Hi,
I have a current limited power supply driving an active-rectifier which will operate a PWM to charge a super-capacitor. In the attached circuit the PWM has been replaced with a diode but the principle is the same (say 100% duty cycle).
Because the super-caps overwhelm the power supply the voltage increases steadily up to 5V at which point the PWM will end. At around 4.5V the power may enable to a USB device and since there's no inductance on the output, that's where the fun starts.
According to LTSpice the ripple is minimal but when I built it in real-life at around 4.75V the USB device I had attached (a Garmin) had visual issues and crashed. I believe (I'm awaiting a new oscilloscope to verify) that the ripple when the capacitor reaches saturation point is greater than simulated. I haven't built it with a PWM yet only using a diode, but that's my theory.
As the AC frequency is low this requires a very large inductor (10H as shown) to smooth the ripple. I'm not an analog engineer and do wonder if there's another way?
Regards,
Andrew
I have a current limited power supply driving an active-rectifier which will operate a PWM to charge a super-capacitor. In the attached circuit the PWM has been replaced with a diode but the principle is the same (say 100% duty cycle).
Because the super-caps overwhelm the power supply the voltage increases steadily up to 5V at which point the PWM will end. At around 4.5V the power may enable to a USB device and since there's no inductance on the output, that's where the fun starts.
According to LTSpice the ripple is minimal but when I built it in real-life at around 4.75V the USB device I had attached (a Garmin) had visual issues and crashed. I believe (I'm awaiting a new oscilloscope to verify) that the ripple when the capacitor reaches saturation point is greater than simulated. I haven't built it with a PWM yet only using a diode, but that's my theory.
As the AC frequency is low this requires a very large inductor (10H as shown) to smooth the ripple. I'm not an analog engineer and do wonder if there's another way?
Regards,
Andrew