Discussion Overview
The discussion revolves around the use of Light Dependent Resistors (LDRs) as variable AC attenuators, specifically focusing on achieving very low on resistance values, ideally under 10 ohms. Participants explore circuit requirements, alternative solutions, and the limitations of LDRs in this application.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
- Mathematical reasoning
Main Points Raised
- One participant expresses a need for an LDR with an on resistance lower than 10 ohms, noting that available LDRs typically have a minimum resistance of 100 ohms.
- Another participant asks for more details about the circuit requirements, suggesting that there are other methods for creating variable attenuators.
- Voltage requirements are discussed, with one participant indicating a range from -600 to 0 volts and a current requirement of 0-100 mA.
- Audio frequencies are specified as the context for the application, which involves an amplifier needing adjustable impedance at a DC bias point.
- A participant reports issues with simulating a MOSFET in LTspice, questioning whether the simulation results are accurate or a glitch.
- Concerns about the capacitance of LDRs are raised, with one participant recalling a previous idea of using them in a pi network configuration but noting potential unsuitability due to internal capacitance.
- Another participant references a datasheet showing a 5 pF capacitance for LDRs, suggesting it may not significantly affect frequency response, but reiterates the concern about on resistance.
- One participant optimally desires an on resistance under 1 ohm, indicating a need for the lowest possible resistance.
- There is a request for a schematic to better understand the circuit, but the original poster declines to share due to the proprietary nature of their project.
- Some participants express skepticism about the feasibility of solving the problem through forum discussions without sharing detailed information.
Areas of Agreement / Disagreement
Participants generally agree on the challenges of using LDRs for low resistance applications, but multiple competing views remain regarding potential solutions and circuit configurations. The discussion remains unresolved regarding the best approach to achieve the desired attenuation.
Contextual Notes
Limitations include the dependence on specific circuit requirements, the potential impact of LDR capacitance on frequency response, and the unresolved nature of the simulation issues in LTspice.
