Zero Volt Switch (ZVS)

A zero volt switch (UPC1701) is a control IC that uses a triac to control alternating current (AC) power.
The name comes from the control method, in which the triac is triggered when the AC power reaches the zero volt point.
AC power controllers that use a triac are generally configured as shown in Figure 1 below. One of the control methods used with this configuration is the "zero volt on/off control method". This involves changing the frequency of turning the triac on and off while the triac is being triggered at the zero volt point (Figure 2).
In Figure 2, while the controller's control signal is ON to operate it, the gate trigger current is output to turn on the triac when the AC voltage is around the zero volt point. If the controller's control signal is then turned off, the controller stops the gate trigger current to turn off the triac.
When a method other than the zero volt on/off control method described above (such as the "phase control method" (see Figure 3)) is used, since a load current flows with precipitous rise at the moment the triac turns on, it may cause radio frequency interference (RFI).
However, with the zero volt on/off method, the triac is turned on by a trigger signal controlled by the zero volt switch, so the load current changes into a sine wave according to the AC power supply voltage waveform (see Figure 2).
This makes it possible to control the power without RFI caused b y electromagnetic radiation.

(2006/05)

In the application example, the uPC1701 is used at 100 V. Can it also be used at 200 V?

Yes, it can also be used at 200 V.
In the application example, the supply voltage is dropped by a series resistor to create a power for the IC.
If the supply voltage is 200 V, the resistance should be doubled.

If the resistance is doubled, however, the uPC1701 is more susceptible to the influences of drive current.

For details, refer to "3-1 Power Supply to ZVS" in the Application Note (Japanese).

Can the uPC1701 be used to control a 20 Hz waveform?

Yes, it is possible.
However, if the frequency decreases, the capacitor constituting the power supply of the IC may be affected.
Calculate the time constants and secure the necessary capacitance.

When the resistance is increased to secure the time constants, the stable operation is influenced by the input bias current of the IC.
It is thus recommended to increase the capacitance to secure the time constants.

Is the upper half of the waveform shown in "1. Basic Application Circuit" (p.18) of the Application Note (Japanese) positive or negative?

The upper half of the waveform is the positive direction.
This waveform is drawn with Vss (negative) as the reference (zero).

The upper half of the waveform is the GND direction.