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AN1295 APPLICATION NOTE
A DEVELOPMENT BOARD TO DRIVE A TRIAC WITH ST52X420 DIRECTLY FROM THE MAINS
Author: A. Cucuccio
1. INTRODUCTION In this application note we intend to provide the user with a flexible and programmable tool to drive a Triac directly from the mains by using the ST52x420 microcontroller and the VB409 VIPower device acting as a 5.2V power supply. We present an electrical schematic representing a general purpose application to use the fuzzy microcontroller ST52x420 without the need of external components with the exception of the VB409. By using the external connectors it is possible to manage the microcontroller's peripherals including digital I/O, A/D converter and Timers. In particular, we will provide an example, written in the high level language of FUZZYSTUDIO TM4.0, to drive a load in phase angle partialization mode (see also AN1221: "A Simple Method to Drive a Triac With ST52x420 Directly From the Main"). The following figure describes the configuration of the board used in this application note: Figure 1. Board Configuration
Vcc=5V Zero crossing
VB409
Zero Crossing
ST52x420
230V~
GND
Load
TRIAC
Firing pulses
The blocks are: - ST52xx: a member of a ST52 microcontroller family - VB409: a VIPower device to obtain a 5.2V power supply direcly from the mains - Zero Crossing: a simple circuit to detect the zero crossing of the mains voltage - Triac: a device to switch on the load - Load: a generic resistive or inductive load
September 2000
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1 2
1 2 3
1 2 3 4 5 6 7 8
22K NTC PB0A PB0 PB6 PB5 PB4 PB3 PB2 PB1 PB0 VCC
PA7 PA6 PA5 PA4 PA3 PA2 PA1 PA0
1 2 3 4 5 6 7 8 9 10
Figure 2. Electric schematic
J8 DEV-PB0 J4 1 2
CAP TH_S INP GND OUT
D2 + 100uF BYW10-30 R7 1M 4 1 2 VCC BTB10-600CW C2 Q1 100pF R5 47K J1 TEST RESET OSCOUT ST52X420 1 2 3 R4 100 C1 VCC 9 10 11 12 15 16 17 PB0/AIN0 PB1/AIN1 PB2/AIN2 PB3/AIN3 PB4/AIN4 PB5/AIN5 PB6/AIN6 PB0A PB1A PB2 PB3 PB4 PB5 PB6
VCC 1 2 3 4 5
220Vac-input VCC 2 IN GND OUT 1
1 2
3
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VCC R2 J6 PC3 J7 J10 CON8 PA[0..7] 5VDC OUT U1 D1 1N4148 C6 J9 D4 1uF PB1 3 PB1A 2 1 DEV-PB1 5 PC0/INT 6 PC1/T0OUT 7 PC2/T1OUT 8 PC3/T2OUT VPP VDD VDDA VSS GNDA U2 VB409 PA0/T0RES PA1/T0OUTN PA2/T1OUTN PA3/T2OUTN PA4/T0STRT PA5/T0CLK PA6 PA7/AIN7 26 28 13 27 14 PA0 PA1 PA2 PA3 PA4 PA5 PA6 PA7 25 24 23 22 21 20 19 18 VCC VDDA R8 220K OSCIN 3 RISUON.4.91Mhz VDDA R9 U3 10K TS831
AN1295 - APPLICATION NOTE
R1
R3 47K
BYT11/600
R6
D3
220K
BYT11/600
F1 2.5A
J3
2 1
J2
2. ELECTRIC SCHEMATIC To have a complete idea of the connection between the various devices present on the board we can refer to the following schematic:
In our application we have also placed a micropower voltage supervisor TS831 that acts as a power-on reset generator for the microcontroller and as a power failure detector.
LOAD
AN1295 - APPLICATION NOTE
The zero crossing circuit is realized with only two resistors and two diodes: R6 to limit the current, R3 to pull-up to 5V the zero crossing signal, D2 to cut a half-wave and D1 (a signal diode) to clamp to ground the zero crossing signal when it goes under the ground. The zero crossing signal is used to sincronize the microcontroller to mains voltage through the external interrupt pin PC0/INT. The VB409 is a fully protected positive voltage regulator. The device is well suited for applications powered from the AC mains and requiring a 5.2V DC regulated output voltage without galvanic isolation. The ST52x420 fuzzy microcontroller can be used to drive the Triac in phase angle partialization mode (see ST52x420 datasheet). To implement this, we need only the zero crossing signal: by triggering this signal with the external interrupt pin (PC0/INT) it is possible, by using the internal Timer, to generate the appropriate firing pulses to switch on the Triac. Note that to have enough current capability in order to fire the triac we use two pins of the microcontroller (PC1 and PC2) connected together (see AN 1221). To fully exploit the potentialities of ST52x420, some connectors have been inserted: - J4: to access the digital I/O PORT_A (or the Timer0 signal when configured in alternate function). - J10: - J8: - J9: - J6: to access the digital I/O PORT_B (or the A/D inputs when configured in alternate function). a switch to connect the PORT_B Pin0 to an on-board NTC device instead of the connector J10. a switch to connect the PORT_B Pin1 to an on board Trimmer device instead of the connector J10. to access directly the digital I/O PORT_C Pin3 (or the Timer2 output when configured in alternate function).
- Dev-PB0: with this jumper it is possible to connect the pin PB0 to the connector J10 or to the on-board NTC sensor. - Dev-PB1: with this jumper it is possible to connect the pin PB0 to the connector J10 or to on-board trimmer R5. - VB409: in this section will be considered the capability of the VB409 to supply an appropriate current to the devices. The behaviour of the VB409 will be described starting with an external capacitor of 47F. The theoretical maximum current the device can supply, can be derived considering that the minimum value on the CAP pin, at the end of the half-period in which the mains is not rectified, must be at least Vout(5V)+V dropout(2V). During this period there is a discharge of the external capacitor at constant current, so the voltage variation on it is linear. Thus, the theoretical maximum current the device can supply is:
Imax=C*Vcapmax/(T/2) In this case T/2=10ms, Vcapmax=12.8-7=5.8V, C=47F and then Imax=27mA.
Considering the current required to drive the linear part of the device it is possible to say that Imax=23mA. With this configuration we have measured the maximum temperature on the device (without heatsink) to be lower than 65C. If we consider an external electrolytic capacitor of 100mF the maximum theoretical current is about Imax=55mA, but practically only 40mA must be considered because at this current value the thermal shutdown acts. For further information about VB409, please refer to the relative datasheet. - TRIAC: with the power supply configuration used it is necessary to use a standard Triac in order to fire it by applying a negative pulse to respect the ground (and therefore respect to A1 Triac pin) through the derivative effect of C6.
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AN1295 - APPLICATION NOTE
3. CONCLUSION In this application note we propose a general purpose board with the goal to have a flexible interface towards the application. This allows to: - generate the firing pulses for a Triac - have a synchronization with an external sinusoidal voltage - generate up to 8 bit PWM signals - read analog or digital sensors - measure the period of an external signal (like a tachometer) - exploit the computation capability of the ST52x420 microcontroller An example on the management of the board (AN1295.fs4) can be found on the ST52 Microcontrollers web site: www.st.com/stonline/prodpres/
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specification mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a trademark of STMicroelectronics (c) 2000 STMicroelectronics - All Rights Reserved FUZZYSTUDIOTM is a registered trademark of STMicroelectronics STMicroelectronics GROUP OF COMPANIES http://www.st.com Australia - Brazil - China - Finland - France - Germany - Hong Kong - India - Italy - Japan - Malaysia - Malta - MoroccoSingapore - Spain - Sweden - Switzerland - United Kingdom - U.S.A.
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