DE102010042029A1 - Operating device for lamps with low-voltage power supply - Google Patents

Abstract

The invention relates to a method for providing a low-voltage voltage for a load (RL), in particular for semiconductor ICs, and a low-voltage supply circuit. The latter is provided with input connections (1, 2) for an input voltage source (SQ), the voltage of which is higher than the low voltage to be generated, with output connections (3, 4) for the load (RL), with a parallel to the input connections ( 1, 2) connected series circuit from a) one with the starting resistor (R2), b) a controllable electronic switch (X1) and c) an energy store (C4), which is connected to the output connections (3, 4), the energy store (C4) is charged in the so-called linear mode via the switch (X1) and a starting voltage for the load (RL) can be generated from the charge. Furthermore, it has d) means (CT) for generating switching pulses for the switch (X1) for operating the same in so-called pulse operation, the energy store (C4) and the switch (X1) forming parts of a switching regulator or DC / DC converter, such that that an operating voltage for the load (RL) can be generated from the charge of the energy store (C4).

Description

The present invention relates to the field of so-called. Low-voltage power supply for a load, in particular for active semiconductor ICs. The invention relates in particular to control gear for lamps (eg. LEDs, OLEDs, halogen, low-pressure and high-pressure gas discharge lamps).

Typically, these DC supply voltages are in the range of less than 15 volts DC. Basically, it is known from the prior art in the field of control gear for lamps, that for a start phase of the operating device immediately after switching on the mains voltage supply from this a first start-low voltage is generated. For this purpose, for example, a series circuit of a starting resistor, an electronic controllable switch and an energy storage by closing the switch, the (rectified) mains voltage supplied. The switch is usually a transistor and the energy store is a charging capacitor, preferably an electrolytic capacitor.

Thus, a DC voltage is applied to the capacitor. This DC voltage runs from zero to a certain voltage below 15 volts high, which is then kept more or less constant.

This DC voltage then supplies an active control circuit of the operating device, which usually controls clocked modules of the operating device. Only in periods in which the control circuit clocks these modules properly, then can be a power supply for the control circuit from a clocked module, and the power loss of the mains voltage supplied starting resistance can be switched off.

It is understood that with reasonable power loss, which is due to the current flow in the starting resistor and the transistor forming the switch, the power removable from the charging capacitor is limited. Accordingly, the starting voltage usually serves only to initiate the starting phase or to cover a particularly low power requirement of a load, unless you take a higher power loss in purchasing.

At one in the DE 10 2008 016 754 A1 Therefore, after passing through the starting phase, which is also referred to herein as "linear operation", the charging capacitor is connected to the center tap of a rectifier half or full bridge described known low-voltage power supply circuit, which is part of an operating device for a light source. The half or full bridge is present anyway in the operating device and is part of a voltage converter for the supply of the light source. The power thus transferred to the charging capacitor is sufficient to cover in the phase following the starting phase also a higher power requirement of a load connected to the output of the low-voltage power supply circuit.

• 1. Sie ist nicht unabhängig steuerbar.
• 2. Das Leistungsangebot ist abhängig von der Halb- oder Vollbrückenfrequenz. Die bekannte Schaltung muss so dimensioniert sein, dass sie bei niedriger Frequenz, also bei 100% licht die benötigte Leistung liefert. Das bedeutet für den Dimmbetrieb, dass die infolge höherer Frequenz zuviel gelieferte Leistung über Zenerdioden „vernichtet” werden muss, was nutzlose Verluste verursacht.
• 3. Wenn die Halb- oder Vollbrücke nicht in Betrieb ist („Stand-By”), muss die benötigte Leistung im Linearbetrieb bereitgestellt werden, was wiederum mit einer höheren Verlustleistung erkauft werden muss.

However, the above-described known low-voltage power supply circuit has the following disadvantages:

• 1. It is not independently controllable.
• 2. The range of services depends on the half or full bridge frequency. The known circuit must be dimensioned so that it provides the required power at low frequency, ie at 100% light. This means for the dimming operation that the over-supplied due to higher frequency power over Zener diodes must be "destroyed", causing useless losses.
• 3. If the half or full bridge is not in operation ("stand-by"), the required power must be provided in linear operation, which in turn must be paid for with a higher power loss.

The invention has for its object a method for providing a low voltage for a load, in particular for semiconductor ICs, which are preferably used in operating devices for lighting, and to provide a corresponding low-voltage power supply circuit, which at least one of the disadvantages of the prior Technology is reduced.

The solutions given in the independent claims are based on the following considerations:
The start-up phase and the necessary components, such as starting resistor, switch and energy storage are maintained. However, the increased energy demand should no longer be covered by tapping an external power source, such as the half or full bridge of an operating device, but from the supplied with mains voltage low-voltage supply circuit itself. For this purpose, this with the mentioned already existing components selectively in a so-called. " Pulse mode "offset to then be operated as a switching regulator or DC-DC converter.

The various types of possible switching regulators or DC-DC converters are described, for example, in the book of U. Tietze and Ch. Schenck "Semiconductor Circuit Technology", Springer-Verlag, 9th edition on pages 563-586 described.

If the input voltage source is the AC mains, the frequency of the switching pulses for the switch should be higher, preferably much higher than the mains frequency. An input voltage, however, is a DC source.

As energy storage, a charging capacitor, preferably an electrolytic capacitor is suitable.

For the practical realization of a switching regulator or DC-DC converter is further proposed that the series circuit of starting resistor, switch, and energy storage nor the primary winding of a transformer is added, the secondary winding is connected in series with a rectifier diode in parallel with the charging capacitor, wherein the switch, the transformer, the rectifier diode and the charging capacitor can then form a flyback converter.

Conveniently, the switch with a current limiting circuit and the energy storage are connected to a voltage limiting circuit. This can for example consist of a parallel to the energy storage Zener diode.

The means for generating the switching pulses for the switch may be formed by a controller which - at least when using the low-voltage power supply circuit in a control device for a light-emitting device is usually present anyway. The controller can also be effective as a voltage regulator at the same time.

Another important development of the invention may consist in that the control input of the switch is connected to a charge pump, which evaluates the generated from the charge of the energy storage operating voltage and causes a change in the mode of operation from linear operation to pulse operation, a potential increase of the switching pulses at the control input of the switch , Such that the switching pulses for the switch overcome the threshold voltage when switching safely.

Further embodiments of the invention are the subject of the dependent claims 2-16 for the circuit and the claims 18-28 for the method. It should be expressly pointed out in this context that the claims are to be expected in full to the disclosure of the description.

Exemplary embodiments of the low-voltage power supply circuit according to the invention are described below with reference to the drawings.

Show it:

1 a first embodiment of the low-voltage power supply circuit,

2 a second embodiment of the low-voltage power supply circuit, which differs from the first embodiment only with respect to the voltage limitation and the specific embodiment of the charge pump.

In the 1 The illustrated low-voltage supply circuit serves to generate from the higher voltage of an input voltage source SQ a low voltage Vcc, with the active semiconductor ICs, such as. B. ASICs can be fed. The low voltage Vcc to be generated in the present case is a DC voltage of, for example, a maximum of 12 volts. The input voltage is in stationary operation a DC voltage with, for example, 400 volts. Since this input voltage is generated by actively switched components (eg active PFC) starting from a mains AC voltage, it can be equal to the peak value of the applied mains voltage during start-up or standby (PFC not yet switched on or off).

The input voltage source SQ is connected to the input terminals 1 and 2 connected to the circuit. Accordingly, the input voltage of a series circuit is made up of an optional circuit breaker SW (having an internal resistance represented by R1), the primary winding L1 of a transformer TR, a controllable electronic switch X1 (in the form of a power FET) and one at the output terminals 3 and 4 lying load RL supplied.

The optional disconnect switch SW switches off in certain states, the circuit shown completely to limit the losses to zero. This is particularly possible if electrical energy for a control circuit can be obtained from a bus line (for example, if the idle state of the bus protocol is not equal to zero). The switch SW is driven by a standby control circuit, not shown.

The starting resistance is denoted by R2. In the event of a start, the series circuit of the capacitors C2, C3 is charged via the starting resistor R2 and thus the gate of X1 is driven via the node R2, C2, R3. X1 is thus in linear operation.

The load RL represents, for example, semiconductor active ICs to be supplied. Parallel to the exit 3 . 4 Furthermore, there is a charging capacitor C4, which is formed by an electrolytic capacitor. Furthermore, it is parallel to the exit 3 . 4 the series connection of the secondary winding L2 of the transformer TR and a rectifier diode D5. And finally, over the exit 3 . 4 another Zener diode D4.

For the purpose of distinction, the controllable electronic switch X1 is hereinafter referred to as "switch", while the optional disconnect switch SW is also referred to below as "disconnector".

The charging capacitor C4 has the function of an energy storage. The Zener diode D4 serves to limit the voltage drop across the charging capacitor C4 to the Zener voltage of-in the present case-12 volts.

In order to limit the current flowing through the switch X1, a current limiting circuit is provided which consists of a shunt (resistor for picking up a voltage signal) R5, a charging capacitor C1 connected in parallel thereto, and a current limiting transistor Q1. The emitter-base path of the transistor Q1 is connected in parallel with the shunt R5 and the capacitor C1. The base of the transistor Q1 is connected to the source of the switch X1, and the collector is connected to the gate of X1 via a resistor R3. The connection point between R1 and the primary winding L1 of the transformer TR is connected through the resistor R2 and the resistor R3 to the gate of the switch X1.

In addition, a charge pump LP is connected to the charge capacitor C4, the exact function of which will be explained later.

The charge pump LP comprises two series-connected pump capacitors C2 and C3, which are between ground and the control input of the switch X1, wherein the series resistor R3 is interposed. To the charging capacitor C2, a resistor R6 is connected in parallel.

A controller CT (which can also be arranged externally) is shown here as a further part of the charge pump LP. He has a connection 5 for supplying the operating voltage Vcc, a ground connection 7 and a connection 6 from which switching pulses for the switch X1 are output. The connection 5 of the controller CT is - as indicated by the two Vcc characters - with the more potential output terminal 3 connected.

Further, the charge pump LP includes a first pump transistor Q3 and a second pump transistor Q2. The emitter of the first pump transistor Q3 is grounded. Its collector is connected both to the base of the second pump transistor Q2 and via a resistor R8 to the hot output port 3 connected. The base of the first pump transistor Q3 is connected via a resistor R4 7 of the controller CT, which is intended to output the switching pulses for the switch X1. The emitter-collector path of the second pump transistor Q2 extends between the connection point of the two pump capacitors C2 and C3 on one side and - with the interposition of a load resistor R7 - the "hot output terminal 3 on the other hand. The emitter-base path of the second pump transistor Q2 is bridged by a diode D3.

The "hot" output port 3 is further connected via a diode D2 and the resistor R3 to the control input of the switch X1.

Now the function of the circuit will be described:

linear operation

First, the circuit breaker SW is opened and the switch X1 is closed, d. H. the power FET is still non-conductive. In order for it to become conductive, the gate potential must be higher than the source potential by the FET threshold voltage (approximately 1.5 to 4.5 volts) when the disconnector SW is switched on. The voltage at the charging capacitor C4 is still zero, the controller CT is still inactive. The voltage at the source of X1 is also zero.

By closing the circuit breaker SW, the first phase of generating a low voltage is initiated, which is referred to as "linear operation".

At the switch X1, that is to say at the source-drain path of the power FET, the full DC input voltage of, for example, 400 V is present in stationary operation (in the standby case or in the start-up phase 310 V at 230 V mains voltage, see above ). The pump capacitors C2 and C3 begin to charge via the resistor R2, with the result that the voltage at the control input of the switch X1 increases. When the threshold voltage is exceeded, the switch X1 starts to become conductive. A current now flows from the input voltage source SQ via the disconnecting switch SW, the resistor R1, the primary winding L1 of the transformer TR, the opened switch X1, the shunt R5 and via the output terminals 3 . 4 in the charging capacitor C4. Since it is at the load RLs are active semiconductor ICs, they will not take power while they are inactive. This applies equally to the Controller CT. The result is that the voltage across the charging capacitor increases approximately linearly. The current through the switch X1 is - as will be described in more detail later - limited by the shunt R5 and the capacitor C1 in conjunction with the current limiting transistor Q1. The capacitor C1 is primarily used to allow later to pass more accurately described pulse currents. It is important that the time constants R2, C2, C3 in relation to the charging time of C1 is very large, so that when switching on the current slowly increases to the value set with the shunt.

The limitation of the current through the switch X1 occurs in that an excessive current has a correspondingly high voltage drop across the shunt R5 result. As a result, the current limiting transistor Q1 becomes increasingly conductive. This in turn reduces the voltage across the source-gate path of switch X1, with the result that the current through X1 is again reduced.

With the current flowing through the switch X1 and the charging of the charging capacitor C4, the voltage at the source electrode of the switch X1 increases. In order to maintain the current flow and still - to increase to the predetermined limit -, the voltage at the gate electrode of the switch X1 must be increased accordingly. This is ensured by the increase in the voltage across the two pump capacitors C2, C3.

When the voltage on the charging capacitor C4 reaches about 3.3 volts, it will be enough to make the controller CT operate. The same applies to the active semiconductor ICs represented by the load RL. This means that the controller CT is now capable of at its output terminal 6 Output switching pulses for the switch X1.

When the voltage at the charging capacitor C4 has reached a value corresponding to the threshold voltage of the FET used (for example 8 V) through the Zener diode D4, the linear mode switches to the so-called "pulse mode". This can be done automatically or externally controlled.

pulse operation

To describe the pulse operation, it is initially assumed that the maximum current predetermined by the current limiting circuit flows through the switch X1, and that the maximum voltage of the charging capacitor C4 is 12 V at the charging capacitor C4. The signal output 6 of the controller CT should initially not give a switching pulse, so practically still at ground potential. Under this condition, the first pump transistor Q3 is still locked, and at the second pump transistor Q2, a base current flows through the resistor R8 with the result that Q2 is conductive. As a result, the connection point of the two pump capacitors C2, C3 has approximately the potential of the charging capacitor C4. The gate electrode (control input) of switch X1 continues to be at a bias potential above 12 volts (about 20 volts) and is higher than the potential at the source electrode by the FET threshold voltage. As a result, current continues to flow through the switch X1, as before in linear mode.

If a switching pulse is now output by the controller CT, this has an increase in the potential at the signal output 6 of the controller CT to ground potential result, whereby the first pump transistor Q3 is turned on. It thus reduces the potential at the connection point of the two pump capacitors C3 and C2 to almost ground potential. Thus, the potential at the gate electrode (control input) of the switch is lowered accordingly, with the result that the switch X1 blocks abruptly. The sudden interruption of the current flow through the inductance of the input winding L1 of the transformer TR results in a freewheeling current, which is transmitted to the secondary winding L2 and used to charge the charging capacitor C4. As can easily be seen, the switch X1, the transformer TR with its two windings L1, L2, the rectifier diode D5 and the charging capacitor C4 form a flyback converter which reduces the input DC voltage of 400 volts substantially to the output low voltage of 12 Converts volts. It is the output 3 . 4 The power which can be taken from the circuit during the pulse operation is higher than that which can be taken from the circuit during the linear phase. Basically, however, the linear operation can be maintained as long as the power limit of the switch X1 and the Zener diode D4 are not exceeded.

The function of the framed charge pump LP is that switching pulses issued by the controller CT are converted at a relatively low voltage amplitude into switching pulses whose amplitude is significantly higher, so high that the FET threshold, which is approximately depending on the FET -Type can be between 1.5 volts and 3.5 volts, is safely swept by the converted switching pulses.

To better identify the individual assemblies, they have been framed. The components involved in the linear operation are framed with a double-dashed double-dot line. The components involved in the pulse operation are through a dot-dash line framed. The components belonging to the charge pump LP are located in a frame which is formed by a dashed line. The same applies to the components which form the energy store C4, the voltage limiting zener diode D4 and the load RL. In 2 the frames are omitted.

The circuit according to 2 differs from the one after 1 Thus, the limitation of the voltage across the charging capacitor C4 is no longer done by a zener diode connected in parallel to this, which inevitably destroys energy, but by a circuit part which contains an additional voltage limiting transistor Q4. The collector of Q4 is connected via the series resistor R3 to the control input of the switch X1. The emitter of Q4 is connected through a Zener diode D4 to the collector of the first pump transistor Q3, and the base of Q4 is connected to the "hot" terminal of the charging capacitor C4. When the voltage across the charging capacitor C4 exceeds the value of 12 volts set by the zener diode D4, a current flows through Q4. This reduces the potential at the base of Q4, thereby reducing the current flow through switch X1, which then causes a corresponding decrease in the charging voltage at C4.

Essential to the voltage limiting variant according to 2 is that this is only active in linear mode. In linear mode, the potential is at the signal output 6 of the controller CT about ground potential, so that the positive electrode of the Zener diode here is virtually at ground.

This additional way of limiting the current flowing through the switch X1 in the linear mode, is only particularly advantageous when working in the pulse mode with the smallest possible pulse duration and possibly also with luckendem or burst mode. This is the case when too few consumers are active and still too much power has to be destroyed. Then, in some circumstances - as far as the power loss is concerned - the linear mode could be the cheaper one. Otherwise, the linear operation is needed only for the start-up phase, until the voltage on the charging capacitor C4 has risen to 8 volts or more, the controller CT is supplied with the operating voltage Vcc and the gate of the switch X1 is supplied with the necessary bias voltage of more than 8 volts can be applied.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008016754 A1 [0006]

Cited non-patent literature

• U. Tietze and Ch. Schenck "semiconductor circuit technology", Springer-Verlag, 9th edition on pages 563-586 [0010]

Claims (25)

Low-voltage supply circuit for a load (RL), in particular for active semiconductor ICs, having input terminals ( 1 . 2 ) for an input voltage source (SQ) whose voltage peak is higher than the supply voltage Vcc to be generated, with output terminals ( 3 . 4 ) for the load (RL), wherein an energy store (C4) is provided which is chargeable in a linear operation of a controllable switch (X1) and from the charge of the energy store (C4) the supply voltage Vcc for the load (RL) can be generated, characterized by a) means (CT) for generating switching pulses for the switch (X1) for operating the same in a pulsed operation, wherein in pulse mode, the energy storage (C4) and the switch (X1) form parts of a switching regulator or DC-DC converter, and from Charging the energy store (C4), the supply voltage Vcc for the load (RL) can be generated. Circuit according to claim 1, with a parallel to the input terminals ( 1 . 2 ) connected series circuit of - a starting resistor (R2), - the controllable electronic switch (X1) and - the energy storage (C4), with the output terminals ( 3 . 4 ) connected is. Low-voltage power supply circuit according to claim 1 or 2, characterized in that the switch (X1) is a transistor, preferably a power FET. Low-voltage supply circuit according to one of the preceding claims, characterized in that the input voltage source (SQ) is an optionally rectified mains voltage or an intermediate circuit voltage generated by an active PFC of a control device for lighting means. Low-voltage supply circuit according to one of the preceding claims, characterized in that the frequency of the switching pulses is higher, preferably much higher than the mains frequency. Low-voltage supply circuit according to one of the preceding claims, characterized in that the energy store (C4) is a charging capacitor, preferably an electrolytic capacitor. Low-voltage power supply circuit according to claim 6, characterized in that the series circuit of resistor (R1), switch (X1), and energy storage (C4) additionally contains the primary winding (L1) of a transformer (TR) whose secondary winding (L2) in series with a rectifier diode (D5) in parallel with the charging capacitor (C4), the switch (X1), the transformer (TR), the rectifier diode (D5) and the charging capacitor (C4) forming a flyback converter. Low-voltage supply circuit according to one of the preceding claims, characterized in that the switch (X1) is connected to a current limiting circuit. Low-voltage supply circuit according to one of the preceding claims, characterized in that the energy store (C4) is connected to a voltage limiting circuit. Low-voltage supply circuit according to one of the preceding claims, characterized in that the means (CT) for generating the switching pulses for the switch (X1) are formed by a controller (CT). Low-voltage power supply circuit according to claim 10, characterized in that the controller (CT) is also effective as a voltage regulator. Low-voltage supply circuit according to one of the preceding claims, characterized in that the control input of the switch (X1) with a charge pump (LP) is connected, which evaluates the generated from the charge of the energy storage (C4) operating voltage and after a change in the mode of linear operation on pulse operation, a potential increase of the switching pulses on the control input of the switch (X1) causes such that the switching pulses for the switch overcome the threshold voltage when switching safely. Low-voltage power supply circuit according to claim 12, characterized in that the charge pump (LP) comprises a first pump transistor (Q3) and a second pump transistor (Q2) that the charge pump (LP) further comprises a first and a second pump capacitor (C2 , C3) connected in series between the control input of the switch (X1) and ground, that the base of the first switching transistor (Q3) is connected to the means (CT) for generating the switching pulses for the switch (X1) the emitter of the first pump transistor (Q3) is grounded, that the collector of the first pump transistor (Q3) is connected to the base of the second pump transistor (Q2) and further via a resistor (R8) to the energy store (C4), in that the emitter of the second pump transistor (Q2) is located at the connection point of the two pump capacitors (C2, C3), that the collector of the second pump transistor (Q2) via a load resistor (R7) to the energy storage (C4) and also one with the Load resistor (R6) connected in series diode (D2) to the control input of the switch (X1) is connected, and that the emitter-base path of the second pump transistor (Q2) with a diode (D3) is bridged. Low-voltage supply circuit according to claim 9, characterized in that the voltage limiting circuit is formed by a Zener diode (D4) connected in parallel with the energy store (C4). Low-voltage power supply circuit according to claim 9 and 13, characterized in that the voltage limiting circuit includes a voltage limiting transistor (Q4) whose collector is connected to the control input of the switch (X1), whose base is connected to the energy store (C4), and whose emitter is connected via a zener diode (D6) and the collector of the first pump transistor (Q3). Low-voltage supply circuit according to claim 9, characterized, in that the current-limiting circuit includes a current-limiting transistor (Q1) whose collector is connected to the control input of the switch (X1), in that with the switch (X1) the parallel connection of a shunt (R5) and a capacitor (C1) is connected in series, and that the emitter-base path of the current-limiting transistor (Q1) is connected in parallel to the shunt (R5) and to the capacitor (C1). Low-voltage supply circuit according to one of the preceding claims, characterized in that the voltage drop across the resistor (R1) is supplied to the control input of the switch via a starting resistor (R2). Operating device for lighting means, comprising a circuit according to one of the preceding claims, which supplies a control circuit of the operating device, preferably comprising an active PFC whose output voltage represents the input voltage source (SQ). Method for providing a low-voltage for a load, in particular for semiconductor ICs, in which an energy store (C4) in the so-called linear mode is charged by an input voltage source (SQ) via a starting resistor (R2) and a controllable electronic switch (X1) and a starting voltage for the load (RL) is generated from the rising charge, at the control input of the switch (X1) in the - following the linear operation - so-called pulse operation switching pulses are supplied, wherein the switch (X1) and the energy storage (C4) are operated as a switching regulator or DC-DC converter, and in which an operating voltage for the load (RL) is generated in the pulse mode from the charge of the energy store (C4). A method according to claim 19, characterized in that the voltage at the energy store (C4) is kept constant. A method according to claim 19 or 20, characterized in that the current through the switch (X1) is limited in linear operation. Method according to one of claims 19 to 21, characterized in that the bias voltage at the control input of the switch (X1) is raised during the transition from linear operation to pulsed operation, such that the switching pulses for the switch (X1) switch the latter safely. Method according to one of claims 19 to 22, characterized in that a DC voltage or a rectified AC voltage is used as the input voltage source (SQ). Method according to one of Claims 19 to 22, characterized in that the alternating current network is used as the input voltage source (SQ) and in that a switch (X1) is used which is only conductive in one direction, for example a transistor , A method according to claim 24, characterized in that the frequency of the switching pulses higher, preferably much higher than the mains frequency is selected.

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