A constant current output circuit with PWM to analog current regulation and OVP protection function

Abstract

The present invention provides a constant current output circuit with PWM to analog current modulation and OVP protection functions, wherein an LED lamp bead is connected between the DC output positive pole and the negative pole of a constant voltage converter; the input end of a reference voltage generator and a voltage sampling circuit is connected to the DC output positive pole; the output ends of the voltage sampling circuit and the reference voltage generator are respectively connected to the two input ends of a first operational amplifier comparator; the output end of the reference voltage generator is also connected to the input end of a PWM control reference voltage circuit; the output end of the PWM control reference voltage circuit and the current sampling resistor Rcs voltage are respectively connected to the two input ends of a second operational amplifier comparator; the output ends of the first operational amplifier comparator and the second operational amplifier comparator are respectively connected to the cathodes of diodes D1 and D2, the anodes of the diodes D1 and D2 are connected to each other and then connected to the input end of an optical coupler, the output end of the optical coupler is connected to the input end of a control IC, and the output end of the control IC is connected to the constant voltage converter.

Description

Technical Field

[0001] The invention relates to LED lighting, and in particular to an LED driving circuit. Background Art

[0002] At present, the driving circuits of LED lighting products on the market have low dimming depth, low-end dimming accuracy, and flicker-free dimming process. The dedicated IC for dimming solutions mainly samples the LED current at the primary side, but does not sample the LED current at full wave. The dimming depth and low-end dimming accuracy are not high when calculated using the relevant equivalent formula. The existing requirements for dimming depth and dimming accuracy are relatively high, and two levels are required. Constant voltage is added in DC to DC, which is relatively costly and has limited IC choices. Summary of the invention

[0003] The main technical problem to be solved by the present invention is to provide a constant current output circuit with PWM to analog current regulation and OVP protection function, and realize intelligent LED driving by using a constant voltage converter. It does not need to use a dedicated control IC to realize ordinary LED driving and LED driving with PWM to analog dimming.

[0004] In order to solve the above technical problems, the present invention provides a constant current output circuit with PWM to analog current modulation and OVP protection function, including: a constant voltage converter, two operational amplifier comparators, a reference voltage generator, a PWM control reference voltage circuit, a voltage sampling circuit and a diode for voltage isolation;

[0005] An LED lamp bead is connected between the DC output positive electrode and the negative electrode of the constant voltage converter; the input ends of the reference voltage generator and the voltage sampling loop are respectively connected to the DC output positive electrode;

[0006] The output ends of the voltage sampling loop and the reference voltage generator are respectively connected to the two input ends of the first operational amplifier comparator; the output end of the reference voltage generator is also connected to the input end of the PWM control reference voltage loop; the output end of the PWM control reference voltage loop and the current sampling resistor Rcs voltage are respectively connected to the two input ends of the second operational amplifier comparator; the output ends of the first operational amplifier comparator and the second operational amplifier comparator are respectively connected to the cathodes of diodes D1 and D2, the anodes of diodes D1 and D2 are connected to each other and then connected to the input end of the optical coupler, the output end of the optical coupler is connected to the input end of the control IC, and the output end of the control IC is connected to the constant voltage converter.

[0007] In a preferred embodiment: the reference voltage generator is TL431, whose input end is connected to the DC output positive electrode through a voltage regulator ZD1 and a resistor R1; the reference voltage generator is used to generate a reference voltage and a VDD voltage.

[0008] In a preferred embodiment: the voltage sampling circuit includes resistors R5, R6, R7, R9 and capacitor C3;

[0009] One end of the resistor R6 is connected to the DC output positive electrode, and the other end is connected to the capacitor C3; the resistor R5 is connected in parallel with the resistor R6 and the capacitor C3; one end of the resistor R7 is connected to the capacitor C3 and the resistor R5, and the other end is grounded through the resistor R9; the connection point between the resistor R7 and the resistor R9 is connected to the input end of the first operational amplifier comparator.

[0010] In a preferred embodiment: the output end of the second operational amplifier comparator is connected to the feedback pin FB of the control IC through an optical coupler U4 and a diode D6.

[0011] In a preferred embodiment: the output end of the voltage sampling loop is connected to the inverting input end of the first operational amplifier comparator, and the output end of the reference voltage generator is connected to the positive input end of the first operational amplifier comparator;

[0012] The output end of the PWM control reference voltage loop is connected to the positive input end of the second operational amplifier comparator, and the voltage of the current sampling resistor Rcs is connected to the negative input end of the second operational amplifier comparator.

[0013] In a preferred embodiment: when the output current is greater than the set value, the voltage at the reverse input terminal of the second operational amplifier comparator is greater than the voltage at the forward input terminal, the output voltage of the second operational amplifier comparator decreases, and the output voltage of the optocoupler increases. The higher the voltage at the FB pin, the shorter the drive time of the converter and the smaller the output current.

[0014] In a preferred embodiment: the PWM control reference voltage loop includes resistors R13, R14, R15, R16, R17, capacitor C7, transistors Q3 and Q7;

[0015] Resistors R14, R15 and R16 are connected in series between the reference voltage and the ground; capacitor C7 and resistor R16 are connected in parallel; resistor R15 and resistor R14 are connected in parallel; resistor R15 is also connected to the base and collector of transistor Q3; the base of transistor Q3 is connected to the collector of transistor Q7, the emitter of transistor Q3 is connected to the emitter of transistor Q7 and is grounded; the base of transistor Q7 is connected to the PWM signal through resistor R17;

[0016] Capacitor C7 is also connected to the non-inverting input terminal of the second operational amplifier comparator.

[0017] In a preferred embodiment: also includes current sampling resistors RS1 and RS2; the sampling resistor RS2 is connected to the negative electrode of the DC output of the constant voltage converter, the sampling resistor RS1 and the sampling resistor RS2 are connected in parallel.

[0018] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0019] The present invention provides a constant current output circuit with PWM to analog current modulation and OVP protection function, which converts the full current on the sampling LED circuit into voltage and compares it with the reference voltage, and feeds back the closed loop to the control IC feedback FB port, the reference voltage can be controlled by PWM analog, and the high-precision small signal comparison amplification output is formed by an operational amplifier, which can ensure the dimming depth and accuracy requirements. The circuit of the present invention solves this problem very well, and the circuit is simple, the design is convenient, the cost is low, and it can be mass-produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a principle block diagram of a preferred embodiment of the present invention;

[0021] Figure 2 4 is a circuit diagram of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments, and all other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making creative work are within the scope of protection of the present invention.

[0023] In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "top / bottom" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0024] In the description of the present invention, it should be noted that, unless otherwise clearly stipulated and limited, the terms "installed", "provided with", "mounted / connected", "connected", etc. should be understood in a broad sense. For example, "connection" can be a wall-mounted connection, a detachable connection, or an integral connection. It can be a mechanical connection or an electrical connection. It can be a direct connection or an indirect connection through an intermediate medium. It can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0025] refer to Figure 1-Figure 2, this embodiment provides a constant current output circuit with PWM to analog current modulation and OVP protection function, including: a constant voltage converter, two operational amplifier comparators, a reference voltage generator, a PWM control reference voltage circuit, a voltage sampling circuit and a diode for voltage isolation;

[0026] An LED lamp bead is connected between the DC output positive electrode and the negative electrode of the constant voltage converter; the input ends of the reference voltage generator and the voltage sampling loop are respectively connected to the DC output positive electrode;

[0027] The output ends of the voltage sampling loop and the reference voltage generator are respectively connected to the two input ends of the first operational amplifier comparator; the output end of the reference voltage generator is also connected to the input end of the PWM control reference voltage loop; the output end of the PWM control reference voltage loop and the current sampling resistor Rcs voltage are respectively connected to the two input ends of the second operational amplifier comparator; the output ends of the first operational amplifier comparator and the second operational amplifier comparator are respectively connected to the cathodes of diodes D1 and D2, the anodes of diodes D1 and D2 are connected to each other and then connected to the input end of the optical coupler, the output end of the optical coupler is connected to the input end of the control IC, and the output end of the control IC is connected to the constant voltage converter.

[0028] In the above circuit, the negative pole of the LED lamp bead is connected to the negative pole of the DC output of the constant voltage converter through the sampling resistor Rcs. The current feedback loop is composed of the sampling resistor Rcs, the resistor R1, the second op amp comparator and the reference voltage generator. When the current is greater than the set value, the voltage of the resistor Rcs is higher than the reference voltage set by the reference voltage generator. The second op amp comparator feeds back the signal processing to the control IC, reducing the current output of the constant voltage converter so that the current flowing through the LED is the set current. Otherwise, the loop control principle is the same. The LED output voltage is compared with the reference voltage through the voltage sampling network sampling voltage. When the output voltage sampling value is greater than the reference voltage, the first op amp comparator outputs a signal to the control IC to turn off the output of the constant voltage converter to achieve the OVP protection function.

[0029] In order to realize the above concept, this embodiment provides a specific circuit such as Figure 2 As shown: the reference voltage generator is TL431, whose input end is connected to the DC output positive electrode through the voltage regulator ZD1 and the resistor R1; the reference voltage generator is used to generate the reference voltage and the VDD voltage. The voltage sampling loop includes resistors R5, R6, R7, R9 and capacitor C3;

[0030] One end of the resistor R6 is connected to the DC output positive electrode, and the other end is connected to the capacitor C3; the resistor R5 is connected in parallel with the resistor R6 and the capacitor C3; one end of the resistor R7 is connected to the capacitor C3 and the resistor R5, and the other end is grounded through the resistor R9; the connection point between the resistor R7 and the resistor R9 is connected to the input end of the first operational amplifier comparator.

[0031] The output end of the second operational amplifier comparator is connected to the feedback pin FB of the control IC through the optical coupler U4 and the diode D6.

[0032] The output end of the voltage sampling loop is connected to the inverting input end of the first operational amplifier comparator, and the output end of the reference voltage generator is connected to the positive input end of the first operational amplifier comparator;

[0033] The output end of the PWM control reference voltage loop is connected to the positive input end of the second op amp comparator, and the current sampling resistor Rcs voltage is connected to the reverse input end of the second op amp comparator. When the output current is greater than the set value, the reverse input voltage of the second op amp comparator is greater than the forward input voltage, the output voltage of the second op amp comparator decreases, and the output voltage of the optocoupler increases. The higher the voltage of the FB pin, the shorter the drive time of the converter, and the smaller the output current.

[0034] In addition, the PWM control reference voltage loop includes resistors R13, R14, R15, R16, R17, capacitor C7, transistors Q3 and Q7; resistors R14, R15 and R16 are connected in series between the reference voltage and ground; capacitor C7 and resistor R16 are connected in parallel; resistor R15 and resistor R14 are connected in parallel; resistor R15 is also connected to the base and collector of transistor Q3; the base of transistor Q3 is connected to the collector of transistor Q7, and the emitter of transistor Q3 is connected to the emitter of transistor Q7 and grounded; the base of transistor Q7 is connected to the PWM signal through resistor R17; capacitor C7 is also connected to the positive input terminal of the second operational amplifier comparator.

[0035] Finally, it also includes current sampling resistors RS1 and RS2; the sampling resistor RS2 is connected to the negative electrode of the DC output of the constant voltage converter, and the sampling resistor RS1 is connected in parallel with the sampling resistor RS2.

[0036] When the above circuit is working, the LED current flows through the current sampling resistors RS1 and RS2 to obtain a voltage that is divided by resistors R10 and R11 and input into the reverse input terminal of the second op amp comparator. The forward input terminal of the second op amp comparator is connected to 2.5*PWM duty cycle (0-2.5V), and the output terminal of the second op amp comparator is connected to the feedback pin FB of the control IC of the constant voltage converter through the diode D6 and the optical coupler U4. When the output current of the constant voltage converter is greater than the set value, the reverse input terminal voltage of the second op amp comparator is greater than the forward input terminal voltage. The lower the output voltage of the second op amp comparator, the greater the input current of the optical coupler U4, the higher the voltage of the FB pin of the control IC, the constant voltage converter reduces the driving time, and the output current becomes smaller. When the output LED current reaches the set value, the op amp input terminal reaches a balance, and the output current of the constant voltage converter remains unchanged to achieve the constant current function.

[0037] Adjusting the PWM duty cycle can change the voltage at the positive input of the second op amp comparator. When the voltage is lowered or increased, the second op amp comparator responds quickly, and the output of the second op amp comparator will accordingly become lower or higher. The input current through the optocoupler U4 becomes larger or smaller, and the voltage of the FB pin becomes higher or lower, adjusting the drive output of the converter to become lower or higher, thereby adjusting the LED output current to become smaller or larger. When the input of the second op amp comparator reaches a balance or the circuit is no longer changing, changing the PWM duty cycle will change the LED output current accordingly, realizing PWM to analog dimming.

[0038] The LED output voltage passes through the sampling resistors R5, R6, R7, R9, and C3 to form a sampling network. The sampling voltage signal is connected to the reverse input of the first op amp comparator. The forward input of the first op amp comparator is connected to the reference voltage 2.5V. The sampling network sampling voltage is equal to 2.5V, which corresponds to an LED output voltage Vovp. When Vled is less than Vovp, the reverse input of the first op amp comparator is less than 2.5V, which is less than the forward input voltage. The first op amp comparator outputs a high voltage, and the diode D5 is cut off. There is no signal feedback to the FB pin, and the LED works normally. When Vled is greater than Vovp, the reverse input of the first op amp comparator is greater than 2.5V, which is greater than the forward input voltage. The first op amp comparator outputs a low voltage, the diode D5 is turned on, the current of the optocoupler U4 increases, and the voltage of the FB pin becomes higher, which is higher than the internal protection limit of the control IC, and the output of the constant voltage converter is turned off to achieve LED voltage overvoltage protection.

[0039] In this embodiment, the constant voltage converter may be a DC-DC converter or an AC-DC converter.

[0040] The above is only a preferred specific implementation of the present invention, but the design concept of the present invention is not limited to this. Any technician familiar with the technical field who uses this concept to make non-substantial changes to the present invention within the technical scope disclosed by the present invention shall be deemed to infringe the protection scope of the present invention.

Claims

1. A constant current output circuit with PWM to analog current regulation and OVP protection function, characterized in that include: Constant voltage converter, 2 op amp comparators, reference voltage generator, PWM control reference voltage loop, voltage sampling loop and diode for voltage isolation; An LED lamp bead is connected between the DC output positive electrode and the negative electrode of the constant voltage converter; the input ends of the reference voltage generator and the voltage sampling loop are respectively connected to the DC output positive electrode; The output ends of the voltage sampling loop and the reference voltage generator are respectively connected to the two input ends of the first operational amplifier comparator; the output end of the reference voltage generator is also connected to the input end of the PWM control reference voltage loop; the output end of the PWM control reference voltage loop and the current sampling resistor Rcs voltage are respectively connected to the two input ends of the second operational amplifier comparator; the output ends of the first operational amplifier comparator and the second operational amplifier comparator are respectively connected to the cathodes of the diodes D1 and D2, the anodes of the diodes D1 and D2 are connected to each other and then connected to the input end of the optical coupler, the output end of the optical coupler is connected to the input end of the control IC, and the output end of the control IC is connected to the constant voltage converter; When the output current is greater than the set value, the voltage at the reverse input terminal of the second op amp comparator is greater than the voltage at the forward input terminal, the output voltage of the second op amp comparator decreases, and the output voltage of the optocoupler increases. The higher the voltage at the FB pin, the shorter the drive time of the converter and the smaller the output current.

2. A constant current output circuit with PWM to analog current regulation and OVP protection function according to claim 1, characterized in that: The reference voltage generator is TL431, and its input end is connected to the DC output positive electrode through a voltage regulator tube ZD1 and a resistor R1; the reference voltage generator is used to generate a reference voltage and a VDD voltage.

3. A constant current output circuit with PWM to analog current modulation and OVP protection function according to claim 2, characterized in that: The voltage sampling loop includes resistors R5, R6, R7, R9 and capacitor C3; One end of the resistor R6 is connected to the DC output positive electrode, and the other end is connected to the capacitor C3; the resistor R5 is connected in parallel with the resistor R6 and the capacitor C3; one end of the resistor R7 is connected to the capacitor C3 and the resistor R5, and the other end is grounded through the resistor R9; the connection point between the resistor R7 and the resistor R9 is connected to the input end of the first operational amplifier comparator.

4. A constant current output circuit with PWM to analog current modulation and OVP protection function according to claim 3, characterized in that: The output end of the second operational amplifier comparator is connected to the feedback pin FB of the control IC through the optical coupler U4 and the diode D6.

5. A constant current output circuit with PWM to analog current modulation and OVP protection function according to claim 4, characterized in that: The output end of the voltage sampling loop is connected to the inverting input end of the first operational amplifier comparator, and the output end of the reference voltage generator is connected to the positive input end of the first operational amplifier comparator; The output end of the PWM control reference voltage loop is connected to the positive input end of the second operational amplifier comparator, and the negative pole of the LED lamp bead is connected to the negative input end of the second operational amplifier comparator.

6. A constant current output circuit with PWM to analog current modulation and OVP protection function according to claim 2, characterized in that: The PWM control reference voltage loop includes resistors R13, R14, R15, R16, R17, capacitor C7, transistors Q3 and Q7; Resistors R14, R15 and R16 are connected in series between the reference voltage and the ground; capacitor C7 and resistor R16 are connected in parallel; resistor R15 and resistor R14 are connected in parallel; resistor R15 is also connected to the base and collector of transistor Q3; the base of transistor Q3 is connected to the collector of transistor Q7, the emitter of transistor Q3 is connected to the emitter of transistor Q7 and is grounded; the base of transistor Q7 is connected to the PWM signal through resistor R17; Capacitor C7 is also connected to the non-inverting input terminal of the second operational amplifier comparator.

7. A constant current output circuit with PWM to analog current modulation and OVP protection function according to claim 6, characterized in that: It also includes current sampling resistors RS1 and RS2; the sampling resistor RS2 is connected to the negative electrode of the DC output of the constant voltage converter, and the sampling resistor RS1 is connected in parallel with the sampling resistor RS2.

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