Direct current (DC) voltage source for providing a DC voltage based on an input voltage and corresponding method

Abstract

A direct current, DC, voltage source arranged for providing a DC voltage based on an input voltage between two input terminals, wherein the DC voltage source comprises: a transformer arranged for receiving a supply current at a first side of the transformer and for converting the supply current into a circulating current at a second side of the transformer; a first input terminal and a second input terminal for receiving an input voltage for setting the DC voltage to be provided by the DC voltage source; a first diode, wherein an anode of the first diode is connected to a first end of the second side of the transformer, and wherein a cathode of the first diode is connected to the first input terminal; a current regulator circuit for ensuring that an amount of current of the circulating current is shunted from the first diode.

Description

Technical Field

[0001] The present disclosure relates generally to the field of voltage interfaces for setting the output current of a light emitting diode (LED) driver, and more particularly to a DC voltage source arranged to provide a precise output voltage based on an input voltage. Background Art

[0002] 1-10V or 0-10V interfaces have been used for dimmable drivers for light sources for many years. Despite the influence of digital interfaces, these types of interfaces remain popular.

[0003] Following its adoption as a dimming interface, the 0-10V interface has become the de facto standard for setting the driver output current in outdoor SSL drivers in the United States. This interface is used as an alternative to setting resistors to match the driver output current to the lighting load used in the application. In contrast to use in dimming applications, the driver may need to have a precise, temperature-independent, and preferably linear transfer curve. This transfer curve is related to the relationship between the setting resistor and, for example, the LED current.

[0004] The above-described interface includes a transformer for creating an isolation barrier between a driver side of the interface and an input side of the interface.

[0005] The transformer is excited on the first side, the driver side, by injecting or extracting current pulses. The current is magnetically coupled to the second side, the transformer's input side, and flows back to the transformer via a first diode, a set resistor, and another resistor. This secondary-side current is called the circulating current.

[0006] The additional resistor forms part of a current regulator circuit that ensures a predetermined amount of current flows through the set resistor. The current regulator ensures that excess current (i.e., the amount of circulating current exceeding the predetermined amount of current) is diverted so as not to flow through the set resistor. This is achieved by providing a shunt path to the set resistor, i.e., an electrical path in parallel with the set resistor.

[0007] One disadvantage of the above interface is that the transfer curve described above becomes inaccurate with increasing amounts of overcurrent. That is, the more overcurrent is shunted by the current regulator circuit, the less accurate the transfer curve becomes. Summary of the Invention

[0008] An object of the present invention is to provide a DC voltage source having an accurate transfer curve.

[0009] Another object of the invention relates to a method of operating such a DC voltage source.

[0010] In a first aspect, a direct current (DC) voltage source is provided, the direct current (DC) voltage source being arranged for providing a DC voltage based on an input voltage between a first input terminal and a second input terminal, wherein the DC voltage source comprises:

[0011] a transformer arranged for receiving a supply current at a first side of the transformer and for transforming said supply current into a circulating current at a second side of the transformer;

[0012] the first input terminal and the second input terminal for receiving the input voltage for setting the voltage to be provided by the DC voltage source;

[0013] a first diode, wherein an anode of the first diode is connected to a first end of the second side of the transformer, and wherein a cathode of the first diode is connected to the first input terminal;

[0014] - A current regulator circuit having two input nodes and one output node, wherein

[0015] a first one of the input nodes is connected to the second input terminal,

[0016] a second one of the input nodes being connected to the first end of the second side of the transformer and shunting the first diode and the first and second input terminals;

[0017] - the output node is connected to the second end of the second side of the transformer,

[0018] wherein the current regulator circuit is arranged to ensure that a predetermined amount of current is removed from the circulating current, wherein the predetermined amount of current flows back to the transformer via the first diode, the first and second terminals and the first of the input nodes via the output node, and to ensure that a remaining current of the circulating current flows back to the transformer via the second of the input nodes via the output node, thereby not flowing via the first node.

[0019] The inventors have found that it may be beneficial if the residual current is also shunted before the first diode. In this way, the residual current will not flow through the first diode. Only a predetermined amount of current flows back to the transformer via the first and second input terminals.

[0020] In the prior art, an overcurrent, or residual current as described above, also flows through the first diode. It has been found that this overcurrent flowing through the first diode is the cause of inaccurate transfer curves. The overcurrent varies and decreases as the voltage across the terminals increases. This introduces nonlinearity and temperature dependence into the transfer curve. This will be explained in more detail with reference to the accompanying drawings.

[0021] The overcurrent also varies significantly with changes in the magnetizing inductance of the transformer, which may have relatively large tolerances and temperature dependencies. The changes in the overcurrent flowing through the first diode caused by changes in the magnetizing inductance of the transformer are not systematic errors and therefore cannot be easily compensated.

[0022] The present disclosure aims to provide a path for excess current that does not involve the first diode. This is achieved by connecting a second of the input nodes to the first end of the second side of the transformer, thereby shunting the first diode and the first and second input terminals. This reduces nonlinearity, temperature dependence, and transfer curve inaccuracies.

[0023] In one example, the first input terminal and the second input terminal are arranged to receive a resistor for setting a DC voltage to be provided by the DC voltage source.

[0024] In one example, the DC voltage source includes a branch diode, wherein the second one of the input nodes is connected to the first end of the second side of the transformer via the branch node.

[0025] The above may require that the anode of the first diode and the anodes of the branch diodes be connected to each other.

[0026] In another example, a forward voltage of the branch diode is equal to or lower than a forward voltage of the first diode.

[0027] The above ensures that an excess current flows via the second one of the input nodes and thus not via the first diode.

[0028] In another example, the current regulator circuit includes a current setting resistor, wherein a first end of the current setting resistor is connected to the second input node, and wherein a second end of the current setting resistor is connected to the output node, wherein the current regulator circuit is arranged to maintain a reference voltage across the current setting resistor such that a resistance value of the current setting resistor defines the predetermined amount of current flowing through a first one of the input nodes.

[0029] The current regulator circuit may, for example, include a three-terminal adjustable shunt regulator.

[0030] In another example, the DC voltage source further includes:

[0031] - A low-pass output filter connected to said first side of the transformer.

[0032] In yet another example, the DC voltage source includes:

[0033] - an output diode connected directly or indirectly to a first end of the first side of the transformer.

[0034] Here, the output diode and the first diode may have the same forward voltage drop.

[0035] More specifically, it may be beneficial if the first diode and the output diode are of the same type. Then, any nonlinear effects of the first diode can be corrected or compensated by the output diode. This compensation is likely to be most effective when both diodes are of the same type, because in this case, both diodes are likely to exhibit the same nonlinear effects.

[0036] In another example, the first and the second input terminals have received the resistors for setting the voltage to be provided by the DC voltage source.

[0037] It should be noted that according to the present disclosure, the DC voltage source is usually sold without a resistor for setting the voltage to be provided by the DC voltage source. The user can actually provide a resistor between the terminals, or alternatively, a voltage source can be provided with an output connected to the terminals for setting the voltage.

[0038] In another example, the branch diodes are Schottky diodes.

[0039] A Schottky diode, also known as a Schottky barrier diode or hot carrier diode, is a semiconductor diode formed by a semiconductor-metal junction. Compared to conventional diodes, it has a lower forward voltage drop and faster switching action.

[0040] In a second aspect, there is provided a method for operating a direct current (DC) voltage source according to any of the preceding examples, wherein the method comprises the following steps:

[0041] - ensuring, by the current regulator circuit, that the predetermined amount of current is removed from the circulating current, wherein the predetermined amount of current flows back to the transformer via the first diode, the first and second terminals, and the first of the input nodes via the output node, and

[0042] - ensuring, by the current regulator circuit, that the remaining current of the circulating current flows back to the transformer via a second one of the input nodes and via the output node, without flowing via the first diode.

[0043] It should be noted that the advantages and limitations disclosed with respect to the embodiments of the first aspect of the invention also apply to the embodiments of the second aspect of the invention, ie the method of operating a direct current DC voltage source.

[0044] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Disclosed is a direct current (DC) voltage source according to the prior art;

[0046] Figure 2 Disclosed is a direct current (DC) voltage source according to the present disclosure;

[0047] Figure 3 Another direct current (DC) voltage source according to the present disclosure is disclosed. DETAILED DESCRIPTION

[0048] Figure 1 A DC voltage source 1 according to the prior art is disclosed. Figure 1 The circuit shown.

[0049] L1a is at least energized by a positive current pulse, such as through C5, R5, or I5. This current is magnetically coupled to L1b, flows via D1 (which is referred to as the first diode in this disclosure), charges C1, and flows back to L1b via Rptc, Rset, and R1.

[0050] Here, Rset is a resistor connected between the input terminals, which sets the output voltage of the DC voltage source. Resistor R1 is a resistor that sets a predetermined current. More specifically, adjustable shunt regulator TL431 is configured to maintain a fixed voltage across R1, which—i.e., a reference voltage—is converted into a fixed, predetermined current. Therefore, the predetermined current also flows through resistor Rset.

[0051] If the voltage across R1 were to exceed the TL431 reference voltage, the TL431 clamps the excess L1b current from its cathode to its anode via R2 (i.e., a low-ohmic path). Thus, the R1 current remains constant in this circuit, ensuring that the output voltage, i.e., the voltage across R4, is based on the resistance value of Rset.

[0052] Therefore, the above-mentioned overcurrent is the residual current of the circulating current described in the appended claims.

[0053] Rptc and Z1 are optional, and if typically used, the Rptc resistance is very low compared to Rset. Therefore, the voltage across L1b will be equal to the D1 forward voltage (i.e., the forward voltage of the first diode) plus the voltage across Rset plus the TL431 reference voltage across R1.

[0054] On the driver side, i.e., to the left of the insulation barrier provided by transformer L1a / L1b, the L1b voltage is reflected across L1a and filtered by R3, C3 for any overshoot of the L1a voltage due to the leakage inductance between L1a and L1b, and then rectified by D3 (i.e., the output diode) into C4 in parallel with R4.

[0055] If L1a and L1b have a 1:1 turns ratio, the D3 Vbe forward voltage cancels the D1 Vbe forward voltage, and so the driver side voltage across R4 is the input voltage and hence a 1:1 representation of the Rset resistance, although it still includes an offset equal to the TL431 reference voltage.

[0056] After each positive current pulse into the point of L1a, the magnetization of L1 may need to be reset before the next positive current pulse via a negative voltage at the point across L1a and L1b.

[0057] D2 and Z2 provide clamping to limit this reset voltage to a safe level. Reverse voltage clamping can also be done on the driver side or on both sides and can be enhanced by reverse current through C5, R5, or optional reverse current through I5. An RC series network snubber can be provided in place of D2 and Z2.

[0058] The Rptc, Z1 circuit on the input side acts as a protection against inadvertent connection of the input terminals to mains voltage. In this case, Z1 limits the voltage in either direction to a safe level, while the Rptc quickly becomes high-ohmic to withstand the mains voltage robustly.

[0059] It has been found that in existing solutions, the excess L1b current clamped in the TL431 flows through the first diode, D1. It varies and decreases with increasing Rset, introducing nonlinearity and temperature dependence in the transfer curve because the D1 and D3 forward voltages no longer completely cancel each other.

[0060] The excess L1b current can also vary significantly with changes in the magnetizing inductance of the L1 transformer, which has a relatively large tolerance and temperature dependency. Since the C5, R5, or I5 current is "fixed" and the L1 magnetizing current varies, the excess L1b current and the D1 current can vary significantly. The change in D1 current due to changes in the magnetizing inductance is not a systematic error and cannot be easily compensated for.

[0061] The present disclosure is directed to separating the sensing path of the L1b current from the overcurrent clamping path.

[0062] The sense path via Rset and R1 provides an accurate constant current flowing through the first diode (ie, D1) and determines the L1b voltage sensed across L1a; the L1b overcurrent flows into the TL431 clamp via a separate branch and not via D1.

[0063] This substantially reduces the inaccuracies, non-linearities and temperature dependencies of the Rset versus provided DC output voltage transfer curve.

[0064] Figure 2 A direct current (DC) voltage source 11 according to the present disclosure is disclosed.

[0065] The DC voltage source 11 is arranged to provide a DC voltage based on the resistance value of a resistor, namely Rset, i.e., a DC voltage across R4 in parallel with C4. Note that the DC voltage provided is based on the voltage between the two terminals, where Rset can be received between the two terminals. Alternatively, the output of the voltage source can be connected to these two terminals.

[0066] DC voltage sources, including:

[0067] - a transformer as shown with reference numerals L1a and L1b, wherein the winding L1a is arranged for receiving a supply current and wherein the transformer is arranged for transforming the supply current into a circulating current at the winding L1b.

[0068] The supply current may be received from a current source indicated by I5 or may be generated from a voltage source via C5 and R5. The transformer also provides an isolation barrier as shown by the dashed line for improving the safety aspects of the DC voltage source 11.

[0069] a first terminal and a second terminal for receiving an input voltage for setting the voltage provided by the DC voltage source. The terminals may be adapted to receive the resistor, for example, by screwing the resistor onto the terminals, by soldering the resistor onto the terminals, by inserting the resistor into the terminals, or in any similar manner.

[0070] a first diode, D1 , wherein an anode of the first diode is connected to a first terminal of the second side of the transformer, and wherein a cathode of the first diode is connected to the first input terminal.

[0071] - a current regulator circuit, in this example in the form of an adjustable shunt regulator TL431, which has two input nodes and one output node, wherein

[0072] - the first input node is connected to the second input terminal;

[0073] a second input node connected to a first end of a second side of the transformer, thereby shunting the first diode and the first input terminal and the second input terminal;

[0074] The output node is connected to a second terminal of the second side of the transformer.

[0075] According to the above, the current regulator circuit is arranged to ensure that a predetermined amount of current is withdrawn from the circulating current, wherein the predetermined amount of current flows back to the transformer via the first diode, the first and second terminals, and the first of the input nodes via the output node, and to ensure that the remaining current of the circulating current flows back to the transformer via the second of the input nodes via the output node, thereby not flowing via the first diode.

[0076] In this particular example, the second input node includes a branched diode as shown as D6 , where the anode of the branched diode D6 is connected to the first end of the second side of the transformer.

[0077] As a result, a predetermined amount of current flows from the transformer back to the transformer via the first diode D1, Rset, and R1. Resistor R1 is coupled between the first input node and the output node of the adjustable shunt regulator TL431. The remaining current, or overcurrent, flows from the transformer via branch diode D6, through optional resistor R2, and to the second input node of the adjustable shunt regulator TL431, where it flows back to the second side of the transformer via the output node of the adjustable shunt regulator TL431.

[0078] exist Figure 2 In the circuit shown, Rptc, Rset, and R1 currents are constant and are the only currents flowing through D1. Therefore, D1 current does not vary with Rset, L1 magnetizing inductance, or temperature.

[0079] If the transfer curve needs to accurately drop to very low voltages, such as a short circuit close to Rset, the forward voltage of branch diode D6 is preferably selected to be lower than the forward voltage of first diode D1. In these cases, D1 and D3 are preferably silicon diodes, while branch diode D6 is preferably a Schottky diode.

[0080] In one example, L1a is driven by current source I5, which delivers current pulses into L1a.

[0081] In one example, the voltage of such an I5 current source is limited to a voltage level just above the voltage across L1a, given the maximum voltage to be detected.

[0082] In another example, the I5 current source does not draw current from L1a.

[0083] Figure 2 The driver side sense may be positive relative to the driver side Gnd reference and increases as the input voltage increases.

[0084] In an alternative implementation, L1a may not be referenced to Gnd but to, for example, a low voltage supply voltage, and the polarity of L1a may be reversed, with the sensed output signal across R4 decreasing as the input voltage or Rset resistance increases.

[0085] Figure 3 Another direct current (DC) voltage source 21 according to the present disclosure is disclosed.

[0086] In one example, I5 draws current from L1a and does not inject current during the magnetic reset of L1. I5 can be a current source to Gnd and can be integrated into an integrated circuit.

[0087] exist Figure 1 、 Figure 2 and Figure 3 The output node mentioned in the description is called the anode side of the adjustable shunt regulator TL431. Excess shunt current enters the adjustable shunt regulator via the cathode side (also called the second input node) and leaves the current regulator via the anode side (also called the output node) of the adjustable shunt regulator.

[0088] Other variations of the disclosed embodiments may be understood and effected by those skilled in the art in practicing the claimed invention by studying the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may perform the functions of several items recited in a claim. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in a claim should not be construed as limiting its scope.

Claims

1. A direct current (DC) voltage source, arranged to provide a DC voltage based on an input voltage between a first input terminal and a second input terminal, wherein a resistor (Rset) is connectable between the first input terminal and the second input terminal, wherein the DC voltage source comprises: a transformer arranged for receiving a supply current at a first side (L1a) of the transformer and for transforming the supply current into a circulating current at a second side (L1b) of the transformer; the first input terminal and the second input terminal for receiving the input voltage to set the DC voltage to be provided by the DC voltage source; - an output terminal (R4) for providing said DC voltage, wherein said output terminal is electrically connected to said first side (L1a) of said transformer; a first diode (D1), wherein an anode of the first diode (D1) is connected to a first end of the second side (L1b) of the transformer, and wherein a cathode of the first diode (D1) is connected to the first input terminal; a branch diode (D6), wherein an anode of the branch diode (D6) is connected to the first end of the second side (L1b) of the transformer; A current regulator circuit (TL431) having an input node, a cathode side, and an anode side, wherein: - the input node is connected to the second input terminal, The cathode side is coupled to the first end of the second side of the transformer via the branch diode (D6) and shunts the first diode (D1) and the first and second input terminals; - the anode side is connected to a second end of the second side (L1b) of the transformer, wherein the DC voltage source further comprises a current setting resistor (R1) coupled between the input node and the anode side, wherein the current setting resistor (R1) is used to set a predetermined amount of current from the circulating current, The current regulator circuit (TL431) is arranged to: ensure that the predetermined amount of current is removed from the circulating current, wherein the predetermined amount of current flows back to the transformer via the first diode (D1), the first input terminal, the second input terminal, and the current setting resistor (R1); and to ensure that the remaining current of the circulating current flows back to the transformer via the branch diode (D6), via the cathode side, and via the anode side, thereby not flowing via the first diode (D1).

2. A DC voltage source according to claim 1, wherein the first input terminal and the second input terminal are arranged to receive a resistor for setting the DC voltage to be provided by the DC voltage source at the output (R4).

3. The DC voltage source according to claim 1, wherein a forward voltage of the branch diode (D6) is equal to or lower than a forward voltage of the first diode (D1).

4. A DC voltage source according to any one of the preceding claims, wherein the current regulator circuit (TL431) is arranged to maintain a reference voltage across the current setting resistor (R1) such that the resistance value of the current setting resistor (R1) defines the predetermined amount of current flowing via the one of the input nodes.

5. The DC voltage source of claim 1, further comprising a low-pass output filter (R, C3) connected between the output terminal (R4) and the first side of the transformer.

6. The DC voltage source according to claim 5, further comprising an output diode (D3) connected directly or indirectly between the output terminal (R4) and the first end of the first side (L1a) of the transformer.

7. The DC voltage source according to claim 6, wherein the output diode (D3) and the first diode (D1) have the same forward voltage drop.

8. The DC voltage source according to claim 1, wherein the branch diode (D6) is a Schottky diode.

9. A method for operating a direct current (DC) voltage source according to any one of the preceding claims, wherein the method comprises the following steps: - ensuring that the predetermined amount of current is removed from the circulating current by the current regulator circuit (TL431), wherein the predetermined amount of current flows back to the transformer via the anode side via the first diode (D1), the first and second input terminals and the input node, and - The current regulator circuit (TL431) ensures that the remaining current of the circulating current flows via the cathode side and back to the transformer via the anode side, thereby not flowing via the first diode (D1).

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