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Tool/software:
Hi.
I am working on implementing a slow peak detector for our power converter, with the goal of detecting output overloads. We have a circuit that monitors the converter's input current and converts it into a PWM signal. At full load, the PWM signal has a peak voltage of 400mV, a duty cycle of 30%, and a frequency of 100kHz. The peak detector is designed to have a slow response to avoid detecting inrush current at startup, which could trigger a false overload flag and shut down the controller (This inrush current can last 100ms).
The circuit performed well at 25°C and 60°C, but when I tested it at 0°C, issues arose. Now, the circuit no longer functions correctly, and the problem appears to be related to the capacitor. Interestingly, when I connect an oscilloscope probe, the circuit operates as expected, and the capacitor voltage is 240mV (which is acceptable) and can work the entire day (I tested myself). However, without the probe, the capacitor overcharges beyond 400mV, triggering the overload flag (this happens after 5-10min). When I measure with a multimeter, I notice the capacitor discharges through the multimeter, which I assume is a similar effect to what happens with the oscilloscope.
Do you have any idea what might be causing this behavior?
P.S.: The picture shows a 100MΩ resistor because PSPICE wouldn't allow me to leave that pin floating.
Hi Jacob.
I noticed that I placed the resistor as a pull-down resistor (1 MΩ) at the output of the diode, and it works fine. However, when I placed it in parallel with the capacitor, the signal doesn’t increase at all.
