Attached is a simplified diagram of my motorcycle's charging circuit. It has a standard 3-phase bridge rectifier circuit--simple enough.

I'm confused about two things:

  1. How is the voltage regulator regulating the voltage here? Only one phase is connected to the regulator which appears only to have a ground.
  2. How does this regulator function? All the example regulator circuits on the internet are either linear regulators or Zener diode reglators. This one seems to involve a thyristor and a diode.

1977 Suzuki GS400X charging circuit:

1977 Suzuki GS400X Charging Circuit

  • \$\begingroup\$ No field winding? \$\endgroup\$
    – winny
    Sep 7, 2018 at 12:28

2 Answers 2


This SCR (not Triac) seems to shunt the core with one phase diode and reverse bias the other phase diode to reduce the generator output in order to regulate. The R divider biases the trigger threshold for 14.2V.

Not as mechanical load efficient as 3 SCR's but works.

Lambda used TRIAC bridges in the old days (the '70's) to pre-regulate DC before higher linear stages as a lab. power supplies. That improved efficiency "somewatt" before SMPS came on the scene.

  • 1
    \$\begingroup\$ Just a nitpick: the symbol used in the schematic is that of an SCR, not that of a TRIAC. \$\endgroup\$ Sep 7, 2018 at 14:26

Old question, but interesting schematic - I would say smarter than today's rectifier-regulators :) Look at the phase on the top(W/G) - it is connected to the rectifier ONLY if lighting switch is ON - i.e. when there is big consumption, and this phase is not regulated!(consumption from the lights is more than a phase energy, suppose) Second phase(W/Bl) connected directly(not regulated, consumption enough) and third phase(Y) is regulated with regulator to ground(over voltage protection).


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