EP3207767A1

EP3207767A1 - Circuit for operating light-emitting diodes with low flicker, and luminous means and luminaire

Info

Publication number: EP3207767A1
Application number: EP15781860.0A
Authority: EP
Inventors: Uwe Wiesner; Norbert Wittschief
Original assignee: Atlas Elektronik GmbH
Current assignee: Atlas Elektronik GmbH
Priority date: 2014-10-14
Filing date: 2015-08-28
Publication date: 2017-08-23
Anticipated expiration: 2035-08-28
Also published as: WO2016058585A1; EP3207767B1; DE102014114853A1

Abstract

The invention relates to a circuit for operating light-emitting diodes with low flicker, wherein the circuit has n LED chains with a particular ordinal number N, wherein n is an integer and is greater than 1 and N is an integer and is greater than 0, an overall supply voltage connection to which a time-dependent supply voltage, in particular a rectified AC voltage, can be applied, and an LED chain connection, and the LED chain connection is set up in such a manner that the individual LED chains are connected with increasing supply voltage and increasing ordinal number N and are disconnected with falling supply voltage and a falling ordinal number, wherein a current storage source is assigned to the overall supply voltage connection and is set up in such a manner that the current storage source is charged in the case of a supply starting voltage and the current storage source impresses a supply current on one of the LED chains in the case of a supply threshold voltage, with the result that this LED chain is connected.

Description

Circuit for low-fl ash operation of light-emitting diodes, as well as light source and luminaire

The invention relates to a circuit for low-fl ash operation of light-emitting diodes, wherein the circuit n LED chains with a respective atomic number N, where n is integer and greater than 1 and N is integer and greater than 0, a total supply voltage terminal at which a time-dependent Supply voltage, in particular rectified AC voltage, can be applied, and has an LED chain circuit and the LED chain circuit is set up such that the individual LED chains connected with increasing supply voltage with increasing atomic number N and switched off with decreasing supply voltage with decreasing atomic number , as well as a bulb and a light.

[02] AC powered LED lights (LED = light emitting diode) are increasingly used because of their favorable properties in terms of light output, life and energy use. For this purpose, the mains-side AC voltage is rectified in general and individual LED chains are controlled.

[03] Over a directional half-wave (180 °) of a sinusoidal AC voltage, the LED chains are not connected over approx. 50 °. Only over the phase angle of about 130 °, at least one or more LED chains are connected, so that during this Time the switched LEDs emit a light signal. This means that about 28% of the time the light emitting diodes do not emit light.

[04] This leads to a so-called flickering. Especially in rooms or places that need to be well lit, such flickering is undesirable, as this easily fatigues the eyes and, for example, an effective work over a working day can not be guaranteed. In particular, when such a light source is viewed from the corner of the eye, some observers also find this flicker uncomfortable.

[05] The object of the invention is to improve the state of the art.

[06] The object is achieved by a circuit for flicker-poor operation of light-emitting diodes, wherein the circuit n LED chains with a respective atomic number N, where the n is integer and greater than 1 and the N is integer and greater than 0, a total supply voltage terminal, on which a time-dependent supply ^¬ voltage, in particular rectified AC voltage, can be applied, and has an LED chain circuit and the LED chain wiring is set up such that the individual LED chains connected with increasing supply voltage with increasing atomic number N and with decreasing Supply voltage can be switched off with decreasing atomic number, wherein the total supply voltage terminal is associated with a current storage source, which is arranged such that at a supply start voltage the power storage source is charged and at a Versorgungsseinsat z voltage, the power storage source at least one of the LED chains, in particular the entire LED chain with atomic number 1 and thus with most LEDs, a supply current impresses, so that this LED chain is connected.

Thus, even at least one LED chain or a part of an LED chain can be switched over the dark phases so that they emit a light signal through the individual LEDs during this time. In particular, due to the fact that seeing is not linear but rather logarithmic, a viewer perceives the perhaps still resulting differences in brightness as extremely low and can not visually or at least barely perceive it with his or her eye. As a result of this, the lighting that is implemented with the present circuit is perceived by people to be very pleasant and also makes it possible to work over a whole working day. Thus, it can be at least ruled out that due to the lighting it comes to an excessive fatigue of the eyes.

[08] The following conceptual is explained.

[09] The "circuit" is in particular an electronic circuit which is designed on a corresponding board with corresponding components, but also free-wired lines and components can implement the circuit. [10] "Flicker-poor operation" is understood to mean, in particular, that complete darkness of all LEDs is excluded or reduced for a corresponding time, In particular, the term flicker-poor also encompasses the term flicker-free, although differences in brightness may continue to exist, but essentially one continuous lighting is given.

[11] "Light Emitting Diodes" in the following also abbreviated to LED (light emitting diode), are in particular

To understand semiconductor devices, which emit light at an applied voltage or in a flowing stream of light, in particular in the optical spectrum of 400-800nm.

[12] The "LED chains" generally comprise several light-emitting diodes.If previously LED chains with multiple light-emitting diodes are used, individual diodes, which are controlled accordingly, are referred to as an LED chain, for example one of the LED chains be formed by one or more Zener diodes (zener diodes).

[13] In particular, the "n" indicates the number of LED strings, and usually between 2 and 10 LED strings, and more preferably between 4 and 6 LED strings are used, and the ordinal number "N" numbers the individual strings. Thus, each individual LED chain with indication of the ordinal number N can be uniquely determined.

[14] The "total supply voltage connection" is formed in particular by a connecting line, which both the single LED chain and the power storage source (direct or indirect) supplied. In particular, a rectified AC voltage with 230V _{rms can be} impressed in this total voltage supply connection. In the present case, this means that generally rectified sinusoidal half-waves occur at the total supply voltage connection

Voltage values between 0 and approx. 325V are present.

[15] The term "time-dependent supply voltage" is understood to mean, in particular, voltages in which the voltage value changes as a function of time or according to a phase angle. <br/> <br/> [0008] Due to the fact that the latter is rectified, especially with an alternating voltage, a time-dependent direct voltage is then present in particular.

[16] By means of the "LED chain wiring", one or more LED strings can be connected in particular depending on the voltage applied to the total supply connection, for example the LED string with the atomic number N = 1 at a rising voltage up to The LED chain with the ordinal number N = 2 can then be connected up to a voltage of 218 V. Up to a voltage of 257 V, the LED chain with the ordinal number N = 3 and up to a voltage of 283V the LED chain with the ordinal number N = 4 and from 320V the LED chain with the ordinal number N = 5 are connected. [17] When the voltage drops, the individual LED chains are switched off again in reverse order, so that the LED chain with the ordinal number N = 5, from 283V the LED chain with the ordinal number 4 and so on is switched off from a voltage of 320V become. It is particularly advantageous if the LED chain wiring realizes Beschälten the individual LED chains by means of switchable power sources. These switchable current sources are in particular set up such that an LED chain current and thus also an LED chain voltage

(Voltage drop on the LED chain or on the LED chains) while operating the LED chain or the LED chains remains substantially constant. This increases the life of the individual LEDs.

[18] The "current storage source" is in particular a circuit or a circuit part which is charged in particular at a "supply start voltage" and which impresses a current of at least one of the LED chains starting from a "supply supply voltage." Thus, a current storage source comprises both one

Charge storage and a charge dispenser, which are respectively activated or deactivated accordingly. This current storage source is arranged in particular "in front of" the LED chains, so that - depending on the wiring of the LED chains - even several or even all LEDs can be supplied by the power storage source.

In another embodiment, the LED chain with the atomic number N more LEDs than the LED chain with the atomic number N + l. For example, the LED chain with atomic number N = l 44 LEDs, the LED chain with atomic number N = 2 24 LEDs, the LED chain with atomic number N = 3 12 LEDs, the LED chain with atomic number N = 4 8 LEDs exhibit. In particular, it is advantageous that the LED chain with the atomic number N = l has most of the LEDs, since this is in particular primarily connected and radiates a basic brightness through the Beschälten, which is increased only slightly by the other LED chains substantially.

To be able to impose a time-dependent DC voltage both the power storage source and an LED chain or multiple LED chains, the

Total supply voltage terminal a rectifier ^¬ circuit, in particular a Graet z-bridge circuit, which converts an AC voltage into a DC voltage.

[21] In the present case, in particular under one

DC voltage understood a voltage that does not change their polarity. Furthermore, an alternating voltage is in particular a voltage at which the polarity changes. Both AC voltage and DC voltage have different voltage values, in particular at different times (phase angles).

[22] In another embodiment, the power storage source has an input branch with an input diode and an input power source and an output branch with an output diode and an output power source. In particular, the diodes are arranged oppositely, so that substantially either the input power source to a memory device impose a current or the output current source of one of the LED chains can impose a current.

Both the input power source and the output power source may have an ohmic resistance, to which a voltage is applied, so that there is a corresponding current flow when the voltage is applied.

[24] In one related embodiment, the input power source or the output power source or the input power source and the output power source may be one

(temporally and / or phase angle dependent) controllable

Constant current source.

[25] Controllable in this context means in particular that the time at which the input current source or the output current source assumes its function as a current source is determined by the applied supply voltage and its phase angle.

[26] A "constant current source" is to be understood in particular as meaning a component which, at least over a certain period of time, provides a substantially non-changing current.

In particular, the two controllable constant current sources can be achieved in that two (one per constant current source) N-channel self-conducting FETs (FET = field effect transistor) with an associated Resistance can be used. The self-conducting N-channel FETs cause in this embodiment, that the voltage across the associated resistor is constant, whereby the resistor essentially causes a constant current flow. Controllable in this context should be understood in particular as a time-dependent or correspondingly voltage-dependent / phase-dependent control and thus as switching on and / or off of the constant current source.

In order to provide a fast and simple component which serves as a current storage source, the current storage source may comprise a capacitor which can serve both as a storage medium and as a source medium.

In the event that the input power source causes a current flow, in particular the

Current storage source and thus the capacitor loaded as a storage medium. In the event that the output current source is to provide a current, the capacitor serves in particular as a source medium and emits charge carriers per time.

[30] In another embodiment, the power storage source includes a modified valley-fill circuit.

[31] This leads in particular to the fact that the current course of the LED chains approximates a sinusoidal course. This is particularly advantageous because it reduces the network operators corresponding transformers can therefore be cost-saving for network operators. In addition, the heat generation of the circuit can be minimized.

[32] One of the reasons for this is that during charging, the capacitors of the modified valley-fill circuit are connected in series. For example, so the capacitors are charged to 320V. As soon as the modified valley-fill circuit takes over the voltage supply of the output current source, the capacitors are connected in parallel. This has the consequence that the voltage is halved accordingly (for capacitors of equal size) and thus for the upper example, a voltage of 160V is applied. In the event that the first LED chain needed to operate 140V, only 20V and not 180V must be converted into heat by the circuit.

[33] Normally, valley-fill circuits are used as passive power factor correction filters to filter unwanted harmonics in electrical power supplies. For this purpose, they have in particular a rectifier. The present modified valley-fill circuit essentially corresponds to the usual valley-fill circuit without a rectifier.

[34] In order for the circuit to emit light for illumination, the circuit has an applied voltage supply which impresses the time-dependent supply voltage of the circuit. [35] In a further aspect of the invention, the object is achieved by a luminous means which has a previously described circuit.

[36] In addition, the object is achieved by a luminaire, in particular street lighting system, indoor

Lighting system, parking garage lighting or

Lighting systems for corridors, hotels, aircraft and ships, which has a previously described light source or a corresponding circuit described above.

Especially for well-lit walkways offer such circuits and lights, since the flicker is reduced and any pedestrians get a well-lit environment.

[38] In the following, the invention will be explained in more detail with reference to exemplary embodiments. Show it

1 shows a schematic representation of a circuit according to the invention with 5 LED chains and an equivalent circuit diagram of a current storage source,

FIG. 2 shows a voltage curve of a half-period from 0 ° to 180 ° for the individual voltages and currents of the circuit from FIG. 1,

Figure 3a is a schematic representation of a simple implementation of

Electricity storage source, Figure 3b is a schematic representation of a

Implementation of the current storage source with constant current sources and

Figure 3c is a schematic representation of a

Power storage source with downstream

Valley fill circuit.

[39] An LED circuit 101 includes a Graetz bridge circuit 103 at the output thereof

Supply line 107 is arranged. The supply line 107 conducts a voltage or sets a potential relative to the ground so that the LED chains 121, 123, 125, 127, 129 are operable. Furthermore, a current storage source, which is shown as an equivalent circuit diagram 111, is arranged on the supply line 107.

[40] At the Graet z-bridge rectifier 103, the supply voltage 105 is present as an AC voltage with 230V _eff . The current storage source 111 comprises two parallel branches which are connected to the supply line 107 on the one hand and to the other via the capacitor 119 are connected to ground. Each of the branches has a blocking diode 113. In the first branch, a first current source 115 and second branch, a second current source 117 is arranged. The two blocking diodes 113 are switched in opposite directions.

[41] The first LED chain with the ordinal number N = 1 has 44 LEDs, the second LED chain 123 with the ordinal number N = 2 has 24 LEDs, the third LED chain 125 with the Ordinal number N = 3 has 12 LEDs, the fourth LED chain 127 with the ordinal number N = 4 has 8 LEDs and the fifth LED chain 129 with the ordinal number N = 5 has a Zener diode.

[42] The first LED chain 121 is the switchable current source 131, the second LED chain 123, the switchable current source 133, the third LED chain 125, the switchable current source 137, the fourth LED chain 127, the switchable current source 139 and the Z Diode 129 associated with the switchable current source 141. Depending on the height of a voltage applied to the supply line 107 with respect to the ground, the individual switchable current sources 131, 133, 137, 139, 141 are switched. Alternatively, the individual switchable current sources 131, 133, 137, 139, 141 are switched depending on the phase angle. This circuit is realized for example with a block CL8800 (Sequential Linear LED Driver) from Supertex® Inc.

[43] Hereinafter, the LED circuit 101 will be explained without the function of the power storage source in its operation. This operation corresponds to the operation of the LEDs according to the prior art.

[44] At the Graet z-bridge rectifier 103, the AC line voltage of 230V _{rms is} applied. As a result, a DC voltage is formed at the output of the Graet Z bridge rectifier 103 and thus on the supply line 107. The first (partly sinusoidal) half-wave of this DC voltage is shown in FIG. 2 in a diagram and identified as supply voltage curve 203. [45] In the present case, initially (phase angle = 0 °), all switchable current sources 131, 133, 137, 139, 141 are connected to ground. With increasing voltage and increasing phase angle first the switchable current source 131, then the switchable current source 133, then the switchable current source 137 and finally the switchable current source 139 is turned off, so that only the switchable current source 141 is connected to ground by the phase angle of 90 °.

[46] Now, with further increasing phase angle and decreasing voltage, the individual switchable current sources 131, 133, 137, 139 are switched to ground in the reverse order. As a result, the LED chains 121, 123, 125, 127, 129 are successively switched off and on.

Alternatively, in the case of the supply voltage forming on the supply line 107 up to a voltage of 142 V, the switchable current source 131 is switched to ground as the only switchable current source. From a voltage of 125V on the supply line 107, the light-emitting diodes of the first LED chain 121 with the ordinal number N = l begin to emit a light. In addition, the switchable current source 131 generates a current which keeps the voltage at the first LED chain 121 constant. With a further increasing supply voltage, the switchable current source 131 is interrupted and the switchable current source 133 is switched through as the only switchable current source, so that a sufficient voltage is applied both to the first LED chain 121 and to the second LED chain 123 and therefore additionally the second LED chain 123 is illuminated. Again, the switchable current source 133 generates a current such that the voltage across the first LED string 121 and the second LED string 123 is constant. This is continued accordingly with further increasing supply voltage for the further LED chains, so that in each case only one of the switchable current sources 131, 133, 135, 137, 139, 141 is connected to ground in succession and the corresponding LED chains are connected.

[48] As soon as the supply voltage reaches the peak value or corresponding peak value at approx. 325V (approx. At 90 °), the voltage values drop accordingly. As a result, the switchable current source 141 is interrupted and the fourth switchable current source 139 is switched through and then interrupted again with a further dropping voltage and the third switchable current source 137 is switched through. This takes place until the switchable current source 131 is turned on again at the end.

[49] The currents flowing through the LED are also shown in the diagram of FIG. 2 and designated by reference numeral 205. The step shape of the current profile 205 is achieved in particular by the design of the switchable current sources 131, 133, 135, 137, 139, 141.

[50] The function of the power storage source is explained in more detail below. [51] As the voltage on the supply line 107 increases, the blocking diode associated with the first current source 115 is operated in the forward direction. The applied voltage at the first current source 115 causes a current to flow, which charges the capacitor 119. As soon as the voltage applied to the capacitor 119 has a higher value than the DC voltage at the supply line 107 (this is the case in particular when the voltage drops again) blocks the diode associated with the first current source 115, so that the first current source 115 is quasi off ,

[52] Conversely, the blocking diode connected to the second current source 117 is now switched in the forward direction, so that the voltage applied to the capacitor 119 at the second current source 117 generates a current (209), which is passed through the diode associated with the second current source 117. This current (209) is impressed, in particular, on the first LED chain 121 and conducted to ground via the switchable current source 131, which is then closed in this case. As a result, the light-emitting diodes of the first LED chain 121 light up, although the voltage actually applied to the supply line 107 may not be sufficient for the operation of the first LED chain (see voltage curve 203).

[53] In a simple embodiment, the first current source 115 and / or the second current source 117 are formed as an ohmic resistor 301. Every other ^ohm, specific resistance, or each part that forms an ohmic resistance, such as a bipolar transistor, can take over this function in the present case.

[54] Alternatively, the first current source 115 and second current source 117 may be configured as constant current sources. For this purpose, the first current source 115 and the second current source 117 comprise a self-conducting N-channel FET. These FETs conduct in the unconnected state between drain and source. By arranged after the resistance feedback to the gate, a constant voltage can be generated at the associated resistor over a wide voltage range, this in turn leads to a constant current flow. This current flow is firstly used to charge the capacitor 119, or the capacitor supplies the second current source 117 with its voltage. The capacitors 305 connected in parallel with the respective resistor serve, in particular, to suppress or avoid oscillating oscillation due to the feedback.

[55] Thus, the first current source 115 and the second current source 117 are formed as a kind of constant current sources.

[56] In a further alternative, instead of the capacitor 119, a modified valley-fill circuit 311 is assigned to the first current source 115 and the second current source 117. The first current source 115 and the second current source 117 may be configured as described above.

[57] During the increasing supply voltage, the first current source 115 charges the first capacitor 313 and the first capacitor 313 Capacitor 315. The capacitors 313, 315 are connected in series. As soon as the supply voltage has fallen accordingly, the first current source 115 is switched off and the second current source 117 is supplied via the capacitors 313, 315, which are now connected in parallel, so that, in turn, it imposes a current on the LED chains.

This leads to the additional current profile, which is provided in FIG. 2 with the reference numeral 211. As can clearly be seen there, the shape of the current profile of the LED chains approximates the form (sine half-wave) of the supply voltage.

LIST OF REFERENCE NUMBERS

101 LED circuit

103 Graet z bridge rectifier

105 alternating voltage

107 supply line

111 Substitute circuit diagram of the current storage source

113 blocking diode

115 first power source

117 second power source

119 capacitor

121 first LED chain

123 second LED chain

125 third LED chain

127 fourth LED chain

129 Zener diode

131 first switchable current source

133 second switchable power source

137 third switchable power source

139 fourth switchable power source 141 power source

201 voltage / current phase diagram

203 Supply voltage curve

205 LED chain current profile

207 capacitor voltage curve

209 Current flow through the additional circuit

211 Influence of the valley fill circuit

301 resistance

303 self-conducting N-channel FET

305 additional capacitor

311 modified valley fill circuit

313 first capacitor

315 second capacitor

317 first valley-fill blocking diode

319 second valley-fill blocking diode

321 third valley-fill blocking diode

Claims

Claims:

A circuit (101) for low-flare operation of light-emitting diodes, said circuit comprising n LED strings (121, 123, 125, 127, 129) having a respective atomic number N, said n being integer and greater than 1 and said N being integer and greater than 0 is, a total supply voltage terminal (107) to which a time-dependent supply voltage (105), in particular rectified AC voltage, can be applied, and an LED chain circuit and the LED chain circuit is arranged such that the individual LED chains with rising supply voltage with increasing atomic number N connected and switched off with decreasing supply voltage with falling atomic number, characterized in that the total supply voltage terminal is associated with a current storage source (111) which is set up so that at a supply start voltage, the power storage source is charged and at a Versorgungsseinsat z voltage the power storage source of one of the LE D chains imprinted a supply current, so that this LED chain is connected.

2. A circuit according to claim 1, characterized in that the LED chain with the atomic number N has more LEDs than the LED chain with the atomic number N + l.

3. A circuit according to one of the preceding claims, characterized in that the

Total supply voltage terminal comprises a rectifier circuit (103), in particular a Graetz bridge circuit, which converts an AC voltage into a DC voltage.

4. A circuit according to one of the preceding claims, characterized in that the current storage source has an input branch with an input diode and an input current source (115) and an output branch with an output diode and an output current source (117).

5. A circuit according to claim 4, characterized in that the input current source and / or the output current source is or are a controllable constant current source.

Circuit according to one of the preceding claims, characterized in that the current storage source comprises a capacitor (119) which serves as a storage medium and as a source medium.

7. A circuit according to any one of the preceding claims, characterized in that the power storage source comprises a modified valley-fill circuit.

8. A circuit according to one of the preceding claims characterized by an applied voltage supply (105) which imposes the time-dependent supply voltage of the circuit.

9. illuminant having a circuit according to one of the preceding claims.

10. light, in particular street lighting, indoor lighting system, parking garage lighting or lighting systems for corridors, hotels, aircraft and ships, which has a light source according to claim 9.