21-41

2020 年度（第 11 回）電気学会東京支部栃木・群馬支所合同研究発表会

EMI Reduction and Frequency Stabilization in Ripple Injection
Type Hysteretic Controlled Switching Converter
Guiyi Dong *, Kento Itoi, Shogo Katayama, Tran Minh Tri
Yasunori Kobori, Anna Kuwana, Haruo Kobayashi,(Gunma University)
Abstract: This paper describes a ripple injection type hysteretic controlled switching converter to meet the requirement for the fast
response, such as in high-speed digital processor applications; it is one of hysteretic and nonlinear control methods. We have investigatedthe problem that when its output current is decreased, the operating frequency is decreased. We have found that its operation becomes incurrent discontinuous modes and the operating period becomes longer when the output current is decreased. Also, the constant operating
frequency range can be expanded by controlling the injection ripple waveform by the periodic detection. Finally, we introduce a phasemodulation method to reduce EMI.
Keywords: hysteretic controlled switching converter, ripple injection, discontinuous current mode, continuous current mode,
EMI Reduction, Frequency Stabilization

1.Introduction

output voltage Vo.

As shown in Fig.1, the circuit consists ofswitch, freewheel diode Di, energy storage inductor L, filter

Many DC-DC converters are widely used in electroniccapacitor C and associated circuits. When the switch is ON,

devices. Hysteretic controlled switching converter is known

the hysteretic controlled converter supplies power to theas a typical control method for high-speed control. Thisload through the switch and the inductor L, and stores part

method does not use a fixed frequency clock, but directlyof the electric energy in the inductor L and the capacitor C.

compares the output voltage with the reference voltage to

After a certain period of time, the switch is turned off, due toenable high-speed switching control. This control method

the self-inductance of the inductor L, the current in thehas the disadvantage that the control frequency fluctuates

circuit will remain unchanged. By controlling the time whensignificantly due to changes in the load current.

the switch is ON and OFF, the output voltage Vo can be

In this paper, first we introduce the principle of ripple

controlled. If the output voltage is detected to control the on

injection type hysteretic control switching converter. Thenand off time to keep the output voltage constant, it will

we introduce that when the output current decreases, itsachieve the purpose of voltage stabilization [3].

operation becomes discontinuous mode and the duty cycle

The comparator compares the output voltage directly

becomes longer. Also, it is analyzed that the constantwith the reference voltage Vref to control the switch output,

operating frequency range can be expanded by controlling

and the PWM signal is generated.

the injection ripple waveform by the periodic detection.

ONFinally, we discuss a circuit that uses phase modulation toVoL

Iout

reduce EMI.
ViDiOFFRL

2 Hysteretic control switching converterC

2.1 Characteristics of hysteretic controlled switching
converter

PWM

R2CompVref

The basic configuration of the step-down hysteretic
controlled switching converter is shown in Fig.1. The current

Fig. 1 Basic hysteretic controlled converter

flows from the switch or the diode to the inductor L and isprovided into the output capacitor C to obtain the low ripple

134The disadvantage of this basic hysteretic controlledcontrolled switching converter is shown in Fig.3. The

switching converter is that the change of the output current

intended ripple is injected into the input of the comparator

greatly changes the operating frequency and that theby connecting the ripple generating circuit CR to both ends

comparator needs a certain amount of ripple.

of the inductor L, so that the operating frequency in

In order to alleviate these problems, a large output

response to the change of the load current can be held

capacitor with a series of equivalent series resistancealmost constant.

(ESR) and a hysteresis comparator are used, so that therippleinjection

typehysteretic

controlled

CbandRfVrip

Cfconstant-on-time (COT) control switching converter can be
ESR

configured.

ESR

Vi

2.2 Operation of the hysteretic switching controlledconverter

Vo

R1RL

Di

C

PWM

R2Comp
VrefFig. 3 Hysteretic controlled converter with ripple injection.

(a) CCM state

3.2 Relationship between output current and operating
frequency(b) DCM state

In the circuit of Fig.3, the values of the main circuitFig.2 CCM state and DCM stateelements are set as follows: input voltage Vin = 10 V, output
The operation modes of the switching converter arevoltage Vout = 3 V, inductor L = 10 mH, output capacitor C =classified into continuous conduction (current) mode (CCM)

220 uF, ESR = 5 mΩ, R1 = 3.9 kΩ, R2= 470 kΩ, Rf = 470 kΩ,and discontinuous conduction mode (DCM) depending on

Cf = 5 nF,

the current flowing through the inductor current. ThemA, the output ripple ΔVout becomes 0.05 mV, and theInductor current is shown Fig2 :operating frequency Fop becomes 1.3MHz. Fig.6 shows theCb = 20 uF. Here, when the output current is 200

relationship between the operating frequency Fop and theDue to the self-inductance of the inductor L, after theoutput current Iout when Iout.is small. We see that the range

switch is turned on, the current increases relatively slowly.

of DCM is ~ 100 mA and the operating frequency F opThe inductor current is shown as below：

becomes lower by decreasing the output current.
Here SAW shows change of period, SAW∝T.

1 T
I out＝  I L (t)dt
T 0

(1-1)

Output current in CCM state is given by

I out = (IB + I T )/2(1-2)

Output current in DCM state is given as follows:

I out = ( I T /2)/{1+ T3 /( Ton + Toff )}(1-3)

3 Hysteretic controlled switching converterwith ripple injection
3.1 Method of ripple injection
The configuration of the ripple injection type hysteretic
Fig. 4. Operation frequency and output current

4
Improvement of operating frequency in DCM state
4.1 Stabilization circuit for ripple injection
When the output current decreases at DCM state, theoperating period T increases to keep the switch on-timeconstant.If the switch on-time is controlled in accordancewith the change of the operation period, the operationperiod

willbecontrolled

constantlyby

thefrequency-to-voltage (F/V) conversion circuit.
The proposed circuit is shown in Fig.9. Using the PWM
waveform, the voltage VH is detected which is in proportion

Fig. 9. Operating frequency before and after correction.

to the operating cycle. This voltage is amplified to generatea modulation voltage Vm which is injected into the ripplearea by the resistance Rm. Vm is used to modulate theripple waveform and control the on- time.

VmodRm

In this section we will introduce phase modulation method
Cb

RfVripin ripple injection type hysteretic controlled switching
converter.

CfVo IoutESRL
Vi

5 EMI Reduction in ripple injection type hysteretic control
switching converter

The proposed circuit shown in Fig.10 is uses phasemodulation method and the clock phase modulation circuitESR

R1

CR2

Di

is shown in Fig.11.it uses CR to delay the Pos edge of theinput PWM signal and generates a delay pulse compared tothe modulation voltage Vm. AND the output resistance

PWM
AMPCompterminal with Di to generate an output PWM signal.
Vref

F/V translation
circuit+-Vref(2V)

Feedback gain Gm

The peak level of the frequency spectrum decreases from
2.6V to 342mV which is -17.6dB reduction which is shown in
Fig.12.But the ripple of output voltage is from 1mV to 2mV
so we should improve the circuit to reduce ripple.

Fig. 7. Proposed circuit for modulation method of time
constant for ripple generation

4.2 Result of simulation
In the above condition, the relationship between I out andthe change of the operating frequency is shown in Fig.12.
Simulation result of proposed circuit in Fig. 9 is shown in
Fig.11.We see that the constant operating frequency range
is approximately equal to that of Iout = 60 mA, while thefrequency change width is improved from ⊿F=1.0MHz to0.3MHz, and the frequency change rate is improved from
α=85% to 20%.

Fig. 10.Phase modulation method in ripple injection typehysteretic controlled switching converter.

Fig. 8. Output current, inductor current and SAW voltage
Fig. 11.Phase modulation method circuitBefore ripple suppression

After ripple suppression

Fig. 12.Spectrum of PWM

Fig. 15. Output voltage ripple of proposed circuit

7 Summary and future challengeThis paper describes a ripple injection type hysteretic
Before phase modulation

controlled switching converter for fast response andconstant operating frequency. We verified the frequency
modulation method in hysteretic controlled switching
converter and discussed the feasibility of modulating thereference voltage. Finally, we analyzed the circuit using

After phase modulation
Fig. 13.Ripple of output voltage

phase modulation method in ripple injection type hysteretic
controlled switching converter，
Our future research is to stabilize the frequency even under

6 Improvement of ripple of output voltage

40mA for the output current, and to analyze ripple injection
type hysteretic controlled switching converter using theIn the above discussion, we can see that the ripple istransfer functions.

Larger.We use the same method as how to improve

References

operating frequency in DCM state , injecting VmN into theripple generating circuit.

(1) T. Sato, "Control Schemes of Switching Converters" in
Handbook of Power Management Circuits, Pan

Vm and VmN get same frequency but opposite phase.

Stanford

We obtain lower ripple 1mV from 2mV which is shown inNabeshima) USA, 2016

Publishers,(Editors:H.

Kobayashi,T

Fig.15.
(2) M. T. Tran , N. Miki, Y. Sun, Y. Kobori and H. Kobayashi,“EMI Reduction and Output Ripple Improvement ofSwitching DC-DC Converters with Linear Swept
Frequency

Modulation”,

IEEE14thInternational

Conference on Solid-State and Integrated Circuit
Technology, Qingdao, China (Nov. 2018)T.
(3)

T.

Zaitsu,K.

Goto,T.

Miyazaki,J.

Yamamoto,“D-CAP2TM Frequency Response Model”,
http://www.ti.com/lit/an/slva546/slva546.pdf

Fig. 14. Proposed circuit for EMI reduction with ripple

suppression