Journal of Robotics, Networking and Artificial Life, Vol. 4, No. 4 (March 2018) 326-329___________________________________________________________________________________________________________Development of NC Power Based on Buck Circuit
Fengzhi Dai*, Yuxing Ouyang, Runhua Mao, Ce Bian, Baochang Wei, Yiqiao Qin, Shengbiao Chang, Qijia Kang

College of Electronic Information and Automation, Tianjin University of Science and Technology,
1038 Dagunanlu Road, Hexi District, Tianjin, 300222, China
E-mail: * daifz@tust.edu.cn
www.tust.edu.cn

Abstract
This paper develops a kind of power-supply module that uses digital control and buck circuit. The module canconvert 220V alternating current into 0-30V direct current. In the aspect of circuit design, it is mainly AC-DC,
DC-DC conversion circuit and SCM minimum system circuit. In the aspect of control circuit, for feedback signal of
current sensor, the power-supply module can obtain average value by multiple methods and remove the mutation
value.
Keywords: Buck circuit, SCM, AC-DC conversion circuit, DC-DC conversion circuit

1. Introduction

the conventional power conversion circuit has acomplicated structure, low stability, easy to generate
errors, and consumes a certain amount of energy
because it needs to withstand a large amount ofresistance.
The main circuit of the NC power based on Buckcircuit is divided into the following three modules: (1)the first module is the AC-DC conversion circuit. Its
function is to convert the 220V AC to the 30V DC
through a transformer, a bridge rectifier module andfilter capacitor. (2) The second module is the DC-DC
conversion circuit. Its function is to convert the 30V DC
to the 0～30V DC through the Buck circuit. (3) The
third module is the microcontroller control circuit, its
main function is to protect the special requirements ofconstant voltage or constant current, through reading thecurrent sensor feedback signal and adjust the PWM duty
cycle to change the voltage output 2.
This paper is organized as follows. Section 2
describes the hardware circuit design, and Section 3
introduces the control strategies. The main circuit
simulation is implemented in Section 4, and theconclusion is presented in Section 5.

With the development of power electronic technology
and digital control technology, more devices combine
these two technologies. This paper develops a power
module that combines MCU with Buck circuit toenhance the digital control of the power supply module
to a certain extent to make up for the lack of traditional
power supply module 1.
At present, the traditional power conversion circuit
uses TL494 as the PWM signal generator and the MOS
tube as the switch element. The regulation of voltage isrealized by building analog circuits and adjusting theresistance of sliding rheostat or potentiometer to change
the duty ratio of PWM.
A closed-loop system can also be formed by building
an analog circuit, but this closed-loop system has asimple structure and low anti-interference ability. The
most important thing is that this conversion method thatbased on the analog circuits has its own insurmountable
shortcomings, such as the inability to display parametersof voltage and current in real time and the disadvantage
of not being able to be adjusted in real time. Moreover,

Copyright © 2018, the Authors. Published by Atlantis Press.
This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).
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Journal of Robotics, Networking and Artificial Life, Vol. 4, No. 4 (March 2018) 326-329___________________________________________________________________________________________________________

2. The hardware circuit design
The basic circuit of the system is divided into step-down
rectifier filter circuit, Buck circuit, measurement circuit,
SCM supply circuit, 430F149 minimum system circuit,
LCD liquid crystal display circuit and independent key
circuit. The step-down rectifier filter circuit is discussed
in Section 2-1. Section 2-2 describes the Buck circuit.
Section 2-3 introduces the 430F149 minimum system
circuit 3.

Fig.2 The buck circuit

2-3. The circuit of the system
Other circuits are related to the control chip. The
430F149 microcontroller peripheral circuits include thereset circuit, crystal oscillator circuit and power supply
circuit. The power supply circuit mainly uses theLM7805 regulator module and LM117 regulator module.
This part of the circuit can change the 30V DC voltage
into 3.3V DC voltage, so as to provide a stable voltage
to control the microcontroller. The circuit of the system
is shown in Fig.3.

2-1. The step-down rectifier filter circuit
This part includes the transformer, full-bridge rectifier
and filter capacitor. The role of the transformer is toconvert the 220V AC to 30V AC. After the rectification
action of the full bridge rectifier module, the alternating
current is converted to direct current, but the waveformof the direct current is unstable. Using the filter
capacitor can make the DC waveform more stable 4. The
step-down rectifier filter circuit is shown in Fig.1.

Fig.1 The step-down rectifier filter circuit

2-2. The Buck circuit
Fig.3 The circuit of the system

Buck circuit is mainly composed of the MOS tube
IRF540, inductor, capacitor and freewheeling diode.
The MOS tube IRF540 is mainly used in the circuit as ahigh-power switching components, which is the core of
the DC-DC circuit. The diode protects the entire circuitby preventing the reverse flow of current. Inductanceand capacitance form a low-pass filter, making thecircuit output current waveform be smoother. The buckcircuit is shown in Fig.2.

3. The control strategies
Well-designed hardware circuits and powerful control
ICs play a crucial role in NC power, but control
strategies are also an integral part to maintain the proper
operation of a device 5. For the NC power that isdeveloped in this paper, the control strategy is mainly
used in the chips on the ACS712 current sensor module
for the feedback signal processing. The system is basedon the signal to adjust the PWM signal output. However,to solve some of the sensor’s problems, we can improve327

Journal of Robotics, Networking and Artificial Life, Vol. 4, No. 4 (March 2018) 326-329___________________________________________________________________________________________________________r

4-1 The AC-DC conversion simulation circuit

the situation to some extent through data processing.
The PWM signal output must also have a certain control
strategy, in order to improve the voltage conversion
capability 6.
Because the ACS712 current sensor feedback is ananalog signal, when the external interference has anabrupt change in value, there will be a measurement
error. The control strategy adopts the method of filtering
the mutation value and obtaining the average value. In
each group of data, five data that have larger absolutedeviation value are deleted, and the five data that havesmaller absolute deviation value are retains. Thus forthe five groups, there are a total of 25 sets of data. We
again average these 25 data, the average as the true
value of the feedback signal.
After obtaining the feedback value of the dataprocessing, we use the difference between the feedback
value and the value that has been set to adjust the duty
cycle of the PWM. Because the load will have a certain
voltage and current limit, so we adjust the PWM duty
cycle, the step value should not be too large, to prevent
overshoot. However, if the step value is too small, it
will make the adjustment time increase, which will not
be conducive to real-time response of the entire system.
Therefore, we set the threshold to adjust the PWM duty
cycle. When the difference between the actual feedback
value and the set value is larger, we adopt a larger step
value to adjust the duty cycle of the PWM, and when
the actual feedback value approaches the set value, thestep value is reduced.
Through this strategy, the voltage conversion abilityof the entire system can be well improved, and thereal-time response of the whole system is good.

In the AC-DC conversion simulation circuit, we set
three measurement points, namely the input voltage Ui,
the transformer output voltage U1i and the rectified
output voltage U1. We use voltmeters and oscilloscopes
as measurement tools. The oscilloscope detects the
waveform of the final output voltage U2 and the time ittakes for the voltage to reach to the steady-state time.
The simulation result of AC-DC circuit is shown in
Tab.1.
Tab.1 The simulation result of AC-DC circuit
Ui (V)n1:n2

U1i (V)U1 (V)

C(uF)

T(ms)

W

220
7:1
31.149 42.357
500
4.924
S
220
8:1
27.492 36.768
500
4.924
S
220
9:1
24.437 32.688
500
4.924
S
220
10:1 21.993 29.234
500
4.924
S
(Note: C: Filter capacitor, T: steady-state time, W:
Waveform, S: stable.)
If we hope that the final output voltage of the overall
circuit U2 ranges between 0～30V, then in the AC-DC
circuit, the output voltage values U1 that is after
rectification must be above 30V. Taking into accountthe MOS tube IRF540 protection and as much as
possible to reduce the heating power, the AC-DC circuit
output voltage values should be as close to 30V.
According to the above two points, when we select thetransformer turns ratio is 9: 1 turns, the circuit can makethe output voltage value U1 is 32.688V.
4-2 The buck circuit simulation
Buck circuit is the core circuit of the NC power supply,and it will directly affect the efficiency of the entire
system, so the parameters of each component isparticularly important 7. All the parameters of thecapacitance and inductance in the Buck circuit are
determined after simulation, so as to keep the output
waveform stable, reducing the time of the Buck circuit
to reach the steady state 8.
From the experimental data in Tab.2 we know thatthe values from simulation and theoretical calculation
are different. Experimental data show that when we
select the capacitance and inductance larger values, thelonger the time is required to reach the steady state, but
the waveform is relatively smooth. When the selected

4. The main circuit simulation
The maximum input voltage of LM78XX series voltage
regulation module is 36V, so the voltage after the filter
module of variable voltage rectifier must be reduced
below 36V. In the Buck circuit, the parameters of
capacitance and inductance will directly affect the timeof the system circuit to reach the steady-state. So, weneed to go through a software simulation to find one ormore sets of optimization data. Section 4-1 introduces
the AC-DC conversion simulation circuit. Section 4-2
introduces the buck circuit simulation.

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Journal of Robotics, Networking and Artificial Life, Vol. 4, No. 4 (March 2018) 326-329___________________________________________________________________________________________________________

ensure the stability of the equipment and formed aclosed-loop control. In the whole system, the analog
circuit part is responsible for the voltage conversion,
while the digital control part is responsible for the
regulation of the system. These two parts work
independently and complement each other, so that thepower supply module is smart and the device is safer
and steadier to supply the power to the load.

capacitance and inductance is small, although thesteady-state time is shorter, the waveform is unstable.
So we choose the middle value of the capacitance andinductance as 470uF and 100mH.
Tab.2 The simulation result of Buck circuit
U1(V)

D

TV(V)

SV(V)

L1(mH)

C12(uF)S(ms)32.688

20%
40%

6.538

5.915

100

470

203.4

13.07512.590

100

470

247.6

60%
80%

19.61319.388

100

470

255.2

26.24025.981

100

470

272.1

90%
90%

29.41229.285

100

470

250.5

29.41229.149

1000

470

397.4

90%
90%

29.41229.275

10

470

101.7

29.41229.275

100

47

68.7

32.68832.68832.68832.68832.68832.68832.688

Acknowledgements
The research is partly supported by the Research Fundfor the Reform in Education from Tianjin Municipal
Education Commission of China (171005704B).
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32.68890%29.41229.338
100
4700
799.9
(Note: D: Duty cycle, TV: Output theoretical value, SV:
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From the circuit simulation results, we determine thetransformer turns ratio of 9:1, and in the Buck circuit,the specific value of the capacitor is 470uf and theinductor value is 100mH.
5. Conclusion
Developed in this paper based on the Buck circuit NC
power supply, it can output any stable voltage values
between 0 ～ 30V, and the values of which can bereal-time displayed. The device can not only be used asa constant current source, but also can be freely
switched to a constant voltage source.
The working hours of the equipment can be set
programmatically, and the equipment can automaticallycalculate and display the voltage, current and consumed
energy values through the load. It has the automatic
alarm function that is used to monitor these values toreach the limited value or not. At the same time, we
incorporated data processing and control strategies to329