DE102006046729B4 - Power supply circuit with temperature-dependent output current and circuit arrangement with a power supply circuit - Google Patents

Power supply circuit with temperature-dependent output current and circuit arrangement with a power supply circuit

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Publication number
DE102006046729B4
DE102006046729B4 DE200610046729 DE102006046729A DE102006046729B4 DE 102006046729 B4 DE102006046729 B4 DE 102006046729B4 DE 200610046729 DE200610046729 DE 200610046729 DE 102006046729 A DE102006046729 A DE 102006046729A DE 102006046729 B4 DE102006046729 B4 DE 102006046729B4
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Prior art keywords
power supply
temperature
supply circuit
current
load
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DE200610046729
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German (de)
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DE102006046729A1 (en
Inventor
Michael Lenz
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Infineon Technologies AG
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Infineon Technologies AG
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Publication of DE102006046729A1 publication Critical patent/DE102006046729A1/en
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Classifications

    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHTING NOT OTHERWISE PROVIDED FOR
    • H05B33/00Electroluminescent light sources
    • H05B33/02Details
    • H05B33/08Circuit arrangements not adapted to a particular application
    • H05B33/0803Circuit arrangements not adapted to a particular application for light emitting diodes [LEDs] comprising only inorganic semiconductor materials
    • H05B33/0884Circuit arrangements not adapted to a particular application for light emitting diodes [LEDs] comprising only inorganic semiconductor materials with monitoring or protection
    • H05B33/0887Circuit arrangements not adapted to a particular application for light emitting diodes [LEDs] comprising only inorganic semiconductor materials with monitoring or protection of the conversion stage
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHTING NOT OTHERWISE PROVIDED FOR
    • H05B33/00Electroluminescent light sources
    • H05B33/02Details
    • H05B33/08Circuit arrangements not adapted to a particular application
    • H05B33/0803Circuit arrangements not adapted to a particular application for light emitting diodes [LEDs] comprising only inorganic semiconductor materials
    • H05B33/0806Structural details of the circuit
    • H05B33/0809Structural details of the circuit in the conversion stage
    • H05B33/0815Structural details of the circuit in the conversion stage with a controlled switching regulator

Abstract

Power supply circuit comprising:
a load current path for connecting a load (7) having an inductive storage element (72), which has a switching element (6),
a current sensor (5) for providing a current measuring signal (S5) dependent on a current (IL) through the load current path,
a drive circuit (2) which provides a clocked drive signal (S2) with a plurality of drive cycles each having a switch-on duration and a switch-off duration for the switch element (6),
a temperature sensor arrangement (4) having a temperature sensor (42) for determining an ambient temperature in the region of the temperature sensor (42) which provides a temperature measurement signal (S4) dependent on the ambient temperature,
wherein the clocked drive signal (s2) is dependent on the current measurement signal (S5) and the temperature measurement signal (S4) and wherein the drive circuit (2) is designed to block the switch (6) during a drive cycle in each case for a fixed predetermined switch-off duration the switch-off duration begins in each case when the current measurement signal (S5) rises to a value dependent on the temperature measurement signal (S4).

Description

  • The The present invention relates to a regulated power supply circuit for providing a supply current for a load, in particular for a load with at least one light-emitting diode (LED), and a circuit arrangement with a power supply circuit.
  • When Replacement for conventional Incandescent lamps are - for example in motor vehicles - increasingly Power LEDs (Power LEDs, Power LEDs) used. These light-emitting diodes have over conventional light-emitting diodes one higher Power consumption and thus a higher light output, subject but also a stronger one Warming. LEDs are usually on Printed circuit board (PCB), which is too high Temperatures are damaged or destroyed can be. Unless sufficient cooling is present, can be mounted on a board light emitting diode to such damage lead the board. This problem is the bigger, the smaller the board and thus the smaller their ability is, in heat dissipate converted power loss.
  • The DE 199 30 174 A1 describes a power supply circuit for a number of series-connected light-emitting diodes, which clocked provides a current for the light-emitting diodes, which is dependent on a temperature.
  • The DE 198 10 827 A1 describes a circuit for powering a light emitting diode. In series with the light emitting diode, a coil and a switch are connected in this circuit, wherein the switch is opened and closed pulse width modulated. A switch-off duration of this switch is dependent on a temperature determined at the light-emitting diode per actuation cycle.
  • The US 2005/0140315 A1 describes a drive circuit for a light emitting diode array. This drive circuit has, in series with the light-emitting diode arrangement, a coil and a pulse-width-modulated, triggered switching element. A control of the switching element is effected by a controller, which is supplied with a signal which causes a lowering of the current flowing through the LED depending on an ambient temperature.
  • task It is the object of the present invention to provide a power supply circuit for one Last, especially for a light emitting diode, available to provide a reliable Supplying the load while protecting the environment from overheating guaranteed and a circuit arrangement with to provide such a power supply circuit.
  • These The object is achieved by a power supply circuit according to claim 1 and solved by a circuit arrangement according to claim 7. advantageous Embodiments of the invention are the subject of the dependent claims.
  • A embodiment The power supply circuit according to the invention comprises a load current path to connect a load having a switching element, a current sensor for Providing a current measuring signal dependent on a current through the load current path, a drive circuit having a clocked drive signal with a plurality each have a duty cycle and a turn-off Control cycles for the Switching element provides, and a temperature sensor arrangement with a temperature sensor for determining an ambient temperature in the range of the temperature sensor, which is one of the ambient temperature dependent Temperature measurement signal provides. The clocked drive signal This power supply circuit has a duty ratio of the current measurement signal and the temperature measurement signal is dependent.
  • The clocked controlled switching element of this power supply circuit controls the power consumption of the power supply circuit and thus the current consumption of the load. This current consumption is from the duty cycle of the switching element driving the drive signal dependent. The Setting the duty cycle This clocked drive signal depending on the temperature allows a Control of power consumption depending on the temperature in the environment of the LED.
  • embodiments The present invention will be described below with reference to FIGS explained in more detail.
  • 1 shows a circuit diagram of an embodiment of a power supply circuit according to the invention comprising a load current path with a switch, a drive circuit for the switch and a temperature sensor arrangement.
  • 2 shows an implementation example for the drive circuit.
  • 3 illustrates the operation of a power supply circuit with a drive circuit according to 2 on the basis of time profiles of selected signals occurring in the power supply circuit.
  • 4 shows a further realization example for the drive circuit.
  • 5 shows a circuit reali Sierungsbeispiel one in the drive circuit according to 4 existing timer.
  • 6 1 illustrates the operation of an embodiment of a power supply circuit according to the invention with a drive circuit according to FIG 4 on the basis of time profiles of selected signals occurring in the power supply circuit.
  • 7 shows an embodiment of a power supply circuit according to the invention having an enable circuit.
  • 8th shows an embodiment of a sensor arrangement.
  • 9 illustrates temperature dependencies of individual in the sensor arrangement according to 8th occurring signals.
  • 10 shows in cross section ( 10A ) and in plan view ( 10B ) a power supply circuit disposed on a carrier according to an embodiment of the invention with a connected load.
  • In denote the figures, unless otherwise indicated, like reference numerals same circuit components and signals with the same meaning.
  • 1 shows a first embodiment of a power supply circuit 10 for powering a load. This power supply circuit 10 has a load current path, which in the example between first and second terminals 11 . 12 the power supply circuit 10 runs. In this load current path is a switching element 6 connected to the clocked power supply of a connectable to the load current load 7 serves and during operation of the power supply circuit by a drive circuit 2 is driven by a clocked drive signal S2. This clocked drive signal S2 has during operation of the power supply circuit to a plurality of time-sequential drive cycles, each having a duty cycle and a turn-off. The switching element 6 In this case, it is activated during the switch-on periods and activated during the switch-off periods. A duty cycle d of this clocked drive signal S2 during a drive cycle is defined by the quotient of the duty cycle during this drive cycle and the total duration of this drive cycle, ie the sum of the duty cycle and the turn-off duration. It therefore applies: d = tone / T = tone / (tone + Toff) (1).
  • volume denotes the duty cycle during a drive cycle, Toff the off duration during this drive cycle and T the duration of the drive cycle.
  • The drive circuit 2 generates the clocked drive signal S2 such that its duty cycle of a load current IL in the load current path and of a by a temperature sensor arrangement 4 provided temperature measurement signal S4 is dependent. Information about the instantaneous value of the load current flowing through the load current IL is the drive circuit 2 in the form of a current measuring signal S5 supplied by a current sensor 5 is provided and that is proportional to the load current IL.
  • The current sensor 5 can be any suitable for the measurement of the load current IL and provision of the current measurement signal S5 current sensor. The current sensor can be realized, for example, by a measuring resistor connected in the load current path, at which the load current causes a voltage drop which corresponds to the measuring signal S5.
  • The switching element 6 For example, it may be realized as a power bipolar transistor or as a power MOS transistor having a plurality of similar parallel-connected transistor cells. In such a realization of the switching element 6 the measurement of the load current IL and thus the provision of the current measurement signal S5 in a manner not shown can be carried out according to the so-called current-sense principle. In this case, the cell field is subdivided into a first group of transistor cells, the so-called load cells, and a second group of transistor cells, the so-called measuring cells. The load cells serve to supply power to a connected load, while the measuring cells are used for current measurement and are operated by suitable control at the same operating point as the load cells. A measurement current flowing through the measuring cells is then based on the quotient of the number of measuring cells to the number of load cells in relation to the load current. The measuring current can be used here - for example, by a measuring resistor - directly to generate a current measuring signal.
  • The temperature sensor arrangement 4 points in the in 1 Example shown a temperature sensor 42 which serves to determine an ambient temperature and that immediately adjacent to the load 7 or also spaced from the load 7 can be arranged. This temperature sensor 42 is to a transducer unit 41 connected by a through the temperature sensor 42 detected ambient temperature dependent on this ambient temperature temperature measurement signal S4 he testifies.
  • The to the load current path of the power supply circuit 10 connected load 7 includes in the illustrated embodiment, a series connection of an inductive storage element 72 , For example, a coil, and at least one light emitting diode 71 . 7n , In the example, two LEDs 71 . 7n connected in series with the inductive storage element, however, as is indicated graphically by dots, depending on a desired lighting situation, any number of light-emitting diodes in series with the inductive storage element 72 be switched.
  • Parallel to the series connection with the inductive storage element 72 and the light emitting diodes 71 . 7n is a freewheeling element 73 connected, which is realized in the example as a diode and which serves, with blocking driven switching element 6 and previously magnetized inductive storage element 72 one by Abkommutieren of the memory element 72 to take over flowing electricity. As an alternative to a passive component, such as the illustrated diode, the freewheeling element 73 in a manner not shown also be realized by an active device, such as a transistor, which is connected as a so-called synchronous rectifier.
  • The freewheeling element 73 is in 1 as part of the load 7 shown. However, there is also the possibility of this freewheeling element 73 in the drive circuit 10 provided. The drive circuit 10 then has an additional connection terminal 16 , in the 1 dashed lines and which serves to the freewheeling element 73 to be connected to the terminal for the supply potential Vs. The load is in such a drive circuit between the first terminal 11 and this other terminal 15 connected.
  • Parallel to the series connection of the load and the load current path, a buffer capacitor can be used to compensate for voltage fluctuations and to smooth the current profile in the supply line to the load of the supply voltage 74 be switched in 1 is shown in dashed lines. A smoothing of the current profile in the supply line is useful here with regard to a reduction of the harmonic content and thus to a reduction of the EMC radiation.
  • To the power supply in the drive circuit 10 existing circuit components can be a power supply circuit 8th (shown in dashed lines), which are connected via a terminal 15 is connected to the terminal for the supply potential Vs, and for example, serves to implement the supply potential for the load to a suitable for the supply of the circuit components potential. Only graphically indicated in 1 Line connections between this power supply circuit 8th and the other circuit components.
  • The basic operation of the illustrated power supply circuit 10 is briefly explained below:
    The series connection of the load current path of the power supply circuit 10 and the load 7 is connected during operation of the power supply circuit between a terminal for a first supply potential Vs and a second supply potential or reference potential GND. In a clocked control of the switching element 6 ie, an alternating conductive drive of the switching element 6 each for a duty cycle and a blocking drive each for a turn-off is - assuming a negligible ON resistance of the switching element 6 - The voltage applied between the terminals for the supply potential supply voltage clocked to the load 7 created and causes a flow of current through the load. The inductive storage element 72 takes at one over the load 7 applied supply voltage, ie during the switch-on of the switching element 6 , Electrical energy, which during each subsequent off periods on the freewheeling element 73 a still flowing current through the LEDs 71 . 7n causes. The inductive storage element 72 provides in this circuit arrangement for a smoothing of the current profile in comparison to a load arrangement in which no such inductive storage element is present and in which the load current with the aid of a limiting resistor would have to be limited, but this leads to a high power loss and thus to a reduction of the overall efficiency would lead to increased heat development.
  • A first embodiment of a drive circuit 2 for generating the clocked drive signal S2 for the switching element 6 is in 2 shown. For better understanding are in 2 next to the drive circuit 2 also the switching element 6 , which is realized in this example as an N-channel power MOSFET, and the current sensor 5 representing the current measurement signal S5. The drive circuit 2 has a flip-flop in the illustrated embodiment 22 with a set input S and a reset input R, at whose set input a clock generator 23 , For example, an oscillator is connected, which generates a clock signal S23 and the flip-flop 22 in time with this clock signal S23 sets. The drive signal S2 is connected to a non-inverting output Q of the flip-flop 22 available, with optional between the flip flop 22 and the switching element 6 a driver circuit 21 is connected, which serves to a signal level of the output signal of the flip-flop 22 to a for driving the switching element 6 implement appropriate signal level. The switching element 6 is at this drive circuit 2 activated when the flip-flop is set.
  • A reset of the flip-flop 22 and thus a blocking control of the switching element 6 occurs in the illustrated drive circuit depending on the current measurement signal S5 and the temperature measurement signal S4. A comparator 24 in this case compares the current measurement signal S5 with the temperature measurement signal S4 and sets the flip-flop 22 each dependent on a comparison of these two signals. In the example, the flip-flop is reset 22 via a comparator output signal S24 of the comparator 24 in each case when the current measurement signal S5 reaches the value of the temperature measurement signal S4.
  • 3 illustrates the operation of a driving circuit according to 2 having power supply circuit based on time profiles of the clock signal S23, the current measurement signal S5 and the temperature measurement signal S4. For purposes of explanation, it is assumed that the power supply circuit is in the steady state, that is, up to the in 3 already shown some driving cycles through which the switching element 6 conductive and blocking was controlled, have taken place. For purposes of explanation, it is also assumed that the clock signal S23 has clock pulses at intervals of a period T and that the flip-flop 22 is set in each case with a rising edge of these clock pulses. Also, for illustration in 3 assume that the duration of the drive cycles is chosen so that the inductive storage element 72 the load 7 in the steady state of the system is not completely abkommutiert during a drive cycle.
  • With setting the flip-flop 22 , and thus with conductive activation of the switching element 6 , the current in the switching element increases 6 , and thus the current measurement signal S5 in a ramp shape, wherein the slope dIL / dt the rising edge of the current waveform is dependent on the applied supply voltage and the inductance value of the inductive storage element 72 , The following applies: dIL / dt = Vs / L, (2) where dIL / dt represents the time derivative of the current IL.
  • The flip flop 22 remains set as long as this and the switching element 6 remains correspondingly conductive until the rising current measurement signal S5 reaches the value of the temperature measurement signal S4. In this power supply circuit, the load current IL flowing through the load current path has a triangular current course that fluctuates around an average value ILm. This average value depends on the temperature measurement signal S4 which is output via the comparator ( 24 in 2 ) and the current measurement signal S5 limits the maximum value of the load current IL upward. 3 shows the time profiles of the current measuring signal S5, the drive signal S2 and the load current IL for two different amplitudes of the current measurement signal S4. For the larger of the two amplitudes for which the waveforms in the left part of the 3 are shown, the average value ILm of the load current IL assumes a higher value than for the smaller value of the temperature measurement signal S4, for which the waveforms in the right part of the 3 are shown. It should be noted that the duty cycle of the drive signal S2 in the steady state of the power supply circuit may be the same for different average values of the load current. The duty cycle of the control signal S2 varies in the basis of 3 However, at least during transition phases of the temperature measurement signal S4 from a first value to a second value, the duty cycle is thus at least temporarily dependent on the temperature.
  • Another embodiment of a drive circuit 2 for generating a drive signal 92 is in 4 shown. Instead of an oscillator circuit is a timing element in this drive circuit 25 provided to the setting input of the flip-flop 22 is connected and the comparator output signal S24 is supplied. This timer 25 causes at the in 4 shown drive circuit a fixed predetermined turn-off duration of the drive signal S2 by the timer 25 the flip flop 22 after a fixed predetermined period of time after the presence of a reset signal sets again. The output signal S24 of the comparator 24 is in this drive circuit 2 both the reset input R of the flip-flop 22 as well as an input of the clock 25 fed. The timer 25 is started with a predetermined edge of the comparator output signal S24, for example, a rising edge, and generates after a predetermined period of time a predetermined edge of the timer output signal S25, for example a rising edge, for setting the flip-flop 22 ,
  • The timer 25 includes reference to FIG 5 For example, an RC element with a resistive element 251 and one parallel to the resistive element 251 switched capacitive storage element 252 , This RC element is over egg NEN switch 257 connected to a terminal for a supply potential V +. With conductive switch 257 becomes the capacitive storage element 252 this timer 25 charged to the value of the supply potential V +. With then blocking switch 257 the capacitive storage element discharges 252 about the resistance 251 , A comparator 253 compares the over the capacitive storage element 252 voltage applied to one by a reference voltage source 254 predetermined reference value and generates that at the output of this comparator 253 applied output signal S25 of the timer depending on a comparison of the reference voltage with the voltage across the capacitive storage element 252 , At the in 5 shown timer, a rising edge of the output signal S25 is generated when the switch is open 257 the voltage across the capacitive storage element 252 has fallen below the value of the reference voltage. An opening of the switch 257 takes place at this timer 25 depending on the output signal S24 of the current measuring signal S5 and the temperature measuring signal S4 comparing comparator 24 , This comparator signal S24 is a reset input R of a flip-flop 255 supplied, which is the switching element 257 controls. With reset of the flip-flop 255 by this comparator signal S24, the switch 257 open, indicating a beginning of the timer 25 predetermined waiting time corresponds. The end of the timer 25 predetermined waiting time is reached when the capacitive storage element 252 about the resistance element 251 is discharged to the value of the reference voltage. By doing this at the output of the comparator 253 applied output signal S25 becomes the flip-flop 255 then put back to the switch 257 close and the capacitive storage element 252 recharge until the next waiting time. Optionally, here at a set input S of the flip-flop 255 a delay element 256 upstream, to a stable functional behavior of the timer 25 to reach.
  • The operation of a power supply circuit with an in 4 shown drive circuit is described below with reference to 6 explained. Is shown in 6 By way of example, a time profile of the current measuring signal S5 depends on the temperature measuring signal S4 for two different values of the temperature measuring signal S4. The regulation of the load current absorption takes place via the temperature measuring signal S4, wherein the switching element 6 is then locked, if that at first conductive switching element 6 ramped rising current measurement signal S5 reaches the value S4. The switching element then remains for a by the timer 25 fixed predetermined switch-off Toff off and is then turned on again for a dependent of the flowing load current IL and the temperature measurement signal S4 duty cycle Ton. In the steady state of the power supply circuit, the duty cycle of the drive signal S2 can assume identical values for different values of the temperature measurement signal S4. However, the duty cycle is fundamentally dependent on the temperature measurement signal S4 and changes, for example, with a change in the temperature measurement signal S4. Thus, the duty cycle initially decreases with decreasing temperature measurement signal S4 until the load current has adjusted to a new signal value adapted to the temperature measurement signal.
  • Depending on how the temperature measurement signal S4 as a function of by the temperature sensor 42 detected ambient temperature is generated, in the previously described power supply circuit with increasing ambient temperature, either a decrease in the load current or the average value of the load current or an increase in the load current can be achieved. The transducer 41 For example, it can be realized in such a way that the temperature measuring signal S4 becomes smaller with increasing ambient temperature. In this case, the load current decreases when using the previously explained control principle with increasing ambient temperature, thereby reducing the power consumption of the load and thus counteract a further increase in the ambient temperature.
  • Especially in the control of LEDs, however, it may be useful to increase the load current IL with increasing ambient temperature. This is based on the finding that the light output of light-emitting diodes decreases with increasing ambient temperature and that this reduction in the light output can be counteracted by an increase in the load current flowing through the light-emitting diodes. Such an increase of the load current with increasing ambient temperature can be achieved by the fact that the transducer 41 is realized so that the temperature measurement signal S4 with rising through the sensor 42 detected ambient temperature increases.
  • For the first explained case of a rising temperature with decreasing temperature measurement signal S4, the sensor 42 and the transducer 41 be realized together by a NTC resistor (NTC = Negative Temperature Coefficient), while for the second case of a rising temperature with increasing temperature measurement signal S4 of the sensor 42 and the transducer 41 can be realized by a PTC resistor (PTC = Positive Temperature Coefficient). Such sensors are known in principle, so that it is possible to dispense with further explanations.
  • Furthermore more complex sensors or sensor arrangements can also be used, For example, sensors that are up to a threshold temperature an increasing measuring signal and from temperatures above the threshold value deliver a sinking measurement signal. The steepness of the measuring signal for temperatures below the threshold is preferably less than the for Temperatures above the threshold. In such a sensor arrangement The load current is initially increased with increasing temperature to a light emitting diode as load the decreasing light output as the temperature increases first to compensate, and from reaching a temperature threshold reduced to overheating to avoid the arrangement.
  • An implementation example of such a sensor arrangement is in 8th shown. 9B shows an output signal S4 of this sensor arrangement 4 depending on the temperature T.
  • The illustrated sensor arrangement 4 has a diode as a temperature sensor 42 on, in series with a first power source 411 between a terminal for a supply potential Vcc of the sensor 4 and a terminal is connected for a reference potential. The power source 411 provides a constant current Ibias1, which is at the forward-biased diode 42 causes a voltage drop Vtemp. This voltage drop Vtemp is temperature-dependent due to the physical properties of a diode and thus provides a measure of the ambient temperature in the region of the diode 42 , The temperature voltage Vtemp is referred to 9A , in which the temperature voltage Vtemp is plotted against the temperature T, decreases with increasing temperature. Within a temperature range of interest for the operation of light-emitting diodes, for example between -40 ° C. and 175 ° C., the dependence of the temperature voltage Vtemp on the temperature T can be regarded as approximately linear.
  • The evaluation circuit 41 The sensor arrangement has two differential amplifiers for evaluating the temperature voltage Vtemp 413 . 414 on, of which a first differential amplifier 413 a first difference signal V413 generated by a difference between a first reference voltage Vptc, by a first reference voltage source 417 is provided, and the temperature voltage Vtemp is dependent. A second 414 the differential amplifier supplies a second difference signal V414, which is a difference between a second reference voltage Vntc, which is supplied by a second reference voltage source 418 is provided, and the temperature voltage Vtemp is dependent. The two differential amplifiers 413 . 414 are like that with the diode 42 and the reference voltage sources 417 . 418 interconnects that the first difference signal V413 increases with increasing temperature, while the second difference signal V414 decreases with increasing temperature T. The first differential amplifier 413 For this purpose, the temperature signal Vtemp are supplied at its inverting input and the first reference voltage Vptc at its noninverting input, and the second differential amplifier 414 For this purpose, the temperature signal Vtemp are supplied at its non-inverting input and the second reference voltage Vntc at its inverting input.
  • The differential amplifiers are realized in such a way that their differential voltages at a voltage difference of zero at their inputs correspond to an offset voltage greater than zero, this offset voltage corresponding, for example, to the offset of the input voltages. For Vtemp = Vptc then: V413 = Vptc. Similarly, for Vtemp = Vntc: V414 = Vntc. The differential voltages V413, V414 are schematically shown in FIG 9A It should be noted that the gradients of the curves of the differential voltages V413, V414 and the slope of the curve of the temperature voltage Vtemp are not shown to scale.
  • The outputs of the differential amplifiers 413 . 414 are reverse-biased diodes 415 . 416 to the output of the sensor arrangement 4 to which the sensor signal S4 is available connected. Between this output and the terminal for the supply potential Vcc is also a second power source 412 connected as a load to the outputs of the differential amplifier 413 . 414 serves. The diodes 415 . 416 Make sure that the smaller of the differential voltages V413, V414 plus a forward voltage of the diode 415 . 416 is output as a temperature measuring signal.
  • The functioning of this in 8th shown sensor arrangement is based on the in 9B illustrated course of the sensor signal S4 over the temperature significantly, wherein the sensor signal S4 in the manner already explained is proportional to the load current IL, so that the in 9B also shows the dependency of the load current IL on the temperature T. In the illustrated sensor arrangement, the first reference voltage Vptc is greater than the second reference voltage. Starting from small temperature values, the first differential voltage V413 is thus initially smaller than the second differential voltage, so that the rising first differential voltage V413 dominates the temperature measurement signal.
  • T 0 denotes in 9 a threshold value of the temperature T at which the temperature-decreasing curve of the second differential voltage V414 curves with increasing temperature increasing second differential voltage intersects. From this temperature, the falling second differential voltage V414 dominates the course of the temperature signal S4. Gains k1 and k2 of the first and second amplifiers 413 . 414 are selected in the illustrated sensor arrangement so that k1 <k2 applies. The steepness of the rising temperature for temperatures less than T 0 temperature signal S4 or the load current is thus less than the slope of the temperature greater than T 0 falling temperature signal S4 or the load current to a rapid lowering of the load current for protection when exceeding the threshold value to achieve over-temperature.
  • The threshold value T 0 or a threshold value over the temperature curve of the diode 42 associated threshold voltage Vtemp 0 is dependent on the first and second reference voltages Vptc, Vntc and the gain factors of the differential amplifiers. At the intersection of the curves of the first and second differential voltages, the following applies: V413 = V414 (3)
  • Taking into account V413 = Vptc + k1 (Vptc-Vtemp) (4a) V414 = Vntc + k2 (Vtemp - Vntc) (4b) follows from equation (1) for the threshold voltage Vtemp 0 : Vtemp 0 = [(1 + k1) * Vptc + (k2 - 1) * Vntc] / (k1 + k2) (5).
  • The temperature threshold T 0 results from this voltage Vtemp 0 based on the course of the temperature voltage Vtemp.
  • Optionally, there is the possibility of the gain of the second differential amplifier 414 much larger than one and much larger than the first differential amplifier 413 to be selected so that the temperature measurement signal S4 drops very steeply when the threshold value T 0 is reached, which results in 9B is shown in dashed lines. The second differential amplifier 414 has in this case a hysteresis, so that the temperature measurement signal S4 when the temperature drops to a further threshold T 0 'again steeply to a through the first operational amplifier 413 predetermined value increases. The threshold voltage in this case corresponds to the second reference voltage, and the temperature threshold T 0 corresponds to a reference temperature Tntc at which the temperature voltage Vtemp corresponds to the second reference voltage Vntc.
  • 7 shows a further embodiment of a power supply circuit according to the invention. This power supply circuit differs from that in 2 represented by the presence of an enable circuit 8th that has an entrance 14 a release signal EN can be fed. This release circuit 8th is, for example, via another connection 15 connected to the terminal for the supply potential VS and is adapted to the voltage or power supply of the remaining circuit components of the power supply circuit, depending on the enable signal EN 10 , in particular the drive circuit 2 and the temperature sensor 4 to ensure. The enable signal EN is, for example, a two-valued signal. The release circuit 8th is for example designed such that, at a first signal level of the enable signal EN, it supplies a voltage supply for the circuit components of the power supply circuit 10 provides to the above-mentioned clocked operation of the switching element 6 sure. At a second signal level of the enable signal EN, the enable circuit interrupts 8th the power supply of the circuit components of the power supply circuit 10 , whereby the switching element 6 via the drive circuit 2 can no longer be controlled to conduct and therefore for the period during which this second signal level of the enable signal EN is present blocks.
  • About the Enable signal may be the power supply circuit through a microcontroller (μC) or another low-voltage or Non-power device can be turned on or off. In not shown Way there is in particular the possibility to provide a plurality of the illustrated power supply circuits, which is controlled by a control circuit the release inputs be activated or deactivated at the same time or with a time delay.
  • The clocked control of the switching element 6 can at the in 7 illustrated power supply circuit 10 a clocked switching on and off of the power supply circuit 10 be superimposed on the enable signal EN. In this case, a pulse-width-modulated signal whose pulse duration is greater than the duration of a drive cycle of the switching element is applied as an enable signal 6 , When controlling light-emitting diodes, this "higher-level" pulse-width-modulated activation of the power supply circuit can be achieved 10 For example, set a perceived by the human eye brightness of the LEDs. During a turn-off phase of the power supply circuit during which the load current drops, in this case the brightness of the light-emitting diodes decreases, while it increases again during a subsequent switch-on phase. If the frequency of the pulse width modulated signal is chosen to be sufficiently high, then perceived by the human eye, this change between light phases and dark phases of the light-emitting diodes as a uniform illumination, the luminous intensity is the lower, the longer the dark phases are.
  • Referring to 10 can the power supply circuit 10 and by the power supply circuit 10 controlled load on a common carrier 100 be arranged. 10A shows this carrier in side view in cross section. 10B shows a plan view of the carrier. The carrier can be realized, for example, as a conventional printed circuit board (PCB), are applied to the interconnects (not shown) for interconnecting the individual components. The power supply circuit 10 is realized, for example, as a integrated circuit having a number of external terminals (not shown) for ensuring a power supply and connecting the load. For the representation in 10 It is assumed that the load is two light emitting diodes 71 . 7n which has in 10 only schematically shown as blocks. For better heat dissipation or for uniform heat distribution on the board, the two LEDs 71 . 7n spaced apart in the lateral direction on the board 100 arranged, wherein the power supply circuit 10 in this case between the LEDs 71 . 7n is arranged. The reference numerals 72 and 74 in 10 denote the blocks or positions of the inductive storage element, and the optionally present buffer capacitor. The dashed lines and the reference numeral 73 provided circuit block represents the freewheeling element in a realization in which the freewheeling element as a separate component outside the drive circuit 10 is realized. Alternatively, this freewheeling element can be integrated in the drive circuit already explained.
  • The board 100 the in 10 The arrangement shown can be used as a heat conductor of the heat generating LEDs 71 . 7n to the temperature sensor ( 42 in 1 ) be used. The temperature sensor can thus be spaced from the heat sources 71 . 7n can be arranged and in particular in the integrated circuit of the power supply circuit 10 be integrated. There is also the option of the temperature sensor 42 as an "external" component of the power supply circuit 10 to realize how this is in 10 is shown in dashed lines. In the case of two light-emitting diodes arranged at a distance from one another, the provision of a temperature sensor in the region of a light-emitting diode is sufficient, provided that the light-emitting diodes 71 . 7n are realized so that it can be assumed that the same heat development at the same load current.

Claims (12)

  1. A power supply circuit comprising: a load current path for connecting an inductive storage element ( 72 ) load ( 7 ), which is a switching element ( 6 ), a current sensor ( 5 ) for providing a current measuring signal (S5) dependent on a current (IL) through the load current path, a drive circuit ( 2 ) comprising a clocked drive signal (S2) with a plurality of drive cycles for the switching element each having a switch-on duration and a switch-off duration ( 6 ) provides a temperature sensor arrangement ( 4 ) with a temperature sensor ( 42 ) for determining an ambient temperature in the region of the temperature sensor ( 42 ), which provides an ambient temperature dependent temperature measurement signal (S4), wherein the clocked drive signal (s2) is dependent on the current measurement signal (S5) and the temperature measurement signal (S4) and wherein the drive circuit ( 2 ) is adapted to the switch ( 6 ) during a drive cycle in each case for a fixed predetermined turn-off period to block, wherein the turn-off each begins when the current measurement signal (S5) increases up to one of the temperature measurement signal (S4) dependent value.
  2. Power supply circuit according to claim 1, wherein the duty cycle with increasing indicated by the temperature measurement signal (S4) Ambient temperature decreases at least temporarily.
  3. Power supply circuit according to one of the preceding Claims, in which the drive signal (S2) in such a way from the temperature measurement signal (S4) and the current measurement signal (S5) depends that the load current with increasing temperature (T) until reaching a threshold value (Tntc) increases and after reaching this threshold (Tntc) decreases.
  4. Power supply circuit according to claim 3, wherein an increase in the current for Temperatures below threshold (Tntc) with lower slope as a drop in the current for Temperatures above the threshold (Tntc) takes place.
  5. Power supply circuit according to one of the preceding claims, in which the switching element ( 6 ) is designed as a power transistor.
  6. Power supply circuit according to one of the preceding claims, comprising an enabling circuit ( 8th ) having an input for supplying a release signal (EN) and which releases the power supply circuit for providing a load current in the load current path depending on the enable signal (EN).
  7. Circuit arrangement with a power supply circuit ( 10 ) according to one of the preceding claims and with a to the load current path of the power supply circuit ( 10 ) connected load ( 7 ), the at least one light emitting diode ( 71 . 7n ) having.
  8. Circuit arrangement according to Claim 8, in which the inductive storage element ( 72 ) in series with the at least one light emitting diode ( 71 . 7n ) is switched and in which a freewheeling element ( 73 ) parallel to a series connection with the at least one light emitting diode ( 71 . 7n ) and the inductive storage element ( 72 ) is switched.
  9. Circuit arrangement according to Claim 7 or 8, in which the power supply circuit ( 10 ) and the load ( 7 ) on a common carrier ( 9 ) are arranged.
  10. Circuit arrangement according to Claim 9, in which the temperature sensor ( 42 ) spaced from the load on the carrier ( 9 ) is arranged.
  11. Circuit arrangement according to one of Claims 7 to 10, in which the power supply circuit ( 10 ) is at least partially integrated in a semiconductor chip separate from the load.
  12. Circuit arrangement according to Claim 11, in which the temperature sensor ( 42 ) in the semiconductor chip of the power supply circuit ( 10 ) is integrated.
DE200610046729 2006-10-02 2006-10-02 Power supply circuit with temperature-dependent output current and circuit arrangement with a power supply circuit Active DE102006046729B4 (en)

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EP3118279A1 (en) 2015-07-14 2017-01-18 odelo GmbH Method for operating oleds as light sources in vehicle lights, oled as light source comprising lighting means and vehicle light equipped with same
EP3389340A1 (en) 2017-04-13 2018-10-17 Valeo Iluminacion Automotive lamp with compensation of the luminous flux of the light source
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