Patent ID: 9662985
Date: 2017-05-30
CPC Classifications: B60L,H02M

Claim:
1. A control circuit for a step-up DC/DC converter, comprising: a switching terminal coupled to receive a voltage at a node connecting an inductor and a rectifier diode; a ground terminal coupled to receive a ground voltage; a switching transistor coupled between the switching terminal and the ground terminal; a pulse modulator that adjusts a pulse signal; and a driver that drives the switching transistor according to the pulse signal, wherein the switching transistor is configured such that its on resistance is switchable between at least two values, and wherein the switching transistor comprises a plurality of transistor elements connected in parallel such that their control terminals are provided independently, and wherein the control circuit is configured such that, when the switching transistor is switched from off to on, the control circuit sets the on resistance of the switching transistor to a first value for a first period immediately after the switching of the switching transistor, following which the control circuit sets the on resistance of the switching transistor to a second value that is smaller than the first value for a second period until the switching transistor is turned off, and wherein on/off states of the respective transistor elements are switched according to switching between the first period and the second period, thereby switching the on resistance of the switching transistor corresponding to a combined resistance of the plurality of switching elements, and wherein the first period is configured to have a length which is equal to or otherwise greater than the reverse recovery time of the rectifier diode.