LED Driver Chopper Circuit Reduces Impedance Power Loss
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Solution Overview
Problem
Conventional LED lighting devices with step-down choppers face challenges in reducing power loss and achieving desired temperature characteristics for switching elements, while also maintaining stable output current and harmonic standards.
Innovation Solution
The LED lighting device incorporates a self-excited drive signal generation circuit and a turn-off circuit with a comparator to control the switching element, reducing impedance power loss and providing a satisfactory temperature characteristic, along with an overvoltage protection circuit and a photocoupler for light adjustment, to ensure stable operation and harmonic compliance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a resistor element is connected between the FET and the transistor to enable turning off of the FET, then the switching operation can be accurately performed, but the power loss of the resistor element increases
Solution Approach 1:
A capacitor is introduced as an intermediary energy storage element between the FET and transistor. The capacitor charges during FET conduction and discharges to provide the turning-off signal for the transistor, eliminating the need for a power-lossy resistor while maintaining accurate switching timing control.
Solution Approach 2:
The patent changes the parameter of the switching control mechanism from a resistive voltage divider to a capacitive charging/discharging system. This parameter change allows the turning-off timing to be controlled by capacitor discharge characteristics rather than resistive voltage drops, significantly reducing power loss while maintaining timing accuracy.
2Loss of energy
If the impedance of the impedance means is reduced to decrease power loss, then the power loss decreases, but the temperature characteristic becomes difficult to control
Solution Approach 1:
The patent implements a feedback mechanism where the capacitor voltage (which reflects the integrated current over time) is fed back to control the transistor switching. This feedback allows the system to maintain stable temperature characteristics by adjusting the switching timing based on actual operating conditions, while using low-impedance paths to minimize power loss.
3Loss of energy
If the base bias voltage is reduced to minimize power consumption, then power consumption decreases, but the transistor turning-on reliability decreases
Solution Approach 1:
The capacitor is pre-charged during the FET conduction period before the transistor needs to turn on. This preliminary charging action ensures that when the FET turns off, the capacitor has sufficient voltage to reliably trigger the transistor without requiring high continuous base bias current, thus minimizing power consumption while maintaining turning-on reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration significantly reduces impedance power loss, stabilizes output current, and meets harmonic standards, enhancing the efficiency and reliability of the LED lighting device.
Implementation Method 1
a self-excited drive signal generation circuit that includes a second inductor magnetically coupled with the first inductor of the step-down chopper and that applies a voltage induced in the second inductor to a control terminal of the switching element as a drive signal to keep the switching element on
Implementation Method 2
comparison means that detects a voltage of the impedance means in the step-down chopper and that outputs, when the detected voltage exceeds a reference value, an output voltage
Implementation Method 3
a switch element that is turned on by the output voltage of the comparison means such that an output terminal of the self-excited drive signal generation circuit is short-circuited and that the switching element is thus turned off
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
There is provided an LED lighting device having a satisfactory temperature characteristic and a small amount of variation in output current. The step-down chopper is provided with a first circuit including the switching element, the impedance means and a first inductor connected in series and a second circuit including the first inductor and a diode connected in series. A self-excited drive signal generation circuit is provided with a second inductor magnetically coupled with the first inductor and applies a voltage induced in the second inductor to the switching element to keep the switching element on. A turn-off circuit outputs an output voltage when the voltage of the impedance means detected by a comparator exceeds the reference value, and the output voltage allows a switching element to turn on to short-circuit the output terminals of the self-excited drive signal generation circuit, resulting in that the switching element is turned off.