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Product(s)

Obsolete

Product(s)

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Product(s)

AN2326

Power supply and timebase delivery circuit

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2

Power supply and timebase delivery circuit

The following figures show circuits which will provide 5V DC to the ST7ULTRALITE and

protect the input capture from overcurrent. If no power supply is needed, the only

component to keep is the resistor on the LTIC input, which is mainly to protect from

overcurrent.

2.1

Basic circuit

This circuit contains a capacitive power supply which converts the 220V/50Hz of the mains,

as well as the 110V/60Hz of the US mains, into 5V DC.

Warning:

be aware that this kind of power supply cannot be used if there are

big current variations.

It also inputs 220V/50Hz to the Lite Timer Input Capture pin (LTIC/PA2) protected by resistor

R2.

The incoming alternating signal on the LTIC input pin is 220V/50Hz. Because of the

clamping diode on the input of the ST7ULTRALITE, the input signal can be considered as a

0-5V square signal.

Figure 5.

Power supply and timebase delivery circuit diagram

The maximum current available in the microcontroller depends on the C2 value. Table 1

gives the maximum average current versus the capacitor value. The average current follows

the equation below:

In the case above, C2 is equal to 220nF so the available current is limited to 4.9 mA in the

case of a European mains. To have the same current levels in the case of the US mains

GND

LTIC

ST7ULTRALITE

zener

5.6V

C1

220µF/16V

1N4148

C2

220nF/400V

R1 47R/0.5W

R2 470k/0.5W

C2

(220V/50Hz)

Mains

Imax

Vmax 2 f C

⋅⋅ ⋅

=