ZHENYOU WANG et al: DESIGN OF A POWER CONVERTER BASED ON UC3842 FOR BLADE ELECTRIC ...

Design of a Power Converter Based on UC3842 for Blade Electric Vehicle

Zhenyou Wang, Qun Sun*, Hongqiang Guo

School of Mechanical and Automotive Engineering, Liaocheng University

Liaocheng, China
*Corresponding author: sunqun@163.com

Abstract — In order to meet the demand of loads on a blade electric vehicle (BEV), a DC switching mode power supply has been
designed based on the current mode pulse width modulator UC3842. This device converts the 64V DC power supply on a BEV into
12V low-voltage power source in order to suit the usage of different loads on the vehicle. The output power of the converter can
reach more than 100W. This paper introduces the principle of the current mode pulse width modulator UC3842, and presents the
design principles of the switch power converter based on UC3842, and the related circuit design, PCB board design as well as
experiments.

Keywords - switching power supply; UC3842; the flyback type switch power supply.

I. INTRODUCTION to improve the operating frequency of the switching power

supply. Using resonant switching mode converter has been
In recent years DC switching mode power supply has adopted in some practical applications [5-7].
been widely used in the area of electron device, such as According to the actual demand of DC power supply in
SPC exchange, communication, electronic inspection and blade electric vehicle (BEV), this paper represents a DC
many types of controlling device, which have greatly power supply converter. The device mainly converts the
helped the rapid development switching mode power fixed 64V DC voltage of storage battery in BEV into other
supply [1]. The costs of switching power supply and linear fixed DC voltages to meet the demand of different loads.
power supply both increase with the rise of the output The DC voltage can output stabilized current with current
power although the rates are different. Beyond some point pulse width modulator U3842, and it can provide the
of the output power, the cost of linear power supply is protection of over-current, over-voltage and under-voltage.
higher than the cost of switching power supply. With the The switching power supply application is of great
development and innovation in power and electron significance in energy saving, resource saving and
technology, the switching power supply has been much environment protection.
developed to reduce its cost [1-2]. In the contents the following parts are included:
Recently, integrated switching power supplies have The analysis of the operating principle of switching
gradually developed towards two directions. One direction power supply, and selection of the working mode;
is the integration of controlling circuit of the switching The main circuit selection and its parameters,
power supply, and recent PWM and PFM ICs can achieve The controlling chip selection and its parameters,
1MHz frequency. Another direction is the realization of The design and creation of high-frequency transformer,
single chip integration with middle and small power Debugging its circuit to testify its correction and
consumption. Because of the characters of the high feasibility.
integration, highly cost effective, simple peripheral circuit
and optimal function index, single chip switching power
supply has become the first choice in the power supply II. DESIGN OF THE SWITCHING POWER SUPPLY
integrated circuit [3]. A.
Generally, the switching power supply contains PWM
and MOSFET. The power tubes of switching power supply B. A. Brief Introduction to UC3842 chip
mostly use bipolar transistors and the switching frequency
can reach tens of kilohertz. While using MOSFET instead UC3842 is a kind of high performance single end
of power tubes, the frequency can reach several hundred output current controlled pulse width modulator. Current
kilohertz [4]. In order to improve the switching frequency, mode control compares the output induction current sensed
high-speed switching devices must be used. Using the from the input of the pulse width comparator with the error
resonant circuit can fit to the switching power supply with amplifier output signal to control the duty cycle of the
megahertz frequency, which is called resonant switching output pulse, so as to ensure the output of the peak inductor
mode. It can greatly increase the switching speed with current to follow the error voltage variations.
small noise and lead to no loss in theory, which is one way UC3842 is a high performance fixed frequency current

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mode controller using a single end output mode, and can signal is provided by the PWM controller. The more
directly drive a bipolar transistor or MOSFET tube, with important parts are the auxiliary power supply and the
advantages of fewer pins, simple peripheral circuit, PWM controlling circuit which will be further explained in
convenient installation and debugging, excellent the following section.
performance and low price. It has protection characteristics
such as under-voltage lockout and current limitation. In B2. The auxiliary power supply
application a UC3842 chip adopts DIP-8 package and its The auxiliary power supply is a single-ended flyback
internal modules mainly include 5.0V reference voltage switching power supply based on UC3842, as shown in
source, oscillator to precisely control the duty cycle Figure 2. The DC voltage of the blade electric vehicle is
adjustment, an attenuator, an over-current detection connected to Pin 7 of UC3842 through R2 [11-13]. When
comparator, PWM lock latch, high gain E/A error amplifier the voltage on Pin 7 reaches 16V open voltage of UC3842,
and output circuit to drive power MOSFET current the controller starts to work. The current consumption is
push-pull. about 15 mA during normal operation, fed by the
transformer coil N2 via D3 and C10. Pin 6 outputs waves
B. Circuit Design of Switching Power Supply according to the RT/CT oscillation frequency and drives the
switching tubes. Pin 8 outputs a 5V reference voltage that
This paper presents a 100W switching power supply charges RT and discharges through an internal current,
developed to meet the demand of different loads in BEV. resulting oscillation in CT. The frequency of the oscillator
The basic technical indices are as the following: is:
64±10％V input DC voltage, f =1.8/（RT×CT）kHz (1)
70V maximum output voltage,
4A maximum output current,
The voltage ripple is no more than 1%. The output 12V DC shown in Figure 2 serves as the
normal operating voltage of the following control chip.
Feedback output voltage is produced meantime using
B1. The Circuit Functionalities
TL431 for over voltage protection. TL431 is a three
The working process is as following. Firstly through R2 terminal programmable parallel voltage stabilizing diode,
the power source provides current to charge the capacitor which has Vout= (1+R1/R2)*Vref. Since the reference
C1, and when C1 voltage reaches the starting threshold 16V, voltage of TL431 is 2.5V, R16 and R17 are used to
UC3842 begins to work and provide a driving pulse configure the reference programming voltage to 12V. Thus
through output pin 6, producing high and low voltage pulse. when the transformer winding N3 output voltage is greater
During the high voltage pulse, the field effect transistor is than 12V, conduction occurs in the linear optical coupler
switched on, the current is passed through the primary side PC817, the transformer N2 winding provides feedback
of the transformer, and the energy is stored in the voltage to Pin 2 of UC3842, leading to increased voltage on
transformer. The field effect tube is cut off when high level Pin 2, and the internal protection circuit starts. The output
pulse through pin 6 is finished. According to Lenz's law, the high level pulse on Pin 6 becomes shorter or disappears,
transformer primary side tries to maintain a constant leading to shutoff of the switching tubes, so as to reduce the
current, resulting in an induced electromotive force that output voltage. In the circuit R4, C2 and D2 constitute the
yields diodes conduction on the secondary side, providing absorbing circuit to eliminate the reverse peak voltage
energy outward [8-10]. At the same time, the feedback coil generated by the inductance leakage of the transformer, so
provides power to UC3842 through the diode D3. as to protect the switch tubes from being burned.
In the actual design, the power converter can be divided
into three parts, namely auxiliary power unit, PWM control
B3. The PWM control circuit
unit and DC/DC conversion unit. The auxiliary power
supply consists of a small power DC/DC isolation PWM controlling circuit mainly provides the PWM
transformer and some other electronic components that signal to the field effect tube that controls the DC/DC
provide a stable and over 10V voltage to the PWM control transformation. When the forestage circuit output voltage
circuit. The PWM control circuit adopts UC3842 and uses reaches open threshold voltage of 16V, UC3842 begins to
the feedback source current to control. It also samples the output PWM pulse wave through Pin 6 to drive the
output voltage, divides voltage for comparison, and feeds MOSFET tube turn on and shut off. The output end of the
the signal back to the PWM controller. The DC/DC circuit uses totem pole output, so as to achieve the effect of
converter is a typical DC buck chopper circuit (Chopper DC chopper. In order to obtain a stable DC power supply,
Buck), which is composed of a field effect transistor, a the circuit is similar to the forestage circuit that uses
continuous current diode and an energy storage capacitor. feedback of output voltage, through TL431 to control
The field effect tube grid is controlled by the PWM wave overload of the output voltage. Through configuration of
period of 20 kHz square wave signal, and the square wave R16 and R19 in the circuit, the reference voltage is

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programmed to pass 13V, so that an output voltage greater Table 1. THE PARAMETERS OF THE TRANSFORMER
than 13V leads to conduction of the optical couplers. This
Parameter Symbol Unit Value Duty ratio
means the compensation signal on Pin 1 is connected to the
feedback input Pin 2, forming loop compensation, so that a Input voltage Vin V 70
shorter time of high level pulse on Pin 6 reduces the duty
Output voltage 1 Vo1 V 12 100%
cycle of the chopper signal, and reduces the output voltage.
In addition, the circuit is also designed with input over Output voltage 2 Vo2 V 25 100%
current protection using Pin 3 of UC3842. Supply current
Input current Ip A 3 100%
through the current transformer (CT) becomes sampled
current following a certain transformation ratio, connects to Output current 1 Io1 A 10 100%
Pin 3 after sampling resistor R3. When the voltage on the Output current 2 Io2 A very small
sampling resistor is greater than 1V, UC3842 stops the
output trigger pulse, shut off the switch tube, thereby Frequency f kHZ 20
protects the switching tube to achieve over-current
protection function.
The transformer selects a ferrite core and the valid area
of magnetic core is Ae=5*5*π=79mm2. The line number of
C. The design of high frequency transformer each transformer primary side winding is
N p  Vin max / 4  fs  Bm  Ae 
The transformer is a custom designed high frequency
transformer, with one primary winding and two secondary 
 64 / 4  20 103  0.2  0.79 10  4  51  (6)
windings, and the first secondary winding is mainly to feed The line number of subsidiary winding is
the external loads and the second secondary windings are
mainly to provide normal operating current to UC3842. N s1  N p / K  51 / 10  3  15.5
The DC voltage source is ranging from 64V to 70V, and N s 2  N p / K  51 / 2  25 (7)
the rated output voltage is 12V. Considering the system
reliability and normal human auditory frequency range The valid value of current and subsidiary side current
within 50-20000Hz, the design of switching frequency are respectively
should be above 20 kHz to reduce the working noise of the
charger. However enlarged switching frequency will I p  3A
increase the loss of the switching tube. Considering the
I s1  I p  N1 / N 2  3  10 / 3  10 A (8)
noise and the efficiency, the switching frequency was set as
20 kHz and T=50us. The rated output is Uo1=12V and the I s 2  I p  N1 / N 3  3  2  1.5 A
output of UC3842 is Uo2=25V.
Assuming the time of MOSFET ranges from dead zone By choosing current density of the line as J=3A/mm2,
to turn-off is Tr=2us, then the maximum duty ratio can be the cross sectional areas of primary side winding line and
represented below, secondary side winding lines are given by
S p  I p / J  2 / 3  0.67 mm 2
Dmax  T  2  Tr  / T  0.92 (2)
S s1  I s1 / J  10 / 3  3.33mm 2 (9)
n1Vin  U o1 / Dmax  13V (3)
n 2Vin  U o 2 / Dmax  27.2V S s 2  I s 2 / J  1.5 / 3  0.5mm 2
n1  n1Vin / Vin min  13 / 64  0.2,
(4) D. Photoelectric linear transmission of PC817
n2  n 2Vin / Vin min  27.2 / 64  0.425 Optocoupler can be used to enable signal transmission
to be realized without direct link between the electrical
Taking into account the losses of components, the input and output signals. However, to achieve linear
proportion was rounded into: transmission of the signal, and to get an amplified electrical
signal, a drive circuit and amplifier circuit must be added,
N1 / N 2  10 / 3, N1 / N 3  10 / 5  2 / 1 (5) as shown in Figure 1.
Rs

The parameters of the transformer are shown in Table 1.

LED driver D2 Amplification
Vs LED Rl
circuit

Figure 1. The sketch map of electro-optical linear transmission

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If the input signal voltage is applied directly on LED the circuit. The circuit structure is shown in above Figure 3,
without a LED drive circuit, the LED luminous intensity where Vbias provided by the DC power supply is the
will become a nonlinear function of the input voltage. This working voltage required by photodiode. Source idrs and rs
means that the electric current and the load on the electrical form the low-frequency small-signal model of photodiode
signal is the nonlinear function of the input voltage. To [15]. Closed loop mutual blocking gain is provided by
ensure that the current flowing through the LED is
proportional to the input voltage, the driving circuit of the Arf  Vo / id  1 / Fg   Rf (10)
LED is very important. In order to make the output voltage
proportional to the input voltage, it is necessary to convert E. Feedback circuit design based on TL431
the current into the voltage of the photodiode. The drive TL431 is a precision adjustable reference power supply
circuit that brings negative feedback to PC817 is given circuit, which has a good regulation characteristics and
below. flexible regulation value set. Its output voltage can be
Rs arbitrarily set to any value from Vref (2.5V) into the
Iol maximum 36V with two resistors. Typical dynamic
impedance of the device is 0.2Ω, and in many applications
Vs
Vol this can be used to replace Zener diode, for example, a
LED
digital voltmeter, op-amp circuit, voltage regulator, and
Vf R1 switching power supply etc. The TL431 principle diagram
is shown in Figure 7.

Figure 2. Series connected negative current feedback circuit for driving Negative

PC817 Ref(R)

In the above figure, Vs is a voltage signal, Rs is the

2.5Vref
input resistance, A is an integrated amplifier that can be
based on LM324. LED is the lighting tube of the
optocoupler, Vo1 is output voltage, Vf is a feedback voltage, Positive(A)
and Rl is the load resistance.
The voltage signal is applied to the non-inverting input Figure 4. The representational structure diagram
terminal of the integrated operational amplifier, and the
load resistor feedback voltage Vf is applied to the inverting It can be seen from Figure 4, an internal 2.5V reference
input terminal of the integrated operational amplifier. When signal is connected to the inverting input of the op amp.
the voltage signal increases, Vf increases and the current Known from amp characteristics, only when the voltage
flowing through Rl increases, thus according to the virtual Ref terminal (inverting terminal) is very close to 2.5V, the
open principle of integrated operational amplifier, current transistor will have a stable, non-saturation current through,
Io1 is flowing through Rl and increases too. Thus the and along with small voltage changes on Ref terminal the
voltage on opto-coupler is proportional to the current [14]. transistor changes current from the 1mA to 100mA. TL431
Rs contains the internal reference voltage of 2.5V, thus when
output feedback is applied onto the Ref end, the device can
rs control the output voltage through a wide range of shunt
Idrs
from the cathode to the anode. The shunt circuit is shown in
Figure 5.
Vbias R1
V+ Vout
R1

R1

Figure 3. Mutual resistance amplifying circuit of the output end

R2
The circuit requires achieving current to voltage
conversion, i.e., the photodiode current changes into an
output voltage, so a mutual resistance amplifier circuit is
needed. In order to reduce the load effect of amplifier input Figure 5. The shunt voltage regulator circuit
and the output, the amplifier input resistance and output
resistance should be small. Therefore voltage parallel When R1 and R2 are specific they introduce negative
negative feedback amplifier circuit should be introduced in

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feedback to Vo, therefore if Vo increases, the amount of

feedback increases, TL431 shunt will increase, which in
turn leads to decreased Vo. Obviously, this deep negative
feedback is stable when VI is equal to the reference voltage,
and at this point Vo=(1+R1/R2)Vref. By choosing different
values of R1 and R2, the output voltage can be obtained
from 2.5V to 36V. In particular, when R1 = R2 it gives Vo
= 5V. The combined circuit diagram of TL43 with PC817 is
Figure 6.
e. Output wave at 10Ω f. Drive voltage wave at 10Ω

LM324N R12 1K
PC817 R13 12K
R14 1K

R15 R16
1K C7 0.01uF 38K
R17 10K
R18 VCC
2K
TL431 R19
10K

g. Output wave at 3Ω h. Drive voltage wave at 3Ω

Figure 6. The cooperating circuit diagram of TL431 and PC817.
Figure 7. The output voltages and waveforms under different loads

III. ANALYSIS OF WXPERIMENTAL RESULTS

In addition, Table 2 lists the corresponding load, duty
This design adopts linear optocoupler to change the cycle, and output voltage at specific conditions.
error amplifier voltage of the feedback circuit to construct a Table 2. EXPERIMENTAL DATA
64V/12V single ended flyback DC-DC switching power
supply. the output voltage of the power supply is stable and Load(Ω) Duty cycle(%) Output voltage（V）
the load capacity is strong. Figure 7 shows the output 100Ω 10% 12.10
voltages and the driving waveforms with varying loads.
25Ω 15% 12.15

10Ω 20% 12.19

3Ω 35% 12.21

From the table it can be seen that when the load current
increases, the duty cycle of the drive signal is also
increased, but the output voltage has been maintained at
a. Output wave at 100Ω b. Drive voltage wave at 100Ω around 12.1V, and the switching power supply load
adaptability is strong.

IV. CONCLUSION

A DC/DC power converter based on UC3842 chip has

been developed to convert high voltage power source from
vehicle battery to PWM controlled low operating voltage.
By utilizing good control characteristics of UC3842,
c. Output wave at 25Ω d. Drive voltage wave at 25Ω
effective on-off control of field effect tube is implemented.
Protection circuit has been designed to prevent over current
and over voltage and to ensure normal operation of the
power converter. The experimental results showed that the
output voltage of the converter is stable when the input
voltage range is from 64V to 70V, which meets the design
requirements. The power converter achieved operating
frequency up to 500 kHz, starting current less than 1 mA,

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voltage adjustment rate of 0.01% / V, and the maximum

duty cycle of 100%. It indicates a good prospect due to
simple peripheral circuit, superior performance and low
cost.
Future work: If the power converter is applied to the
actual work, the safety of power converter and heart
dissipation of circuit modules are needed to improve. It
needs large number of experiments, in order to texting the
safety in actual work.

REFERENCES

[1] Q. J. Hou, L. Q. Zhang and D. G. Xu. “Analysis of the basic

principle and the development trend of switching power supply.”
Manufacturing Automation Industry, vol. 12, pp. 160-162, Sept.
2010.
[2] S. Hobrecht. “Single IC, five output switching power supply system
for portable electronics.” Analog Circuit Design, vol. 3, pp: 207-208,
Feb. 2015.
[3] J. Q, Zhu, D. Xie, F. Wang, T. Q. Cao. “Study on the Harmonics of
Switching Power Supply.” Procedia Engineering, vol. 29, pp.
2098-2102, Feb. 2012.
[4] C. Si, Z. Q. Meng, Y. D. Chen. “Development of a Soft-Switching
Power Supply for Ozone Generation Based on Phase-Shifted
Control.” Procedia Engineering, vol. 23, pp. 690-694, Dec. 2011.
[5] K.M. Tsang, W.L. Chan. “A single switch DC/DC converter with
galvanic isolation and input current regulation for photovoltaic
systems.” Solar Energy, vol. 119, pp. 203-211, Sept. 2015.
[6] A. Roshala, S. Avanesova, E. Koktsinskaya, et al. “Design and
analysis of Switching Network Units for the ITER coil power
supply system.” Fusion Engineering and Design, vol. 86, pp.
1450-1453, Oct, 2011.
[7] E. Feinberg, J. Hu, E. Yuan. “A stochastic search algorithm for
voltage and reactive power control with switching costs and ZIP
load model.” Electric Power Systems Research, vol. 133, pp.
328-337, Apr. 2016.
[8] C. Maria, L. Cananà. “Markov switching of the electricity supply
curve and power prices dynamics.” Physica A: Statistical Mechanics
and its Applications, vol. 391, pp. 1481-1488, Feb. 2012.
[9] Y. J. Ma, Y. G. Yang, X. S. Zhou. “The Application of Power
Electronic Switches in High Voltage Quick Switching Device.”
Procedia Engineering, vol. 29, pp. 466-469, Feb. 2012.
[10] M. Uno, K. Tanaka. “Pt/C catalyst degradation in proton exchange
membrane fuel cells due to high-frequency potential cycling
induced by switching power converters.” Journal of Power Sources,
vol. 196, pp. 9884-9889, Dec. 2011.
[11] M. Kalantar, S.M. Mousavi G. “Posicast control within feedback
structure for a DC–DC single ended primary inductor converter in
renewable energy applications.” Applied Energy, vol. 87, pp.
3110-3114, Oct. 2010.
[12] P. Becker, E. Hymon, B. Folkmer, Y. Manoli. “High Efficiency
Piezoelectric Energy Harvester with Synchronized Switching
Interface Circuit.” Procedia Engineering, vol. 47, pp. 394-397, Nov.
2012.
[13] L. Zhang, L. Yang, J. Yang, et al. “Power supply design for the
filament of the high-voltage electron accelerator.” Nuclear
Instruments and Methods in Physics Research Section A:
Accelerators, Spectrometers, Detectors and Associated Equipment,
vol. 804, pp. 94-98, Dec. 2015.
[14] H. Wu, G. F. Shen, Y. Z. Chen. Feasibility of an electromagnetic
compatibility method for MRgFUS using a wire mesh screen.
Ultrasonics, vol. 72, pp. 15-23, Dec. 2016.
[15] J. L. Roldanc, R. Pater, et al. “Development of non-intrusive
monitoring for reactive switching of high voltage circuit breaker.”
International Journal of Electrical Power & Energy Systems, vol. 61,
pp. 219-228, Oct. 2014.

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