FR3131132A1 - STARTING CONTROL DEVICE FOR A PEAK CURRENT CONTROL CONVERTER. - Google Patents

Abstract

A start control device for a peak current controlled converter, the device being configured to limit the start current and comprising: an insulated gate field effect transistor (MOFSET) comprising a source (S), a drain (D) and a gate (G); a current measurement resistor (Rshunt_2) connected between the source (S) and the drain (D); a trim capacitor disposed between the gate (G) and ground; and an adjustment resistor (Rtime) connected to the gate (G) and receiving a control voltage (Cmde) synchronized on a signal (PWM) of pulse width modulation converter controlled in peak current. Figures for the abstract: [Fig.2]

Description

Start control device for a peak current controlled converter.

The invention relates to a starting control device for a converter controlled (for example switching power supply) in peak current (or which derive from the same principle, that is to say a measurement of the current which serves as a modulating wave in instead of the triangular or sawtooth signal of the traditional voltage control) by a commercial controller on which the current limit setting is external.

The start of a converter equipped with a commercial controller is almost systematically uncontrolled, as a result of the initialization time of the soft start function or "Soft-Start" in English. This shortcoming generates an uncontrolled inrush current.

Works dealing with digitally controlled converters are known which, by nature, do not have these characteristics of non-control of the current in the initial start-up phase.

schematically represents the conventional structure of an analog (step-down) converter 2 based on control by current measurement which serves as a modulating wave, in this case by peak current.

Converter 2 is supplied by a source 1, and supplies a load 3.

Converter 2 includes an input filter FE which ensures emission and susceptibility performance with respect to source 1.

The converter 2 comprises a switch module MI comprising power switches to ensure energy conversion (based on the principle of switched-mode power supplies).

The converter 2 comprises a voltage loop module BT and a current loop module BC which make it possible to carry out the comparison then the generation of the pulse width modulation by a PWM module.

Converter 2 includes a soft start module or "soft-start" DD to start properly, i.e. start monotonously and controlling the inrush current.

On the example of the , the input filter FE comprises a coil or inductor Se and a capacitor Ce, and the output filter FS comprises a coil or inductor Ss and a capacitor Cs.

The switch module MI comprises an inverter INV, and two insulated-gate field-effect transistors M_T, M_B.

The pulse-width modulation generation module PWM comprises a comparator C and an RS flip-flop A2, and the soft-start module DD comprises a switch Sss, a capacitor Css and a source Source_I.

The voltage loop module BT includes a source Vref, a switch Sref, two impedances Z1 and Z2, and a corrector PI, and the current loop module BC includes a shunt resistor Rshunt or current measurement resistor and a gain GI.

On starting, the Sss switch of the DD soft start module is closed. The output voltage of converter 2 follows the image of the voltage of point Ref which evolves according to a ramp produced by the pair Source_I and Css. When the ramp reaches a voltage close to the reference voltage Vref corresponding to the image of the output voltage level (after the filter FS) of the steady state of the converter 2, the switch Sss opens and the switch Sref closes. farm. The system switches to steady state, the PWM signal, corresponding to the pulse width modulation signal, varies in order to obtain VFB=Vref, with VFB representing the input voltage of the PI comparator of the LV voltage loop module.

Current analog controllers do not fully satisfy starting current control.

Almost systematically, for current analogue converters on the market, the start of starting is not controlled. The initial conditions of the converter are not satisfactory (integrating effect of the corrector). This initialization time generates a current inrush despite the existing DD soft start module. To a lesser extent, the transition between starting and steady state can cause a current jump

An object of the invention is to overcome the problems mentioned above, and in particular to control the inrush current when starting a converter controlled by current measurement serving as a modulating wave.

• un transistor à effet de champ à grille isolée comprenant une source, un drain et une grille ;
• une résistance de mesure de courant connectée entre la source et le drain ;
• un condensateur de réglage disposé entre la grille et la masse ; et
• une résistance de réglage connectée à la grille et recevant une tension de commande synchronisée sur un signal de modulation de largeur d'impulsion du convertisseur contrôlé en mesure de courant qui sert d’onde modulante.

There is proposed, according to one aspect of the invention, a starting current limiting device for a converter controlled by current measurement serving as a modulating wave by external current limiting adjustment, the device comprising:

• an insulated gate field effect transistor comprising a source, a drain and a gate;
• a current-measuring resistor connected between the source and the drain;
• a trim capacitor disposed between the gate and ground; And
• a trimming resistor connected to the gate and receiving a control voltage synchronized to a pulse width modulation signal from the current-controlled converter which serves as a modulating wave.

• une première phase correspondant au démarrage du convertisseur, durant laquelle la résistance interne du transistor décroit linéairement jusqu'à une valeur de saturation ;
• une deuxième phase correspondant au fonctionnement du convertisseur durant laquelle le transistor est saturé.

According to one embodiment, the device is configured to operate in two phases:

• a first phase corresponding to the starting of the converter, during which the internal resistance of the transistor decreases linearly to a saturation value;
• a second phase corresponding to the operation of the converter during which the transistor is saturated.

• un module filtre d'entrée ;
• un module interrupteur ;
• un module boucle de courant connectée à un dispositif selon l'une des revendications précédentes ;
• un module boucle de tension ;
• un module de modulation de largeur d'impulsion ;
• un module de démarrage doux ; et
• un module filtre de sortie.

It is also proposed, according to another aspect of the invention, a converter controlled by current measurement serving as a modulating wave comprising:

• an input filter module;
• a switch module;
• a current loop module connected to a device according to one of the preceding claims;
• a voltage loop module;
• a pulse width modulation module;
• a soft start module; And
• an output filter module.

For example, the converter configured to be controlled in peak current mode.

There is also proposed, according to another aspect of the invention, a switching power supply comprising a converter as previously described.

The invention will be better understood on studying a few embodiments described by way of non-limiting examples and illustrated by the appended drawings in which the figures:

schematically illustrates a converter controlled by current measurement serving as a modulating wave by external adjustment of current limitation, according to the state of the art;

schematically illustrates a starting current limiting device for a converter controlled by current measurement serving as a modulating wave by external current limiting adjustment, according to one aspect of the invention;

schematically illustrates a converter provided with a device of the , according to one aspect of the invention;

schematically illustrates the operation of a converter of the , according to the state of the art;

schematically illustrates the operation of a converter of the , according to one aspect of the invention; And

schematically illustrates the realization of the control signal of the device, according to one aspect of the invention.

In all of the figures, the elements having identical references are similar.

There schematically represents a starting current limiting device for a converter controlled by current measurement serving as a modulating wave by external current limiting adjustment, according to one aspect of the invention.

• une résistance de mesure de courant Rshunt_2 connectée entre la source S et le drain D ;
• un condensateur de réglage Ctime disposé entre la grille G et la masse ; et
• une résistance de réglage Rtime connectée à la grille G et recevant une tension de commande Cmde synchronisée sur un signal PWM de modulation de largeur d'impulsion du convertisseur contrôlé en mesure de courant qui sert d’onde modulante.

The device comprises an insulated gate field effect transistor MOFSET comprising a source S, a drain D and a gate G;

• a current measuring resistor Rshunt_2 connected between source S and drain D;
• an adjustment capacitor Ctime arranged between the gate G and ground; And
• an adjustment resistor Rtime connected to the gate G and receiving a control voltage Cmde synchronized on a pulse width modulation PWM signal from the converter controlled in current measurement which serves as a modulating wave.

The principle is based on the linear operation of the MOSFET. We act on the gain of the current measurement (variable resistor Rvariable2).

During a first phase, at t=0, the insulated-gate field-effect transistor MOFSET is controlled slowly and synchronously with the PWM signal (it is the time constant of the resistor/capacitor couple which makes it possible to adjust more or less the decrease time of the resistance Rvariable2 of the MOSFET transistor and therefore the time of linear operation. The choice of the binomial Rtime/-Ctime makes it possible to adjust the time that one wishes to limit the starting current. This adjustment makes it possible to control the evolution of the signal V _gs (control voltage between gate G and source S of the MOSFET transistor) Its internal resistance Rvariable2 decreases linearly to its saturation value (Rvariable2_sat << Rshunt_2).

During a second phase, the MOFSET transistor is saturated, the shunt resistor Rshunt_2 is almost short-circuited, and the current measurement is governed by the shunt or current measurement resistor Rshunt, of the current loop module BC, which makes it possible to ensure the full performance of the converter.

This solution is independent of the time constants of the circuit because the synchronization signal is the PWM signal.

There schematically represents a converter provided with a device of the , in this case a converter according to the wherein the current loop module BC further comprises a device of the according to one aspect of the invention.

There schematically represents the operation of a converter of the , in which, during an entire initialization (start-up) phase, the voltage V _COMP of the signal COMP is at the high end. Current limitation is achieved by the Ipeak stop (well beyond the maximum current required by the load and its dynamics).

There represents conventional operation with a maximum duty cycle of 50%.

In comparison, the schematically represents the operation of a converter of the , according to one aspect of the invention, in which the originality of acting on the transient part (initialization time) without intervening in the steady state.

There shows the effects of limiting the peak current on starting thanks to the Ipeak limit which has become adjustable over time. This limit is imposed well below the steady state on the start-up phase, which makes it possible to reduce the duty cycle and therefore the peak currents in the entire converter.

As shown on the , the control signal Cmde is produced from the PWM signal. A monostable, ie a circuit keeps in memory a change of level allows to shape the signal to obtain the operation described below. Depending on the configuration of the monostable, in the absence of a certain number of PWMs (eg stoppage of the converter), it can be reset in order to prepare a new start if necessary.

As depicted in :
- in phase 0: delay (1.3ms in this example) due to the threshold voltage VGS(th) of the MOSFET transistor. This delay does not affect operation.
- in phase 1: linear operation of the MOSFET transistor. The equivalent resistance at Rshunt_2 decreases allowing the current limit setting to be increased.
- in phases 2 and 3: the MOSFET transistor is saturated. The current limit setting becomes fixed and is used to supply the current required for the load (following start-up and steady state).

The solution makes it possible to overcome the initialization problem of most analog controllers on the market in order to control without compromise the amplitude of the currents in the converter and more precisely the input current on which there are significant constraints.

Claims (5)

Starting current limiting device for a converter controlled by current measurement serving as a modulating wave by external current limiting adjustment, the device comprising:

• an insulated gate field effect transistor (MOFSET) comprising a source (S), a drain (D) and a gate (G);
• a current measuring resistor (Rshunt_2) connected between the source (S) and the drain (D);
• a trim capacitor (Ctime) disposed between the gate (G) and ground; And
• an adjustment resistor (Rtime) connected to the gate (G) and receiving a control voltage (Cmde) synchronized on a pulse width modulation signal (PWM) converter controlled in current measurement which serves as a modulating wave.

Device according to claim 1, configured to operate in two phases:

• a first phase corresponding to the starting of the converter, during which the internal resistance of the transistor (MOFSET) decreases linearly to a saturation value;
• a second phase corresponding to the operation of the converter during which the transistor (MOFSET) is saturated.

Converter controlled in current measurement serving as a modulating wave comprising:

• an input filter module (FE);
• a switch module (MI);
• a current loop module (BC) connected to a device according to one of the preceding claims;
• a voltage loop module (BT);
• a pulse width modulation (PWM) module;
• a soft start (DD) module; And
• an output filter module (FS).

Converter according to claim 3, configured to be controlled in peak current mode. Switching power supply comprising a converter according to claim 4.