FIELD OF THE INVENTION
The present invention relates to power conversion apparatus and, more particularly, to
switching power converter apparatus and method of its operation. The present invention
is directed to the current mode controlling (CMC) of a dc-dc converter through inductor
current filtering. Advantageously, a load-independent regulation is achieved in a current
mode controlled (CMC) dc-dc converter. The present invention is thus directed to
switching power converters adapted for improving load regulation, output impedance,
line regulation, bandwidth and phase margin. The switching power converter of the
present invention retains the improved line regulation, audio-susceptibility, bandwidth
and phase margin of the current mode control, and in addition, it improves output
impedance and load regulation. The achieved output impedance is much lower than that
using the current mode control, and similar to that of the voltage mode control with
reduced resonant peaking at high frequency. The converter of the invention is capable of
providing a cost effective means to switching power converter system with potential for
wide scale use in a variety of electrical and electronic instruments/equipments including
the computer systems catering to research establishments, manufacturers,
semiconductor industries developing products in related field with significant economic
advantage.
BACKGROUND ART
It is known in the field of control of power conversion equipments that switching power
converters are used to convert a direct current (DC) voltage into a disered stable DC
voltage, different from the input, with high efficiency. They are often used in electronic
devices such as mobile phones and computers etc. Switching power converter circuits
often include one or more switching elements, such as metal-oxide semiconductor FETs
(MOSFETs) that selectively couple a DC power source to an inductor, such that the
inductor is periodically charged and discharged to produce a DC output voltage. They also
alternatively couple and decouple a voltage source to a load. An output filter, such as one
comprising an inductor and a capacitor, removes high frequency switching noise to
produce the desired average output voltage.

It is also very common in related prior art of switching converters that are categorized
as the buck converter, boost converter, buck/boost converter and flyback converter.
During high and medium load conditions, a converter operates in the continuous
conduction mode (CCM), when the current through the inductor (inductor current) never
reaches zero at steady state, or else it enter into the discontinuous conduction mode
(DCM).
In spite of the variations in the supply voltage and the load current, a controller
maintains the average output voltage of the converter at a desired reference value. In
the voltage mode control (VMC) scheme for converter control, the same is accomplished
by using a closed feedback voltage loop. The VMC scheme offers improved load
regulation, but suffers from poor line regulation, bandwidth and phase margin. The above
limitations are overcome using the current mode control (CMC), wherein an additional
current feedback loop is used, as compared to the VMC. However, the CMC has poor load
regulation and high output impedance. According to the existing art, the power supply
designed for microprocessor load, requires very tight load regulation, and large
bandwidth and stability margin. Both the VMC and CMC schemes thus suffer from their
usual drawbacks and limitations to meet the load regulation efficiency to the required
level.
Load-current feed-forward in the CMC, remains an alternative way in improving load
regulation and bandwidth. However, beside the requirement of an additional current
sensor, it requires an accurate matching between two sensing resistors (i.e. for sensing
inductor current and load current), which is very difficult because of the temperature
dependency. Apart from that, the additional sensor consumes additional power, thereby
reducing efficiency.
The literature search in the related field revealed that the feed-forward mechanism,
especially using the load current, is quite useful in the CMC for improving load regulation
and bandwidth [such as in published documents by R. J. King, "Feedforward Control Laws
for the Buck Converter," in Proc. IEEE 4th Workshop on Computers in Power Electronics,
1994, pp. 192-197; J. Y. Guo, "Investigating feed-forward mechanism in current mode
control," in Proc. IEEE APEC, 2006, pp. 1008-1013; R. Redl, B. P. Erisman, and Z.

Zansky, "Optimizing the Load Transient Response of the Buck Converter," in Proc. IEEE
APEC, 1998, pp. 170-176].
The estimated load-current feed-forward and adaptation [as revealed in A. V. Peterchev
and S. R. Sanders, "Load-Line Regulation With Estimated Load-Current Feedforward:
Application to Microprocessor Voltage Regulators," IEEE Transactions on Power
Electronics, vol. 21, no. 6, pp. 1704-1717, November 2006; & G. Eirea and S. R.
Sanders, "Adaptive Output Current Feedforward Control in VR Applications," IEEE
Transactions on Power Electronics, vol. 23, no. 4, pp. 1880-1887, July 2008] requires
digital implementation and may not be feasible in a purely analog implementation. The
use of load current feed forward has been presented to improve the transient
performance for a step change in the load current in a hysteretic current-mode-controlled
buck converter [as revealed in the publication by R. Redl and IM. O. Sokal, "Near-
optimum dynamic regulation of DC-DC converters using feed-forward of output current
and input voltage with current-mode control" IEEE Transactions on Power Electronics,
vol. 1, no. 3, pp. 181-192, July 1986], in which the zero output impedance is achieved
by using a unity-feed-forward gain. A comprehensive analysis by considering a CMC buck
converter has been revealed in the prior art literature [e.g. G. K. Schoneman and D. M.
Mitchell, "Output Impedance Considerations for Switching Regulators with Current-
Injected Control," IEEE Transactions on Power Electronics, vol. 4, no. 1, pp. 25-35, July
1989]. The general conditions for achieving zero output impedance have been derived in
prior patentpn US Patent, Patent No. 4885674, 1989, by L. D. Varga and N. A. Losic,
titled "Synthesis of Load-Independent Switched-Mode Power Converters"]
A theoretically consistent treatment of the effect of load-current feed-forward in a
regulated converter is presented in prior publication [as in M. Karppanen, M. Hankaniemi,
T. Suntio, and M. Sippola, "Dynamic Characterization of Peak-Current-Mode-Controlled
Buck Converter With Output- Current Feedforward," IEEE Transactions on Power
Electronics, vol. 22, no. 2, pp. 444-451, March 2007] which says that exact matching of
both the sensing resistors (inductor current and load current) results in an output
impedance equivalent to that of the VMC with reduced resonant peaking. This is very
difficult in practice because of the temperature dependency of those resistors, and any
mismatch tends the behaviour towards that of the CMC. Furthermore, inappropriate
output impedance may destabilize the system [ such as revealed in M. Hankaniemi, M.
Karppanen, and T. Suntio, "Load-imposed instability and performance degradation in a

regulated converte," IEE Proc.-Electr. Power Appl., vol. 153, no. 6, pp. 781-786,
November 2006].
Sensorless current mode control (SCM) [as revealed in prior literatures by ] P. Midya, P.
T. Krein, and M. F. Greuel, "Sensorless current mode control - an observer based
technique for dc-dc converters," IEEE Transactions on Power Electronics, vol. 16, no. 4,
pp. 522-528, July 2001; & J. W. Kimball, P. T. Krein, and Y. Chen, "Hysteresis and Delta
Modulation Control of Converters Using Sensorless Current Mode," IEEE Transactions on
Power Electronics, vol. 21, no. 4, pp. 1154-1158, July 2006], is very useful in improving
line-to-output immunity and reference tracking. But, it may not be sufficient for
improving dynamic performance during a load transient, which has been improved by
combining both the CMC and the SMC in parallel dc-dc converters. In most of the SCM
techniques, the inductor current is estimated by integrating the voltage across the
inductor. It requires a prior knowledge of the accurate value of the inductor for which a
precise inductor with very low DC resistance (ESL), is required. However, the ESL of the
inductor depends on temperature as well as the operating frequency for which it might
require a compensating circuit.
There has thus been a need in the existing art for developing an efficient converter
system to solve the problem of switching power converter load regulation in the current
mode control(CMC). The present invention attempts to achieve the same without
requiring sensing of load current, means for load-independent regulation without
sacrificing the superior features of the current mode control such as line regulation,
audio-susceptibility, bandwidth and phase margin. Also the output impedance is
maintained at favorably low value. The converter system of the invention would ensure
improving the load regulation, output-impedance and energy efficiency significantly over
the existing methods, more preferably for low voltage high current applications.
OBJECTS OF THE INVENTION
It is thus the basic object of the present invention to provide a switching power
converter adapted for load-independent regulation of a switching power dc-dc converter
in current control mode without additional load-current feed-forward and a manner of

achieving energy efficient load regulation with controlled output impedance solely
through a simple filter network incorporated in series with the current sensor.
A further object of the present invention directed to a switching power converter for load-
independent regulation of switching power dc-dc converter in current control mode
wherein superior line regulation, bandwidth, phase margin and audio susceptibility of the
CMC are retained.
A still further object of the present invention directed to a switching power converter for
load-independent regulation of switching power dc-dc converter in current control mode
wherein requirement of load-current feed forward exactly matching with the sensing
resistor is eliminated and thus avoiding the need of use of any additional current sensor.
A still further object of the present invention directed to a switching power converter for
load-independent regulation of switching power dc-dc converter in current control mode
wherein energy efficient power conversion is achieved by maintaining favored low output
impedance made alike as of the VMC reduced or without resonant peaking.
SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided a switching
power converter comprising:
a power circuitry and a control circuitry;
said control circuitry having a filter network in series with the current sensor
adapted for improved output impedance and load regulation.
A further aspect of the present invention is directed to switching power converter
comprising a band pass filter adapted for improved line-regulation, bandwidth and phase
margin.

A still further aspect of the present invention is directed to switching power converter
comprising current control scheme involving a filtered current component.
A still further aspect of the present invention is directed to switching power converter
comprising a voltage feedback loop adapted for regulating the output voltage.
A still further aspect of the present invention is directed to switching power converter
comprising a ramp signal with added filtered inductor current adapted for improving
bandwidth, phase margin and line regulation.
According to yet another aspect of the present invention directed to said switching power
converter comprising a low pass filter (LPF) with bandwidth, fL in series with the current
sensor for further improving regulation, bandwidth and phase margin.
A still further aspect of the present invention is directed to said switching power
converter wherein fL is preferably limited upto 5fs where fs is the switching
frequency.
A still further aspect of the present invention directed to said Switching power converter
wherein a high pass filter (HPF) with the bandwidth, fH is considered in series with the
LPF for improving load regulation and output impedance.
According to yet another aspect of the present invention directed to said switching power
converter wherein a lower limit for fH, is fixed preferably ensure improved

bandwidth, phase margin, line regulation, audio-susceptibility and load-independent
regulation.
A still further aspect of the present invention is directed to said switching power
converter wherein a unity gain in LPF and HPF is desired and the overall filter structure is
adapted to take the form of a band pass filter.
The present invention and its objectives and advantages are described in greater details
with reference to the following non-limiting exemplary illustrations.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1: is the schematic illustration of the circuit diagram for conventional load
regulation system for dc-dc switching power converter using load current feed-forward in
CMC with additional current sensor for accurate matching between two sensing resistors.
Figure 2: is the schematic illustration of the circuit diagram for conventional load
regulation system for dc-dc switching power converter according to the present invention
using filtered current control scheme eliminating use of the additional current sensor.
Figure 3: is the schematic illustration of the graphical presentation of the control
waveform achieved using the system according to the present invention
Figure 4: is the schematic illustration of the comparative graphical plot of the
performance comparison in respect of Loop gain for FCC being filter based scheme of the
present invention, as compared to the CMC and the VMC.
Figure 5: is the schematic illustration showing the comparative graphical plot of
performance comparison in respect of Output Impedance of FCC as compared to CMC
and VMC
Figure 6: is the schematic illustration of the comparative graphical plot of performance
comparison in respect of Audio-Susceptibility of FCC as compared to CMC and VMC.

Figure 7: is the schematic illustration of the experimental results showing the control
waveforms obtained using the system of the present invention.
Figure 8: is the schematic illustration of the experimental result in respect of response of
the load regulation system according to the invention to a load current step-up of 1A to
2.8 A.
Figure 9: is the schematic illustration of the experimental result in respect of response of
the load regulation system according to the invention to a load current step-down of 2.8
A to 1A.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING FIGURES
The systems and methods described herein comprise a switching device that maintains
an average output voltage across the load resistance by alternately connecting the
output terminal between a first supply rail, such as a voltage source terminal and a
second supply rail, such as a ground terminal. A n-type power meta-semiconductor-field-
effect transistor ("MOSFET") may be used to connect the output terminal to the voltage
source terminal and a diode may be used to connect the output terminal to the ground
terminal. The n-type power FET and the diode operate on a mutually exclusively basis as
follows: at the start of every clock cycle the current through the n-type power MOSFET
starts rising, and when it reaches a desired peak value a ramp signal, the n-type power
FET is turned off and the diode gets forward biased, i.e. it is turned on; at the end of the
clock period the n-type MOSFET is turned on again, and the diode gets reversed biased,
i.e. it is turned off. The current output by the switching regulator passes through an
inductor and across a capacitor that cooperate to form an output filter. An instantaneous
inductor current may be determined by comparing a voltage drop across a resistance,
placed in series with the inductor. The waveform of the current through the inductor is,
for example, triangular in shape. Therefore, the ripple current, which is obtained after
filtering the actual inductor current (current through inductor) remains triangular in
nature. Accordingly, the desired average output current is achieved independent of
switching duty factor, inductor and capacitor value of the output filter, input supply

voltage, or output voltage. In addition, the switching behavior is stable, and also does
not require any output current feed-forward.
As already described, the present invention is directed to developing a system and
method for load-independent regulation for switching power converters to convert a
direct current voltage into different stable dc voltage with high efficiency in current
control mode ensuring superior line regulation, bandwidth, phase margin and audio-
susceptibility of the CMC are retained.
Reference is first invited to the accompanying Figure 1 that schematically illustrates the
conventional load regulation system for dc-dc switching power converter using load
current feed-forward in the CMC. The inductor current 120 is sensed through a sensing
resistor 109, placed in series with the inductor 111, and the voltage across 109 gives
120. The load current is sensed following the similar approach as mentioned earlier using
a sensing resistor 117. At the beginning of a clock period, which is synchronized with
128, 104 is high, which turns MOSFET 139 on, i.e., 103 and 105 are shorted, and current
120 starts rising; the MOSFET 139 then couples the input 1.01 with the output 112. Gate
signal 104 remains on until signal 132 reaches the signal 127, which is subtraction of
load current 118 from the sum of a ramp signal 139 and the sensed inductor current
110; a comparator 133 is employed to identify the time of switching transition. Then,
gate signal 104 becomes low, and the MOSFET 139 turns off, and the diode 106 becomes
forward biased; the diode 106 then connects the output to the ground 119. The input of
the gate of the MOSFET, 104 is obtained through a latch circuit 135, which is used to
avoid multiple switching, followed by a driver 138, which converts the output of a digital
logic signal from latch 135 to a sufficient high level signal 138, capable of driving a power
MOSFET 139. It is noted that in spite of the variations in the supply voltage and the load
current, a controller maintains the average output voltage of the converter at a desired
reference value. It is also experience in conventional voltage mode control (VMC) scheme
for converter control, the same is accomplished by using a closed feedback voltage loop.
Although, such conventional VMC scheme offers improved load regulation, but suffers
from poor line regulation, bandwidth and phase margin. These limitations are usually
overcome using the current mode control (CMC), wherein an additional current feedback
loop is used, as compared to the VMC and as clearly apparent from the accompanying
Figure 1. However, the CMC has poor load regulation and high output impedance.
According to the existing art, the power supply designed for microprocessor load,

requires very tight load regulation, and large bandwidth and stability margin. Both the
VMC and CMC schemes thus suffer from their usual drawbacks and limitations to meet
the load regulation efficiency to the required level.
Load-current feed-forward in the CMC, as achieved in the conventional systems as one
shown in Figure 1, has been an alternative way in improving load regulation and
bandwidth. This requires an additional current sensor 117 apart from inductor current
sensing using 110. However, besides the requirement of additional current sensing, it
requires an accurate matching between two sensing resistors i.e. for sensing inductor
current 109 and load current 117, which is very difficult because of the temperature
dependency. Apart from that, the additional sensor 117 consumes additional power,
thereby reducing efficiency.
Reference is now invited to the accompanying Figure 2 that illustrates the schematically
the load regulation for dc-dc switching power converter according to the present
invention in a representative circuit diagram that is directed to avoid the disadvantages
and limitations of the prior art CMC system as stated above whereby load-independent
regulation is achieved in a current mode controlled dc-dc converter. The inductor current
237 is sensed through a sensing resistor 209, placed in series with the inductor 211, and
the voltage across 209 gives 237. At the beginning of a clock period, which is
synchronized with 228, 204 is high, which turns MOSFET 238 on, i.e., 203 and 205 are
shorted, and current 237starts rising; the MOSFET 238 then couples the input 201 with
the output 212. Gate signal 204 remains on until signal 222 reaches the signal 230,
which is the sum of filtered current 224, which is obtained by passing the sensed inductor
current 210 through a filter 223, and a ramp signal 227; a comparator 231 is employed
to identify the time of switching transition. Then, gate signal 204 becomes low, and the
MOSFET 238 turns off, and the diode 206 becomes forward biased; the diode 206 then
connects the output to the ground 216. The input of the gate of the MOSFET, 204 is
obtained through a latch circuit 233, which is used to avoid multiple switching, followed
by a driver 236, which converts the output of a digital logic signal from latch 233 to a
sufficient high level signal 236, capable of driving a power MOSFET 238. The switching
converter according to the present invention as illustrated in accompanying Figure 2.
clearly shows two of its different portions-the Power circuit unit and the Control Circuit
unit. The present scheme offers load-independent regulation without needing an
additional load-current feed-forward mechanism for achieving improved load/line

regulation, band width and phase margin but by simply incorporating a simple filter
network in series with the current sensor. Output impedance is made same as that of the
VMC with reduced resonant peaking. The load regulation and output impedance is
controlled solely through the filter network in the current mode control(CMC) wherein
superior features of line regulation, bandwidth, phase margin and audio-susceptibility is
favorably retained. The compensating network is simplified in the present scheme to a
proportional controller only.
Reference is now invited to the accompanying Figure 3 that illustrates the control
waveform of the scheme according to the present system in which top one indicates
filtered current, marked as 224, lower than that indicates switching waveform, marked as
227, lower than the above one indicates modified switching waveform, marked as 230,
and the bottom ones indicates the duty ratio signal, marked as 234. It is evident from
the present filtered current control scheme that a new current control scheme is
introduced with the addition of filtered current component 224 in Figure 2. A voltage
feedback loop is considered for regulating the output voltage. A ramp signal with added
filtered inductor current is utilized to improve bandwidth, phase margin and line
regulation. The accompanying Figure 3, shows the controlled output voltage wave form
against time cycle using the voltage feedback loop and said ramp signal with added
filtered inductor current.
Further in the present control scheme, a low pass filter (LPF) 223 in Fig. 2 with
bandwidth, fL is considered in series with the current sensor for further improving
regulation, bandwidth and phase margin. In this scheme when fL < fs, where fs is the
switching frequency, it results in average current mode control, thus degrading
bandwidth and phase margin. Again when fL is further increased such that
fs< fL <4fs, it results in improved band width, associated with harmonic distortion
because of missing few major harmonic content of the inductor current ripple. It has
been found that fixing an upper limit of fL = 5fs do not degrade noise characteristics
and degrades noise characteristic beyond this value due to switching transition. Also the
content of major power spectrum of the input current is confined up to Sfs and hence
do not distort the current waveform but will reduce the high frequency noise.

Reference is now invited to the accompanying Figure 4, that illustrate the comparison of
loop gain of the present scheme (FCC) as compared to conventional CMC and VMC. The
comparison is derived as graphical plot of the noise magnitude in dB and phase margin
respectively against the frequency domain for each of the CMC, VMC and the dc-dc
switching power converter filter current control scheme (FCC) according to the present
invention through inductor current filtering.
A lower LPF gain results in poor phase margin and bandwidth as it reduces the effect of
the current dynamic, which can be improved by increasing the gain. However, a much
higher gain results in higher overshoot during transient and hence it is better to consider
a unity gain.
A high pass filter with the bandwidth, fH is considered in series with the LPF 223 in
Figure 2 for improving load regulation and output impedance. A higher fH (greater than
fL) results in the VMC as it discards the current information, thus degrading bandwidth,
phase margin, line regulation and audio-susceptibility. A decrease \nfH results in
improved line regulation, but harmonic distortion as it ignores fundamental component
and few harmonics of the inductor current ripples. A further reduction in fH results in
load independent regulation, improved line regulation, bandwidth, phase margin and
audio-susceptibility, but increases output impedance at reasonably low frequency and
resonant peaking at high frequency. For results in decreased output
impedance with much reduced resonant peaking and it is also found that the output
impedance of this embodiment is like that of the voltage mode control without resonant
peaking.
It has been experimentally established that fixing a lower limit for fH such that
j ensures improved bandwidth, phase margin, line regulation, audio-
susceptibility and load-independent regulation. A much lower HPF gain degrades fast-
scale stability and transient response. On the other hand its much higher value, while
improving fast-scale stability, results in higher over-shoot during transient. It is thus
optimum to consider a unity HPF gain. The over all filter structure thus takes the form of

a band pass filter. The above comparative observations are presented in the graphical
plot of output impedance and audio susceptibility in the accompanying Figure 5 and
Figure 6 respectively.
The experimental results of the controlled waveform according to the switching power
converter load regulation using a band pass filter and control through inductor current
filtering are illustrated in the accompanying Figure 7, for low volt high current
application wherein the upper plot indicates the control voltage, marked as 222, and the
lower one indicates the modified switching waveform marked as 230 in Figure 2.
The response of the system for controlled dc output according to the present invention is
presented in the accompanying Figure 8 for the step-up load of 1A to 2.8 A wherein the
upper plot indicates the output voltage, voltage across the load resistance marked as
214, and lower one indicates the inductor current, marked as 120 in Figure 2. Likewise,
Figure 9 shows response for step-down load of 2.8A to 1A wherein red colored one
indicates the output voltage, voltage across the load resistance marked as 214, and blue
colored one indicates the inductor current, marked as 120 in Figure 2.
It is thus possible by way of the present invention to developing a switching power
converter apparatus through inductor current filtering and a method of its energy
efficient operation. The switching power converter for load regulation is directed to
current mode controlling (CMC) of converter through inductor current filtering.
Advantageously, a load-independent regulation is achieved in a current mode controlled
(CMC) dc-dc switching power converter wherein said system and method is directed to
improving load regulation, output impedance, line regulation, bandwidth and phase
margin, using an additional filter circuit in series with the current sensor. The present
invention retains the improved energy efficient line regulation, audio-susceptibility,
bandwidth and phase margin of the current mode control, and in addition, it improves
output impedance and load regulation. The invention is adapted to be applied
advantageously in devices such as a monolithic controller IC for controlling dc-dc
converters, mainly for low-voltage-high-current application, like a Voltage Regulator
Module. The achieved output impedance is much lower than that using the current mode
control, and also the resonant peaking at frequency has been reduced thus enabling wide
scale application in related field in electronic/computer or semiconductor industries for
reliable power conversion in related equipments and instruments with less energy
consumption and improved operational efficiency.

WE CLAIM:
1. Switching power converter comprising:
a power circuitry and a control circuitry;
said control circuitry having a filter network in series with the current sensor
adapted for improved output impedance and load regulation.
2. Switching power converter as claimed in claim 1 comprising a band pass filter
adapted for improved line-regulation, bandwidth and phase margin.
3. Switching power converter as claimed in anyone of claims 1 or 2 comprising
current control scheme involving a filtered current component.
4. Switching power converter as claimed in anyone of claims 1 to 3 comprising a
voltage feedback loop adapted for regulating the output voltage.
5. Switching power converter as claimed in anyone of claims 1 to 4 comprising a
ramp signal with added filtered inductor current adapted for improving bandwidth,
phase margin and line regulation.
6. Switching power converter as claimed in anyone of claims 1 to 5 comprising a low
pass filter (LPF) with bandwidth, fL in series with the current sensor for further
improving regulation, bandwidth and phase margin.
7. Switching power converter as claimed in claim 6 wherein fL is preferably limited
upto 5fs where fs is the switching frequency.

8. Switching power converter as claimed in anyone of claims 1 to 7 wherein a high
pass filter (HPF) with the bandwidth, fH is considered in series with the LPF for
improving load regulation and output impedance.
9. Switching power converter as claimed in claim 8 wherein a lower limit for fH, is
fixed preferably to ensure improved bandwidth, phase margin, line
regulation, audio-susceptibility and load-independent regulation.
10. Switching power converter as claimed in anyone of claims 1 to 8 wherein a unity
gain in LPF and HPF is desired and the overall filter structure is adapted to take
the form of a band pass filter.
11. Switching power converter substantially as hereindescribed and illustrated with
reference to the accompanying figures.

The present invention relates to switching power converters and, in particular, to system and method for improving load regulation, output impedance, line regulation, bandwidth and phase margin. This requires simply an additional filter circuit in series with the current sensor. The operation of the present scheme is similar to the voltage mode control along with the incorporation of the filtered current with ramp signal. The switching power converters as of the present invention is capable of retaining the improved line regulation, audio-susceptibility, bandwidth and phase margin of the current mode control, and in addition, it improves output impedance and load regulation. The achieved output impedance is much lower than that using the current mode control and similar to that of the voltage mode control with reduced resonant peaking at high frequency.