# Lossless current sensing and its application in current mode control

Semtech

^{1}15 Jun 2008-pp 4086-4091

TL;DR: In this paper, it is revealed that the lossless current sensing structure is very similar to the well known Maxwell bridge and a "speedy capacitor" could be added to the LCS circuitry to significantly improve the sensed current signal to noise ratio and avoid jittery operation in wide DC-DC conversion ratio applications.

Abstract: In this paper, it is revealed that the lossless current sensing structure is very similar to the well known Maxwell bridge. The matching condition in lossless current sensing is the same as the balance equation in Maxwell bridge. In practice, it is difficult to meet the matching condition due to the parameter value variations. However, it is shown that in current mode control, at certain time constant mismatching situations, the circuit dynamic response actually could be improved. Furthermore, a "speedy capacitor" could be added to the lossless current sensing circuitry to significantly improve the sensed current signal to noise ratio and avoid jittery operation in wide DC-DC conversion ratio applications.

##### Citations

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24 Jul 2009

47 citations

### Cites methods from "Lossless current sensing and its ap..."

...In today’s industrial multiphase interleaving buck converters, the DCR current sensing method [74-82] is adopted for achieving the above three functions....

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TL;DR: In this article, the authors proposed a current-mode hysteretic buck converter with a spur-free constant-cycle frequency-hopping controller that fully eliminates spurs from the switching noise spectrum irrespective of variations in the switching frequency and operating conditions.

Abstract: This paper proposes a current-mode hysteretic buck converter with a spur-free constant-cycle frequency-hopping controller that fully eliminates spurs from the switching noise spectrum irrespective of variations in the switching frequency and operating conditions. As a result, the need for frequency regulation loops to ensure nonvarying switching frequency (i.e., fixed spurs location) in hysteretic controllers is eliminated. Moreover, compared to frequency regulation loops, the proposed converter offers the advantage of eliminating mixing and interference altogether due to its spur-free operation, and thus, it can be used to power, or to be integrated within noise-sensitive systems while benefiting from the superior dynamic performance of its hysteretic operation. The proposed converter uses dual-sided hysteretic band modulation to eliminate the inductor current imbalance that results from frequency hopping along with the output voltage transients and low-frequency noise floor peaking associated with it. Moreover, a feedforward adaptive hysteretic band controller is proposed to reduce variations in the switching frequency with the input voltage, and an all-digital soft-startup circuit is proposed to control the in-rush current without requiring any off-chip components. The converter is implemented in a 0.35- μ m standard CMOS technology and it achieves 92% peak efficiency.

41 citations

### Cites background from "Lossless current sensing and its ap..."

...This method causes less loss and consumes less power than other passive and active current sensing techniques [20]....

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11 Jul 2011TL;DR: In this article, current through the inductor is sensed to determine when to turn off or on the switching transistors, and a summing circuit is applied to a PWM comparator to control the duty cycle of the switch.

Abstract: In a current mode controlled switching power supply, current through the inductor is sensed to determine when to turn off or on the switching transistors The inductor current has a higher frequency AC component and a lower frequency DC component The AC current feedback path, sensing the ramping ripple current, is separate from the DC current path, sensing the lower frequency average current Separating the current sensing paths allows the signal to noise ratio of the AC sense signal to be increased and allows the switching noise to be filtered from the DC sense signal The gain of the DC sense signal is adjusted so that the DC sense signal has the proper proportion to the AC sense signal The AC sense signal and the DC sense signal are combined by a summing circuit The composite sense signal is applied to a PWM comparator to control the duty cycle of the switch

38 citations

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TL;DR: In this article, a coupled sense winding method was proposed to increase the corner frequency of the sensing circuit by more than two orders of magnitude, which can be used to compensate for induced voltages due to the inductor.

Abstract: The lossless inductor current sensing method is well-known and is frequently applied in the measurement of output current in DC-DC converters due to its low cost and simplicity. This technique uses a low-pass filter that is matched to the inductance (L) and winding resistance to compensate for induced voltages due to the inductor. However, the waveform fidelity above the corner frequency of the inductor is generally poor due to large production tolerances and thermal drift. In this letter, we propose the use of a coupled sense winding, which increases the corner frequency of the sensing circuit by more than two orders of magnitude. We show, as an example, that for a 3.85 muH inductor the corner frequency of the measurement circuit can be increased from 36 Hz using the conventional approach to 5.8 kHz using the coupled sense winding method. Above the new corner frequency, a low-pass filter is still required but may now be constructed using a smaller capacitor and with improved high-frequency response.

13 citations

### Cites background from "Lossless current sensing and its ap..."

...low-pass filter in order to determine the current flowing through it [1]–[3]....

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01 Sep 2015

TL;DR: In this article, a low pass filter is used to estimate the inductance and the series resistance of the inductor coil in a single-phase boost-type switch-mode rectifier.

Abstract: Boost-type switch-mode rectifiers (SMR) commonly use a resistor or a magnetic current sensor to measure the instantaneous input or inductor current that is used as the feedback to the current controller. In this paper a novel current sensorless scheme is described that computes the inductor current from the measured inductor voltage in a single-phase boost-type SMR using an adaptive low pass filter. This calculation requires an estimate of the inductance and the equivalent series resistance of the inductor coil. Both these parameters are dependent on operating conditions and hence have to be updated continuously. This is done using an adaptive model of the inductor that computes these parameters of the inductor once in every half cycle of the input current. The adaptation scheme is robust against parameter variations. Simulation and experimental results confirm the effectiveness of the proposed technique which provides comparable performance to standard measured feedback current scheme both under steady-state and transient conditions.

9 citations

##### References

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TL;DR: In this paper, a current-mode control power convertor model that is accurate at frequencies from DC to half the switching frequency is described for constant-frequency operation, using a simple pole-zero transfer function, which is able to predict subharmonic oscillation without the need for discrete-time z-transform models.

Abstract: A current-mode control power convertor model that is accurate at frequencies from DC to half the switching frequency is described for constant-frequency operation. Using a simple pole-zero transfer function, the model is able to predict subharmonic oscillation without the need for discrete-time z-transform models. The accuracy of sampled-data modeling is incorporated into the model by a second-order representation of the sampled-data transfer function which is valid up to half the switching frequency. Predictions of current loop gain; control-to-output; output impedance; and audio susceptibility transfer functions were confirmed with measurements on a buck converter. The audio susceptibility of the buck converter can be nulled with the appropriate value of external ramp. The modeling concentrates on constant-frequency pulse-width modulation (PWM) converters, but the methods can be applied to variable-frequency control and discontinuous conduction mode. >

790 citations

### "Lossless current sensing and its ap..." refers methods in this paper

...To investigate the mismatching effect on the current mode control, we developed a small signal model as shown in Fig. 5, based on the classical work on continuous time model for current mode control in [ 10 ]....

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TL;DR: In this article, a novel current-sensing and current-sharing technique is proposed for interleaved quasisquare-wave (QSW) VRM topologies, which can be controlled simply in parallel converters without a current transformer and current sensing resistors.

Abstract: Future generations of microprocessors are expected to exhibit much heavier loads and much faster transient slew rates. Today's voltage regulator module (VRM) will need a large amount of extra decoupling and output filter capacitors to meet future requirements, which will basically make the existing VRM topologies impractical. As a candidate topology, the interleaved quasisquare-wave (QSW) VRM exhibits very good performance, such as a fast transient response and a very high power density. The difficulty with the application of the interleaved parallel technology is the current-sharing control. In this paper, a novel current-sensing and current-sharing technique is proposed. With this technique, current sharing can be controlled simply in parallel converters without a current transformer and current-sensing resistors. In addition, this technique can be easily integrated with an IC chip. The four-module paralleled QSW VRM is used to evaluate this technique. Experimental results verify that with this technique, the VRM has a high power density, high efficiency and a fast transient response. The concept of the current sharing technique is also generalized and extended.

247 citations

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Semtech

^{1}TL;DR: In this article, a current sense circuit for a DC-to-DC power converter accurately senses the output inductor current without adversely affecting efficiency of the power converter, where the current sense signal produces a current signal having amplitude sufficiently above the noise floor so that accurate load control is achieved.

Abstract: A current sense circuit for a DC-to-DC power converter accurately senses the output inductor current without adversely affecting efficiency of the power converter. The current sense circuit produces a current sense signal having amplitude sufficiently above the noise floor so that accurate load control of the power converter is achieved. Specifically, the DC-to-DC power converter includes at least one power switch connected to an input voltage source. At least one phase sensing switch is connected to the input voltage source in parallel with the at least one power switch. A pulse width modulation circuit provides common control pulses for the at least one power switch and the at least one phase sensing switch responsive to a current sense signal. An output inductor is connected to the at least one power switch and to a load. A current sensor is coupled to the output inductor and providing the current sense signal to the pulse width modulation circuit corresponding to current passing through an internal DC resistance of the output inductor. The current sensor further includes a filter that includes an on-state resistance of the at least one power switch. The current sensor further includes a second filter adapted to remove noise from the current sense signal when the at least one phase sensing switch and the at least one power switch change state.

106 citations

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21 Jan 1994

TL;DR: In this paper, a switch mode power converter with an overload protection system is described, which includes an input stage having an input voltage source, a switching circuit for coupling said input source to an output stage, and an error amplifier responsive to the voltage derived by a second filter and a reference voltage.

Abstract: A switch mode power converter having an overload protection system is disclosed. The system includes an input stage having an input voltage source. A switching circuit for coupling said input source to an output stage is provided. The output stage further includes a first filter circuit providing an output current to a load circuit. A second filter circuit is coupled to the output stage providing a voltage proportional to the output current and to internal temperature of the switch mode converter. An error amplifier responsive to the voltage derived by a second filter and a reference voltage, generates an error signal proportional to the difference of the voltage applied to the error amplifier. The error signal adjusts the operating parameters of the switching circuit.

25 citations

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Bosch

^{1}TL;DR: In this article, the voltage drop through a choke itself is measured by summing circuits, which may form the algebraic sum or difference, respectively, of the voltages across the chokes.

Abstract: To equalize current flow through a pair of chokes supplying a d-c load from a d-c source, and, if desired, to limit current flow through either a single choke or both to a predetermined maximum value, without using measuring shunts, the voltage drop through the choke itself is being measured by summing circuits, which may form the algebraic sum or difference, respectively, of the voltages across the chokes, the sum or difference signals then being passed through low-pass filters to form signals representative of inductive voltage difference of two chokes, or of the voltage drop through one or both of them, which signals are then applied to respective regulators which, in turn, control the duty cycle of one or two semiconductor switches, respectively connected in series with the respective chokes.

24 citations