Collection of switching mode power supply circuit diagrams, please collect it quickly

We all know that Switch Mode Power Supply (SMPS), also known as switching power supply and switching converter, is a high-frequency power conversion device and a type of power supply. Its function is to convert a level of voltage into the voltage or current required by the user through different forms of architecture. 1. Working principle of PWM switching power supply integrated control IC-UC3842

UC3842 working principle

The following figure shows the internal block diagram and pin diagram of UC3842. UC3842 adopts a fixed operating frequency pulse width controllable modulation method. There are 8 pins in total. The functions of each pin are as follows: ① Pin is the output end of the error amplifier, and external resistor-capacitor components are used to improve The gain and frequency characteristics of the error amplifier; ② pin is the feedback voltage input terminal. The voltage of this pin is compared with the 2.5V reference voltage of the non-inverting terminal of the error amplifier to generate an error voltage, thereby controlling the pulse width; ③ pin is the current detection input terminal. When detecting When the voltage exceeds 1V, the pulse width is reduced to make the power supply in an intermittent working state; ④ pin is the timing terminal, and the operating frequency of the internal oscillator is determined by the external resistor-capacitor time constant, f=1.8/(RT×CT); ⑤ pin is the common ground . terminal; ⑥ pin is the push-pull output terminal, with a totem pole internal structure, the rise and fall time is only 50ns, and the driving capacity is ±1A; ⑦ pin is the DC power supply terminal, with under and over-voltage locking functions, and the chip power consumption is 15mW; Pin ⑧ is the 5V reference voltage output terminal and has a load capacity of 50mA.

UC3842 internal schematic block diagram

UC3842 is a PWM switching power supply integrated controller with excellent performance, wide application and simple structure. Since it has only one output terminal, it is mainly used for audio terminal control switching power supply.

Pin 7 of UC3842 is the voltage input terminal, and its starting voltage range is 16-34V. When the power is turned on, VCC﹤16V, the output of the input voltage Schmitt comparator is 0. At this time, no reference voltage is generated and the circuit does not work; when Vcc﹥16V, the input voltage Schmitt comparator sends a high level to 5V. . Voltage regulator generates a 5V reference voltage. On the one hand, this voltage supplies the internal circuit of the . pin to work. On the other hand, it provides a reference voltage to the outside through pin ⑧. Once the Schmitt comparator flips to high level (after the chip starts working), Vcc can change within the range of 10V-34V without affecting the working status of the circuit. When Vcc is lower than 10V, the Schmitt comparator flips to low level again and the circuit stops working.

When the reference voltage regulator source has a 5V reference voltage output, the reference voltage detection logic comparator outputs a high-level signal to the output circuit. At the same time, the oscillator will generate an oscillation signal of f=/Rt.Ct based on the external Rt and Ct parameters of pin ④. One channel of this signal is directly added to the input end of the totem pole circuit, and the other channel is added to the PWM pulse width. Control the RS flip-flop. The set end, the R end of the RS type PWN pulse width modulator is connected to the output end of the current detection comparator. The R terminal is the duty adjustment control terminal. When the R voltage rises, the Q terminal pulse widens, and at the same time the pulse width sent by pin ⑥ also widens (the duty cycle increases); when the R terminal voltage drops, the Q terminal pulse narrows. At the same time, the pulse width sent by pin ⑥ also becomes narrower (the duty cycle decreases).

The timing sequence of each point of UC3842 is as shown in the figure. Only when point E is high level, there is a signal output, and when points a and b are both high level, point d will send out high level, and point c will send out low level. Otherwise, point d will send out high level. Point c sends out low level, point c sends out high level. ②Pin is generally connected to the output voltage sampling signal, also called feedback signal. When the voltage of pin ② rises, the voltage of pin ① will decrease, and the voltage of terminal R will also decrease, so the pulse of pin ⑥ becomes narrow; conversely, the pulse of pin ⑥ becomes wider. ③Pin is the current sensing end. Usually, a small value sampling resistor is connected in series to the source or emitter of the power tube to convert the current flowing through the switching tube into voltage, and introduce this voltage into the pin. When the load short circuit or other reasons cause the power tube current to increase and the voltage on the sampling resistor exceeds 1V, pin ⑥ will stop pulse output, which can effectively protect the power tube from damage.

2. 12V, 20W switching DC regulated power supply circuit composed of TOP224P

The 12V, 20W switching DC regulated power supply circuit composed of TOP224P is shown in the figure. Two integrated circuits are used in the circuit: TOP224P three-terminal monolithic switching power supply (IC1) and pc817A linear optocoupler (IC2). The AC power supply is rectified and filtered by UR and Cl to generate DC high voltage Ui, which supplies power to the primary winding of the high-frequency transformer T. VDz1 and VD1 can clamp the peak voltage generated by leakage inductance to a safe value and attenuate the ringing voltage. VDz1 uses a P6KE200 transient voltage suppressor with a reverse breakdown voltage of 200V, and VDl uses a 1A/600V UF4005 ultra-fast recovery diode.

The secondary winding voltage is rectified and filtered by V Li, C2, Ll and C3 to obtain the 12V output voltage Uo. The Uo value is set by the sum of the VDz2 stable voltage Uz2, the forward voltage drop UF of the LED in the optocoupler, and the voltage drop on R1. Other output voltage values ​​can also be obtained by changing the turns ratio of the high-frequency transformer and the voltage stabilization value of VDz2. R2 and VDz2 also provide a dummy load for the 12V output to improve the load regulation rate at light load. After the feedback winding voltage is rectified and filtered by VD3 and C4, it supplies the required bias voltage of TOP224P. The control terminal current is adjusted by R2 and VDz2, and the voltage stabilization is achieved by changing the output duty cycle.

The common mode choke L2 can reduce the common mode leakage current generated by the high-voltage switching waveform of the primary winding connected to the D terminal. C7 is a protection capacitor used to filter out interference caused by the coupling capacitance of the primary and secondary windings. C6 can reduce the differential mode leakage current caused by the fundamental wave and harmonics of the primary winding current. C5 can not only filter out the peak current applied to the control terminal, but also determine the self-starting frequency. It also compensates the control loop together with R1 and R3.