced. Vice versa. , achieving the purpose of voltage stabilization.
    (4) Reverse peak voltage absorption circuit
    The buffer protection circuit composed of Rs, C4 and VD6 is mainly used to limit the reverse peak voltage generated by the leakage inductance of the switching transformer. This
peak voltage is generated in the switch After the power tube is turned off, the energy in the leakage inductance charges C4 through VD6 and absorbs this part of the energy. The switching
tube Qi is made to work in the safe area, which reduces the turn-off loss of Qi and also reduces the switching current at the output end. The voltage level is greatly reduced, thereby playing a protective
role.
    (5) Output circuit
    The power supply has a total of 7 output circuits, and the DC output voltages are +30 V, +22 V, +16 V, +13 V, +8 V, + 5V,
+3.3V.