AN_SPMC65_O0322_en_V1.2

Zero Cross Detection V1.2 - Nov 01, 2006

English Version

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Zero Cross Detection

© Sunplus Technology Co., Ltd. PAGE 1 V1.2 - Nov 01 2006

Important Notice

SUNPLUS TECHNOLOGY CO. reserves the right to change this documentation without prior notice. Information

provided by SUNPLUS TECHNOLOGY CO. is believed to be accurate and reliable. However, SUNPLUS

TECHNOLOGY CO. makes no warranty for any errors which may appear in this document. Contact SUNPLUS

TECHNOLOGY CO. to obtain the latest version of device specifications before placing your order. No

responsibility is assumed by SUNPLUS TECHNOLOGY CO. for any infringement of patent or other rights of third

parties which may result from its use. In addition, SUNPLUS products are not authorized for use as critical

components in life support systems or aviation systems, where a malfunction or failure of the product may

reasonably be expected to result in significant injury to the user, without the express written approval of Sunplus.



Revision History

Revision Date Translated By Remark Page

Number(s)

V1.2 2006/11/01 Li Jing Proofreading

V1.1 2006/03/07 Li Jing Translate ‘Zero Cross Detection V1.1, Chinese version’



Table of Content PAGE

1 System Design.................................................................................................................................... 4

1.1 System Design Description ........................................................................................................... 4 1.2 System Block Diagram .................................................................................................................. 4 1.3 MCU Resource .............................................................................................................................. 4

2 Hardware Design ................................................................................................................................ 6

2.1 Function......................................................................................................................................... 6 2.2 Design Principle............................................................................................................................. 6 2.3 Time Error Between Interrupt Generation Point and Actual Zero Point of AC220V ...................... 8

3 Software Description.......................................................................................................................... 9

3.1 Source File .................................................................................................................................... 9 3.2 Subroutines ................................................................................................................................... 9 3.3 Variables ...................................................................................................................................... 10

4 Flowcharts..........................................................................................................................................11

4.1 Main Flowchart .............................................................................................................................11 4.2 Interrupt Subroutine......................................................................................................................11 4.3 Display Subroutine ...................................................................................................................... 12


© Sunplus Technology Co., Ltd.

1 System Design

1.1 System Design Description

This document is intended to guide you how to detect the zero crossing point for AC220V on SUNPLUS SPMC65x series. Here we use SPMC65P2404A*28P as an example for demonstration purpose.

1.2 System Block Diagram

SPMC65P2404A*28P

IRQ0

Figure 1-1

1.3 MCU Resource

MCU Resource

RAM Zero crossing

Main program

Initialization

Interrupt procROM

Zero crossing

Hardware on zero crossing interrupt

Interrupt INT0 externaPB4

I/O PORT PORTA

PAGE 4 V1.2 - Nov 01 2006

Transform Commute

6 LEDs showing

16MHz2

AC220v

6

1

System Block Diagram

Occupation Memo

display 1 byte

15 bytes

38 bytes

ess 31 bytes

display 31 bytes

l interrupt triggered by rising edge in

Not used Only PA0~PA5



MCU Resource Occupation Memo

PORTB INT0 external interrupt Only PB4

PORTC Not used

PORTD Not used



2 Hardware Design

2.1 Function

This application is taking SPMC65P2404A*28P as the main controller to detect the zero crossing point of AC220V through the external interrupt on SUNPLUS SPMC65x series, which mainly performs the following three functions.

Triac trigger. Through detecting the zero crossing point, the turn-on time of triac can be controlled, thus to control the voltage.

Relay protection. When using relay to control AC220V power on/off, if the relay is closed around the peak voltage of AC220V, a larger spark will occur thus to shorten the relay lifetime and generate the electromagnetic interference (EMI); if closed at the zero crossing point, these influences will be decreased.

Timing. AC220V has a frequency of 50Hz and a period of 20ms. After performing the full-wave rectification, the interrupt occurs at each zero crossing point at a 10ms interval.

2.2 Design Principle

As shown in Figure 2-1, 220V AC (alternating current) is converted into 9V AC by transformer. After full-wave rectification, AC can be used to detect the zero crossing directly. and the filter capacitor c1 can connect with the other circuit (such as the circuit based on 7805 voltage regulator). In this power supply circuit diagram, D1 is used to isolate the parts of rectification and filtering so as to keep the waveform of ZDS and offer source for zero detection.

The sample signal is obtained at the zero point, and then it is connected with two 10K resistors to divide the voltage. After that it connects a triac, which operates on Switching mode. When the base voltage Vbe≥0.7V, the triac is turned on and the low voltage is output to PB4; otherwise, the triac is turned off and the high voltage is output to PB4. The corresponding relationship between the sample signal at the zero point and the input signal of PB4 is shown in Figure 2-2. Since the rising edge in PB4 will trigger a 10ms external interrupt, when the interrupt occurs, AC220V is just at the zero point.

In this application, six LEDs are adopted for display, which are refreshed when the zero crossing interrupt occurs. The LEDs refresh frequencies are shown as follows:

LED0 50HZ blink:

10ms on, 10ms off, synchronize with the zero point of power supply

LED1 25HZ blink:




LED2 12.5HZ blink:


LED3 6.25HZ blink:


LED4 3.125HZ blink:


LED5 1.5625HZ blink:


AC220v--AC9v

PA1

Zero10k

10k

1k

1k

~

~+ -

PA4

LED0

1k

D1

0.1u

LED3

1k

1k

AC220v

PA5

Zero

10k

LED4

+ C1

LED2

8050

1k

PA0

PB4

PA2

1k

LED1

LED5

+5V

PA3

Figure 2-1 Zero Crossing Detection Schematic



Figure 2-2 Corresponding Relationship Between the Sample Signal at the Zero Point (upper) and the Input Signal in PB4 (lower)

2.3 Time Error Between Interrupt Generation Point and Actual Zero Point of AC220V

Figure 2-3 Actual Interrupt Generation Point

When the voltage decreases to 0.7V, as shown in Figure 2-3, the rising edge occurs on PB4 and the interrupt occurs at the same time. Between the interrupt generation point and the actual zero point of the AC220V, we can see a time error which is related to the output voltage of the transformer and the voltage dividing of the resistance connected to the triac. In this circuit, the ideal calculation for the time error between the interrupt generation point and the actual zero point is:

0.7=4.5√2 *sin(w * t)

where 4.5√2 is obtained by dividing the peak voltage 9√2 with two 10K resistors.

W=2*3.14* f (f 为 50Hz)

After calculation, t=350us.

Measured in practical via oscillograph, the time error between the interrupt generation point and the actual zero point is approximately 500us.



3 Software Description

3.1 Source File

File Name Function Type

main.asm Main process Source file (Sample)

Zero_Detect.asm Zero cross detection process Source file (User)

SPMC65P2404A.inc SPMC65X symbol definition Head file

3.2 Subroutines

V_Reset

Content Memo

Input None Output None Description Vector address pointed after MCU power on reset Caller main.asm

V_IRQ

Content Memo

Input None Output None

Description Zero crossing display which synchronizes with the zero point of power supply.

Caller main.asm

F_Main

Content Memo Input None Output None Description Wait for the generation of zero crossing interrupt. Caller Main.asm



F_Light

Content Memo

Input None

Output None

Description Drive the LED which synchronizes with the zero point of power supply

Caller Zero_Detect.asm

F_IO_Init

Content Memo

Input None

Output None

Description Initialize PA5~PA0 as the low level output pins, PB4 as the input pin.


F_IRQ0_Init

Content Memo

Input None

Output None

Description Configure PB4 as external interrupt which is triggered on the rising edge.


3.3 Variables

IB_10msCount

Content Memo

Description 10ms counter, which increases 1 every 10ms.

Size 1byte

Initialization Random

Symbol None

Content $0~$FF



4 Flowcharts

4.1 Main Flowchart

Start（V_Reset）

Initialization for interrupt (F_IRQ0_Init)and IO port (F_IO_Init)

Circular wait

Figure 4-1 Main Flowchart

4.2 Interrupt Subroutine

V_IRQ

Zero crossingdisplay（F_Light）

Return

Figure 4-2 Main Flowchart



4.3 Display Subroutine

F_Light

（IB_10msCount）+ 1

Return

Send bit5~bit0 of IB_10msCount toPA5~PA0 for display

Figure 4-3 Zero Crossing Display

AN_SPMC65_O0322_en_V1.2

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