LED Driver Circuit Presets Gate Potential to Suppress Early Effect
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Solution Overview
Problem
Conventional LED driver circuits experience variations in output current due to the Early effect, leading to undesirable changes with output voltage fluctuations, necessitating a solution for maintaining constant current delivery.
Innovation Solution
The proposed LED driver circuit incorporates a current source, current mirror, amplifier, and presetting circuit with a delay circuit and logic to control the transistor's gate potential, ensuring constant current driving by using a combination of transistors and logic gates to manage voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a current mirror circuit is used to generate output current, then the circuit structure is simple, but the output current varies with output voltage due to the Early effect
Solution Approach 1:
The patent introduces a feedback mechanism where the amplifier detects the output voltage and adjusts the gate potential of the output transistor accordingly. The feedback signal is derived from the output voltage and fed back to the gate of the output transistor through the amplifier, creating a closed-loop system that automatically compensates for Early effect variations and maintains constant output current.
Solution Approach 2:
The patent dynamically changes the gate potential parameter of the output transistor based on output voltage variations. By adjusting the gate potential in response to output voltage changes, the circuit compensates for the Early effect and maintains stable output current, transforming a static parameter into a dynamically controlled one.
2Reliability
If cascade-connected transistors with amplifier feedback are used to suppress Early effect, then output current stability improves, but device complexity increases
Solution Approach 1:
The patent applies preliminary action by presetting the gate potential of the output transistor before the actual current driving operation begins. The presetting circuit prepares the gate potential in advance based on expected operating conditions, allowing the amplifier to start from an optimized initial state and reducing the complexity of continuous adjustment during operation.
3Speed
If the gate potential is preset with predetermined timing after control signal, then transient response characteristics improve, but circuit complexity increases due to presetting circuit
Solution Approach 1:
The presetting circuit performs preliminary action by setting the gate potential to an optimal value before the main current driving operation begins. This advance preparation ensures that when the control signal is applied, the transistor is already in a favorable state for rapid response, significantly improving transient response characteristics without requiring complex real-time adjustment mechanisms.
Solution Approach 2:
The presetting circuit operates periodically in sync with the control signal timing. It activates at specific intervals corresponding to the control signal periods, presetting the gate potential at the appropriate moment in each cycle. This periodic operation achieves improved transient response while keeping the presetting circuit relatively simple by only activating when needed.
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
The solution effectively maintains a constant output current by presetting the transistor's gate potential, reducing variations and improving transient response characteristics, thus stabilizing current delivery despite changes in output voltage.
Implementation Method 1
transistors N1 and N2 operate as a current mirror circuit so that when reference current Iref flows through transistor N2, the mirror current also flows through transistor N1, forming output current Io
Implementation Method 2
amplifier 104 operates as a negative feedback circuit, and the gate potential of output transistor N5 is controlled corresponding to variations in the output voltage, so that the output current can be kept constant
Implementation Method 3
the output current Io will vary with changes in the output voltage due to the Early effect
Data Source
AI summary
A driver is provided. The driver generally comprises a current source, a current mirror, an amplifier and a presetting circuit. The current source is generally adapted to provide a reference current to the current mirror. The transistor is coupled to the current mirror. The amplifier has the first input that is coupled to the current mirror, a second input that is coupled to a node between the transistor and the current mirror, and an output that is coupled to the control electrode of the transistor. The presetting circuit is coupled to the control electrode of the transistor so that it can preset the potential of the control electrode of the transistor to a potential that allows current driving of the transistor with a predetermined timing after a control signal is received.