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Close the switch! Middle potentiometer varies output voltage. Potentiometer on the left veries current limit threshold.
Further inspecting the previous version I decided it's more prudent to place the current sensing resistor in the collector chain of the output transistors, because voltage variations in the collector chain do not influence the output of an emitter follower. Also, I've decided to abandon the discrete high side current sensing because it's highly unreliable. Extremely small variations in any of the surrounding components, lead to great errors in measurement. I've decided to go with the MAX471 incorporated current sensing IC. It has an incorporated 35mOhm sensing resistor and doesn't require any external components, just a 2k pulldown output resistor, and provides reasonable error rate throughout the required measurement range. The output ranges from 0V to 30V with current protection range from 20mA to 3A. The circuit still isn't final, further revisions include stability improvements against oscillations, a proper reference voltage source, a proper relay driver, and an overshoot protection, specifically characteristic to the design. The negative supply rail will enable with a delay, and so will the current protection. Instantaneous power surges at power on may occur if the output is shorted, which may damage some of the components. Appropriate op amps for the circuit are LF412ACN.
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