ML4833CS

July 2000 PRELIMINARY ML4833* Electronic Dimming Ballast Controller GENERAL DESCRIPTION The ML4833 is a complete solution for a dimmable or a non-dimmable, high power factor, high efficiency electronic ballast. The BiCMOS ML4833 contains controllers for “boost” type power factor correction as well as for a dimming ballast. The ML4833 was designed to minimize the number of external components required to build an electronic ballast. The PFC circuit uses a new, simple PFC topology which requires only one loop for compensation. This system produces a power factor of better than 0.99 with low input current THD. An overvoltage protection comparator inhibits the PFC section in the event of a lamp out or lamp failure condition. The ballast controller section provides for programmable starting sequence with individually adjustable preheat and lamp out-of-socket interrupt times. The IC controls lamp output power through feedback. The ML4833 provides a power down input which reduces power to the lamp, for GFI, end of life, etc. FEATURES s s s s s s s s s s Complete power factor correction and dimming ballast control in one IC Low distortion, high efficiency continuous boost, peak current sensing PFC section Programmable start scenario for rapid or instant start lamps Lamp current feedback for dimming control Variable frequency dimming and starting Programmable restart for lamp out condition to reduce ballast heating Internal over-temperature shutdown replaces external heat sensor PFC overvoltage comparator eliminates output “runaway” due to load removal Low start-up current > IRT: tDIS(VCO) ≅ 600 × CT Figure 7. Typical VCC and ICC Waveforms when the ML4833 is Started with a Bleed Resistor from the Rectified AC Line and Bootstrapped from an Auxiliary Winding. STARTING, RE-START, PREHEAT AND INTERRUPT The lamp starting scenario implemented in the ML4833 is designed to maximize lamp life and minimize ballast heating during lamp out conditions. The circuit in Figure 8 controls the lamp starting scenarios: Filament preheat and lamp out interrupt. CX is charged with a current of IR(SET)/4 and discharged through RX. The voltage at CX is initialized to 0.7V (VBE) at power up. The time for CX to rise to 4.8V is the filament preheat time. During that time, the oscillator charging current (ICHG) is 2.5/RSET. This will produce a high frequency for filament preheat, but will not produce sufficient voltage to ignite the lamp or cause significant glow current. After cathode heating, the inverter frequency drops to FMIN causing a high voltage to appear to ignite the lamp. If lamp current is not detected when the lamp is supposed to have ignited, the lamp voltage feedback coming into pin 8 remains below 1.25V, the CX charging current is shut off and the inverter is inhibited until CX is discharged by RX to the 1.2V threshold. Shutting off the inverter in this manner prevents the inverter from generating excessive heat when the lamp fails to strike or is out of socket. Typically this time is set to be fairly long by choosing a large value of RX. (8) IC BIAS, UNDER-VOLTAGE LOCKOUT AND THERMAL SHUTDOWN The IC includes a shunt clamp which will limit the voltage at VCC to 15V (VCCZ). The IC should be fed with a current limited source, typically derived from the ballast transformer auxiliary winding. When VCC is below VCCZ – 1.1V, the IC draws less than 0.48mA of quiescent current and the outputs are off. This allows the IC to start using a “bleed resistor” from the rectified AC line. To help reduce ballast cost, the ML4833 includes a temperature sensor which will inhibit ballast operation if the IC’s junction temperature exceeds 120°C. In order to use this sensor in lieu of an external sensor, care should be taken when placing the IC to ensure that it is sensing temperature at the physically appropriate point in the ballast. The ML4833’s die temperature can be estimated with the following equation: 9 ML4833 0.625 RSET RX/CX 9 CX RX 6.8 + 1.2/6.8 INTERRUPT 8 1.25V – + – R Q S DIMMING LOCKOUT INHIBIT 1.2/4.8 + HEAT – A summary of the operating frequencies in the various operating modes is shown below. Operating Mode Preheat Dimming Lock-out Dimming Control Operating Frequency [F(MAX) to F(MIN)] 2 F(MIN) F(MIN) to F(MAX) TYPICAL APPLICATIONS Figure 8. Lamp Preheat and Interrupt Timers LFB OUT is ignored by the oscillator until CX reaches 6.8V threshold. The lamps are therefore driven to full power and then dimmed. The CX pin is clamped to about 7.5V. Figure 10 shows a schematic for a dimming power-factor corrected 60W ballast, designed to operate two F32T8 fluorescent lamps connected in series. 6.8 4.8 RX/CX 1.2 .65 0 HEAT DIMMING LOCKOUT >1.25 INT INHIBIT Figure 9. Lamp Starting and Restart Timing 10 F1 TP4 D3 D1 6 R11 T1 C3 C2 D13 D9 C10 R13 C20 + R1 D12 D6 R20 D10 C22 C17 R14 C19 R10 R22 R19 18 17 16 15 14 13 12 11 10 R24 D11 TP2 R16 C8 TP5 1 5 T5 10 6 TP1 8 6 7 1 R8 3 2 1 9 8 C9 B R7 R18 T4 4 C23 R Y Y B Q3 R D5 C26 C25 Q1 7 2 R12 L2 D4 D2 R6 6 3 9 8 T2 D7 R17 Q2 10 C1 D8 L1 HOT 220 VAC NEUTRAL 1 2 3 4 5 6 7 R25 9 RXCX CRAMP INTERRUPT GND RSET RTC T PGND OUT B LFB OUT OUT A LAMP FB PFC OUT PDWN VCC PIFB PEAO PVFB ML4833 U1 VREF PDWN R4 Figure 10. 220V Dimming Ballast R3 R2 8 C7 C11 C6 R15 R5 C5 TP3 C4 R23 C14 C13 C15 C12 C16 D1 R6 Q1 4 D2 3 C1 R7 C4 C2 5 R4 DIMMER CONTROL INTERFACE SUBASSEMBLY 6 R8 R1 R5 C3 R3 3 2 + – U2 + – 4 7 8 1 R2 C24 R21 C21 T1 U1 VIOLET GRAY ML4833 REMOTE MANUAL DIMMER 0–10VDC 11 ML4833 PHYSICAL DIMENSIONS inches (millimeters) Package: P18 18-Pin PDIP 0.890 - 0.910 (22.60 - 23.12) 18 PIN 1 ID 0.240 - 0.260 0.295 - 0.325 (6.09 - 6.61) (7.49 - 8.26) 0.045 MIN (1.14 MIN) (4 PLACES) 1 0.050 - 0.065 (1.27 - 1.65) 0.100 BSC (2.54 BSC) 0.015 MIN (0.38 MIN) 0.170 MAX (4.32 MAX) 0.125 MIN (3.18 MIN) 0.016 - 0.022 (0.40 - 0.56) SEATING PLANE 0º - 15º 0.008 - 0.012 (0.20 - 0.31) Package: S18 18-Pin SOIC 0.449 - 0.463 (11.40 - 11.76) 18 0.291 - 0.301 0.398 - 0.412 (7.39 - 7.65) (10.11 - 10.47) PIN 1 ID 1 0.024 - 0.034 (0.61 - 0.86) (4 PLACES) 0.050 BSC (1.27 BSC) 0.095 - 0.107 (2.41 - 2.72) 0º - 8º 0.090 - 0.094 (2.28 - 2.39) 0.012 - 0.020 (0.30 - 0.51) SEATING PLANE 0.005 - 0.013 (0.13 - 0.33) 0.022 - 0.042 (0.56 - 1.07) 0.009 - 0.013 (0.22 - 0.33) 12 ML4833 ORDERING INFORMATION PART NUMBER ML4833CP (End of Life) ML4833CS (Obsolete) TEMPERATURE RANGE 0°C to 85°C 0°C to 85°C PACKAGE Molded DIP (P18) SOIC (S18) © Micro Linear 1997 is a registered trademark of Micro Linear Corporation Products described in this document may be covered by one or more of the following patents, U.S.: 4,897,611; 4,964,026; 5,027,116; 5,281,862; 5,283,483; 5,418,502; 5,508,570; 5,510,727; 5,523,940; 5,546,017; 5,559,470; 5,565,761; 5,592,128; 5,594,376; Japan: 2598946; 2619299. Other patents are pending. Micro Linear reserves the right to make changes to any product herein to improve reliability, function or design. Micro Linear does not assume any liability arising out of the application or use of any product described herein, neither does it convey any license under its patent right nor the rights of others. The circuits contained in this data sheet are offered as possible applications only. Micro Linear makes no warranties or representations as to whether the illustrated circuits infringe any intellectual property rights of others, and will accept no responsibility or liability for use of any application herein. The customer is urged to consult with appropriate legal counsel before deciding on a particular application. 2092 Concourse Drive San Jose, CA 95131 Tel: 408/433-5200 Fax: 408/432-0295 DS4833-01 13