Datenblatt-Suchmaschine für elektronische Bauteile |
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FAN4146 Datenblatt(PDF) 5 Page - Fairchild Semiconductor |
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FAN4146 Datenblatt(HTML) 5 Page - Fairchild Semiconductor |
5 / 10 page © 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com FAN4146 • Rev. 1.0.0 5 Functional Description Refer to Figure 1 and Figure 3. The FAN4146 is a two-wire GFCI controller for AC ground-fault-circuit interrupters. The internal rectifier circuit is biased by the AC line during the positive half cycle of the AC line voltage. The internal 12V shunt regulator uses a precision temperature-compensated bandgap reference. The combination of precision reference circuitry and precision sense amplifier provides for an accurate ground-fault tolerance. This allows for selection of external components with wider and lower-cost parameter variation. Due to the low quiescent current, a high value external series resistor (R1) can be used which reduces the maximum power wattage required for this resistor. The 12V shunt regulator generates the reference voltage VREF for the sense amplifier’s (A1) non-inverting input (AC ground reference) and supplies the bias for the delay timer (t1), comparators (C1 & C2), and the SCR driver. The secondary winding of the sense transformer is directly DC coupled to the inverting input of the sense amplifier at pin 5 (VFB). The RSET resistor converts the sense transformer’s secondary current to a voltage at pin 6 (AmpOut). This voltage is compared to the internal window comparator (C1 & C2) and, when the AmpOut voltage exceeds the +/-VTH threshold voltage, the window comparator triggers the internal delay timer. The output of the window comparator must stay HIGH for the duration of the t1 timer. If the window comparator’s output momentarily goes LOW, the t1 timer resets. If the window comparator’s output is still HIGH at the end of the t1 pulse, the SCR driver enables the current source I1 and disables Q1. The current source I1 then enables the external SCR, which energizes the solenoid, opens the contact switches to the load, and removes the hazardous ground fault. The window comparator allows detection of a positive or negative IFAULT signal independent from the phase of the line voltage. An internal under-voltage lockout circuit disables the SCR driver if the voltage at pin 3 (LINE) is below 7.5V. This prevents the SCR from energizing the solenoid when the SCR’s anode voltage is below 65V. The sense transformer typically has a toroidal core made of laminated steel rings or solid ferrite material. The secondary of the transformer is typically 1000 turns of #40 wire wound through the toroid. The primary is typically one turn made by passing the AC hot and neutral wires through the center of the toroid. When a ground fault exists, a difference exists between the current flowing in hot and neutral wires. The primary difference current divided by the primary-to-secondary turns ratio is the current that flows through the secondary wire of the transformer. Calculation of RSET Resistor The AmpOut signal must exceed the window comparator’s VTH threshold voltage for longer than the delay timer and calculated by: VTH=IFAULT x 1.41 x RSET x COS(2π x (t/2P)) / N (1) RSET = (VTH x N) / (1.41 x IFAULT x COS(π x t/P)) (2) where: VTH =3.5V IFAULT = 5mA (UL943B) t = 1ms (timer delay) P = Period of the AC Line (1/60Hz) N = Ratio of secondary to primary turns (1000:1) RSET = 505K Ω (511KΩ standard 1% value) In practice, the transformer is non-ideal, so RSET may need to be adjusted by up to 30% to obtain the desired Ifault trip threshold. Calculation of VOS Trip Threshold Error Since the sense coil is directly connected to the feedback of the sense amplifier, the VOS offset introduces an Ifault threshold error. This error can be calculated as follows: %Error=100 x (VOS x RSET) / (RIN + RLDC + RLAC) / VTH (3) where: VOS = +/-450µV (worst case) +/-150µV (typical) RSET = 511K Ω RIN = 470 Ω (typical value) RLDC = 75 Ω (sense coil secondary DC resistance) RLAC = 1.5 KΩ (AC(jωL) impedance of sense coil), L= 4H, f= 60Hz) VTH = 3.5V %Error= +/- 3.2% (worst case) +/- 1.1% (typical) |
Ähnliche Teilenummer - FAN4146 |
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Ähnliche Beschreibung - FAN4146 |
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