Regulated power supply circuit design

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Overview:
The rectification and filtering circuit, the AC-DC conversion circuit, and the DC-DC voltage conversion conversion circuit constitute the subject of this research. Rectifier filter circuit and AC-DC converter circuit: consisting of filter capacitor, isolation transformer, bridge rectifier stack and other components, to achieve 15 ~ 20V output voltage on the secondary side of the isolation transformer, after filtering to provide 18-26V DC to DC-DC Input voltage. DC-DC conversion circuit: It is a pulse width modulation circuit composed of UC3843 and its peripheral circuits, Schottky diode, power inductor, fast power FET, etc. The system forms a closed loop feedback loop by adjusting the sampling resistor. The system has the advantages of high precision, low voltage adjustment rate, fast adjustment speed, high efficiency, small output ripple, etc., and achieves very good functions.

1 The design of the regulated power supply shows that the types of DC-DC conversion are divided into: isolated and non-isolated. Although the input and output isolation is relatively high, the isolation transformer has disadvantages such as magnetic flux leakage and loss, which will cause efficiency degradation. According to the requirements of this study, input and output isolation is not required, so the final decision is to choose non-isolated mode. Several options are as follows:
1.1 The series switching circuit has a duty cycle of D. The PWM wave controls the switching transistor Q1 to achieve such an effect, alternately turning on or off, and then obtaining a stable DC output voltage Uo on the load R via the L and C filters. This circuit is a step-down type circuit, and the output voltage of 30--36V required by the problem cannot be realized.

1.2 Parallel Switch Circuit The series switch circuit is similar to the parallel switch circuit principle, but this circuit is a boost type circuit. When the switch is turned on, the inductor starts to store energy. When the switch is turned off, the inductor energy starts to output. Therefore, as long as the inductor winding is reasonable, it can reach the demand of 30-36V, and the output voltage Uo exhibits continuous smoothing characteristics. (figure 1)

figure 1

1.3 Series-parallel switch circuit The following is a series-parallel switch circuit form, also known as buck-boost switch circuit, reverse switch circuit. This circuit can function regardless of the pulsating DC voltage before the switching transistor VT1, higher or lower than the stable voltage at the output. In fact, this circuit is in series with a switching circuit that is followed by a parallel switching circuit. The energy storage characteristics of the inductor are used to realize the buck-boost, and the circuit control type is relatively complicated.
Considering that this design only needs to be boosted, choose option two. (figure 2)

figure 2
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