Method for Controlling an Output of an Electrical AC Voltage

Abstract

A method for controlling an output of an electrical AC voltage U comprising the following steps: switching on a current flow I induced by the AC voltage as soon as an absolute value of the AC voltage U exceeds a switching-off target voltage, and switching on the current flow I as soon as the absolute value for the AC voltage U falls below a switching on target voltage. The switching-off target voltage and the switching-on target voltage are defined as positive and the switching-on target voltage is lower than or equal to the switching-off target voltage. The method according to the invention serves to dim an LED lamp in a brightness range of 0% to 100% of a maximum brightness of the LED lamp.

Claims

1. A method for controlling an output of an electrical AC voltage, comprising the following steps: switching off a current flow induced by the AC voltage as soon as a value for the AC voltage exceeds a switching-off target voltage, switching on a current flow as soon as the value of the AC voltage falls below a switching-on target voltage, characterized in that the switching-off target voltage and the switching-on target voltage are positive, the switching-on target voltage is lower than or equal to the switching-off target voltage, the output is applied as an input to at least one LED lamp, and a brightness of the LED lamp can be controlled in a brightness range of 0% to 100% of a maximum brightness of the LED lamp.

2. The method according to claim 1, characterized in that the switching-on target voltage is substantially equal to the switching-off target voltage.

3. The method according claim 1, wherein at least one of the switching-on target voltage and the switching-off target voltage is variable.

4. A dimmer for controlling an output of an electrical AC voltage, comprising: a switch element for switching a current flow induced by the AC voltage on and off, a control element connected to the switch element for generating a control voltage, wherein the control device is configured to activate the switch element such that an output is provided that is based on a switching-off target voltage and a switching-on target voltage.

5. The dimmer according to claim 4, further comprising a rectifier, and wherein the switch element comprises a transistor.

6. The dimmer according to claim 5, wherein the control element comprises a potentiometer.

7. (canceled)

8. The dimmer according to claim 4, wherein the transistor comprises a MOSFET.

9. The dimmer according to claim 8, wherein the transistor comprises a normal blocking MOSFET.

10. The dimmer according to claim 4, wherein the control element comprises an adjustable control element that enables varying at least one of (i) the switching-off target voltage, and (ii) the switching-on target voltage.

11. The dimmer according to claim 10, wherein the control element comprises a potentiometer that enables adjustment of at least one of (i) the switching-off target voltage, and (ii) the switching-on target voltage.

12. The dimmer according to claim 10, wherein the switching element comprises a normal blocking MOSFET.

13. The dimmer according to claim 4, further comprising a rectifier, wherein the switching element comprises a transistor, and wherein the control element comprises a potentiometer configured to adjustably set (i) the switching-off target voltage, and (ii) the switching-on target voltage.

14. The dimmer according to claim 13, wherein the transistor comprises a normal blocking MOSFET.

15. The dimmer according to claim 14, further comprising at least one LED driven by the output.

16. The dimmer according to claim 4, further comprising a plurality of LEDs electrically connected to the output.

17. The dimmer according to claim 4, wherein the switching-off target voltage and the switching-off target voltages are positive voltages.

18. The dimmer according to claim 4, wherein the switching-off target voltage and the switching-off target voltages are absolute voltages.

19. The dimmer according to claim 4, wherein the control device is configured such that the output is maintained at a positive AC voltage.

20. The method according to claim 1, wherein the current flow induced by the AC voltage is switched off when an absolute value of the AC voltage exceeds the switching-off target voltage.

21. The method according to claim 20, wherein the current flow is switched on when the absolute value of the AC voltage becomes less than the switching-on target voltage.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] An exemplary embodiment of the invention shall be explained below based on the drawings. Therein:

[0020] FIG. 1 shows a schematic circuit diagram for an assembly having a dimmer and an LED lamp, and

[0021] FIG. 2 shows a temporal course of a period of an applied AC voltage as well as a current flow that is switched on and off according to the method according to the invention, when an ohmic load is connected thereto.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] FIG. 1 shows circuit diagram of an assembly comprising a dimmer 2 and an LED lamp 4. The dimmer 2 and the LED lamp 4 are connected to a voltage source 6. A periodic AC voltage U is provided by the voltage source 6, in particular a mains AC voltage.

[0023] The LED lamp 4 comprises an input-side coupling capacitor 8 for limiting the flowing current. A rectifier 10 composed of four diodes 12 is connected to the coupling capacitor 8. The rectifier 10 serves to convert an input AC voltage to a DC voltage. In order to smooth the DC current, a smoothing capacitor 14 is connected downstream of the rectifier 10. Two LED elements 16 are connected in series for converting the DC current to light. Alternatively, the LED lamp 4 can also comprise one or more than two LED elements 16.

[0024] LED lamps 4 of this type are known. They have the disadvantage that a brightness emitted from the LED elements 16 cannot be dimmed by means of conventional dimmers. Furthermore, an undisrupted operation is not ensured with conventional dimmers. The reason for this is that the voltage jumps caused by conventional dimmers induce disruptive current pulses at the capacitors 8 and 14. These current pulses cause disruptive noise and can damage components of the LED lamp or the conventional dimmer.

[0025] In the assembly shown here, the LED lamp 4 is connected via a connecting lead 18 to the dimmer 2 and the voltage source 6. The dimmer 2 has an input-side rectifier 20, which corresponds to the rectifier 10 of the LED lamp 4 in terms of its construction and function. The rectifier 20 is connected to a switch element 22, which serves to switch the current on and off.

[0026] In the present exemplary embodiment, the switch element 22 is a transistor, in particular a normal blocking metal-oxide-semiconductor field-effect transistor (MOSFET). This means that without control voltage, the MOSFET 22 blocks the current flow through the dimmer 2. In order to enable current flow, a gate 24 of the MOSFET 22 is connected to a control output 26 of a control element 28. The control element 28 can use voltage dropping via the MOSFET 22 for its own current supply. The voltage dropping via the MOSFET 22 is proportional to the value for the AC voltage U when the transistor is switched off and no voltage is applied to the load. The control element 28 can induce a control voltage at the gate 24 via the control output 26. With an induced control voltage the MOSFET 22 becomes conducting. Applying the control voltage at the gate 24, a current flow through the LED lamp 4 can be switched on. The switching off or interrupting of the current flow is obtained through the control element 28 by switching the control voltage at the gate 24 off. The current flow through the dimmer 2 is thus switched on and off by the control element 28. In particular, a current flow is only possible when a control voltage is applied to the gate 24 of the MOSFET 22. By switching the current flow on and off by means of the dimmer 2, the voltage and output tapped into by the connecting lead 18 is varied.

[0027] The method for switching the dimmer shall be explained below, based on FIG. 2. For this, the temporal course of a period of the applied AC voltage U is depicted in FIG. 2. For this, the curve of the AC voltage U is plotted along the time axis t. Moreover, a current I flowing through the dimmer 2 is plotted over the time axis t in FIG. 2, when an ohmic load is connected thereto. When an LED lamp 4 is connected, the current flow is approximately proportional to the derivation of the voltage over time.

[0028] The AC voltage U runs in a sine wave over time t. This means that it passes through a zero crossing at the start of the depicted period, at the middle of the depicted period, and at the end of the depicted period in each case. After passing through the first zero crossing at the start of the period, the AC voltage U increases, and thus its absolute value increases. Because the control element 28 applies a control voltage at the gate 24 of the MOSFET 22 at this point in time, the current I also flows, which is approximately proportional to the derivation of the AC voltage as a function of time. When the absolute value for the AC voltage U exceeds a switching-off target voltage 30, the control element 28 switches the control voltage at the gate 24 off, and the MOSFET 22 blocks the current flow. The current I decreases abruptly to 0. After passing through its maximum, the AC voltage U decreases. As soon as the absolute value of the AC voltage falls below a switching-on target voltage 32, the control element 28 applies a control voltage to the gate 24, and activates the MOSFET 22. The current I is again applied abruptly.

[0029] When the MOSFET 22 is blocked, the current flow I is interrupted.

[0030] In order to obtain the advantages of the method described above, it is necessary that the switching-off target voltage 30 and the switching-on target voltage 32 are defined as positive. The switching-on target voltage 32 must not be greater than the switching-off target voltage 30. In the example shown here, the switching-on target voltage 32 is substantially equal to the switching-off target voltage 30. This means that the switching-on target voltage 32 is at least 80%, in particular at least 90%, in particular at least 99% of the switching-off target voltage 30. The difference between the switching-off target voltage 30 and the switching-on target voltage 32 is less than twice the drop in voltage at the smoothing capacitor 14. As a result, voltage jumps at the capacitors 8, 14 of the LED lamp 4 are prevented. Disruptive current pulses at the capacitors 8, 14 are avoided.

[0031] By switching on and off, the current flow I is temporally interrupted. It is interrupted in particular in the ranges of the maximum absolute value of the AC voltage U. As a result, the average current flow, and thus the output tapped at the connecting lead 18, is reduced. If the switching-off target voltage 30 and the switching-on target voltage 32 are substantially equal, the average current flow as well as the output applied to the LED lamp 4 are approximately proportional to the switching-off target voltage 30 or the switching-on target voltage 32. The power applied to the LED lamp 4 can thus be controlled continuously by defining the switching-off target voltage 30 and the switching-on target voltage 32. As a result, it is possible to control the brightness of the LED lamp 4 in a brightness range of 0% to 100% of the maximum brightness of the LED lamp 4.

[0032] Because the temporal course of the AC voltage U is predefined, the exceeding of the switching-off target voltage 30 can be assigned to a switching-off point in time 34. The switching on when the voltage has fallen below the switching-on target voltage 32 can be assigned to a switching-on point in time 36. In the time interval from the switching-off point in time 34 to the switching-on point in time 36, the current flow I is zero.

[0033] After the current flow I has been switched back on at the switching-on point in time 36, the absolute value of the AC voltage U decreases until the AC voltage U passes through a zero crossing. Because the absolute value of the AC voltage U is independent of the sign of the AC voltage U, the switching procedures are also carried out when the poles are reversed. The switching off of the current flow I occurs here at a switching-off point in time 34′, the switching back on of the current flow I occurs at a switching-on point in time 36′.

[0034] Due to the periodic course of the AC voltage U, the switching-off points in time 36, 36′ and the switching-on points in time 34, 34′ correlate with twice the frequency of the AC voltage U. The periodic temporal course of the AC voltage makes it possible thereby to define the switching procedures by means of the switching points in time 34, 34′, 36, 36′, instead of the target voltages 30, 32. The control element 28 can thus also be designed as a timer correlated with the periodicity of the AC voltage U, which defines the switching points in time 34, 36, 34′, 36′ through the temporal course of the control voltage.

[0035] Other circuits can also be used for the dimmer. The exemplary embodiment shown here has the advantage of a simple and robust construction.

[0036] The important aspect of the dimmer is that a switch element 22 is provided with which the current flow can be switched on and off, and that a control element 28 is provided, which controls the switch element 22. The control element 28 equalizes the absolute value of the applied AC voltage U to a switching-off target voltage 30 and/or a switching-on target voltage 32. In order to set these target voltages, it is advantageous when the control element 28 includes a potentiometer 38, with which the target voltages 30, 32 can be set.

[0037] Alternatively to the normal blocking MOSFET 22, a normal conducting MOSFET may be provided. This means that the current I flows in the absence of a control voltage at the control output 26 of the control element 28. The current I is then switched off by applying the control voltage.

[0038] In an exemplary embodiment that is not shown, numerous LED lamps connected in parallel are connected to the dimmer, each of which comprises an input-side coupling capacitor.