DE102004016907B4 - switching regulators - Google Patents

Abstract

Switching regulator for converting a DC input voltage (UE) into a DC output voltage (UA), comprising - a longitudinal branch formed between an input DC voltage connection (2) and a DC output voltage connection (1) comprising at least one switching transistor (4) - a smoothing capacitor (7) at the DC output voltage connection (1 ) and ground of the switching regulator, and - a multivibrator (16), which is supplied by the DC output voltage (UA) and generates a pulse-width-modulated control signal (19) with a controllable pulse / pause ratio, which the gate input of the switching transistor ( 4) for switching on and off of the switching transistor (4), characterized in that the multivibrator (16) is a digital multivibrator, which is a standard block in CMOS technology of the type 4047, the threshold input (25) having a reset input (MR), a clock output (OSCout) and an output (Q) that the digital multivibrator (16) at the clock output (OSCout) provides a clock signal (24), which is transformed with a resistor-capacitor circuit (13, 14) in a triangular voltage (12), wherein the delta voltage is applied to a DC voltage component (9), which from an error amplifier (10) is generated as a function of the output voltage (UA) that the dc voltage applied to the delta voltage at the reset input (MR) of the digital multivibrator (16) is applied, wherein when the dc voltage applied to the delta voltage threshold (25) the reset input (MR) is activated and a "1" state output to the output (Q) of the digital multivibrator (16) is switched to a "0" state, whereby the pulse / pause ratio of the pulse width modulated control signal is controlled.

Description

The invention relates to a switching regulator for converting a toleranced input DC voltage in a constant regulated DC output voltage, wherein the switching regulator includes a switching transistor and a longitudinal inductance in the longitudinal branch and a freewheeling diode is arranged in the shunt branch between the output of the switching transistor and ground and a smoothing capacitor at the output of the switching regulator. The control of the switching transistor via a pulse width modulated drive signal, in which the ratio pulse / pause is set in dependence of the regulated DC output voltage.

State of the art

Out DE 100 65 421 B4 a switching regulator is known, which converts a DC input voltage into a DC output voltage and contains a transistor for switching an inductor in the longitudinal branch. As a transistor, a self-conducting field effect transistor is used, which is driven by a control transistor in response to the longitudinal current. Since this circuit is current controlled, the output voltage has high tolerance variations. Furthermore, the current sensor in the longitudinal branch causes power losses, since the complete supply current flows through a sensor resistance.

Linear Application Brief LL 49E-8/87, Texas Instruments, describes a switching regulator in which the switching transistor is controlled as a function of the output voltage. In this case, a very sensitive control of the switching transistor is achieved by the interconnection of three operational amplifiers, thereby providing a nearly constant output voltage with low voltage fluctuations. In this arrangement, however, the use of three operational amplifiers is to be regarded as disadvantageous, since these components have a high power dissipation and are quite expensive in relation to standard digital components. Another disadvantage is the increased space required to provide this circuit on a printed circuit board.

With DE 11 35 080 A is a switching regulator for keeping constant a DC voltage known in the longitudinal branch of a switching transistor 4 is provided, which is controlled by a multivibrator circuit with two transistors. The base electrode of one of the transistors is connected to a partial output voltage. The variations in the output voltages affect the collector current of a controlling transistor to change the conduction periods of the transistors of the multivibrator relative to each other and thereby adjust the time periods during which the series arm switching transistor conducts. However, the output partial voltage is not supplied to an error amplifier, but the base electrode of one of the transistors to keep the multivibrator going. Rather, the pulses delivered by the multivibrator to the base electrode of the switching transistor are controlled by the collector current of the controlling transistor. Since a multivibrator inevitably oscillates back and forth, which depends on the base coupling of the transistors, the change in the conduction periods of the transistors of the multivibrator is only possible to a limited extent. Only a narrow rule width of the ratio between pulses and pulse pauses is achieved.

Datasheets UC1841 and UC1573, labeled Programmable, Off-Line, PWM Controller, and Buck Pulse Width Modulator Step-Down Voltage Regulator, respectively, show block diagrams of large scale circuits to meet higher switching frequency accuracy requirements. A connection to a switching regulator for converting an input DC voltage into a regulated DC output voltage is not shown.

The EP 0 862 260 A2 discloses a charge pump circuit in which charge is pumped onto a pump capacitor and from there to an output capacitor to achieve a voltage up to twice the supply voltage at the output terminal. For this there are pairs of transistors that are turned on and off alternately. The output voltage is regulated by negative feedback of the output voltage to one of the pairs of transistors which charge the pumping capacitor. For the regulation, a voltage tapped at a voltage divider is compared with a reference voltage in a comparator whose output is connected to a constant current source which operates in conjunction with a sawtooth generator for switching on or off switching diodes. As a result of the feedback, the turn-on time of the controlled transistor pair varies, and it is therefore possible to adjust the charge level of the pump capacitor so that the average output voltage of the output terminal reaches a predetermined value.

task

The invention is based on the object to provide a switching regulator for converting a DC input voltage with a high tolerance range in a nearly constant DC output voltage, the switching regulator requires little space on a circuit board and has a low power loss at a very constant output voltage.

Solution of the task

The object is achieved by the features listed in claim 1. In this case, a self-locking voltage-controlled field effect transistor is provided in the longitudinal branch between the input DC voltage and the DC output voltage as a switching transistor. The control of the gate input takes place with the aid of a pulse-width-modulated control signal, which is generated by means of a digital multivibrator. The digital multivibrator generates the pulse-width-modulated control signal for switching the switching transistor on and off and a clock which is converted in a simple manner with a resistor and a capacitor to a delta voltage and is supplied with a DC voltage component. The supply of the digital multivibrator is done with the regulated output DC voltage, whereby the circuit has a low power loss. The DC voltage applied to the triangular signal, with its connection to the digital multivibrator, determines the pulse / pause ratio of the control signal for the switching transistor. The reference potential for the error amplifier is derived in a simple manner from the regulated output voltage, so that a very accurate detection of the actual value for the output voltage is achieved.

In the following the invention will be described with reference to an embodiment and the associated figures.

LIST OF REFERENCE NUMBERS

1

regulated DC output voltage UA

2

Tolerance-input DC voltage UE

3

series inductance

4

switching transistor

5

Freewheeling diode

6

resistance

7

smoothing capacitor

8th

bypass transistor

8a

bypass transistor

9

Control connection for bypass transistor and DC voltage component

10

Error amplifier, controlled shunt regulator

11

Resistor for voltage divider for reference voltage

11a

Resistor for voltage divider for reference voltage

12

Triangular voltage for pulse width generation

13

Transverse capacitance for signal conversion

14

Series resistance for signal transformation

15

Branch resistor for adders

16

digital multivibrator

17

pulse width modulated output of the digital multivibrator

18

Capacitor for potential adjustment

19

Control signal for switching transistor

20

Compensation resistor for error amplifier

21

Supply input for digital monostable vibrator

22

Reference potential for error amplifier

23

to be measured output DC voltage for error amplifier

24

oscillator clock

25

Input threshold for reset input

Heading of the figures

1 : shows a simplified circuit diagram of the switching regulator according to the invention.

2 : shows a simplified circuit diagram of the switching regulator according to the invention with an alternative arrangement of a bypass transistor.

3 : shows an example of the waveform of the delta voltage at too low DC output voltage.

4 : shows an example of the waveform of the delta voltage at high DC output voltage.

embodiment

In 1 a circuit arrangement for the switching regulator according to the invention is shown. This is for the switching transistor 4 used in the longitudinal branch, a self-locking field effect transistor, which periodically turns on and off the current through the longitudinal branch. Behind the switching transistor 4 is an arranged inductance 3 connected, wherein a first terminal to the output of the switching transistor and the cathode of a freewheeling diode 5 , a second connection to the output 1 is connected for the output DC voltage UA. In normal operation, when the switching transistor 4 is periodically switched on and off, the switching transistor receives 4 a pulse width-modulated periodically clocked control signal 19 on his gate connection. The pulse width of the control signal 19 determines how long the switching transistor is switched on within a switching period. Is the switching transistor 4 Switched on longer within one switching period, becomes the output 1 transmit more energy for the DC output voltage UA. Is the switching transistor 4 switched on shorter within a switching period, becomes the output 1 for the output DC voltage UA transmitted less energy. The pulse width modulated periodically clocked control signal 17 is in a possible embodiment with a digital multivibrator 16 generated and via a series capacitor 18 as a potential-adapted control signal 19 to the gate input of the switching transistor 4 guided. A between the potential-adapted control signal 19 and the input DC voltage lying resistance 6 serves for equipotential bonding of the capacitor 18 for potential adaptation. Particularly advantageous is the use of an integrated circuit HCF4047 as described in "ST, Low Power monostable / astable multivibrator, September 2001". This digital multivibrator 16 contains a built-in programmable oscillator with a clock output OSCout, which provides a stable clock frequency 24 outputs. In addition, this integrated circuit contains 16 an output Q, which outputs half the clock frequency of the oscillator, wherein the "1" state of the output Q via a reset input MR at any time to "0" can be reset. The digital multivibrator 16 is parameterized such that at the beginning of the clock period of the generated clock 24 the output Q is set to a constant "1" state, and thus nearly the level of the supply input 21 for the digital multivibrator 16 accepts. When activating the reset input MR of the digital multivibrator 16 the output Q is reset to the "0" state and thus receives ground potential. Thus, the ratio between the active and inactive state of the reset input MR, the pulse / pause ratio of the output signal 17 controlled. This is one of the digital multivibrator 16 Clock output to the OSCout output using a resistor 14 in series and a capacitor 13 converted to ground in a delta voltage and this with a DC component 9 applied. When using a digital multivibrator as a standard module in CMOS technology, the threshold is the inputs, so also for the reset input MR, always proportional to a partial value to the supply voltage, in the case of the embodiment, therefore, to a partial value DC output voltage UA.

The DC voltage component is in the error amplifier 10 which in a preferred embodiment consists of a controlled standard shunt regulator. The error amplifier 10 is well known and may in one embodiment advantageously consist of an adjustable shunt regulator, as described in "SEMTECH, Revision April 2, 2001: SC431", with the associated resistive circuitry. The reference voltage 22 receives the error amplifier 10 via the constant divider ratio from the actual voltage to be measured 23 in proportion to the resistance 11a to the total value of the series connection of the resistors 11a and 11 ,

In 3 is a diagram of the generation of the pulse width modulated output signal 17 depending on the triangle voltage 12 shown at too low output voltage UA. The error amplifier receives a low reference potential 22 , whereby the output potential 9 of the error amplifier is increased. Thus it is achieved that at a higher DC voltage component of the triangular voltage of the threshold value 25 the reset input MR is reached earlier at each clock period and is canceled again later, whereby the ratio pulse / pause of the pulse width modulated control signal 17 gets smaller. As the switching transistor 4 When the pause signal is turned on, it means that the switching transistor 4 is opened longer and thus provides more energy for converting a DC input voltage UE into a DC output voltage, whereby the too low DC output voltage UA increases after one or more clock periods to the desired value.

In the opposite case is achieved, as in 4 shown in a diagram that at a lower DC component 9 the triangular voltage of the threshold 25 of the reset input at each clock period is reached later and canceled earlier, whereby the ratio pulse / pause of the pulse width modulated control signal 17 is extended. Consequently, this means that the switching transistor 4 is closed longer and thus provides less energy to convert a DC input voltage UE in a DC output voltage UA, whereby the excessive DC output voltage UA decreases after one or more clock periods to the desired value.

As in 1 and 2 becomes the power supply 21 of the digital multivibrator 16 provided by the regulated output DC voltage UA, which is usually less than the tolerance-sensitive input DC voltage UE. This leads to a low power consumption of the digital multivibrator 16 ,

Furthermore, in the in 1 illustrated embodiment for improving the startup behavior of a bypass transistor 8th provided that a constant active control signal 19 for switching transistor 4 so that it is active for the period as long as the error amplifier 10 not yet active and thus its exit to the resistance 20 is high impedance. In this state, the potential at the control input of the switching transistor 4 pulled to nearly 0 volts, whereby on the negative control voltage between the gate input and the source output of the switching transistor 4 becomes conductive.

In the in 2 illustrated alternative embodiment for improving the startup behavior is a bypass Transitor 8a as a bridge to the switching transistor 4 with its drain entrance to the entrance 2 for the input DC voltage UE and with its source output to the output 1 switched for the DC output voltage UA. The control input 9 gets over the resistance 20 be the potential of the input DC voltage UE, while the source output is still 0 volt potential. As for this bypass transistor 8a a field effect transistor is used as the enhancement type, the positive control voltage UGS causes a turn-on of the bypass transistor 8a ,

Claims (8)

Switching regulator for converting a DC input voltage (UE) into a DC output voltage (UA), comprising - one between an input DC voltage connection ( 2 ) and a DC output voltage terminal ( 1 ) formed longitudinal branch, the at least one switching transistor ( 4 ) - a smoothing capacitor ( 7 ) at the output DC voltage terminal ( 1 ) and ground of the switching regulator, and - a multivibrator ( 16 ), which is supplied by the DC output voltage (UA) and a pulse-width-modulated control signal ( 19 ) is generated with a controllable pulse / pause ratio which the gate input of the switching transistor ( 4 ) for switching the switching transistor on and off ( 4 ), characterized in that the multivibrator ( 16 ) is a digital multivibrator, which is a standard device in CMOS technology of the type 4047, which has a threshold value ( 25 comprising a reset input (MR), a clock output (OSCout) and an output (Q), that the digital multivibrator ( 16 ) at the clock output (OSCout) a clock signal ( 24 ), which is provided with a resistor-capacitor circuit ( 13 . 14 ) into a triangular voltage ( 12 ) is converted, wherein the delta voltage with a DC component ( 9 ), which is supplied by an error amplifier ( 10 ) is generated as a function of the output voltage (UA) that the dc voltage applied to the delta voltage at the reset input (MR) of the digital multivibrator ( 16 ), wherein, when the delta voltage applied to the dc voltage component reaches the threshold value ( 25 ), the reset input (MR) is activated and an input to the output (Q) of the digital multivibrator ( 16 ) is switched to a "0" state, whereby the pulse / pause ratio of the pulse width modulated control signal is controlled. Switching regulator according to claim 1, characterized in that the pulse-width-modulated control signal ( 19 ) to a first input of a capacitor ( 18 ) and a second input of the capacitor ( 18 ) to the gate input of the switching transistor ( 4 ) as well as a resistor ( 6 ) with the input DC voltage connection ( 2 ) connected is. Switching regulator according to one of Claims 1 to 2, characterized in that the error amplifier ( 10 ) in the case of a deviation of the DC output voltage (UA) to a smaller value than a desired value, a higher DC component ( 9 ), and in the case of a deviation of the DC output voltage (UA) to a higher value compared to the setpoint value, a lower DC component ( 9 ) generated. Switching regulator according to one of Claims 1 to 3, characterized in that the switching transistor ( 4 ) is a self-blocking field effect transistor whose gate input is connected across a resistor ( 6 ) with the input voltage (UE) and via a capacitor ( 18 ) to the output (Q) of the digital multivibrator ( 16 ) connected is. Switching regulator according to one of Claims 1 to 4, characterized in that the error amplifier ( 10 ) is a controlled shunt regulator whose input is connected to a voltage divider ( 11 . 11a ), which in turn is connected to the DC output voltage. Switching regulator according to claim 5, characterized in that a bypass transistor ( 8th ) between the output DC voltage terminal ( 1 ) of the switching regulator and the gate input of the switching transistor ( 4 ), wherein the gate input of the bypass transistor ( 8th ) from the output of the error amplifier ( 10 ) is driven. Switching regulator according to claim 5, characterized in that a bypass transistor ( 8a ) between the output ( 1 ) of the switching regulator and the input ( 2 ) of the switching regulator, wherein the gate input of the bypass transistor ( 8a ) from the output of the error amplifier ( 10 ) is driven. Switching regulator according to one of Claims 1 to 7, characterized in that the longitudinal branch has a longitudinal inductance ( 3 ) and a freewheeling diode ( 5 ) in a shunt branch between the output of the switching transistor ( 4 ) and mass is arranged.

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