Author Topic: Low Power Zero Crossing Detector Uses Auxiliary Voltage From Flyback  (Read 707 times)

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Offline chris_leysonTopic starter

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Given the importance of reducing standby (OFF) power consumption in many household appliances, here is my best effort so far at a 50/60 Hz zero crossing detector. To be fair all the credit should go to Robert W. Hilsher for his design idea "A Unique Discrete Zero-Crossing Detector" EDN 1999.
In the attached LTSpice schematic, voltage source V1 represents the 115/230VAC line input, D1 to D4 is the bridge rectifier supplying a small flyback SMPS and voltage source V2 represents its auxiliary supply. Note: Resistor R2 is included to load the bridge rectifier so that D1-D4 simulate correctly.
Power consumtion for the cicuit shown is a little over 13mW, 11mW for the AC drive into R1 and about 2.5mW supplied by the SMPS auxiliary supply driving the opto-coupler LED D6 at a peak current of around 1mA. Bench measurements agree well with the simulation and the circuit has been tested at 300VAC line voltage, and all the way down to 20VAC, that's due to the Sanken STR4A164 flyback. Not yet tested for surge or fast transients so some additional protection may be needed. Back end signal processing on the secondary side, opto output, is not shown but adds a few mW.
EDIT: Schematic corrected for correct AC line voltage.
« Last Edit: July 25, 2020, 05:03:18 pm by chris_leyson »
 

Offline NiHaoMike

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Re: Low Power Zero Crossing Detector Uses Auxiliary Voltage From Flyback
« Reply #1 on: July 25, 2020, 04:03:35 pm »
Have you considered a capacitive voltage divider?
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Offline chris_leysonTopic starter

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Re: Low Power Zero Crossing Detector Uses Auxiliary Voltage From Flyback
« Reply #2 on: July 25, 2020, 06:51:01 pm »
Hi NiHaoMike, to honest yes, however, at the time I was using a different zero crossing detector. A variation on "Mains-driven zero-crossing detector uses only a few high-voltage parts" again from EDN. Resistor values were chosen to provide about 1.5mA opto-coupler drive and power consumption was about 45mW at 230VAC or 800uA opto drive and 12mW at 115VAC.
Unfortunately the circuit arrangment doesn't work with capacitive voltage dividers, it needs its own separate bridge rectifier and it uses half or full wave rectified sine drive depending on how you arrange the diode bridge, either for 50/60Hz or 100/120Hz pulses. I really didn't like the rectified sine drive and the LED drive current is given by CdV/dt so it will be half the current at 115VAC.
I like Robert Hilsher's circuit arrangment because it is a true zero crossing detector that is quite robust and the RC filter on the Live input helps filter out any noise. The only drawback is the need for a DC supply, however it is 3X improvement in terms of power at 230V.
« Last Edit: July 25, 2020, 07:13:46 pm by chris_leyson »
 


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