Explain how linear and switching regulators hold voltage steady, read Figure E7-2, and calculate battery time and regulator heat.
Syllabus: Power supplies and voltage regulators; solar array charge controllers
Compendium articles on the ideas in this lesson, beyond what the exam asks.
Practise the 15 pool questions for this group. Answers are shuffled, and every one comes with a one-line "why".
A Zener diode is the stable voltage reference. It holds the transistor's base steady. The pass transistor (Q1) conducts more or less current so the output stays constant. Nothing is switched, so it is a linear regulator.
RememberZener = reference. Pass transistor = varied conduction keeps the output constant. C2 bypasses ripple around D1.
A series regulator puts the control element in the path (three-terminal IC regulators are this kind). A shunt regulator puts it across the output, so it loads the unregulated source.
A series regulator turns the excess voltage into heat. Dropout voltage is the minimum input-to-output difference needed to keep regulating.
RememberHeat = (input voltage − output voltage) × output current. Dropout = minimum input-to-output voltage.
A switchmode regulator switches the input fully on and off. The duty cycle of those pulses, fed to a filter, sets the average output.
It switches at a high frequency, so the transformer and filter parts can be much smaller. That makes it lighter and cheaper than an equivalent linear supply.
RememberSwitchmode: vary the duty cycle of pulses into a filter. High frequency means small parts.
Filter capacitors in series share the voltage by their leakage, which is never equal. Equal resistors across each one force an even split. The same resistors also discharge the capacitors when power is off and supply a minimum load: all three are correct.
A step-start limits turn-on current so the filter capacitors charge gradually.
RememberEqual resistors: equalize voltage, discharge, minimum load. Step-start: gradual capacitor charging.
Solar panels and batteries are DC. An inverter turns that DC into AC.
RememberOperating time = capacity (Ah) ÷ average current (A). Inverter = DC to AC.