Relay Switching Module with Contact Protection HM226
Total Page：16
File Type：pdf, Size：1020Kb
Engineering Sample Information MODULE ASSEMBLY HM226 - L / T REVISION 5.0 2007 Dec 11 Relay Switching Module with Contact Protection HENDON SEMICONDUCTORS 1BUTLER DRIVE HENDON SA 5014 AUSTRALIA HM226 - L / T Protected Relay Switching Module CONTENTS 1 FEATURES 2 GENERAL DESCRIPTION 3 QUICK REFERENCE DATA 4 CONNECTIONS AND LAYOUT 5 CIRCUIT DIAGRAMS 6 FUNCTIONAL OVERVIEW 7 CIRCUIT DESCRIPTION 8 HM226 MODULE LOGIC CONTROL 9 HM226 MODULE THERMOSTAT 10 IMPORTANT ELECTRICAL SAFETY WARNING 11 REFERENCES 12 DOCUMENT HISTORY 13 DEFINITIONS 14 COMPANY INFORMATION 15 DISCLAIMER 2007 Dec 11, Revision 5.0 2 Engineering Sample Information HM226 - L / T Protected Relay Switching Module 1 FEATURES 2 GENERAL DESCRIPTION • Protects relay contacts from damage due to arcing of The HM226 as supplied is an electromechanical mains voltage in high load applications thermostat for heating loads up to 10 amps. It can also be • Relay control does not suffer from the heat dissipation configured as a logic controlled switch. It uses a relay and limitations of similar triac control solutions triac to control the load. It is designed to operate from 230Vac mains power, and can be designed to operate • Uses a small inexpensive triac to momentarily protect from 110/120Vac. It uses the IES5541A Relay Driver with the relay from arcing during switching Contact Protection integrated circuit to control the relay • Relay switching can be either temperature sensor and triac. triggered or digitally controlled An electronically switched relay is ideal in situations where • Designed to drive resistive and inductive loads up to heat dissipation from a triac is an issue. However, relays 2.3kW are usually only rated for around 100,000 electrical • Uses common NTC thermistor temperature sensors switching cycles, failing due to contact degradation. Until • Significantly reduces Electro-Magnetic Interference now this has prevented their use in thermostats, which (EMI) by zero crossing load switching require regular switching to maintain the desired temperature. The HM226 uses a triac to conduct the initial • Greatly extends the lifetime of the relay contacts in and final load current of each relay switching cycle, constant switching applications minimizing relay contact arcing. • Allows fast relay switching for improved temperature Using the IES5541A and a triac, the relay life can be control, without causing early relay failure extended to over 10 times the relay’s rated electrical • Provides a complete sensing and control solution for switching cycles. This enables relay control in constant resistive and inductive loads switching high load applications such as home heating, cooking appliances and fabric care products. 3 QUICK REFERENCE DATA SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNIT VSUP AC supply voltage (note 1) 207 230 253 V ILOAD load current −−10A Tstg storage temperature range −25 − +85 °C Tamb operating ambient temperature in free air 0 − +70 °C range Note 1. The operating voltage range can be set to any desired AC range by selection of power supply resistors. Application circuits are easily designed for 100−120 V, or even an extended voltage range such as 100 to 250 V. 2007 Dec 11, Revision 5.0 3 Engineering Sample Information HM226 - L / T Protected Relay Switching Module 4 CONNECTIONS AND LAYOUT 70mm TOP VIEW Load Neutral 61mm Active Load 0V θ 100k +5V NTC / Logic Input BOTTOM VIEW Load Active Neutral Load Fig.1 HM226 PCB connections and layout 2007 Dec 11, Revision 5.0 4 Engineering Sample Information 2007 Dec 5.0 11, Revision 5 5 DIAGRAMS CIRCUIT ACTIVE ACTIVE Rm Rp R11 Load 39k 220k 10k C3 2W 1nF C6 250Vac LOAD 100nF R2 X2 Lk2 220k R1 R6a 220k T2 D4 NTC or Logic Input 5k1 BC856 BAS16 RE1 R6b C5 48V DC 5k1 ZD2a ZD2b R3 4.7uF Lk3 0R C7 230Vac 47nF Mains D1 X2 Supply 8 5 S1G TR1 VR1 PWR TSEN R12 BT137 R4 100k 2 SENS SG 10k/ 600E 4 Lk4 C4 Switching Module Protected Relay IC1 2.2uF IES5541A R14 47R 7 CAP TG LED 6 Vee COM Ra R5 Lk1 1 3 R7 R9 R8 VDR 220k 10k 3k9 330R 10k SCR1 BT168GW R10 Engineering Sample Sample Engineering Information 10k HM226 T -L/ T1 BC857 NEUTRAL R13 C2 C8 D2 Rb C1 47k 100uF 100nF BAS16 HM226rev2schematic 470k 470nF 25V Fig.2 HM226 Module complete circuit diagram 2007 Dec 5.0 11, Revision 6 5.1/ LogicControl Schematic -L HM226 ACTIVE ACTIVE Rp R11 Load 220k 10k C3 2W 1nF 250Vac LOAD R6a T2 D4 Logic Input 5k1 BC856 BAS16 RE1 R6b C5 48V DC 5k1 ZD2a 4.7uF Lk3 230Vac Mains Supply 8 5 TR1 PWR TSEN Lk4 BT137 2 SENS SG 600E 4 IC1 Switching Module Protected Relay IES5541A 7 CAP TG LED 6 Vee COM Ra Lk1 1 3 R7 R9 R8 220k 3k9 330R 10k SCR1 BT168GW R10 Engineering Sample Sample Engineering Information 10k T1 HM226 T -L/ BC857 NEUTRAL R13 C2 D2 Rb 47k 100uF BAS16 HM226rev2logic 470k 25V Fig.3 Basic schematic of the HM266 Logic Control Module HM226 - L / T Protected Relay Switching Module 6 FUNCTIONAL OVERVIEW The HM226 Relay switching module with contact 6.1 Technical background protection provides a general purpose platform for relay The HM226 contains a relay driver with contact protection control of loads up to 10A. The relay can be triggered by a IC (IC1); the IES5541A. The module is designed to NTC (negative temperature coefficient) thermistor or an showcase the relay contact protection that is offered by the external digital logic source. The HM226 is designed IES5541A in constant switching applications. In its most around the IES5541A IC and uses a triac to prevent arcing common applications a load is thermostatically controlled of the relay contacts during switching to extend the relay by the module using an external NTC as the temperature lifetime. sensor. Two options for controlling the HM226 are included in the The HM226 uses an inexpensive low coil voltage DC relay design. An NTC can be used to provide an input to the rather than an AC driven relay. A network of diodes, module in order to switch the relay. Alternatively a digital resistors and capacitors allow the DC relay to be switched input from such devices as a microcontroller or FPGA (field using a SCR from AC mains. programmable gate array) can be used to control the switching of the load. These control options suit a wide Although the triac may carry the load current during variety of applications in heating element control and the switching the heat dissipated in the triac is not significant home appliance market. in this application as the triac only conducts the load current for very short periods of time during relay opening The HM226 can accommodate a wide temperature sense and closing operations. range. To vary the range the designer only needs alter the resistor values in the temperature sensing part of the For a detailed description of the functioning of the circuit. For more accurate temperature control, circuitry IES5541A integrated circuit refer to the Data Sheet can be included external to the HM226. The NTC chosen “IES5541A Relay Driver with Contact Protection”. will also affect the range and sensitivity of the HM226. A relay driven load is preferable to a triac driven load in situations where heat dissipation is an issue. A triac switching a 10A load requires a large heatsink and may need to be mounted remotely from the PCB. A relay can switch a 10A load with no heat dissipation issues, allowing it to be mounted on the PCB to provide a more compact device. A relay’s main drawback is the arcing that can occur between the contacts of the relay during switching. This leads to burning, pitting and increased resistance, eventually leading to failure of the contacts. The HM226 all but eliminates arcing of the relay contacts. The IES5541A provides a means for protecting the relay contacts during switching using a small inexpensive triac. When the IES5541A senses the first signs of arcing across the relay contacts during relay open/close, the triac is fired. The triac is also refired 8 times at regular intervals for four full mains cycles when the relay is closed. For a mains frequency of 50Hz for example, this time window where the triac may be triggered will be 80ms. The HM226 consists of the basic HM226 printed circuit board and comes preasembled with all the components required to implement a logic controled switch function. 2007 Dec 11, Revision 5.0 7 Engineering Sample Information HM226 - L / T Protected Relay Switching Module 7 CIRCUIT DESCRIPTION This section describes the circuit design approach used in 7.4 Choice of Thermistor application of the IES5541A relay driver IC. In the HM226 It is necessary to choose a thermistor which has a there are options to satisfy different application needs and resistance of at least 1,000 Ω at the operating temperature ranges. temperature, otherwise the voltage across the thermistor will be too small to provide accurate and adequate 7.1 Mains Supply Voltage sensitivity. It is also important to ensure that the thermistor The HM226 circuit using the IES5541A have been can be mounted in a way that is electrically safe, is designed for Australian standards, where the normal protected from the access of moisture, and which provides supply voltage is 230 Volts. However the IES5541A is good thermal contact to the intended thermal measuring interfaced to the mains supply by a number of high voltage point. resistors which can be selected to suit the design supply voltage range. 7.5 Thermistor Mounting Considerations The considerations involved in choosing the power supply, As the thermistor is electrically live to mains voltages it SCR and triac drive components are the current draw of must be adequately insulated for use in each application.