[ Detailed circuit diagrams for regulated power supplies, DC-DC power supplies, switching power supplies, etc., packed with useful information!]
I. Regulated Power Supply
1. 3-25V Adjustable Voltage Regulator Circuit Diagram
This regulated power supply has an adjustable range of 3.5V to 25V, a large output current, and uses an adjustable Zener diode circuit to obtain a satisfactory and stable output voltage.
Working principle: After rectification and filtering, the DC voltage is supplied to the base of the regulating transistor by R1, causing the regulating transistor to conduct. When V1 is conducting, the voltage passes through RP and R2, causing V2 to conduct, and then V3 also conducts. At this time, the emitter and collector voltages of V1, V2, and V3 no longer change (its function is exactly the same as that of a Zener diode). Adjusting RP can obtain a stable output voltage. The ratio of R1, RP, R2, and R3 determines the output voltage value of this circuit.
2. Circuit diagram of a 10A 3-15V regulated adjustable power supply
Whether repairing computers or making electronic products, a regulated power supply is indispensable. Below is an introduction to a regulated power supply with a continuously adjustable DC voltage from 3V to 15V and a maximum current of 10A. This circuit uses the TL431, a high-precision standard voltage source integrated circuit with temperature compensation characteristics, which makes the voltage regulation accuracy higher. Unless there are special requirements, it can basically meet the needs of normal maintenance. The circuit is shown in the figure below.
II. Switching Power Supply
1. Working principle of PWM switching power supply integrated control IC-UC3842
UC3842 Working Principle
The following diagram shows the internal block diagram and pinout of the UC3842. The UC3842 uses a fixed-frequency pulse-width modulation (PWM) method and has 8 pins. The functions of each pin are as follows:
① The first pin is the output terminal of the error amplifier. External resistors and capacitors are used to improve the gain and frequency characteristics of the error amplifier.
Pin ② is the feedback voltage input terminal . The voltage at this pin is compared with the 2.5V reference voltage at the non-inverting input of the error amplifier to generate an error voltage, thereby controlling the pulse width.
③ Pin 3 is the current detection input terminal. When the detected voltage exceeds 1V, the pulse width is reduced to make the power supply work intermittently.
④ Pin 4 is the timing pin. The operating frequency of the internal oscillator is determined by the external resistor-capacitor time constant, f = 1.8 /(RT × CT).
⑤ The feet are common ground;
⑥ The foot is a push-pull output terminal with an internal totem pole design. The rise and fall time is only 50ns, and the driving capability is ±1A.
Pin ⑦ is the DC power supply terminal, which has undervoltage and overvoltage lockout functions, and the chip power consumption is 15mW;
Pin ⑧ is the 5V reference voltage output terminal, with a load capacity of 50mA.
UC3842 internal principle block diagram
The UC3842 is a high-performance, widely used, and relatively simple PWM switching power supply integrated controller. Since it has only one output terminal, it is mainly used for switching power supplies with audio terminal control.
2. A 12V, 20W switching DC regulated power supply circuit composed of TOP224P.
The circuit of a 12V, 20W switching DC regulated power supply composed of TOP224P is shown in the figure. The circuit uses two integrated circuits: TOP224P three-terminal monolithic switching power supply (IC1) and PC817A linear optocoupler (IC2).
The AC power supply, after rectification and filtering by UR and Cl, generates a high-voltage DC Ui, which supplies power to the primary winding of the high-frequency transformer T. VDz1 and VD1 can clamp the voltage spikes 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 VD1 uses a 1A/600V UF4005 ultrafast recovery diode.
The secondary winding voltage is rectified and filtered by VD2, C2, L1, and C3 to obtain a 12V output voltage Uo. The value of Uo is set by the sum of the stable voltage Uz2 of VD2, the forward voltage drop UF of the LED in the optocoupler, and the voltage drop across R1. Other output voltage values can be obtained by changing the turns ratio of the high-frequency transformer and the regulated voltage of VD2. R2 and VD2 also provide a dummy load for the 12V output to improve the load regulation under light load conditions. The feedback winding voltage is rectified and filtered by VD3 and C4 to supply the bias voltage required by the TOP224P.
The main technical specifications of this power supply are as follows:
AC input voltage range: u=85～265V;
Input power 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℃.
III. DC-DC Power Supply
1. Circuit diagram for 3V to +5V and +12V converters
Battery-powered portable electronic products generally use low power supply voltages to reduce the number of batteries, thereby reducing the size and weight of the product. Therefore, 3 to 5V is commonly used as the operating voltage. To ensure the stability and accuracy of the circuit operation, a regulated power supply is required.
If a circuit operates at 5V but requires a higher operating voltage, this often poses a challenge for designers. This article introduces a circuit composed of two boost modules that solves this problem and requires only two batteries for power.
This circuit is characterized by few external components, small size, light weight, and stable +5V and +12V outputs, meeting 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.
The circuit is shown in the diagram above. It consists of an AH805 boost converter and an FP106 boost converter. The AH805 is a boost converter with an input of 1.2–3V and an output of 5V, capable of outputting 100mA current when powered by 3V. The FP106 is a surface-mount boost converter with an input of 4–6V and a fixed output voltage of 29±1V, capable of outputting up to 40mA. Both the AH805 and FP106 have a level-controlled power-off control terminal.
