Self-Excited Push-Pull Converter With Constant Current Base Bias
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Solution Overview
Problem
Existing self-excited push-pull converters face issues with poor adaptability to increasing operating voltages, leading to increased no-load loss and decreased conversion efficiency, as well as poor surge handling capabilities, which can damage transistors.
Innovation Solution
Incorporating a constant current source between the base of the transistors and the power supply end, replacing the traditional bias resistor, to maintain a constant base current and prevent excessive collector current, thereby entering a new push-pull oscillation mode that limits transistor operation within safe parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a traditional bias resistor is used between the base of the transistors and the power supply end, then the circuit structure is simple, but the no-load loss increases and conversion efficiency decreases at elevated operating voltages
Solution Approach 1:
The patent changes the electrical parameter characteristics by replacing the passive bias resistor with an active constant current source circuit. This circuit uses transistors (Q3, Q4), resistors (R3, R4, R5), and capacitor C2 to create a circuit that actively regulates base current, transforming the biasing mechanism from voltage-dependent to current-stable, thereby reducing no-load loss at elevated voltages
Solution Approach 2:
The patent introduces an intermediary constant current source circuit between the power supply and the transistor bases. This intermediary circuit (comprising Q3, Q4, R3, R4, R5, C2) acts as a buffer that decouples the direct voltage relationship, providing stable base current while isolating the main power circuit from voltage fluctuations, thus reducing energy loss
2Device complexity
If a traditional bias resistor is used between the base of the transistors and the power supply end, then the device complexity is low, but the conversion efficiency decreases at elevated operating voltages
Solution Approach 1:
The patent transforms the bias circuit from a simple resistive voltage divider to an active current-regulating circuit. By changing the operational parameters from voltage-based to current-based control using transistors Q3 and Q4, the circuit achieves superior energy efficiency and conversion performance at elevated operating voltages despite increased component count
3Power
If the operating voltage increases, then the power supply capability is enhanced, but the transistor current increases excessively causing damage
Solution Approach 1:
The patent implements negative feedback through resistors R4 and R5 in the constant current source circuit. This feedback mechanism continuously monitors the current flow and adjusts the base drive signals to transistors Q1 and Q2, preventing excessive current when operating voltage increases, thereby protecting the transistors from damage while maintaining power supply capability
Solution Approach 2:
The patent applies preliminary protective action by designing the constant current source circuit to preemptively limit base current before excessive collector current can develop. The circuit proactively regulates current flow through transistors Q3 and Q4, preventing the conditions that would lead to transistor overload and damage before they occur
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 solution significantly reduces no-load power consumption and increases conversion efficiency at elevated operating voltages, while providing enhanced surge protection and maintaining stable operation.
Implementation Method 1
Incorporating a constant current source between the base of the transistors and the power supply end, replacing the traditional bias resistor, to maintain a constant base current
Implementation Method 2
the two ends of primary coils NB1 and NB2 of the coupling transformer B... The secondary coil NS of coupling transformer B is connected with the output filter circuit
Implementation Method 3
C1, parallel connected with bias resistor R1... the capacitor C (parallel connected between the collectors of the push-pull transistors)
Implementation Method 4
Due to the inductance L1 in series with the power supply circuit... the circuit output is close to the sine wave
Data Source
AI summary
A self-excited push-pull converter, where between the bases of the push-pull converter's transistors (TR1, TR2) and the effective power suppler there is provided a constant current source (II), which provides a constant current to the bases of the transistors. With the working voltage increases, the circuit enters into an operating mode not based on the core-saturation working mode, because the transistors' base current is limited by the constant current source and consequently the transistors' collector current cannot increase.