A capacitor added to a classic voltage divider introduces a predictable delay before enabling another component, such as a DC-DC converter or logic device. The RC Voltage Divider Delay Calculator determines key timing parameters based on the divider components, input voltage, and the required threshold voltage.

Calculate Time Constant

The RC Time Calculator uses the following parameters to determine key timing characteristics:

Final capacitor voltage (V_final) - the final steady-state voltage the capacitor charges to, determined by the resistor divider ratio.
Time constant (τ, tau) -  determines the charging speed of the capacitor and depends on the Thevenin equivalent resistance of the divider and the capacitor value.
Threshold Voltage (V_threshold) - the required voltage level at which the target circuit becomes enabled or activated.
This is the voltage required, for example, at the Enable pin of a DC-DC converter, or the minimum logic-high level needed by a microcontroller input.
The calculator determines how long it takes for the capacitor to charge up to this user-specified threshold.

The capacitor in the circuit follows an exponential charging equation:

V(t) = V_final * (1 - e^(-t / τ))

where V_final is the final voltage the capacitor will reach, τ (tau) is the time constant, and t is time.

The voltage divider defines the maximum voltage the capacitor will reach:

V_final = Vin * (R2 / (R1 + R2))

The time constant τ determines the speed of how the capacitor charges and is calculated as:

τ = (R1 * R2) / (R1 + R2) * C

A higher τ value means a slower charge time.

To determine the delay before a device turns on, we calculate the time required for the capacitor to reach the specified threshold voltage:

t_enable = -τ * ln(1 - V_threshold / V_final)

This is the startup delay that occurs before the controlled circuit (such as a DC-DC converter or logic input) becomes active.

This formula calculates how long it takes for the capacitor voltage to reach the required level.

Summary

The RC Delay Time Calculator models the charging behavior of a capacitor in a voltage divider configuration. It is useful for estimating startup delays, power sequencing timing, enable-pin activation, and analog filtering performance.

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