Alternator voltage regulator teardown and analysis
My copy of KiCad is being stubborn today, so we'll need to make due with a hand drawn schematic.
This is a very simple circuit, using a large power transistor and a smaller transistor to switch the larger one. The switching transistor is controlled by a Zener diode, Z1 on the circuit. When the voltage rises high enough, it flows through the zener diode and turns on the smaller transistor, which switches the large one off. When the voltage is low enough, current through Z1 shuts off, the large transistor switches on, and grounds the field coil. There is a capcitive coupling between the output of the power transistor and the switching transistor that limits the maximum switching speed. The reason for this is that switching off the power transistor creates a large voltage spike, which the D1 diode dumps back into the supply voltage. If the switching is too rapid, this will send too much current through D1 and can burn out D1, or even the 12 volt feed wire.
This is a rather simple circuit and rather similar to Chrysler's original design that Mattix posted in the other thread. One conspicuously absent feature is any sort of temperature compensation; batteries often need more charging voltage at lower temperatures.
My copy of KiCad is being stubborn today, so we'll need to make due with a hand drawn schematic.
This is a very simple circuit, using a large power transistor and a smaller transistor to switch the larger one. The switching transistor is controlled by a Zener diode, Z1 on the circuit. When the voltage rises high enough, it flows through the zener diode and turns on the smaller transistor, which switches the large one off. When the voltage is low enough, current through Z1 shuts off, the large transistor switches on, and grounds the field coil. There is a capcitive coupling between the output of the power transistor and the switching transistor that limits the maximum switching speed. The reason for this is that switching off the power transistor creates a large voltage spike, which the D1 diode dumps back into the supply voltage. If the switching is too rapid, this will send too much current through D1 and can burn out D1, or even the 12 volt feed wire.
This is a rather simple circuit and rather similar to Chrysler's original design that Mattix posted in the other thread. One conspicuously absent feature is any sort of temperature compensation; batteries often need more charging voltage at lower temperatures.