DE102006033348A1 - Input direct current voltage converting method for e.g. TV set, involves deriving switch signal from oscillator signal of frequency variable oscillator for controlling secondary-sided controllable switches at common duty cycles - Google Patents

Abstract

The method involves deriving a switch signal from an oscillator signal of a frequency variable oscillator for controlling secondary-sided controllable switches (41, 42) at common duty cycles. The oscillator signal is supplied to a threshold value comparator. The switch signal in-phase with the oscillator signal, is supplied to a galvanic separation unit e.g. optocoupler. A resonance controller (6) is provided for regulating an output direct current voltage by a synchronous frequency variable control of primary-sided controllable switches (31, 32) e.g. MOSFET transistors. An independent claim is also included for a resonance converter for converting an input direct current voltage into an output direct current voltage.

Description

The The invention relates to a method for converting a DC input voltage in a DC output voltage by means of a resonant converter with the features specified in the preamble of claim 1 and a Resonance converter, which works after the procedure.

at Resonant transducers are DC / DC converters, which are preferably a high input DC voltage, such as of 300 V, in one or a plurality of comparatively small output DC voltages, e.g. of 20 V, convert. Such resonant converters are used in particular for Power supply of electronic devices, e.g. of televisions. Especially become resonant converters for converting a rectified mains voltage, such as. of 230 V or 110 V, used.

to power transmission usually becomes one Transformer used, which at the same time a galvanic isolation between the input and output DC voltage allows.

at Resonant converters, a resonant circuit ensures that controllable switches, such as. Transistors, essentially in current or voltage zero be switched on or off. This will cause switching losses in the transistors and radio interference reduced. The resonant circuit typically consists of a series or Pa rallelschaltung of an inductance and a capacitance. He can also several inductors and have capacities. Furthermore, the resonant circuit primary or secondary side operate. Usually is a primary or secondary winding of the transformer part of the resonant circuit.

In As a rule, to regulate the output DC voltage resonant converter with fixed duty cycle and variable switching frequency, the pulse length at least essentially half the oscillation period of the resonant circuit equivalent. This can be easily switched on or switching off the controllable switches in the zero oscillation respectively.

To control the primary-side controllable switch so-called resonance controller are available as integrated electronic components. In the event that the rectification takes place on the secondary side by means of controllable switches, a further controller or driver module is required, which provides corresponding control signals. Such controllers are complex and include not only timers, a transformer for potential separation but also drivers or inverters. Such another controller or such a driver circuit is for example from the WO 01/26209 known.

It Object of the invention, a method and a resonant converter indicate, in which the circuit complexity less is.

The The object is achieved by a method having the features of the patent claim 1 solved. Advantageous method steps are described in the dependent claims 2 to 5 called. In claim 6 is a working according to the method Resonant converter and advantageous circuit variants in the dependent claims 7 to 16 indicated.

According to the invention is a Blocking signal from an oscillator signal of the oscillator for driving of the at least one secondary side derived controllable switch.

Thereby The circuit complexity is reduced considerably. Another Controller or driver module can be advantageously eliminated.

typically, is the oscillator an oscillator signal output available, which for setting a predeterminable minimum switching frequency, e.g. of 100 kHz, serves. Under the scheme, this exemplary Switching frequency of 100 kHz increase many times as e.g. at 400 kHz. To set the switching frequency is this the oscillator signal output by means of one or more passive Components such as e.g. by means of a capacitor, connected externally. Usually - but not necessarily - is such an oscillator already integrated in a resonance controller. The oscillator can also be signal technology as a separate component be connected to the controller.

The special about the invention is that an existing anyway oscillator signal which already uses the essential temporal information for deriving the blocking signal includes. The essential temporal Information is the oscillator frequency as well as the oscillator phase. As a result, the time reference for the secondary side to be controlled is clearly defined Given a switch.

has the oscillator signal on a rectangular shape, so this can be as direct Blocking signal for controlling the secondary-side controllable switch be used.

According to one embodiment the oscillator signal is fed to a threshold comparator. has the oscillator signal is a triangular or sinusoidal waveform on, with a suitable determination of switching thresholds is a rectangular comparator signal derivable as a blocking signal.

Alternatively or additionally, according to a Another embodiment, the oscillator signal or the comparator signal supplied to a galvanic separation unit.

Thereby Advantageously, a galvanic isolation between the primary side Oscillator signal or comparator signal and the secondary side Blocking signal reached. A galvanic isolation of the oscillator signal or the comparator signal is necessary if a galvanic Separation of DC input voltage and DC output voltage is desired.

in the In particular, the blocking signal is at least substantially in phase to the oscillator signal.

According to one another embodiment the method is the control of the secondary controllable Switch with a constant duty cycle. The duty cycle can e.g. 70:30, with the blocking time for the secondary controllable switch is less than the remaining release time.

Thereby can control the secondary controllable switch so made that a first part of the secondary side Switch at the first half of the resonance circuit or off and that a second part of the secondary side Switch on the second half of the oscillation on or off.

According to one embodiment of the resonant converter has this a signal conditioning unit on, which from the oscillator signal of the oscillator, the blocking signal for controlling the at least one secondary-side controllable switch derives. The signal conditioning unit may include a threshold comparator and / or have a galvani cal separation unit. The galvanic Separating unit may e.g. an optocoupler or a transformer or a transformer be. About that In addition, the signal conditioning unit in the resonance controller be integrated. In this case, the resonance controller corresponding outputs for controlling the secondary side controllable switch on.

has the optocoupler, for example, a switching hysteresis and is this input side connected to a triangular oscillator signal, so the opto-coupler can already output the blocking signal to the output side direct control of a switching contact of a secondary side Switch. Be the optocouplers also the input side antiparallel interconnected, so are the respective output side blocking signals complementary to each other. Both blocking signals can then e.g. two secondary-sided Control switch in push-pull.

According to one particular embodiment of the Invention, the resonant converter on a monitoring unit. These gives a blocking signal when exceeded a predetermined voltage on at least one of the secondary windings out. In particular, the predefinable voltage is significantly higher than that Rated output AC voltage, e.g. over more than 10%. such secondary surges can e.g. at a faulty control of the secondary-side controllable switch occur.

one another embodiment According to the secondary side controllable switch on a control contact. This tax contact can e.g. be a gate or a base of a transistor. The respective Control contact is over a resistor connected to the DC output voltage to turn on of the secondary side Switch connected. In addition, the respective control contact via decoupling diodes with the blocking signal and possibly with the blocking signal to Turn off the secondary side Switch connected.

Thereby is a circuit of the secondary side controllable switch with a few commercially available components possible.

To an embodiment Rectifier diodes are parallel to the secondary-side controllable switches connected. these can at least temporarily, a current induced in the secondary windings rectify.

Preferably the rectifier diodes are Schottky diodes. These have the leading role Condition a particularly low voltage drop of about 0.3 to 0.5V on.

Especially are the primary and secondary-sided controllable switch switching transistors. These can be bipolar or unipolar Be transistors. Particularly suitable are field effect transistors, such as. JFET or in particular MOSFET transistors. MOSFET transistors have a very low on-resistance in the conducting state over the so-called source-drain path, such as of 10mΩ, up. Such Transistors can then because of the low contact resistance a large part of secondary side rectifying rectifying diode take over the parallel rectifier diode. The power loss and the required cooling surface of the secondary-side synchronous rectifier reduce in an advantageous manner.

Further advantageous embodiments and preferred embodiments of the invention are the dependent claims remove.

The invention and advantageous Ausführun The same will be described in more detail below with reference to the following figures.

It demonstrate:

1 a block diagram of the resonant converter according to the invention or the method according to the invention,

2 by way of example a circuit arrangement of a resonant converter according to the invention in detail,

3 for example, a waveform of an oscillator signal according to 2 .

4 a derived from the oscillator signal lock signal and

5 in each case by the two secondary-side switch temporally staggered rectifier currents according to 2 ,

1 shows a schematic diagram of the resonant converter according to the invention 1 , which corresponds to the method according to the invention. In the middle part of the 1 are synchronous rectifiers 3 . 4 represented by a transformer 2 are coupled. The two synchronous rectifiers 3 . 4 have controllable switches 31 . 32 ; 41 . 42 - symbolized by a controllable rectifier symbol - on. The reference symbol UE is a DC input voltage, the reference symbol UA denotes the output DC voltage.

In the example of 1 has the resonant converter 1 a primary-side resonant circuit 5 which consists of a series circuit of a capacitor C1 as a capacitance and a leakage inductance of the coil 21 of the transformer 2 exists as inductance. With the reference number 21 . 22 By way of example, two secondary windings connected in series are designated.

In the upper part of the 1 is an example of a potential separator 8th shown. It transmits a feedback signal FB derived from the DC output voltage UA for controlling the DC output voltage UA to a resonance controller 6 , The resonance controller 6 lies in the example of 1 at the voltage level of the primary side of the resonant converter 1 , FB 'denotes the galvanically isolated feedback signal corresponding to FB.

On the potential isolator 8th can be omitted if a potential separation for power supply of downstream electrical or electronic components is not required.

Alternatively, the resonant circuit 5 be arranged on the secondary side. Furthermore, alternatively, the resonance controller 6 at the voltage level of the secondary side of the resonant converter 1 lie.

The resonance controller 6 represents corresponding control signals not further designated for controlling the primary-side controllable switch 31 . 32 to disposal. The control is such that a secondary-side AC voltage at the transformer 2 is induced. The control takes place synchronously and with a switching frequency in the kHz range, in particular in a range of hundreds of kilohertz to several hundred kilohertz.

For controlling the secondary-side controllable switches 41 . 42 serves a blocking signal SG, which is derived from an oscillator signal OS. The oscillator signal OS is located at an output of an oscillator 61 , In the example of 1 is the oscillator 61 already in the resonant controller 6 integrated.

Alternatively, the oscillator 61 a separate component, which with the resonance controller 6 is technically connected.

In the example of 1 represents the oscillator 61 a triangular oscillator signal OS ready. The oscillator signal OS is a signal conditioning unit 7 of the resonant converter 1 fed. If in the feedback line FB a potential separator 8th is provided, must also the signal conditioning unit 7 contain a potential separator. The signal conditioning unit 7 derives from the oscillator signal OS, the blocking signal SG for controlling the secondary side controllable switch. The signal conditioning unit 7 also contains a potential isolator, which can be dispensed with, unless a potential separation is required.

2 shows an example of a circuit arrangement of a resonant converter according to the invention 1 in detail. In the left middle part of the 2 are terminals for connecting the input DC voltage UE to see. The input DC voltage UE is smoothed by means of a capacitor C2. The capacitor C2 is the resonant circuit of the capacitor C1 as a capacitance and the leakage inductance of the coil 21 downstream as inductance. The sink 21 is at the same time the primary winding of the transformer 2 , For electrical excitation of the resonant circuit, the resonance controller 6 For example, two outputs SW1, SW2 for controlling the primary-side switch 31 . 32 on.

The primary-side switches 31 . 32 are preferably switching transistors, in particular self-blocking MOSFET transistors. These show In addition to very low transmission losses, a defined blocking behavior when switching on the resonant converter 1 on. To control the transistors 31 . 32 is the respective gate with the two outputs SW1, SW2 of the resonance controller 6 connected.

On the left part of the resonance controller 6 an oscillator signal output OSC is shown. The output OSC is at play with a resistor R1 and a capacitor C3 for adjusting the switching frequency of the resonance controller 6 wired.

2 provides at the oscillator signal output OSC the oscillator signal OS with a typically triangular waveform. For signal processing, the oscillator signal OS on the input side of the signal conditioning unit 7 fed. This has a threshold comparator 71 on, which forms from the triangular oscillator signal OS a rectangular comparator signal KS by inversion. In the event that no galvanic isolation of the comparator signal KS is required, this signal KS can directly as a blocking signal SG for the secondary-side switch 41 . 42 be used.

Furthermore, the signal conditioning unit 7 an optocoupler 72 as potential separation unit. In the course of the signal, the blocking signal SG essentially corresponds to that of the inverted comparator signal KS.

In the middle part of the 2 are exemplary two secondary windings 22 . 23 of the transformer 2 to see. Both windings 22 . 23 are connected in series, wherein at the center tap of the series circuit, the output DC voltage UA is applied. The capacitor C4 shown is used for smoothing the DC output voltage UA. The respective free end of the secondary windings 22 . 23 is in the example of 2 in each case via a rectifier diode D1, D2 and via a respective secondary-side controllable switch 41 . 42 connected to the secondary-side reference potential, that is the ground. The secondary windings 22 . 23 are connected according to their sense of winding so that during the first half of the resonant circuit oscillation, the first diode D1 and during the second half of the resonant circuit oscillation, the second diode D2 becomes conductive.

According to the invention, the control of the secondary-side controllable switch takes place 41 . 42 such that the otherwise usually by the diodes D1, D2 flowing current from the respective switch 41 . 42 is taken over. The from the respective secondary side switch 41 . 42 taken over current has the reference i1, i2.

On the two diodes D1, D2 can also be dispensed with, in particular when self-blocking transistors, such as e.g. MOSFET transistors, be used with defined blocking behavior.

Alternatively, the sole use of self-conducting transistors is conceivable. In this case, an auxiliary voltage and a circuit for defined start of the resonant converter 1 to be required.

According to the invention, the respective control contact, such as the gate in the case of a field effect transistor 41 . 42 , connected via a resistor R2, R3 to the DC output voltage UA. This will cause the respective secondary side switches 41 . 42 switched on.

To turn on only one of the two switches 41 . 42 to accomplish, is the respective control contact of the switch 41 . 42 via a respective diode D5, D6 with the not lying on the reference potential switching contact of the other switch 41 . 42 connected. That means that the switch 42 with acquisition of the rectifier current i1 by the secondary winding 22 is blocked via the diode D6. Analog is the switch 41 with acquisition of the rectifier current i2 by the secondary winding 23 blocked via the diode D5.

Both switches 41 . 42 can thus only turn on alternately. An unintentional simultaneous switching on of both switches 41 . 42 is prevented according to the invention.

According to the invention, a switching of the two switches 41 . 42 released only during certain periods. These periods are also periodic and synchronous to the primary-side oscillator signal OS. For this purpose, the respective control contact of the two switches 41 . 42 via decoupling diodes D3, D4 connected to the blocking signal SG. Indicates the blocking signal SG, as in the example of 2 shown, a low signal level, such as about 0 V, so the two control contacts of the switching means 41 . 42 "pulled" to the low voltage potential, thereby blocking the two transistors 41 . 42 , On the other hand, the blocking signal SG is a switching on of the two transistors 41 . 42 free, if this has a high signal level. In this case, the respective transistor 41 . 42 take over the current through the diode D1, D2.

With the reference number 9 is a protection unit called which a blocking signal BS in the presence of an overvoltage UM at one of the two secondary windings 22 . 23 outputs. Furthermore, the blocking signal BS is also in the case of a short circuit, ie when the output DC voltage UA un ter a minimum allowable output DC voltage UAmin (UA <UAmin) falls, output, which is evaluated as a further switching criterion. In the example of 2 the blocking signal BS is also connected to the two decoupling diodes D3, D4. Exceeds now, for example, a voltage U22, U23 on a secondary winding 22 . 23 a predeterminable overvoltage value UM or the output DC voltage UA falls below a minimum value of about 90% of UA, so may a not further designated switch of the monitoring unit 9 the two secondary-side switches 41 . 42 lock. In this case, the control voltage at the respective control contact of the two switches 41 . 42 pulled to a low voltage level analogous to the low signal level at the blocking signal SG.

3 shows an example of a waveform of an oscillator signal OS according to 2 , In the example of 3 the oscillator signal OS is triangular. With T0 is a time with the maximum signal value of the oscillator signal OS, denoted by T1 a time with a minimum signal value. The oscillator signal OS is periodic. This is indicated by the dashed continued line.

4 shows an inverse derived from the oscillator signal OS, inverted locking signal SG. This has a rectangular waveform. The blocking signal SG is eg by means of a threshold value comparator 71 derivable from the oscillator signal OS. In the example of 4 the blocking signal SG has a same phase to the oscillator signal OS. The blocking signal SG has, for example, a duty ratio of 30:70. The blocking time for the two secondary-side switches 41 . 42 is thus smaller than the release time. The duty cycle as well as the phase offset can depend on the technical parameters of the switches used 41 . 42 also have other values, such as a duty cycle of 40:60.

5 shows in each case by the two secondary-side switch 41 . 42 temporally staggered flowing rectifier currents i1, i2 according to 2 , The solid line shows the time course of the first secondary-side controllable switch 41 flowing current i1. The dashed line shows the time course of the second secondary-side controllable switch 42 flowing current i2. The two release times or release periods are always phase-shifted by 180 ° with respect to each other. The two switches 41 . 42 are therefore operated in push-pull.

1

Resonant converter, DC / DC converter, power supply

2

transformer

3

primary synchronous rectifier

4

secondary synchronous rectifier

5

resonant circuit

6

resonant controller

7

Signal conditioning unit

8th

potential Breaks

9

monitoring unit

21

Kitchen sink, primary

22 23

secondary windings

31 32

primary controllable switch

41 42

secondary taxable switch

61

oscillator

71

threshold comparator

72

galvanic Separation unit, optocouplers, transformers

BS

blocking signal

C1-C3

capacitors

D1-D6

diodes

ERROR

error input

FB, FE '

Feedback signal

i1, i2

electricity through the secondary-side switches

KS

comparator

OS

oscillator signal

OSC

oscillator output

R2-R3

resistors

SG

blocking signal

SW1, SW2

Outputs to Control of the primary controllable switch

t

Time

T0, T1

timings

U22, U23

Voltage at secondary winding 22 respectively. 23

UA

DC output voltage

UE

DC input voltage

AROUND

Overvoltage value

Claims (17)

Method for converting a DC input voltage (UE) into a DC output voltage (UA) by means of a resonant converter ( 1 ) with - a transformer ( 2 ) with at least one primary winding ( 21 ) and at least one secondary winding ( 22 ), - at least one synchronous rectifier ( 3 . 4 ) with at least one controllable switch ( 31 . 32 ; 41 . 42 ) and - a controller ( 6 ) with a variable frequency oscillator ( 61 ) for controlling the DC output voltage (UA) via a synchronous frequency-variable control of the primary-side controllable switch ( 31 . 32 ), characterized in that a blocking signal (SG) from an oscillator signal (OS) of the oscillator ( 61 ) for controlling the at least one secondary-side controllable switch ( 41 . 42 ) is derived. A method according to claim 1, characterized in that the oscillator signal (OS) a threshold value comparator ( 71 ) is supplied. Method according to claim 1 or 2, characterized in that the blocking signal (SG) of a galvanic separation unit ( 72 ) is supplied. Method according to one of the preceding claims, characterized in that the blocking signal (SG) is substantially in phase to the oscillator signal (OS). Method according to one of the preceding claims, characterized in that the control of the secondary-side controllable switch ( 41 . 42 ) takes place with approximately the same duty cycle. Resonance converter for converting a DC input voltage (UE) into a DC output voltage (UA) with - a transformer ( 2 ) with at least one primary winding ( 21 ) and at least one secondary winding ( 22 . 23 ), - a primary and secondary synchronous rectifier ( 3 . 4 ) each having at least one controllable switch ( 31 . 32 ; 41 . 42 ) and - a controller ( 6 ) with a variable frequency oscillator ( 61 ) for controlling the DC output voltage (UA) via a synchronous frequency-variable control of the primary-side controllable switch ( 31 . 32 ), characterized in that the resonant converter comprises a signal conditioning unit ( 7 ), which consists of an oscillator signal (OS) of the oscillator ( 61 ) a blocking signal (SG) for controlling the at least one secondary-side controllable switch ( 41 . 42 ). Resonance converter according to claim 6, characterized in that a threshold value comparator ( 71 ) is connected on the input side to the oscillator signal (OS). Resonance converter according to claim 6 or 7, characterized in that the resonant converter at least one galvanic separation unit ( 72 ), which on the input side with the oscillator signal (OS) or with a comparator signal (KS) of Schwellwertkomparators ( 71 ) and the output side is connected to the blocking signal (SG). Resonant converter according to claim 8, characterized in that the galvanic separation unit ( 72 ) is an optocoupler or a transformer. Resonance converter according to one of claims 6 to 9, characterized in that the signal conditioning unit ( 7 ) outputs the inhibit signal (SG) substantially in phase with the oscillator signal (OS). Resonant converter according to one of claims 6 to 10, characterized in that the signal conditioning unit ( 7 ) the secondary-side controllable switches ( 41 . 42 ) with approximately the same blocking signal duration. Resonant converter according to one of claims 6 to 11, characterized in that the resonant converter is a monitoring unit ( 9 ) which, when a predeterminable voltage (U21, U22) is exceeded, is applied to at least one of the secondary coils ( 21 . 22 ) outputs a blocking signal (BS). Resonance converter according to one of claims 6 to 12, characterized in that the monitoring unit ( 9 ) outputs a blocking signal (BS) when falling below a minimum output DC voltage UAmin. Resonance converter according to one of claims 6 to 13, characterized in that - that the secondary-side controllable switch ( 41 . 42 ) have a control contact, - that the respective control contact via a with the output DC voltage (UA) connected resistor (R2, R3) for switching on the secondary-side switch ( 41 . 42 ) and - that the respective control contact via decoupling diodes (D3, D4) with the blocking signal (SG) and possibly with the blocking signal (BS) for switching off the secondary side switch ( 41 . 42 ) connected is. Resonance converter according to one of claims 6 to 14, characterized in that parallel to the secondary-side controllable switches ( 41 . 42 ) Rectifier diodes (D1, D2) are connected. Resonant converter according to claim 15, characterized in that the rectifier diodes (D1, D2) are Schottky diodes. Resonance converter according to one of claims 6 to 16, characterized in that the primary and secondary side controllable switch ( 31 . 32 ; 41 . 42 ) Switching transistors, in particular self-blocking MOSFET transistors, are.