Consists of a display unit and control, measurement and protection unit from short circuit.
The unit display and control
Indicator - LCD display-based controller НD44780, 2 lines, 16 characters each. Voltage control is built into the PWM controller ohms. Its duty cycle is governed by the encoder, each step of which leads to increase or decrease the voltage by 0.1 volts on the output of the PSU. A complete revolution of the encoder 2 volts. Since the PWM can change the voltage on the storage tank only in the interval from 0 to 5 volts, is applied shelter with a gain of 5. Therefore, the actual voltage at the output of the PSU is regulated in the range 0 - 25 volts.
The regulatory element is a powerful composite transistor CTA. With the emitter of the regulating transistor through the upper shoulder of the divider (2 X 8,2 K) is feedback, so that even at high currents in the load voltage is maintained on a strictly predetermined level up to hundredths of a volt.
The measuring part is a dual - channel ADC (Microchip), which measures the actual voltage at the output of the PSU and the voltage drop across a shunt resistor, reinforced Oh that is directly proportional to consumed by the load current. The heart design is the controller.
The unit is protected against short circuit in the load. Made a separate device connected between the rectifier and regulating element. Current tripping - 5 A. Selected resistor C in the base circuit of the transistor Manager key CTG.
(click to enlarge)
Setting
Is the selection of resistors marked with an asterisk to match readings LCD real current and voltage at the output of the PSU.
Details
The shunt is taken from the broken multimeter, the resistance of about 0.01 Ohms. The initial state of the contacts of the encoder is described in the schematic diagram, it can be of any appropriate these conditions. In addition to the rotation, he has HV contacts that are closed without fixing clicking on the shaft.
Transistors n-p-n without marking can be KT315 or any low-power, similar to the chip housing. Transistor p-n-p in the key backlight control can be any medium power.
How to use BP
The encoder regulated voltage 0 - 25 volts in 0.1 volt. With brief (less than 0.5 sec) clicking on the knob turns on/off the backlight. When pressed for more than 0.5 seconds is written to the set voltage in the nonvolatile memory of the controller.
Full project for MPLAB you can download here.
Author: Sergey, Kremenchuk, Ukraine, 8-050-942-35-95 or email This email address is being protected from spambots. You must have JavaScript enabled to view it. ; Publication: www.cxem.net