1. Regulated power supply

1. 3～25V voltage adjustable voltage regulator circuit diagram

The adjustable range of this regulated power supply can be adjusted arbitrarily between 3.5V～25V, the output current is large, and the adjustable voltage regulator tube circuit is adopted to obtain a satisfactory and stable output voltage.

Working principle: After rectification and filtering, the DC voltage is provided by R1 to the base of the regulator tube to turn on the regulator tube. When V1 is turned on, the voltage passes through RP and R2 to turn on v2, and then V3 is also turned on. At this time, V1, The emitter and collector voltages of V2 and V3 no longer change (its function is exactly the same as that of a Zener tube). Adjust RP to get a stable output voltage. The ratio of R1, RP, R2 and R3 determines the voltage value output by this circuit.

2. 10A3～15V regulated power supply circuit diagram

Regardless of overhauling computers or electronic production, the stabilized power supply is inseparable. The following introduces a regulated power supply with a continuously adjustable DC voltage from 3V to 15V, the maximum current can reach 10A, the circuit uses temperature compensation characteristics, high precision The standard voltage source integrated circuit TL431 makes the voltage regulation accuracy higher. If there is no special requirement, it can basically meet the normal maintenance and use. The circuit is shown in the figure below.

2. Switching power supply

1. Working principle of PWM switching power supply integrated control IC-UC3842

UC3842 working principle

UC3842 adopts a fixed operating frequency pulse width controllable modulation method, a total of 8 pins, and the functions of each pin are as follows:

① The pin is the output end of the error amplifier, and an external resistance-capacitance element is used to improve the gain and frequency characteristics of the error amplifier;

②The pin is the input terminal of the feedback voltage. The voltage of this pin is compared with the 2.5V reference voltage at the non-inverting end of the error amplifier to generate an error voltage to control the pulse width;

③The pin is the current detection input terminal. When the detection voltage exceeds 1V, the pulse width is reduced to make the power supply in an intermittent working state;

④The pin is the timing terminal. The operating frequency of the internal oscillator is determined by the external RC time constant, f=1.8/(RT×CT);

⑤The foot is the public ground;

⑥The pin is a push-pull output terminal, the internal is totem pole, the rise and fall time is only 50ns, the driving capacity is ±1A;

⑦The pin is the DC power supply terminal, with under-voltage and over-voltage lockout functions, and the chip power consumption is 15mW;

⑧Pin is the 5V reference voltage output terminal and has a load capacity of 50mA.

UC3842 internal principle block diagram

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

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

The 12V, 20W switching DC regulated power supply circuit formed by TOP224P is shown in the figure. Two integrated circuits are used in the circuit: TOP224P type three-terminal monolithic switching power supply (IC1), pc817A type linear optocoupler (IC2).

The AC power source is rectified and filtered by UR and Cl to generate a 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 the leakage inductance to a safe value, and can attenuate the ringing voltage. VDz1 uses P6KE200 transient voltage suppressor with a reverse breakdown voltage of 200V, and VDl uses 1A/600V UF4005 ultra-fast recovery diode.

The secondary winding voltage is rectified and filtered through V, C2, Ll and C3 to obtain a 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 be obtained by changing the turns ratio of the high-frequency transformer and the voltage regulation value of VDz2. R2 and VDz2 also provide a dummy load for 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 bias voltage required by TOP224P.

The main technical indicators of this power supply are as follows:

AC input voltage range: u=85～265V; input grid frequency: fLl=47～440Hz; output voltage (Io=1.67A): Uo=12V; maximum output current: IOM=1.67A; continuous output power: Po= 20W (TA=25℃, or 15W (TA=50℃); voltage regulation rate: η=78%; maximum output ripple voltage: ±60mV; operating temperature range: TA=0～50℃.

3. DC-DC power supply

1. Circuit diagram of 3V to +5V, +12V

Portable electronic products powered by batteries generally use low power supply voltages, which can reduce the number of batteries and achieve the purpose of reducing product size and weight. Therefore, 3~5V are generally used as the working voltage to ensure the stability and accuracy of the circuit. A regulated power supply is required.

If the circuit uses a 5V working voltage, but another higher working voltage is required, this often makes the designer difficult. This article introduces a circuit that uses two boost modules to solve this problem, and only needs two batteries to supply power.

The circuit is characterized by few external components, small size, light weight, stable output +5V, +12V, and meets the requirements of portable electronic products. The +5V power supply can output 60mA, and the +12V power supply has a maximum output current of 5mA.