DETECTION AND CONTROL MECHANISM FOR TAIL CURRENT IN A BIPOLAR JUNCTION TRANSISTOR (BJT)-BASED POWER STAGE

摘要

A bipolar junction transistor (BJT) may be used in a power stage DC-to-DC converter, such as a converter in LED-based light bulbs. A closed-loop control system may be implemented with the power stage to monitor a tail current of the BJT. The closed-loop control system may include a first comparator for monitoring a base voltage while a pull-down current source is coupled to the base of the BJT. Additionally, a second comparator may be included for monitoring the base voltage after the pull-down current source is decoupled from the base of the BJT. The delay time for turning off the BJT may be determined by monitoring output from the first and second comparators. The forward base current applied to the base of the BJT may be adjusted based on the determined delay time to reduce the delay time and thus reduce excess power dissipation by the BJT.

主权项

1. A method, comprising:
switching on a control signal to operate a bipolar junction transistor (BJT) for a first time period to charge an energy storage device; driving forward base current to a base of the bipolar junction transistor (BJT) during the first time period at a first current level; switching off the control signal to operate the bipolar junction transistor (BJT) for a second time period to discharge the energy storage device to a load; determining a time period for current through the bipolar junction transistor (BJT) to decay to below a threshold current value after switching off the control signal; and adjusting the first current level based, at least in part, on the determined time period.