TPR constant voltage constant current high-precision DC stabilized power supply analysis - News - Global IC Trade Starts Here.

The design of this DC regulated power supply is based on a modular approach, divided into four main functional blocks: the series DC regulated power supply with adjustable amplification and constant voltage control; the constant current regulation and conversion display section; the reference power supply; and the automatic AC voltage adjustment circuit on the transformer secondary side. The complete circuit diagram is shown in the figure. 1. **Series DC Regulated Power Supply and Constant Voltage Circuit** This part includes transistors T1, T2, T10, T11, an operational amplifier (IC1), and voltage adjustment potentiometers P1 and P2. The reference voltage is used to control the base voltage of T2, adjusting the conduction level of the regulator transistor to maintain stable output. P1 and P2 serve as coarse and fine adjustment controls for voltage. The non-inverting input of IC1 is connected to both the reference voltage and the adjusted voltage, while the inverting input receives a sampled voltage. This comparison helps regulate the current through the adjustment tube, ensuring stable operation. 2. **Constant Current Circuit (Current Limiting Circuit)** When the preset current limit is reached, the output current remains constant while the output voltage drops proportionally as the load increases. This circuit uses IC2 and a 0.15Ω sampling resistor, along with a constant voltage/constant current switching display system. The non-inverting input of IC2 gets its reference voltage from P3 and W1, while the inverting input is connected to the front end of the sampling resistor via a 1kΩ resistor. If the sampling voltage exceeds the reference, IC2’s output drops, lowering the Vb of T2, which reduces the output voltage but keeps the current constant. In constant voltage mode, T8 turns on and T9 turns off, lighting the green CV indicator. When current limiting activates, IC2’s output goes to zero, turning off T2. 3. **Reference Regulated Power Supply** This section consists of TL431, 78L12, and T3. The TL431 provides a 2.5V reference and compares error voltages to control T3. The 78L12 regulates the base voltage of T3, stabilizing the +15V output used to power IC1 and IC2, as well as the reference voltages for the constant voltage and current circuits. The +6V output is also used for the main regulated power supply. As shown in the diagram, the high precision of the TPR-3003 power supply is mainly achieved through dual high-precision voltage regulators. 4. **AC Voltage Automatic Switching Circuit** To reduce the voltage difference between input and output, the power supply automatically switches between three AC voltage levels (14V, 24V, and 32V) using a detection circuit involving T4, T5, T6, and T7. The secondary output of the transformer provides these voltages, and the switching occurs at +10V and +20V outputs. When the output is below 10V, T6 turns on, activating the 14V low gear. At 10V, T7 activates the 24V high gear, and at 20V, T4 activates the 32V high gear. This ensures a consistent voltage difference during operation.

**Operation Method** Before using the power supply, it's essential to calibrate the current limit. After turning on the power, adjust the voltage to the desired value, then turn the knob to the constant current (CC) position. A short-circuit line is connected across the + and - terminals, and the current is adjusted to the set limit. Once set, remove the short-circuit line to enter normal operation.

**Common Faults and Maintenance** 1. **Voltage Adjustment Knob Not Working** This may be due to a faulty 6V Zener diode in the reference power supply, leading to no sampling voltage for the adjustment potentiometer. A failed Zener can cause the voltage to read maximum or minimum. 2. **Current Regulator Fails During Short Circuit** First, check if IC2 is functioning properly. Then verify the reference voltage. The most critical component is usually the W1 trimming potentiometer. If P3 is unsoldered, the current output may reach its maximum. 3. **Constant Current Mode Issues** When P3 is turned left, the CC red light should be on, and the CV green light off. If the voltage reading isn’t zero, there might be an issue with IC2. If pins 1 and 4 of IC2 are shorted, the voltage display could be zero, often due to improper replacement after damage.

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