Voltage Generator Base Current Compensation Circuit
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Solution Overview
Problem
Conventional base current compensation circuits in voltage regulators limit the range of output voltage regulation due to the requirement for Vref to be at least 0.3 volts below ground, restricting the allowable Vout range and not functioning adequately in floating configurations.
Innovation Solution
A base current compensation technique that directly compensates the current source setting Vref, allowing operation independent of Vref and Vout levels by adjusting the current drawn through the Rset resistor, applicable to both positive and negative voltage regulators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional base current compensation circuit is used, then the base current error is compensated, but the output voltage range is limited to at least 0.3 volts below ground
Solution Approach 1:
The compensation circuit is segmented into two independent parts: (1) a base current sensing circuit that measures the base current of the input transistors, and (2) a compensation current injection circuit that adds the measured base current to the reference voltage node. This segmentation allows the compensation function to operate independently of the output voltage level, enabling regulation down to ground potential.
Solution Approach 2:
An intermediary current mirror circuit is introduced to transfer the base current measurement to the reference voltage node without requiring a direct connection between the compensation circuit and the output voltage. This intermediary mechanism decouples the compensation function from the output voltage level constraints.
2Reliability
If the reference voltage is set 0.3 volts below ground for compensation, then base current compensation works, but floating configurations cannot be supported
Solution Approach 1:
The compensation circuit is designed with universal applicability to multiple regulator configurations (grounded and floating) by using a differential voltage sensing approach that measures the voltage difference across the base-emitter junctions rather than referencing to a fixed ground potential. This allows the circuit to function reliably in both grounded and floating configurations.
Solution Approach 2:
The circuit parameters (particularly the sensing voltage levels and current mirror scaling factors) are designed to be scalable and adjustable based on the specific application requirements. This allows the same basic compensation topology to be adapted to different output voltage ranges, including floating configurations where the entire regulator operates at a non-ground potential.
3Device complexity
If a fixed reference voltage is used, then the circuit is simple, but the output voltage cannot be regulated close to ground
Solution Approach 1:
The reference voltage is made dynamic rather than fixed by using a current source that generates a voltage proportional to the measured base current. This dynamic reference voltage automatically adjusts with operating conditions, enabling the output to be regulated close to ground while maintaining proper compensation. The dynamic nature adds minimal complexity compared to a fixed reference.
Data Source
AI summary
In one embodiment, a regulator circuit for generating a regulated output voltage Vout has an error amplifier using a pair of bipolar transistors at its front end. The error amplifier compares the regulated output voltage to a reference voltage Vref. A precision current source draws a first current through a user-selected set resistance to generate the desired Vref. The regulator circuit controls a power stage to cause Vout to be equal to Vref. The base current into one of the bipolar transistors normally distorts the current through the set resistance. A base current compensation circuit is coupled to the current source to adjust the first current by a value equal to the base current to offset the base current. Therefore, Vref is not affected by the base current. The error amplifier may be in a linear regulator or a switching regulator. The compensation circuit may be used in other applications.