Use a dual 12V main output transformer to make a 0-25V 0-5A, equipped with peripheral accessories as shown in the figure:
It's a voltage and current test line. Not the same as the dual-display digital header
OUT + and OUT- on the board are the main power output connected to the red and black binding posts
The A + A- terminal is connected to the thick red black of the digital meter, and the 5V output next to 7805 is connected to the thin red black line of the meter
The small letter V + connects to the thin yellow line of the header (V- is connected to the negative electrode of the pointer)
NTC is connected to the thermistor FAN is connected to the cooling fan
Responsibility statement:
Since the product is provided as a kit, the kit also needs to be assembled by itself, including electronic components soldering, circuit debugging, etc. are complex actions that require experience.
This kit provides all components and circuit schematics, but the transformer, housing, voltage and current meter need to be prepared by the user! The user must understand that failures due to unsuccessful assembly may be caused by various unexpected reasons and bear the losses on their own.
Electronic products are closely related to electricity, please confirm whether to purchase according to your electronic production capabilities,
This kit does not provide any technical support, please carefully read the kit schematic diagram and related debugging instructions before purchasing, and confirm that you can complete the independent debugging before buying, thank you for your cooperation!
About the principle, characteristics and use of adjustable constant voltage and constant current power supply:
The principle of constant pressure and constant current:
According to U = IR, R = U / I:
If R> (U / I), the power supply is working normally.
If R <(U / I), I is constant, the power supply constant current part is protected, and the output voltage drops until the condition R = (U / I) is met.
characteristic:
The so-called constant voltage, that is, the voltage can be constant to a value, adjustable constant voltage, that is, this constant voltage value is adjustable.
The so-called constant current, that is, the current can be constant to a value, adjustable constant current, that is, this constant current value is adjustable.
use:
The adjustable constant voltage constant current power supply needs to set the constant current protection value before use, and then set the output voltage, and then start working.
First adjust the output voltage of the power supply to about 5V, short-circuit the output, adjust the current output knob to set the protection current to the value you need, cancel the short circuit, adjust the voltage to the required value, connect the experimental equipment and start working.
For example, the working voltage of a circuit is about 0.3A at 12V, and the operation is as follows.
Adjust the output voltage of the power supply to about 5V, short circuit output, adjust the current output knob to set the protection current 0.5A (slightly larger than the operating current), cancel the short circuit, adjust the voltage to 12V, connect the circuit and start the experiment.
If the circuit board is placed on the metal during the test, part of the circuit is short-circuited, so that the current increases sharply. When the current rises to 0.5A, the power supply constant current protection part works even if the output voltage drops to protect the test equipment.
Common sense:
After the AC voltage is filtered by the full-wave rectifier capacitor, the DC voltage is about 1.414 times the AC voltage.
For example, after the AC voltage of 10V is filtered by the full-wave rectifier capacitor, the DC voltage is approximately equal to 14V. Selection of relay switching point:
The AC input voltage minus 5V equals the switching voltage.
For example, transformer tap 0-15V-25V-35
Then the switching voltage of the first stage is 15V-5V = 10V, that is, switching to the 25V tap at 10V.
The switching voltage of the second stage is 25V-5V = 20V, that is, it is switched to the tap of 35V at 20V.
Regarding whether the relay is switched or not, it can be judged by measuring the voltage across R17. The voltage of R17 (DC) divided by 1.414 is approximately equal to the current tap voltage (AC).
Preparation before commissioning:
After the installation is checked and checked (the capacitor and diode on the output must be installed; TIP3055 must be installed on a large radiator), if you do not connect the ammeter, please short-circuit the ammeter contact "A", and then power on.
Please refer to the schematic diagram:
Measure C1, C2 voltage, should be normal at 12-25V.
Measure C11 voltage, less than 30V is normal.
Measure C15 voltage, 12V is normal.
If the above voltage is abnormal, please check whether the transformer is powered, whether the taps are connected incorrectly, and whether the components are installed incorrectly. Repeat the above steps until the voltage is normal.
Commissioning process:
Adjust VR3 and VR4 so that the voltage of pins 2 and 6 of U2 chip is above 10V
(Take U4's 4 feet as reference point).
The voltage across R17 should be the voltage after the first-stage tap rectification and filtering of the transformer.
The A-RP current knob is adjusted to the middle, and the constant current indicator LED1 should not be lit at this time.
Adjust the V-RP, the voltage can be adjusted around 0-18V (R17 voltage) is considered normal.
The output voltage is adjusted to the voltage of the first stage relay switching point