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| C1 | C2 | Actual Vout | Error (%) |
|---|
Given: Vin=10V AC, C1=100nF, C2=470nF
Given: Vin=1000V, C1=1nF, C2=10nF
Given: Vin=5V RF, C1=22pF, C2=68pF
A capacitive voltage divider splits an AC voltage using two capacitors in series instead of two resistors. The output taken across the second capacitor follows Vout = Vin × C1 / (C1 + C2). Note the ratio is the opposite intuition from a resistor divider: the output is proportional to the series capacitor C1, because in a series string the smaller capacitor drops the larger share of the voltage.
A capacitive divider dissipates almost no power — capacitors store and return energy rather than turning it into heat — so it is the natural choice for high-voltage AC sensing and RF, where a resistive divider would waste power and heat up. It also blocks DC, passing only the AC component. The trade-off is that it only works with AC: the division ratio comes from capacitive reactance (XC = 1/(2πfC)), so it depends on the signal being time-varying.
Like its resistive cousin, a capacitive divider must feed a high-impedance load or the ratio shifts. Any load resistance forms a high-pass filter with the capacitors, so the divider behaves ideally only well above that corner frequency. For precise RF work the stray capacitance of the board and the probe must be included in C2.
High-voltage AC measurement and metering, RF impedance matching and antenna tuning networks, the feedback tap of Colpitts and Clapp oscillators, capacitive touch and level sensing, and coupling/attenuating signals without a DC path.
Does it work with DC? No — capacitors block DC, so a capacitive divider only divides AC or changing signals. Use a resistive divider for DC.
Why does the smaller capacitor get more voltage? In series, all capacitors carry the same charge (Q); since V = Q/C, the smaller capacitance develops the larger voltage.
A capacitive divider splits voltage in inverse proportion to capacitance:
V1 = Vin × C2 / (C1 + C2)
The opposite capacitor appears in the numerator, which is the reverse of the resistive case. The reason is that series capacitors all carry the same charge, and since V = Q/C, the smaller capacitor develops the larger voltage.
At DC a capacitor is an open circuit, so there is no defined division at all — the steady-state voltage is set by leakage resistance, which is poorly controlled and varies with temperature and age. A capacitive divider works only on AC or on transients, and any DC component needs resistors in parallel to define the operating point.
This is also why high-voltage dividers are often built as combined RC networks: the resistors set the DC division while the capacitors maintain the same ratio at high frequency, where resistor stray capacitance would otherwise distort the response.
Because reactance is 1/(2πfC), both capacitors change impedance together with frequency, so the ratio stays constant. That is the appeal. The ratio only breaks down when stray capacitance — to the probe, the enclosure or the board — becomes comparable to the divider capacitances, which is why high-voltage dividers are physically laid out with such care.
V1 = Vin × C2/(C1+C2). The opposite capacitor appears on top because series capacitors share the same charge, so the smaller one develops the larger voltage.
Because series capacitors carry equal charge and V = Q/C. With the same charge, smaller capacitance means larger voltage.
No. At DC a capacitor is an open circuit, so the steady-state division is set by uncontrolled leakage resistance. Capacitive dividers work on AC or transients, and need parallel resistors to define any DC operating point.
Because it dissipates almost no power, which matters when measuring a high-voltage bus continuously. A resistive divider across the same bus would waste energy and heat up.
Adjusting the trimmer capacitor in a 10:1 oscilloscope probe so the capacitive division ratio matches the resistive one. When they match, the response is flat and a square wave shows square corners rather than overshoot or droop.
Not in principle, since both capacitors' reactances scale together. It changes in practice when stray capacitance becomes comparable to the divider values, which is why high-voltage dividers need careful physical layout.