DE10103817B4 - DC-DC converter - Google Patents

Abstract

DC-DC converter, in which a first capacitor (C1) is connected between a first pair of terminals (1, 1 ') and in parallel, the series connection of a first and a second controllable switch (T1, T2) and in parallel to the second controllable switch (T2) the series connection of a coil (L1) and a second capacitor (C2), the terminals of the second capacitor (C2) form a second pair of terminals (2, 2 '), in which further a control circuit (RS) is provided which the controllable switch (T1, T2) depending on the strength and the direction of the current through the coil (L1) drives such that the output voltage of the converter assumes a constant value and either the voltage on the first pair of terminals (1, 1 ') or the voltage on the second pair of clamps (2, 2 '), characterized in that the two controllable switches are sense field-effect transistors (T1, T2), each of which is associated with a current detection circuit (SDS1, SDS2), which a current direction detection circuit (SRDS) is connected downstream, by means of the current of that field effect transistor ...

Description

The The invention relates to a DC-DC converter, wherein between a first Terminal pair a first capacitor and parallel to the series circuit from a first and a second controllable switch and at the parallel connection to the second controllable switch, the series circuit is arranged from a coil and a second capacitor, wherein the connections of the second capacitor form a second pair of terminals, in which Furthermore, a control circuit is provided which the controllable switch dependent from the current through the coil such that the output voltage of the converter assumes a constant value and either the voltage on the first pair of terminals or the voltage on the second pair of terminals.

Around Measuring the current through the coil is often a shunt resistor in series switched to the coil and the voltage drop across this shunt resistor fed to a controller.

adversely However, with such a shunt resistor is that in today solutions the ohmic losses caused by it are considerable. A Reduction of the shunt resistor is hardly possible because its value is already more at the bottom of the allowable range settled and a higher one Accuracy of the following amplifier after pulls.

One Another disadvantage of a shunt resistor is that its use an electronic circuit requires a fast amplifier and very precise resistors having.

A known DC-DC converter ( US 5,138,249 A ) has a sensor that detects the positive and negative current peaks regardless of the current direction.

Also, a circuit arrangement for correcting a power factor is known ( US 5,757,635 A ) in which the on time of a sense field effect transistor is controlled based on a control voltage generated by a control voltage generator.

Another known circuit arrangement ( EP 0 397 102 81 ) has sensing elements capable of determining the current through a switch to a load.

Based on the state of the art US 5,138,249, A The invention has for its object to provide a DC-DC converter, which allows a simple current measurement.

The The object is achieved by a DC-DC converter according to claim 1.

According to claim 1 are used as switches Sense field effect transistors, the next to the usual Source terminal have a sense terminal, where a current can be tapped, the proportional to the source current, however, much smaller Than this is, leaving almost no losses due to the measurement of the current.

The Measurement is advantageously carried out with a current-controlled Power source, for example, with a current mirror circuit can be realized.

Of the DC-DC converters can be used both as a down-converter and as an up-converter be used, wherein the control circuit is designed such that they automatically generate the appropriate control signals. she has for this purpose a current direction detection circuit and a current control circuit.

The Invention will be described below with reference to an embodiment with the aid of Figures closer explained. Show

1 a block diagram of a DC-DC converter according to the invention and

2 a principle circuit for a current detection circuit

1 shows an embodiment of a DC-DC converter according to the invention. Between the terminals of a first pair of terminals 1 . 1' a first capacitor C1 and the series circuit of a first sense field effect transistor T1 and a second sense field effect transistor T2 is arranged.

Sense Field Effect Transistors are transistors having a second source terminal at the a small current proportional to the source current can be tapped can, thereby easily measuring the source current can be done.

Parallel to the second sense field effect transistor T2, the series circuit of a coil L1 and a second capacitor C2 is arranged, wherein the terminals of the second capacitor C2, a second pair of terminals 2 . 2 ' form.

Of the DC-DC converters can be used both as a down-converter and as an up-converter be used, depending on which of the pairs of terminals as input terminal pair is used.

Around To obtain a constant output voltage must in any case the On time of the transistors T1, T2 are regulated, depending on from the current through the coil L1 by means of a control circuit RS.

Of the Current through the coil L1 corresponds to the current through each switched sense field effect transistor T1 or T2 and can in according to the invention by detecting the current at the respective sense output of a Transistors are determined.

At the sense outputs of the sense field-effect transistors T1, T2, current detection circuits SDS1, SDS2 are provided for this purpose, which are provided in accordance with FIG 2 can be designed as current-controlled current sources. Current-controlled current sources can be realized for example with current mirror circuits. It is only essential that the sense output of a sense field effect transistor is connected as low as possible to the source terminal of the transistor.

At the exits The current detection circuits SDS1, SDS2 are each a resistor R1 and R2 provided to the respective current in a voltage reshape. The voltages are then a switch S1 or S2 coupled low pass from the resistors R3 and R4 and the capacitor C3 supplied. The capacitor C3 of the low pass then results in a voltage which corresponds to the mean value of the current through the coil L1.

The Sense field effect transistors only deliver an accurate sense current, if they are traversed by the current in the drain-source direction. In the case that the DC-DC converter is operated as a down converter, that is, at the first pair of terminals, a higher voltage of, for example, 42V is applied and the second pair of terminals a low voltage of, for example 14V can be tapped should, only the first sense field effect transistor in the drain-source direction flowed through by the current, so that for an accurate measurement only Sensing current fed to the low-pass shall be.

Out For this reason, the switches S1 and S2 are provided, the alternative either the sense current of the first sense field effect transistor T1 or the second sense field effect transistor T2 to the low pass Give R3, R4, C3. The switches S1, S2 are thereby from a current direction detection circuit SRDS actuated, which in turn is dependent on the output signals of two comparators K1, K2 is controlled, whose reference inputs with a reference voltage be acted upon by the current direction detection circuit SRDS and their signal inputs with the voltages applied to the resistors R1 and R2 become. This ensures that only the comparator K1 or K2 switches through, at whose input a positive voltage is applied, which means the associated one Sense field effect transistor T1 or T2 in the drain-source direction of Current is flowing through.

In the case that the DC-DC converter is operated as a step-up converter, ie that at its second terminal pair 2 . 2 ' a low voltage is applied and at its first terminal pair 1 . 1' a higher voltage can be tapped, there may be operating cases in which the current through the coil L1 changes its direction, that has different signs. This means that both sense field-effect transistors are traversed in partial regions of the current profile in the drain-source direction by the coil current, but the coil thereby in a different direction. In order to average the corresponding current components with the correct sign in the low-pass R3, R4, C3, the switch S2 is preceded by an inverting amplifier INV, which forwards the voltage at the resistor R2 inverted to the low-pass filter.

to Regulation of the output voltage, the sense field effect transistors T1, T2 by pulse width modulated Signals alternately switched on and off. These signals will be generated by a current control circuit SRS and the gate terminals of the Sense field effect transistors T1, T2 supplied. The current control circuit SRS is used to determine the correct pulse width from the voltages the resistors R1 and R2 passing through the currents the sense field effect transistors T1, T2 are proportional and of one of the current average value determined in the low pass R3, R4, C3 obtained control voltage. The voltages at the resistors R1 and R2 are applied to the signal inputs of comparators K3, K4 placed. The reference inputs the comparators K3, K4 are supplied with the control voltage. This is known in the literature as Peak Current Mode.

The Control voltage is from the voltage at the low pass R3, R4, C3 means a circuit obtained in the illustrated embodiment with a microcontroller and a D / A converter is formed. However, it is also possible, this circuit in the specialist familiar, purely analog circuit technology build.

The described DC-DC converter according to the invention can be operated in both directions both as a step-down converter and as a step-up converter Depending on the operating mode, the signals required for regulation are automatically selected.

Claims (1)

DC-DC converter, in which a first pair of terminals ( 1 . 1' ) a first capacitor (C1) and in parallel the series circuit of a first and a second controllable switch (T1, T2) and in parallel to the second controllable switch (T2), the series circuit of a coil (L1) and a second capacitor (C2 ), wherein the terminals of the second capacitor (C2) a second pair of terminals ( 2 . 2 ' ), in which a control circuit (RS) is further provided, which controls the controllable switches (T1, T2) depending on the strength and the direction of the current through the coil (L1) such that the output voltage of the converter assumes a constant value and either the voltage at the first pair of terminals ( 1 . 1' ) or the voltage at the second pair of terminals ( 2 . 2 ' ), characterized in that the two controllable switches Sense field effect transistors (T1, T2), each associated with a current detection circuit (SDS1, SDS2), which is followed by a current direction detection circuit (SRDS), by means of which the current of that field effect transistor (T1 or T2), which is traversed by the current in the drain-source direction, is selected for evaluation in the control circuit (RS).