Systems, circuits, devices and methods related to voltage converters. In some embodiments, a control system for a voltage converter can include a driving unit configured to generate a driving signal having a pulse width and a frequency. The driving signal is provided to a voltage conversion circuit to control conversion of an input voltage into an output voltage. The control system can further include a modulation unit configured to modulate the pulse width of the driving signal based on the output voltage to thereby allow adjustment of the output voltage. The control system can further include a control circuit configured to adjust the frequency of the driving signal based on the modulated pulse width. Such a control system can be useful in situations such as when the output voltage is close to the input voltage, or when a load being driven by the output voltage is relatively low.