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Low-losses e-Starter for compressors

Low-losses e-Starter for compressors. December 2007. CONTENTS. X0205 (back side). Board objective e-STARTER from ST New principle Breadboard schematics Explanation Breadboard performances Power consumption Immunnity Reliability & RoHS compliance Advantages / Drawbacks. ACST6-7ST.

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Low-losses e-Starter for compressors

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  1. Low-losses e-Starter for compressors December 2007

  2. CONTENTS X0205 (back side) • Board objective • e-STARTER from ST • New principle • Breadboard schematics • Explanation • Breadboard performances • Power consumption • Immunnity • Reliability & RoHS compliance • Advantages / Drawbacks ACST6-7ST

  3. PTC Klixon Klixon LINE LINE PTC PTC RUN RUN START START Board objective Compressor LINE Klixon • Single phase compressor • Frige & freezer applications • Starters solutions: • Automatic turn-off relay • Expensive, poor reliability • Positive Coefficient Temperature Resistor (PTC) • High leakage current to keep the PTC hot, in high impedance mode • High power losses in OFF state • New solution for low-losses starter Vac START RUN Thermostat STARTER

  4. New principle Today PTC behavior versus mains voltage & compressor state IPTC (10A/div) IPTC (10A/div) VPTC (100V/div) VPTC (100V/div) Compressor OFF time < 1’ Mains: 264V RMS / Start capacitor Compressor OFF time > 10’ Mains: 198V RMS PTC voltage level increase is representative of long-enough start winding conduction

  5. Klixon Compressor Klixon Vac Vac PTC Control PTC Control T T Thermostat e-STARTER Thermostat New principle Connection diagram, with or without capacitor No capacitor Start or Run capacitor

  6. IA VAK VC2 VC1 Latch-up Level detection New principle ST solution to turn-off the start winding once the voltage across the PTC is high enough ZVS circuit

  7. New principle Explanation (1/2) • As soon as the mains voltage is applied: • T2 is on, thanks to the gate current provided by R2 • So T1 is turned on thanks to the gate current provided by T2 • At each Zero current crossing, the reapplied voltage across T1/T2 trigger back T1. • Both T1 and the PTC are then ON IA (5A/div) VAK (20V/div) PTC 1st step: T1 conduction

  8. New principle Explanation (2/2) • When the PTC conduction time lasted enough to start the compressor, its voltage suddenly rises • This voltage rises is sensed by R3/R4 divisor bridge. • If the level is higher than Dz level, the Thyristor achieved by Q1 and Q2 is latched • M1 is then turned on • As M1 is ON, there is no more gate current to trigger T2 • So T1 stays OFF • The PTC is also turned off. • No more current circulates through the PTC, so no power is dissipated by it. VC1 VC2 IA (5A/div) VC1 (10V/div) VC2 (10V/div) 2nd step: T1 turn-off

  9. Breadboard performances Stand-by power consumption IPTC (50mA/div) VPTC (100V/div) • Today PTC: • Current leakage to keep the PTC OFF ~ 30 mA • PTC losses at OFF state ~ 2 - 2.5 W • E-STARTER OFF state losses: • Assumptions: max line RMS voltage = 230 V • RMS voltage across e-STARTER = 350 V (with RUN cap.) • R2 + R3 power losses = 240 mW • Only 40mW typically for a 115V RMS application PPTC (5W/div) Stand-by losses divided by 10 ! (and also 0.6 to 1.5W saved on auxiliary winding !)

  10. Thermostat Klixon e-STARTER PTC ON OFF Delay Similar to PTC behavior Breadboard performances e-STARTER ON/OFF cycle Klixon • ON time = time to heat-up the PTC • Max: 1 to 6s according to PTC behavior • OFF time = ON time of both the thermostat & the klixon • Delay to turn-on back the e-STARTER = time to cool-down the PTC • Approximately 5-20 s • From end of last start-up ! Vac e-STARTER Thermostat

  11. Breadboard performances ON state behavior • ON state losses: • ACST6 conduction losses ~ 6 W max • Assumptions: 7A max peak current, Tj = 125°C, Vto/Rd spec. • R3 power losses ~ 0.5 mW • Only 30V typ. peak across the PTC; half-cycle mode • Max current versus conduction time to keep Tj < 125°C:

  12. Breadboard performances IEC61000-4-4 tests results Test conditions: Spike frequency: 5kHz Burst duration: 15ms Burst frequency: 3Hz Test duration: 60s Compressor 230V-50Hz E-starter board IEC61000-4-4 fast transient voltages generator No spurious turn-on up to 2kV (no permanent failure up to 4.5 kV)

  13. e-STARTER reliability ACST6-7ST QualPack results • Operating life test • Test conditions • ACST6 in TO220-AB, no heatsink • 14.5 A DC during 0.1s(equivalent to 11A RMS during 1s) • Thermal stress: Tj increases from 25 °C to 95 °CRq: Tj increase = 35°C for 5A RMS during 3s • No failure on 30 devices after 450 Kcycles • « Stalled rotor » test • Test conditions • ACST6 in TO220-AB, no heatsink • 13 A DC during 2.6 s(equivalent to 11A RMS during 0.5s then 2A RMS during 2.5s) • Thermal stress: Tj increases from 25 °C to 155 °C • No failure on 20 devices after 10 Kcycles

  14. 4.5cm 3.5cm e-STARTER reliability e-STARTER safety • UL compliance • Flammability: all our resins are UL94V0 compliant • No insulated packages required here (UL1557 not applicable) • EN60730 standard • ACST diode mode / short-circuit failure: • No safety issue as the PTC will protect the motor windings from overheating • Control board short-circuit failure: • Use a copper track which will blow-up if the motor current goes through it(normal current for the control board < 1 mA) Klixon PTC Control T Thermostat

  15. RoHS compliance • RoHS compliance • All ST component are RoHS compliant • PB < 1000 ppm (lead finish, solder balls) • Other heavy metals banned by RoHS directive are not present in STM products (lead free => RoHS compliant) • Exception : RoHS directive do not ban the use of Lead (Pb) in Frit seal glass and in High Pb-content alloys ( > 85%Pb) • Chemical compounds: refer to « ST chemical book »

  16. Vac Klixon PTC C Control Thermostat Advantages / Drawbacks • Advantages: • Remove PTC losses:Control circuit losses 240 mW compared to 2.5W with today PTC • No EMI noise (ZVS operation) • No half-cycle conduction • Faster reaction time (in case of mains interrupt) • Less risk of stalled rotor during short mains interrupt • RUN capacitor overvoltage protection • Possible to use lower voltage capacitors (less expensive) • Drawbacks: • Added components • No ZVS at plug-in (not a problem)

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