CNC regulated power supply production

CNC DC Power Supply Manufacturing

1. System composition and principle overview

Compared with the traditional voltage-stabilized power supply, the digitally controlled DC power supply designed in this paper has the characteristics of convenient operation and high voltage stability. Its output voltage is digitally displayed. The principle block diagram is shown in Figure 1. It consists of six parts. The output voltage is adjusted by the "+" and "-" keys to control the reversible counter to count up and down respectively. The binary digital output of the reversible counter is divided into two paths: one is used to drive the digital display circuit to indicate the value of the power supply output voltage; the other enters the D/A conversion circuit. The D/A converter converts the digital quantity into an analog voltage in proportion, and then adjusts the output voltage required by the output stage through the emitter follower control. In order to achieve the normal operation of the above-mentioned circuits, it is necessary to make ±15V and ±5V DC power supplies and a group of unregulated 12~17V DC voltages.

2. Specific implementation circuit

According to the block diagram of the above digital control DC power supply, a digital control power supply with an output voltage of 0 to 9.9V is designed using an integrated circuit. The detailed circuit principle is shown in Figure 2.

1. Circuit Introduction
Two push button switches are used as voltage adjustment keys to connect to the up-count and down-count input terminals of the reversible counter. The reversible counter is formed by cascading two 4-digit decimal synchronous up/down counting integrated blocks 74LS192. The carry and borrow output terminals of the first block are connected to the up-count terminal and down-count terminal of the next group respectively. The total counting range of the two-stage counter is from 00000000 to 10011001 (i.e. 0-99).
The digital display decoding driver uses two 74LS248 integrated blocks. The 74LS248 is a four-wire-seven-segment decoder/driver with internal output pull-up resistors. It converts the binary-decimal 8421 code transmitted from the counter into decimal code and drives the digital tube to display the digital number.
The digital-to-analog conversion circuit uses two DAC0832 integrated blocks, which is an 8-bit digital-to-analog converter. Only the high 4-bit digital input terminals are used here. Since DAC0832 does not contain an operational amplifier, an external operational amplifier is required to form a complete DAC. The low-level DAC output analog quantity is shunted by a 9:1 shunt and then added to the high-level DAC output analog quantity and sent to the operational amplifier. The operational amplifier converts it into an analog output voltage proportional to the value of the digital input. The operational amplifier uses a low-noise, high-speed, high-quality operational amplifier NE5534 with a zero adjustment terminal.
The output stage of the adjustment uses an operational amplifier as an emitter follower to ensure that the output voltage of the adjustment tube is accurately consistent with the output voltage of the D/A converter. The adjustment tube uses a high-power Darlington tube to ensure that the output current value of the circuit meets the design requirements. The ±15V and +5V regulated power supplies required for the operation of each part of the digital control power supply are provided by fixed integrated voltage regulators 7815, 7915 and 7805. The input voltage required by the adjustment tube can be obtained by simple rectification and filtering, but it is required to provide a current of 5A.
2. The circuit debugging
and adjustment steps are as follows:
1) Input the number 00000000, short RE1, RE2, RF, adjust the zeroing potentiometer Rw of the op amp, and use a digital multimeter to detect the output voltage Vo = 0 ± 1mV.
2) Input the number 10011001, adjust RE1, RE2, RF, and make the output voltage Vo reach the predetermined full-scale value of 9.9V.
3. Main technical indicators
The voltage output range of the digital control DC power supply designed in this paper is 0 ~ 9.9V, the step value is 0.1V, the output ripple voltage is not more than 10mV, and the output current is 5A.
III. Improvement measures
The output voltage of this power supply is still limited. When a higher output voltage is required, without changing the adjustment accuracy (i.e., the step value), as long as the cascade number of counters and the number of corresponding D/A converters are increased, the digital display indication range is expanded, and the high voltage output op amp is selected, the requirements can be easily met. When positive and negative symmetrical output voltages are required, the purpose can be achieved by simply adding another set of power supplies and making slight changes to the D/A converter and the output adjustment circuit.