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How to compute RC charge time in Python using UliEngineering

You can easily compute the RC charge time to reach a target voltage using the UliEngineering Python library:

rc_charge_time.py
from UliEngineering.Electronics.RC import rc_charge_time
from UliEngineering.EngineerIO import *

# Compute time to charge to 90% of final voltage
time = rc_charge_time("10k", "100nF", 0.90)
print(f"Time to 90% charge (10k, 100nF): {format_value(time, 's')}")

# Compute time to charge to 99% of final voltage
time = rc_charge_time("1k", "1uF", 0.99)
print(f"Time to 99% charge (1k, 1µF): {format_value(time, 's')}")

Example output

rc_charge_time_output.txt
Time to 90% charge (10k, 100nF): 2.30 ms
Time to 99% charge (1k, 1µF): 4.61 ms

The RC charge time represents the time required for a capacitor to charge to a specific percentage of its final voltage through a resistor. This calculation is essential for timing circuits, debounce circuits, and understanding the transient response of RC networks. The charging follows an exponential curve, with the capacitor never truly reaching 100% charge in finite time.

The charge time is computed using the formula: $t = -\tau \ln(1 - \text{ratio})$, where $\tau = RC$ is the time constant and the ratio is the target voltage as a fraction of the final voltage (e.g., 0.90 for 90%). For example, reaching 90% charge takes approximately 2.3 time constants, while reaching 99% takes approximately 4.6 time constants.

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