WO2014180967A2

WO2014180967A2 - Monitoring circuit for a switched-mode power supply and use of a monitoring circuit

Info

Publication number: WO2014180967A2
Application number: PCT/EP2014/059492
Authority: WO
Inventors: Robert Ruef; Peter Busch
Original assignee: Fujitsu Technology Solutions Intellectual Property Gmbh
Priority date: 2013-05-10
Filing date: 2014-05-08
Publication date: 2014-11-13
Also published as: WO2014180967A3

Abstract

The invention relates to a monitoring circuit (ÜS) for a switched-mode power supply with a rectifier circuit (G) for rectifying a primary mains alternating current (AC). The monitoring circuit (ÜS) comprises two resistance dividers (W1, W2) each comprising two resistors (R1, R2, R3, R4). The resistors (R1, R2, R2, R4) are each connected in series between a phase conductor (PH1, PH2) of a mains connection before the rectifier circuit (G) and a reference point after the rectifier circuit (G). The monitoring circuit further comprises a subtraction device (OP) with two inputs, wherein each of the two inputs of the subtraction device (OP) is connected between the resistors (R1, R2, R3, R4) of one of the resistance dividers (W1, W2) in each case. The invention further relates to the use of a monitoring circuit.

Description

description

Monitoring circuit for a switching power supply and use of a monitoring circuit

The invention relates to a monitoring circuit for a switching power supply, which is a rectifier circuit for

Rectifying an AC line voltage. The

The invention further relates to the use of a

such monitoring circuit.

Various types of switched-mode power supplies for supplying portable computers and other electronic devices with a secondary DC voltage generated from a primary AC mains voltage are known in the art. Basically, such switching power supplies have a relatively high efficiency and allow the

Design of lightweight and cost-effective power supplies for a variety of applications.

However, a disadvantage of known switching power supplies lies in the fact that they have a relatively poor efficiency in the so-called low-load range, ie in a work area in which the secondary-output power represents only a small fraction of a possible output power. In order to increase the efficiency of such switching power supplies, switching times of the switching power supply can be correlated with the primary AC line voltage. For heavy load changes or low output power of the switching power supply, it may be due to the arrangement of the

Rectifier come to it, that a reference to the primary mains AC voltage is lost for a short time. The object of the invention is to describe a circuit with which a reference to a primary mains AC voltage can be produced. Furthermore, it is an object of the invention to describe the use of such a circuit.

According to a first aspect of the present invention, a monitoring circuit for a switching power supply having a rectifier circuit for rectifying a primary

Mains AC voltage described. The monitoring circuit comprises two resistor dividers, each comprising two resistors, each in series between a

Phase line of a mains connection before the

Rectifier circuit and a reference point after the

Rectifier circuit are connected. The

Monitoring circuit further includes a

Subtraction device with two inputs, wherein each of the two inputs of the subtraction device between the resistors in each case one of the resistor divider

connected.

The switching power supply includes a rectifier circuit. The rectifier circuit can be a

Bridge rectifier circuit consisting of four diodes. By the circuit described in the first aspect, a reference to a primary AC line voltage can be made, even if the switching power supply is operated in low load operation or if strong load changes occur.

Because the mains AC voltage to two

Resistance dividers is measured, and the signals are subtracted from each other, it is ensured that a signal to Is made available, which is related to the signal of the primary AC line voltage in relation.

According to an advantageous embodiment is in each case a

Capacitor parallel to the resistors of the

Resistor divider connected closest to the reference point. By having capacitors in parallel with the

Resistors are connected, offer themselves

Filter options to the monitoring circuit too

dimension.

According to a further advantageous embodiment, the reference point is an output-side ground potential. According to a further advantageous embodiment, the subtraction device comprises an operational amplifier, which is connected as a subtractor.

According to a further advantageous embodiment, the positive input of the operational amplifier is subjected to an offset. The fact that the operational amplifier is operated with a bias voltage ensures that the output signal is always positive. This is necessary, for example, in cases when the output signal is to be made available to a microcontroller directly, without further processing.

According to a further advantageous embodiment, the signal output of the operational amplifier is electrically connected to a microcontroller for controlling the switching power supply. Characterized in that the output signal of the operational amplifier is provided directly to a microcontroller available, can be dispensed with further processing circuits. According to a further advantageous embodiment, an output signal of the subtraction device has a direct relation to the voltage characteristic of the primary

AC line voltage. The fact that the output signal has a direct relation to the primary AC line voltage, can be dispensed with further processing of the signal. Such a reference can be, for example, the phase position or zero crossings of the amplitude of the primary

AC mains voltage. According to a second aspect of the invention, the use of a monitoring circuit according to the first aspect is described in a switched mode power supply in which reference is made to a primary mains alternating voltage signal for switching. According to an advantageous embodiment of the invention, the use of a monitoring circuit in a

Switching power supply described the strong load changes

is subject. In the event of heavy load changes, the reference to the primary mains AC voltage may break. By using a monitoring circuit according to the first aspect, a signal which is not influenced by the load can also be received in these cases.

According to a further advantageous embodiment, at low output power of the switching power supply in each case one complete half-wave of the primary mains AC voltage used to generate a secondary DC voltage.

In that a complete half-wave of the primary

Mains AC voltage for generating a secondary

DC voltage can be used, the efficiency of the

Power supply can be increased. This is especially important when the switching power supply is operated in low load operation. Thus, switching losses during operation of a switching power supply can be reduced by 10 percent or less of its maximum output power.

The invention will be explained in more detail with reference to different embodiments with reference to the attached figures. In the different

Embodiments will use the same reference numerals for the same or similar components.

Show it:

Figure 1 is a block diagram with the

Essential components of a switching power supply Figure 2 is a circuit diagram of a possible

Monitoring circuit

FIG. 3 shows a signal curve of a voltage signal which corresponds to a measured voltage curve of a circuit according to FIG. 2 and a current profile of a load output of a switched-mode power supply; 4 shows a circuit diagram of a monitoring circuit according to a first embodiment of the invention, FIG.

Figure 5 shows a voltage waveform of an output signal of

Subtraction device and a current waveform of the load output of the switching power supply,

Figure 6 is a circuit diagram of a monitoring circuit according to a second embodiment of the invention, and

FIG. 7 shows a voltage curve according to the circuit of FIG

6th

In Figures 1, 2, 4 and 6 are respectively similar

Components designated by the same reference numerals. This is merely for the sake of clarity and does not necessarily mean that the corresponding components have the same values or are the same components. So can

For example, a resistor Rl of the circuit according to Figure 2 have a different value, such as a resistor Rl of

Circuit according to FIG. 4.

The primary AC line voltage AC shown in Figure 1 may have different peak voltages.

For example, the AC line voltage AC may be dependent on a country in which the circuit is used

have different peak voltages. It is usual

for example, a value of 230 V AC. For the invention, however, it is irrelevant which size the

Mains AC voltage has.

The circuit diagrams of Figures 1, 2, 4 and 6 show relevant to the understanding of the invention circuit parts. Out For clarity, parts of the circuits of a switching power supply have been omitted, which are not essential to the understanding of the invention. Figure 1 shows a circuit diagram of the primary-side parts of a switching power supply, which are essential to the invention. FIG. 1 shows an input for a primary alternating mains voltage AC. From the input lead two phase lines PH1 and PH2 to a rectifier circuit G. At the

Output side of the rectifier circuit G is a

Capacitor C3 and a load RL connected. In particular, the load RL may be a downstream one

Switching converter for generating a regulated, secondary

DC voltage to supply an electrical device from the unregulated, pulsating primary DC voltage at the output of the rectifier circuit G act. The

Output side of the rectifier circuit has a

Ground potential GND at the node to which the capacitor C3 and the load RL are connected. The

Monitoring circuit ÜS is between the two

Phase lines PH1 and PH2, as well as the output side

Ground potential GND switched.

Figure 2 shows a circuit diagram according to a possible

Monitoring circuit ÜS for a switching power supply. The

Monitoring circuit ÜS according to Figure 2 consists of two

Diodes Dl and D2, each one of the two

Connect phase lines PH1 and PH2 to a resistance divider W consisting of two resistors R1 and R2. Via the two diodes Dl and D2 are connected by the connection to the

Phase lines PH1 and PH2 of the primary AC line voltage AC respectively the positive half-waves of the primary

Mains AC voltage to the two resistors Rl and R2 the resistance divider W out. At the resistor R2, a voltage signal can be tapped, which a

amount sinusoidal course corresponds. FIG. 3 shows a voltage and a current profile. The current profile, marked here with symbols, is the course of a current on the output side of the switching power supply. The current breaks in one place. In addition to the current flow on the output side of the switching power supply is the

Voltage curve of the measured primary, rectified

AC line voltage AC shown. The course corresponds to the measured at the output side of the rectifier circuit G signal of the monitoring circuit of Figure 2. From the

Graphs show that the measured primary

Mains AC voltage at the time when the load current drops to zero breaks. As a result, the reference to the actual primary AC line voltage AC is partially lost. FIG. 4 shows a circuit diagram according to an embodiment of a monitoring circuit ÜS according to the invention. The monitoring circuit ÜS in this case comprises a

Resistor divider Wl consisting of the resistors Rl and R2, which between the phase line PH1 of the primary

Mains AC voltage AC and the reference point at which

output-side ground potential GND. Between the second phase line PH2 of the primary AC line voltage AC and the output side ground potential GND is a second resistor divider W2, consisting of the resistors R3 and R4. In each case parallel to the resistors R2 and R4

Capacitors Cl and C2 switched. A

Subtraction device OP, in the embodiment a

Operational amplifier, which connects as a subtractor is connected to the circuit such that the

positive input of the operational amplifier is connected to the first resistor divider Wl between the resistors Rl and R2 and the negative input of

Operational amplifier is connected to the second resistor divider W2 between the resistors R3 and R4.

This wiring is followed by the inputs of the

Subtraction device OP the individual signals, which lie on the phase lines PH1 and PH2 to the resistor dividers Wl and W2. Now breaks the output of the

Switching power supply, so also drops the output current.

Accordingly, a monitoring circuit US, as described in Figure 1, a collapse of the primary

Detect mains AC voltage AC. Characterized in that in the embodiment according to the invention, the voltage signals of the individual phase lines PH1 and PH2 of the primary

AC supply voltage AC are subtracted from each other, a relative output signal is generated. By doing that

Output signal of the subtraction device OP indicates the relative difference and not from the falsified by the blocking bridge rectifier primary

Mains AC voltage depends, the reference to the primary AC line voltage AC continues to exist.

In FIG. 5, on the one hand, both the current profile of the

Switching power supply shown as well as the output signal of the subtraction device OP according to the circuit of Figure 4. As can be seen, the burglary of the illustrated

Current waveform of the output signal of the switching power supply has no effect on the amplitude or the behavior of the

Output signal of the subtraction device OP. Characterized in that the two signals of the two phase lines PH1 and PH2 of the primary AC line voltage AC are subtracted from each other, produces a signal which is both positive and

has negative sections. Here, the zero crossings are each clearly defined and correspond to the zero crossings of the primary AC line voltage AC. With the help of this signal one has a direct relation to the actual one

primary AC line voltage AC. The signal of

Subtraction device OP can be used, for example, for switching individual stages of the switched-mode power supply.

As a result, switching on and off depends on the

Zero crossings of the primary AC line voltage AC possible. Thus, it is possible, for example, to turn on a switching stage of a high-power switching power supply at the beginning of a half-wave and at the end of the same half-wave again

off. This allows optimal utilization of the transmitted power of a half-wave, which

an advantage over conventional switching power supplies

effect at least in the efficiency.

FIG. 6 shows a further circuit diagram of a circuit according to an exemplary embodiment of the invention. In the circuit diagram shown there are additional components

plotted against those previously described

Monitoring circuits ÜS provide further benefits.

Basically, the monitoring circuit ÜS, which is shown in FIG. 6, corresponds to that

Monitoring circuit ÜS, which with respect to Figure 4

has been described. In addition to the described

Monitoring circuit ÜS according to Figure 4 was in the

Embodiment, the circuit shown in Figure 6, an additional resistor R5 in series with a

DC source DC provided which parallel to the Resistor R2 of the first resistor divider Wl are.

This will cause an offset to the positive input of the

Operational amplifier applied. As a result, the output signal of the operational amplifier is shifted to the positive range. Here, the negative

Supply voltage -VCC of the operational amplifier are connected to ground, since the displacement in the positive region no negative bias is required. The offset of the operational amplifier may be 1.5 V, for example. The fact that the offset is a positive signal from

Operational amplifier is output, this signal can be processed easier. Thus, it is possible, for example, the output signal V ₀ UT of the operational amplifier, which is the reference to the primary AC line voltage AC

indicates directly to an input of a microcontroller

supply. In this case, a further preprocessing of the output signal V ₀ UT of the operational amplifier is not necessary.

A voltage waveform output from the operational amplifier which has been subjected to an offset according to the circuit of FIG. 6 is shown in FIG. The voltage curve, which is shown in FIG. 7,

corresponds basically to the voltage curve, which is shown in Figure 5. However, the voltage range is shifted to the positive here. As with the circuit according to the circuit diagram from FIG. 4, the voltage signal from FIG. 7 is directly related to the actual primary AC line voltage AC. In the embodiments, with respect to the

Circuit diagrams have been described according to Figure 4 and Figure 6, the capacitances Cl and C2 optional Filtering options to efficiently dimension the circuit.

Another advantage of a monitoring circuit according to the invention is that influences of

Bridging rectifier diode forward voltage in the

Do not include the output signal of the operational amplifier. Bridging rectifier diode forward voltage depends on current flow and temperature. While other possible monitoring circuits Üs this type of error

should take into account, by subtracting the two voltage signals of the phase lines PH1 and PH2 by the subtraction device OP this influence is avoided. The resistor divider Wl and W2 can

High voltage resistor divider to be adapted specifically to the given voltages. Here, a divider ratio of the resistors R1 and R2 is preferably identical to the dividing ratio of the resistors R3 and R4. To increase the dielectric strength, the resistors Rl and R3 may each consist of several resistors, which are connected in series. In the illustrated in Figure 6

Embodiment, the proportion of the resistors Rl, R2 and R5 is identical to the division ratio of

Resistors R3 and R4.

Thus, a circuit for error-free

Input voltage detection in a power supply described. The circuit is not only in static operation, in which at any time a direct reference from the input side of the bridge rectifier is given to the output side, an accurate output signal V ₀ UT, but also at strong

Load changes or very low output power. Reference sign list

AC primary AC line voltage PH1, PH2 phase line

W, Wl, W2 resistor divider

G rectifier circuit

D1, D2 diode

RL load

R1 to R5 resistance

Cl to C3 capacitor

DC DC voltage source

OP subtraction device

GND ground potential

-VCC negative bias

VQUT output signal

Claims

claims

A monitoring circuit (ÜS) for a switching power supply with a rectifier circuit (G) for rectifying a primary AC line voltage (AC) comprising

- Two resistor divider (Wl, W2), each comprising two resistors (Rl, R2, R3, R4), each in series

between a phase line of a mains connection in front of the rectifier circuit (G) and a reference point after the rectifier circuit (G) are connected, and

- A subtraction device (OP) with two inputs, each of the two inputs of the subtraction device (OP) in each case between the resistors (Rl, R2, R3, R4) each one of the resistor divider (Wl, W2) is connected.

2. Monitoring circuit according to claim 1, characterized

characterized in that the rectifier circuit (G) comprises a bridge rectifier circuit.

3. Monitoring circuit according to claim 1 or 2, characterized in that in each case a capacitor (Cl, C2)

parallel to the resistors (R2, R4) of the two

Resistor divider (Wl, W2) is connected to the

Closest to the reference point.

4. Monitoring circuit according to one of claims 1 to 3, characterized in that the reference point a

output side ground potential (GND) at an output side of the rectifier circuit (G).

5. Monitoring circuit according to one of claims 1 to 4, characterized in that the subtraction device (OP) an operational amplifier connected as a subtractor.

6. Monitoring circuit according to claim 5, characterized

characterized in that the positive input of the

Operational amplifier is applied with an offset.

7. Monitoring circuit according to claim 6, characterized

characterized in that a signal output of

Operational amplifier is electrically connected to a microcontroller.

8. Monitoring circuit according to one of claims 1 to 7, characterized in that an output signal (V ₀ UT) of the subtraction device (OP) is a direct reference to the voltage waveform of the primary AC line voltage (AC).

9. Use of a monitoring circuit according to one of claims 1 to 8 in a switched-mode power supply, in which reference is made to a primary mains alternating voltage (AC) for switching.

10. Use of a monitoring circuit according to claim 9, characterized in that at low output power of the switching power supply in each case a complete half cycle of the primary AC line voltage (AC) is used to generate a secondary DC voltage.