BJT Power Converter Controller Using Control Winding Short-Circuit
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Solution Overview
Problem
Switched-mode power converters (SMPCs) using bipolar junction transistors (BJTs) face challenges in achieving high efficiency and cost-effectiveness due to BJTs' slower switching characteristics, requiring innovative control methods to minimize switching losses and stabilize operation under varying conditions, especially in self-oscillating converters with capacitive series elements.
Innovation Solution
The method involves controlling a self-oscillating power converter by selectively providing a short-circuit across a control winding, monitoring the load winding current, and removing the short-circuit when the current drops below a threshold, while also using a current monitoring element to adjust the timing of clamp removal and power source connection to minimize switching losses and ensure stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If BJTs are used as switching elements in SMPC, then cost is reduced, but switching efficiency deteriorates due to slower switching characteristics
Solution Approach 1:
The control circuit applies a short-circuit clamp to the control winding before the BJT switches off, preparing the magnetic field in advance to facilitate faster current commutation. This preliminary action reduces the storage period and linear period of the BJT switching transition, thereby reducing switching losses while maintaining cost-effectiveness of BJT usage
Solution Approach 2:
The control circuit monitors the current in the control winding and uses this feedback to determine the optimal timing for applying and removing the short-circuit clamp. This feedback mechanism ensures that the clamp is applied at the precise moment when it can most effectively accelerate switching transitions, minimizing switching losses while maintaining BJT cost advantages
2Loss of energy
If a short-circuit clamp is applied to the control winding to accelerate BJT switching, then switching efficiency is improved, but device complexity increases
Solution Approach 1:
The control circuit combines multiple functions into a single integrated controller that simultaneously monitors control winding current, determines clamp timing, and controls the short-circuit switch. This merging of functions reduces overall device complexity despite adding the clamp mechanism, as it eliminates the need for separate monitoring and control circuits
Solution Approach 2:
The control winding serves multiple purposes: it provides base drive current to the BJT, enables current sensing for timing detection, and acts as the target for the short-circuit clamp to accelerate switching. This multi-functionality reduces the need for additional dedicated components, thereby limiting the increase in device complexity
3Loss of energy
If the short-circuit clamp timing is optimized to minimize switching losses, then switching efficiency is improved, but control precision requirements increase
Solution Approach 1:
The control circuit replaces mechanical or fixed-timing clamp mechanisms with an electronically controlled switch that is timed based on real-time current monitoring. This substitution allows for precise, adaptive timing control that can be accurately set and maintained, reducing the impact of manufacturing tolerances on clamp timing precision
4Loss of energy
If current monitoring is used to determine clamp removal timing, then switching efficiency is improved, but additional components are required
Solution Approach 1:
The control winding serves dual purposes: providing base drive current to the BJT and enabling current sensing for timing detection. By using the existing control winding for both switching control and current monitoring, the invention avoids adding dedicated sensing components, thereby limiting the increase in device complexity while still achieving optimized clamp removal timing
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 approach optimizes switching efficiency, reduces power consumption under no-load conditions, and maintains stable operation by accurately controlling the switching frequency and load sensing, thereby enhancing the overall performance and efficiency of SMPCs while minimizing additional component costs.
Implementation Method 1
the base of the BJT being connected to a drive winding, said drive winding being magnetically coupled to a load winding
Implementation Method 2
providing a controlled collapse of the magnetic field generated by current flowing in the control winding, thereby forcing turn-off of the BJT
Implementation Method 3
monitoring the current flowing in the load winding by reference to the current in the control winding
Data Source
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AI summary
A power converter controller and methods for its operation are provided that can control a power converter using estimates of the output power of the converter without requiring a connection to the secondary side of the converter transformer. A self-oscillating power converter that uses a Bipolar Junction Transistor (BJT) as a switch by manipulating the current flowing in a control winding is also provided. The controller is able to determine the optimum time to remove a short circuit applied to the control winding, as well as being able to determine the optimum time to pass current through the control winding. The controller can further draw power from the power converter using the control winding. The controller is capable of maintaining the midpoint voltage of the power converter in the case that the converter has more than one switch. The controller further controls entry and exit into a low-power mode in which converter oscillations are suppressed.