Capacitive Transformerless Power Supply Calculator

Omni Calculator's capacitive transformerless power supply calculator helps you find your circuit's output voltage and input current.

Keep with us in this article to explore:

• What is a transformerless power supply circuit​?

• How to make a transformerless 12V power supply​?

• How do we increase the current in a transformerless power supply​?

• How do you calculate Zener voltage​​ in a capacitive power supply​?

• Can a capacitor convert AC to DC​?

So, let us help you to avoid a short-circuit with the capacitive transformerless power supply calculator.

A transformerless power supply circuit is a huge term for a DC (direct current) power supply that converts a high AC (alternating current) input voltage​ to a small DC voltage.

There are two types of transformerless power supply circuits: capacitive and resistive. The capacitive transformerless power supply uses a capacitor to reduce the input voltage, while the resistive power supply uses a resistor to reduce the current, dropping the voltage.

The main differences between these two power supplies are their dissipation of energy as heat and their sizes. The capacitive power supply dissipates a lower amount of energy as heat and is also compact, allowing it to be applied to small devices such as LED lighting, electric fans, rice cookers, and powering switches, dimmers, or timers in smart home setups, for instance.

A capacitive transformerless power supply consists of a Zener diode as a voltage regulator ($D_1$)​, a dropper capacitor ($C_1$), a diode to a proper flow of the current ($D_2$), a smooth capacitor ($C_2$), and a resistor ($R_1$). The circuit diagram below shows an example of a standard capacitive power supply.

Now that we have the general definition of a capacitive transformerless power supply, let us see how it works and the equations behind it.

As we saw in the previous section, a transformerless power supply is a voltage divider circuit​ that uses a capacitor to convert high AC input voltage​ (120V or 230V) to low DC voltage (3V, 5V, or 12V) without relying on a bulky transformer. The main objective of this tool is to compute the input current and the output voltage for the capacitive power supply.

The input current can be determined using the following equation:

where:

• $I_{\mathrm{in}}$ — Input current;
• $V_{\mathrm{RMS}}$ — RMS (root mean square) value of the input AC voltage.
• $V_z$ — Regulated DC voltage output determined by the Zener diode;
• $f$ — Frequency of the AC input voltage​;
• $C_1$ — Capacitance of the voltage dropping capacitor; and
• $R_1$ — Resistance.

The Zener diode is a semiconductor that allows current to flow in a given direction—just like other standard diodes—when the voltage on it exceeds a specific value called the Zener breakdown voltage. The working mechanism of the Zener diode is based on a quantum tunneling process called the Zener effect, discovered by Clarence Zener.

Moreover, the output voltage of our DC power supply​ can be computed using the formula below:

where:

• $V_{\mathrm{out}}$ — Output voltage; and
• $V_d$ — Forward bias voltage on the second diode.

We are pretty sure that understanding all the concepts behind this voltage divider circuit​ is not easy. But you do not need to worry; the capacitive transformerless power supply calculator is here to do the hard work for you.

In this example, we will show how easy and intuitive using our calculator is. Thus, let us consider the following set of parameters for our voltage divider circuit:

• $V_{\mathrm{RMS}} = 110\, \mathrm{V}_{\mathrm{AC}}$;
• $V_z = 5.1\,\mathrm{V}$;
• $V_d = 0.6\,\mathrm{V}$;
• $f = 59.5\,\mathrm{Hz}$;
• $C_1 = 0.38\,\mathrm{\mu F}$; and
• $R_1 = 517\,\Omega$.

By substituting them in our tool, we can determine the respective values for the output voltage and the input current: $V_{\mathrm{out}} = 4.5\,\mathrm{V}$ and $I_{\mathrm{in}} = 9.9\,\mathrm{m A}$.

You should always remember that our calculator works backward and forward, so you can use a given input current and output voltage to determine other parameters, such as the forward bias voltage.