STCC05-B Datasheet, PDF (3/13 Pages) STMicroelectronics – HOME APPLIANCE CONTROL CIRCUIT

STCC05-B
■ The reset circuit
This circuit ensures a Low Voltage Detection (LVD) of the output of the regulator. Most micro-controllers
have an active RESET pin in the low state: so, the /RST pin will be active at low state.
The reset comparator senses the regulator voltage V_DD. The /RST pin goes high when V_DD is higher than
the high threshold V_H = 3.75V and after a delay time T_UP; and is low when the V_DD decreases below the
low threshold V_L = 3.4V after the delay time T_DW.
These delays are set by an external capacitor C_UP connected to the /RST pin and depend on the trigger
thresholds of /RST: For C_UP = 100nF, T_UP= 400µs with V_TH= V_H/2; T_DW= 200µs with V_TH= V_L/2.
■ The Zero Voltage Synchronization ZVS circuit
The Zero Voltage Synchronization ZVS circuit generates the signal ZVS that synchronizes the whole oper-
ation with the AC line cycle (20 ms on 50 Hz or 16.7 ms on 60 Hz). This signal allows the MCU to control
the AC loads and achieve the timing functions.
The input pin SYN is an image of the mains voltage. It is connected to either the power supply transformer
through a resistor R_ZV or an opto-coupler that is controlled directly by the AC line voltage. The circuit is
protected against fast line transient voltages: a robust ESD protection and a 30µs digital filter are imple-
mented to provide a higher immunity to the MCU operation. Its output signal ZVS is inverted respect to the
input signal V_SYN.
SYN
COM
25 kΩ
70 kΩ
30 kΩ
V_DD
30 µs FILTER
S₁
Q
S₂
ZVS
■ The relay coil drivers
These robust circuits allow a DC relay coil to be driven by an MCU output. The relay coil has a minimum
resistance of 580Ω and has a power up to 0.25W for V_PS = 12 V. These characteristics are representative
of 3A relays such as FTR-F3AA-12V or JQ1A-12V series.
The output stage is made of a transistor and a demagnetization diode. The transistor is referred to the
ground COM, has a DC current rating of 50mA; and its collector is connected to the output RL_I (I=1, 2, 3).
The diode is connected between the output pin RL_I and the supply pin V_PS.
Moreover, a fourth coil driver has an extended 150mA current capability to be able to drive the coil of a
relay having a 130Ω minimum resistance and a 1.1W maximum power. These characteristics are repre-
sentative of 20A relays such as G4A-E-DC12, OMIF-S-112 or UKH12S series.
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