+12V, 0.5A monolithic switching regulated power supply circuit

The circuit of the +12V, 0.5A monolithic switching regulated power supply is shown in the figure. Its output power is 6W. When the input AC voltage changes within the range of 110~260V, the voltage regulation rate Sv≤1%. When the load current changes significantly, the load regulation rate SI=5%~7%. To simplify the circuit, a basic feedback method is used here. After the power is turned on, the 220V AC power first undergoes bridge rectification and C1 filtering to obtain a DC high voltage of about +300V, and then passes through the primary coil N1 of the high-frequency transformer to provide the required operating voltage to WSl57. The pulse width modulated power signal output from the secondary coil N2 is high-frequency rectified and filtered by VD7, C4, L and C5 to obtain a +12V, 0.5A regulated output. The voltage on the feedback coil N3 is rectified and filtered by VD6, R2, and C3, and then the control current is added to the control terminal C. The absorption loop composed of VD5, R1, and C2 can effectively suppress the reverse peak voltage on the drain. The voltage stabilization principle of this circuit is analyzed as follows: when Uo↓ is caused for some reason, the feedback coil voltage and control terminal current also decrease, and when the error voltage Ur↑ generated inside the chip, the pulse duty cycle of the PWM comparator output Compared with D↑, through MOSFET and buck output circuit, Uo↑ can finally maintain the output voltage unchanged. vice versa. In order to suppress the common mode interference between the primary and secondary, a 1500pF/2kV high-voltage ceramic voltage C6 is connected in parallel to the non-inverting terminals of N2 and N3. VD5 can choose UF4005 (1A/600V) ultra-fast recovery diode. VD6 selects 1N4148 silicon high-speed switching diode. VD7 must use a Schottky diode above 3A/40V, optional B82-004 type (15A/40V). C2 should choose a high-voltage ceramic capacitor of 2200pF/1kV. R1 is the bleeder resistor of C2, which can prevent the charge accumulated on C2 from forming high voltage after power failure. In order to reduce the no-load voltage, a minimum load resistor of 560Ω is connected in parallel to the output end. The high-frequency transformer can choose domestic E-20 ferrite core. Its cross-sectional area Sj=0.25cm2. The winding method should be to wind N1 first, then N2, and finally N3, and pay attention to the polarity of the coil. The wire diameter and number of turns of the enameled wire used in each winding are marked in the figure.