LED constant current source control circuit capable of rapidly achieving steady state
By introducing an operational amplifier AMP, an NMOS transistor MN, a PMOS transistor MP, and a monostable circuit into the LED driver circuit, a 20ns instantaneous high pulse is generated to quickly reach a steady state, solving the delay problem caused by the gate capacitance of the NMOS transistor in the traditional circuit, improving the dimming accuracy and reducing the cost.
Patent Information
- Application Number
- CN202511267474.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-05
- Publication Date
- 2025-11-04
AI Technical Summary
In traditional LED driver circuits, the gate parasitic capacitance of the NMOS transistor causes the constant current source current to take too long to reach steady state, affecting the accuracy of PWM dimming.
By employing an operational amplifier AMP, an NMOS transistor MN, a PMOS transistor MP, a constant current source IB, and a monostable circuit, a 20ns instantaneous high pulse is generated to quickly raise the gate voltage of the NMOS transistor MN to near the steady-state voltage, thereby shortening the time to reach steady state.
It greatly shortens the LED turn-on time delay, improves PWM dimming accuracy, and achieves fast steady-state without increasing additional power consumption. The structure is simple and the cost is low.
Smart Images
Figure CN120897291A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of circuit, in particular to the technical field of LED driving circuit structure, and more particularly to an LED constant current source control circuit capable of reaching steady state quickly. BACKGROUND
[0002] In the LED driving circuit, in order to improve the PWM dimming precision, it is required to quickly turn on the constant current source of the LED and make the current of the constant current source reach steady state in a very short time.
[0003] The conventional LED driving circuit is shown in FIG. 1. Figure 1 When different reference voltages are set, the current of the LED is as follows: (1) When the PWM signal is high, the circuit starts to work, and the gate voltage GATE of the NMOS tube MN starts to rise. Due to the power consumption limit and the influence of the parasitic capacitance C of the gate of MN, the time t required for the gate voltage of MN to reach steady state from zero is: (2) The capacitance C is the parasitic capacitance of the gate of MN, V GS is the voltage difference between the gate and the source of MN, and I is the current provided by the output stage of the operational amplifier AMP.
[0004] Usually, the parasitic capacitance C of the gate of the NMOS tube MN is about 10 pF, if V REF is set to 1 V, V GS is set to 1 V, and the current provided by the output stage of the operational amplifier is 10 uA. Then, according to formula (2), the time required for the NMOS tube MN to reach steady state is about 2 us. The delay of 2 us will have a great influence on the precision of PWM dimming. For example, if the PWM signal is 100 KHz and the duty cycle is 50%, the theoretical on-time of the LED constant current source in one period is 5 us. However, due to the influence of the delay of 2 us, the actual on-time of the LED to maintain the theoretical current value in one period is only 3 us.
[0005] Therefore, how to provide a control circuit capable of reaching steady state quickly has become a problem to be solved in the field. SUMMARY
[0006] The present application aims to overcome the above-mentioned shortcomings in the prior art and provide an LED control circuit capable of reaching steady state quickly.
[0007] In order to achieve the above-mentioned purpose, the LED constant current source control circuit of the application for quickly reaching steady state comprises an operational amplifier AMP and an NMOS tube MN, a plurality of LEDs are connected in series between an input voltage VIN and the drain of the NMOS tube MN, the non-inverting input terminal of the operational amplifier AMP is connected with a reference voltage V REF , the inverting input terminal is connected with the source of the NMOS tube, the signal input terminal is connected with a PWM signal, the output stage is connected with the gate of the NMOS tube MN, and further comprises a constant current source I B , a monostable circuit and a PMOS tube MP, the input terminal of the monostable circuit is connected with the PWM signal, the output terminal of the monostable circuit is connected with and controls switches S1 and S2; when the PWM signal is high, the monostable circuit generates a transient high pulse and controls the switches S1 and S2 to be connected, the front end of the constant current source I B is connected with a power supply VDD, and the rear end of the constant current source I B is connected with the gate of the NMOS tube MN through the switch S1; the gate of the PMOS tube MP is connected with the reference voltage V REF , the source is connected with the gate of the NMOS tube MN through the switch S2, and the drain is grounded.
[0008] In the LED constant current source control circuit for quickly reaching steady state, the length t of the transient high pulse generated by the monostable circuit is 20 ns.
[0009] In the LED constant current source control circuit for quickly reaching steady state, the constant current source I B is determined according to the following formula: Wherein, C is the gate parasitic capacitance of the NMOS tube MN, V GS is the gate-source voltage of the PMOS tube MP.
[0010] In the LED constant current source control circuit for quickly reaching steady state, the PWM signal is a 100KHz PWM dimming signal with a duty ratio of 50%, and the LED conduction time in one period is 4.98us.
[0011] When the PWM signal is high, the OneShot monostable circuit generates a transient high pulse with a time of about 20ns, the signal turns on the switches S1 and S2, and the bias current I BThe gate voltage of the NMOS tube MN is rapidly pulled to the vicinity of the steady state voltage, thereby greatly shortening the delay of the LED conduction time, greatly improving the LED dimming precision, and the circuit does not generate additional static power consumption, has simple structure, and is very low in application cost. BRIEF DESCRIPTION OF DRAWINGS
[0012] Figure 1 The traditional LED driving circuit is shown in Fig. 1. Figure 2 The LED constant current source control circuit for rapidly reaching steady state is shown in Fig. 2. DETAILED DESCRIPTION
[0013] In order to more clearly understand the technical content of the present application, the following embodiments are described in detail.
[0014] Please refer to Figure 2 The LED constant current source control circuit for rapidly reaching steady state is shown in Fig. 2.
[0015] In an embodiment, the LED constant current source control circuit for rapidly reaching steady state comprises an operational amplifier AMP and an NMOS tube MN, a plurality of LEDs are connected in series between an input voltage VIN and the drain of the NMOS tube MN, the non-inverting input terminal of the operational amplifier AMP is connected to a reference voltage V REF , the inverting input terminal is connected to the source of the NMOS tube, the signal input terminal is connected to a PWM signal, and the output stage is connected to the gate of the NMOS tube MN.
[0016] The LED constant current source control circuit for rapidly reaching steady state further comprises a constant current source I B , a monostable circuit and a PMOS tube MP, the input terminal of the monostable circuit is connected to the PWM signal, and the monostable circuit output terminal is connected to and controls switches S1 and S2; when the PWM signal is high, the monostable circuit generates a transient high pulse and controls the switches S1 and S2 to be connected, the front end of the constant current source I B is connected to a power supply VDD, and the back end of the constant current source I B is connected to the gate of the NMOS tube MN through the switch S1; the gate of the PMOS tube MP is connected to the reference voltage V REF , the source is connected to the gate of the NMOS tube MN through the switch S2, and the drain is grounded.
[0017] In a preferred embodiment, the length t of the transient high pulse generated by the monostable circuit is 20 ns. The constant current source I B is determined according to the following formula: wherein C is the gate parasitic capacitance of NMOS transistor MN, V GS is the gate-source voltage of PMOS transistor MP. The PWM signal is a 100KHz PWM dimming signal with duty cycle of 50%, so the LED on-time is about 4.98us in one period.
[0018] In the application of the present application, the LED constant current source control circuit of the present application can quickly reach steady state according to the gate parasitic capacitance C of NMOS transistor MN and the reference voltage V REF , and set the bias current I B to a value so that the gate voltage GATE of NMOS transistor MN is charged to the vicinity of the steady state point within 20ns, i.e. V REF + V SG2 , wherein V SG2 is the source-gate voltage of PMOS transistor MP. After the 20ns high pulse, both switches S1 and S2 are in the off state. Compared with the conventional circuit, the present application does not generate additional power consumption. Since the present application greatly shortens the delay of LED on-time, the dimming accuracy is also greatly improved. Similarly, for a 100KHz PWM dimming signal with duty cycle of 50%, the LED current on-time is about 4.98us of the theoretical value in one period.
[0019] Under the same conditions, the conventional circuit needs about 2us to reach steady state from the start, while the control circuit of the present application only needs about 20ns. Since the time to reach steady state is greatly reduced, the PWM dimming accuracy is improved. At steady state, the present application does not increase the power consumption compared with the conventional circuit.
[0020] When the PWM signal is high, the OneShot monostable circuit generates a transient high pulse with a time of about 20ns, which turns on switches S1 and S2, and the bias current I B quickly pulls up the gate voltage of NMOS transistor MN to the vicinity of the steady state voltage, thereby greatly shortening the delay of LED on-time and greatly improving the LED dimming accuracy. The circuit of the present application does not generate additional static power consumption, has a simple structure, and is very low in application cost.
[0021] In this specification, the present application has been described with reference to its specific embodiments. However, it is obvious that various modifications and changes can be made without departing from the spirit and scope of the present application. Therefore, the specification and drawings should be considered as illustrative rather than limiting.
Claims
1. A fast steady-state LED constant current source control circuit, comprising an operational amplifier AMP and an NMOS transistor MN, wherein a plurality of LEDs are connected in series between an input voltage VIN and the drain of the NMOS transistor MN, and the non-inverting input terminal of the operational amplifier AMP is connected to a reference voltage V. REF Its inverting input is connected to the source of the NMOS transistor, its signal input is connected to the PWM signal, and its output stage is connected to the gate of the NMOS transistor MN. Its features are, Also includes constant current source I B A monostable circuit and a PMOS transistor MP are used. The input of the monostable circuit is connected to the PWM signal, and the output of the monostable circuit is connected to and controls switches S1 and S2. When the PWM signal is high, the monostable circuit generates a momentary high pulse and controls switches S1 and S2 to connect. The constant current source I... B The front end is connected to the power supply VDD, and the constant current source I... B The rear end is connected to the gate of the NMOS transistor MN via the switch S1; the gate of the PMOS transistor MP is connected to the reference voltage V. REF Its source is connected to the gate of the NMOS transistor MN through the switch S2, and the drain of the PMOS transistor MP is grounded.
2. The LED constant current source control circuit for rapidly reaching steady state according to claim 1, characterized in that, The duration t of a momentary high pulse generated by the monostable circuit is 20 ns.
3. The LED constant current source control circuit for rapidly reaching steady state according to claim 2, characterized in that, The constant current source I B Determined according to the following formula: Where C is the gate parasitic capacitance of the NMOS transistor MN, V GS This is the gate-source voltage of the PMOS transistor MP.
4. The LED constant current source control circuit for rapidly reaching steady state according to claim 2, characterized in that, The PWM signal is a 100kHz PWM dimming signal with a 50% duty cycle, and the LED conduction time is 4.98µs in one cycle.