| 摘要 |
A modified bootstrap circuit utilized, for example, in a high voltage DC/DC CMOS buck converter to convert a high input voltage (e.g., 24V) to a regulated voltage (e.g., 4V) for use, for example, by an LED driver circuit. The bootstrap circuit utilizes a feedback diode and a PMOS switch to avoid high reverse diode voltages across a low voltage bootstrap diode. A bootstrapped buck converter implements the bootstrap circuit to generate a high gate voltage on a high-side NMOS switch during all operating phases. The PMOS switch is controlled by the NMOS switch's output voltage to pass a system voltage (e.g., 5V) through the bootstrap diode whenever the output voltage drops low (e.g., 0V), and to shut off when the output voltage subsequently rises such that the feedback diode forward biases to pass the output voltage to the anode of the bootstrap diode.
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