PLESSEY Semiconductors SL443A SL443A ZERO VOLTAGE SWITCH The SL443A is a symmetrical burst control integrated circuit in an 8-pin DIL plastic package and is mainly intended for manual heat control applications, for example cooker hot plates and powerful hair dryers. SPECIAL FEATURES 1, Weil defined load power/potentiometer dis- placement characteristics 2. High immunity against spurious triac firing under noisy mains environment (automatic spike filtration) 3. Enables compliance with Cenelec EN50,006/ BS5406-1976 (A) Switching rate controlled (B) symmetrical burst control 4. Very low external component count 5. Triac firing pulses inhibited whilst the ICls power supply is being established. COMMON [J 8f] POT. SLIDER AC INPUT [J f) cr ts 60) PULSE DELAY CAPACITOR TRIAS FIRING PULSE [J * of Ret 7) DP8 Fig. 1 Pin connections (top) APPLICATIONS HM Cooker hotplates @ Powerful hairdryers RAMP GENERATOR 6 SPIKE 7 PERIOD PULSE GENERATOR ZERO VOLTAGE LOW Veo INHIBIT CIRCUIT COMMON t dt | CROSSING DETECTOR DELAYED PULSE GENERATOR Ro 2 { AC INPUT = {}- fl + 4 COMMON f tT 7 SERIES STABILISER Fig. 2 SL443A block diagram 29 SL443A CIRCUIT DESCRIPTION The externally current limited AC supply is applied to the device, and rectification followed by shunt regulation provides a 14V DC supply. This is externally smoothed before application to the 7:0V'series stabiliser which feeds the resistance bridge. The stabiliser must be within regulation, or operation of the Low Vcc Inhibit circuit will result. This circuit overrides all other circuitry and prevents unsuitable firing pulses from being supplied to the triac at switch-on. The current limited AC supply aiso drives the Period Pulse Generator (PPG) and zero voltage crossing circuits. The PPG produces a single short duration pulse for each completed mains cycie and serves two purposes. Firstly it is used to clock logic information such that the circuit behaves in a symmetrical manner and only complete mains cycles are applied to the load. Secondly the pulse is used to switch timing components in the ramp generator and this enables long time constants to be achieved without having to resort to the use of ELECTRICAL CHARACTERISTICS Test Conditions (unless otherwise stated) Tame -= 25C electrolytic capacitors. The zero voltage crossing detector controls a pulse generator that has a delayed output. The delay is necessary since, with loads that are slightly inductive or low power resistive, the triac load current may not reach its required holding level at zero voltage point. Both delay and pulse duration are defined by an external capacitor and this further serves the purpose of filtering out spikes which occur in the zero crossing region. Automatic rejection takes place of spikes having a duration of up to 50 per cent of the normal width of the triac firing pulse. , The comparator amplifier has differential inputs and these are used to compare the potential appearing on the slider of the control potentiometer with that of the ramp waveform. The output of this amplifier controls the logic circuitry and the potentiometer setting defines the fraction of the ramp period for which the triac is in conduction so controlling the power in the load. All voltages measured with respect to common (pin 1) Value Characteristic Min. Typ. Max. | Units Conditions Shunt regulating voltage pin 3 14.7 Vv I3 -= 16mA Shunt regulating voltage pin 3 16 Vv I3 ... 16mA, . Tamb = ~ 75C Supply voltage trip level pin 3 12.2 Vv eSupply current (less la AV, 2x Is) See Note 1 2 mA Potentiometer supply pin 5, Vs 6.8 7.0 7.6 Vv Potentiometer resistance range 18 140 kQ Triac gate drive pin 4 Open circuit ON voltage 8.5 Vv Open circuit OFF voltage 01] V Output current into 2V drain 80 100 mA Output current into 4V drain 50 70 mA Output current into short circuit 200 mA Internal drain resistance 800 Q Control input pin 8 Bias current 1 HA Internal reference ramp start 0.3 0.5 0.7 ramp finish Vs 0.5) Vs-0.3 | Ve~ 0.1 * Period of ramp generator T 27 30 33 s (Re =100K, C, = 0.68) (RMS mains voltage=220v) Pin 6 output impedance R6 215 27 32.5 kQ @ The supply current is 0.45 x (RMS current fed into Pin 2) %& Period of ramp = T = 2 x Cr x Rp x (RMS mains voltage) seconds 30 ABSOLUTE MAXIMUM RATINGS Voltages Voltage on pin 8, Voltage on pin 4, Ve-1 Va-1 Currents Supply current, pin 2 peak value + lam Non-repetitive peak current (tp > 250S) + lasm Output current, pin 5 Is Output current, pin 4, average value la (AV) Temperatures Operating ambient temperature Storage temperature Power Dissipation SL443A Max 10v Max 10v Max 50mA Max 200mA Short circuit protected Max 10mA Short circuit protected Tams 10 to 75C Tsta 55 to +125C See Fig. 3 280 J 200 180 Rthy-a= 200 C/W Re Ping OUTPUT IMPEDANCE (RB) C=CD CAPACITOR CONNECTED TO PIN 6 = . 5 * 100 a 50 a so 100 150 Tamp (C) Fig. 3 Power dissipation x Y mA nh AC MAINS WAVEFORM QUTPUT OF PERIOD PULSE GENERATOR OUTPUT OF ZERO CROSSING GENERATOR EXPANOED ZERO CROSSING PERIOD PULSE FIRING PULSE Fig. 4 Method of control 31 SL443A T T 1 t INTERNAL RAMP. a-" VOLTAGE. REFERENCE a ! I | { Control is effected by varying the number of complete mains cycles applied to the foad in the fixed timing period T. | i Ly NDA AAA a PPPTTT { 1 ' ' ZERO POWER | INTERMEDIATE POWER { MAXIMUM POWER I 1 1 I Fig. 5 Method of control INCREASE > POWER 100 3 SLSL3A 220V + 10". ~ 50 Hz PERCENTAGE POWER 93 100 PERCENTAGE POTENTIOMESER TRAVEL Component values Rp 8.2kQ 5% 7W Rp 100kQ (Control characteristic of linear potentiometer is shown in Fig. 7} This characteristic applies to a linear potentiometer. Cs 220uF 16V Different control characteristics are easily obtained by Ct 0.47uF (Ramp period = 20 seconds nominal) using a non-linear potentiometer and/or offset resistors Cp 1.5nF +10% in the potentiometer circuit. TRIAC TAG.255 ~ 400 Fig. 6 Cooker hotplate contro/ Fig. 7 Output power v. potentiometer displacement 32