Power supply with microcontroller control 0-25 volts. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Power supply with microcontroller control 0-25 volts. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power Supplies

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It consists of an indication and control unit, a measuring unit and a short circuit protection unit.

Display and control unit

Indicator - LCD display based on the HD44780 controller, 2 lines of 16 characters. Voltage control is carried out by the built-in PWM ohm controller. Its duty cycle is regulated by an encoder, each step of which leads to an increase or decrease in voltage by 0,1 volts at the PSU output. A full turn of the encoder is 2 volts. Since PWM can change the voltage on the storage tank only in the range from 0 to 5 volts, an op-amp with a gain of 5 is used. Thus, the actual voltage at the PSU output is regulated within 0 - 25 volts.

The regulating element is a powerful composite transistor KT827A. Feedback is provided from the emitter of the regulating transistor through the upper arm of the divider (2 X 8,2 k), due to which, even at high currents in the load, the voltage is maintained at a strictly specified level up to hundredths of a volt.

measuring part - a two-channel ADC (Microchip) that measures the real voltage at the PSU output and the voltage drop across the shunt resistor, amplified by the op-amp, which is directly proportional to the current consumed by the load. The heart of the design is the controller.

The block of protection against short circuit in loading. Made in the form of a separate device included between the rectifier and the regulating element. The protection trip current is 5 A. It is selected by a 47k resistor in the base circuit of the transistor controlling the KT825G key.

(click to enlarge)

Setting

It consists in the selection of resistors, marked with an asterisk, to match the LCD readings with the real current and voltage at the PSU output.

Details

The shunt is taken from a broken multimeter, its resistance is about 0,01 ohm. The initial state of the encoder contacts is described in the circuit diagram, it can be any corresponding to these states. In addition to rotation, it has external contacts that close without fixing when the shaft is pressed.
Unmarked npn transistors can be KT315 or any low-power ones like them in a chip package. The pnp transistor in the key that controls the backlight can be of any medium power.

How to use BP

The encoder regulates the voltage 0 - 25 volts in steps of 0,1 volts. With a short (less than 0,5 sec) press on the knob, the backlight turns on / off. When pressed for more than 0,5 seconds, the set voltage is recorded in the non-volatile memory of the controller.

Power supply with microcontroller control 0-25 volts. Photo BP

Full project for MPLAB you can download here.

Author: Sergey, Kremenchug, Ukraine, 8-050-942-35-95 or email blaze2006@ukr.net; Publication: cxem.net

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