Buffer amplifier and LED improve PWM power

Posted on Sep 6, 2012

Figure 2 shows another approach that requires additional components but delivers the full magnitude of the voltage ramp to Pin 3 of IC1 and provides the approximately 1V-dc offset that Reference 1 requires. Transistors Q1 and Q2, resistors R1 and R2, and LED D3 form an emitter-follower amplifier for the ramp voltage available at IC1, Pin 7 across timing capacitor C1. This arrangement provides reliable current-mode operation over the full range from no-load to full-load output current by delivering a sawtooth drive with a dc offset to IC1`s ramp input. Diode D3, a yellow LED, performs a 1.7V level translation without introducing any substantial signal loss. The component values not shown depend on the application.

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