Solid-state sensing switches that protect people and equipment

Solid-state sensing switches that protect people and equipment. Summary: This article provides a typical introduction to the principles and applications of temperature and current sensing ICs produced by Raytheon and Teledye Components. . Taiqin Dyne's solid thermal switch IC replaces the expensive, vibration-sensitive bimetallic temperature sensor. Leitong's IC device detects leakage current of 5mA and is molded into a flexible wire device, which will enter homes, offices and Products for protecting people and equipment in factories. The common features of both products are small size and low price, about one dollar each. Temperature and current sensing ICs are products that will find their way into homes, offices, and factories. Text Two cheap chips manufactured by U.S. companies Ray Energy and Taikin Dyne Components help overcome two dangers inherent in every part of an electrical or electronic device - water and heat. Taikindyne ICs are the leading member of a new family of solid-state thermal switches that replace expensive, vibration-sensitive, double-layer metal sheet temperature sensors commonly used in applications ranging from coffee makers to home heating thermostats. The Taikindyne device is a low power, two-wire Ground Fault Intermittent (GFI) controller. Although it is designed to be used on hair dryers, it can be used as a safety component on items such as hair dryers. Because the purpose of Taiqin Dyne and Leitong IC is to provide consumers with low-priced products: to be small in size and as low as possible. Both the SC620 and TSC621 in Taikindyne ICs sense temperature: the TSC620 uses a monolithic ion-implanted resistor with an absolute accuracy of ±30°C, while the TSC621 uses an external thermistor. TSC620 can replace the instantaneous action thermal switches installed on many equipment or motors, providing simple on-off protection and/or control, etc. These ICs operate high and low temperature, user-programmable (with two resistors) setpoint inputs, and control logic outputs in groups of three. They provide a simple, yet versatile, multi-value temperature alarm or control system. A TSC620 and less than two dozen inexpensive components can make a complete home heating-cooling thermostat. 　　Figure 1. When the temperature of the chip rises to the specified upper and lower set values, the TSC620 temperature sensing switch produced by Taiqin Dyne Components Company is programmed to sense. When it reaches the upper set value, first turn on the MOSFET and then turn on the electric fan. When its temperature drops to the lower set value, it turns off. Connect a 90KΩ to 200KΩ resistor between each programming input and the power supply that determines the high and low temperature setpoints (Figure 1). The two logic outputs, Low and High follow the following truth table: Whenever the chip (or external thermistor) rises to the temperature programmed by their respective resistors, its Low and High outputs go high . That is, when the temperature rises, the lower limit output first becomes high, and then the upper limit output becomes high. When the chip (or thermistor) temperature drops, approximately two degrees below its programmed value, the limit outputs each go low. In a typical application, it could turn on an electric fan and alert the owner (human or silicon) when the low limit becomes high. If the temperature rises enough to cut off the upper limit, the system may stop working and turn off the alarm. When the sensed temperature rises to the upper setpoint, the control's logic output goes high, and when it falls below the lower setpoint, the control's logic output goes low. No more electric shocks! The working principle of Thundercom devices is that if an electric shock accident occurs, two AC lines will be cut off in less than 24ms. This means that it must detect a leakage current of 5 or 10mA (US regulations are 5mA, European regulations are 10mA) and cut off the line when it is 2Hz less than the power frequency of 50 or 60Hz. These two main characteristics affect the cost, design and time to market of a hair dryer alone. In order to detect and interrupt the leakage current of a ground fault, the RV4140 solves the problem on the other hand: no changes to the existing hair dryer design are required; Only a two-wire line is required between the wall outlet and the hair dryer (Figure 2). 　　The current solution is that you need three wires from the GFI to the hair dryer, and this third wire connects to a metal plate inside the hair dryer. This metal plate and third wire add to the cost. This metal plate requires redesign for both existing and newly designed hair dryers, as well as tooling changes, further increasing costs and design time. Finally, every new design and every redesign must be certified or recertified by UL, thus extending the time to market. The RV4140 and its circuitry eliminate such problems. It is shaped into a cordless device and, once certified, can be used to connect to any hair dryer or to any other device. To further reduce cost and size, the RV4140 contains a full-wave bridge rectifier, which must be added to common GFIICs (including the Thundercom RV4145). The core part of the detector is a current transformer with an annular laminated iron core or a solid iron oxide core. A ground fault creates a difference between the live and neutral currents. The amplified and rectified current generates an error voltage on pin I. If this error voltage is greater than the reference voltage on pin 3, comparator C closes and the SCR is enabled, thus opening the relay and the circuit to the hair dryer. Translated by Zhou Di from "ELECTRONIC DESIGN" originally published in "Practical Electronic Digest"