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 Safety / Protection Circuits
Safety / Protection:  # - G        H - Q        R - Z

Last Updated: November 30, 2017 10:28 AM
Circuits Designed by Dave Johnson, P.E. :
Sound Triggered Night Light -  A while back, I received a schematic from a guy by the name of Karl.  He described a situation he and his wife found themselves in aboard a cruise ship in the Caribbean.  They were staying in a room toward the inside of the ship, which did not have any port holes, windows or a balcony. . . Circuit by David A. Johnson P.E.-August, 2013

Capacitance Proximity Switch
Draws very low power - Ideal for battery-powered applications
6 Models Available - Call 806-368-7747

Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

Solid-State Flasher Has Short-Circuit Protection -  01/16/97 EDN Design Ideas:  The circuit in Figure 1 switches an inductive or resistive grounded load using a bootstrapped, n-channel, power MOSFET.  The circuit features short-circuit, reverse-polarity, and transient-input-voltage-spike protection.  The input voltage, VDD, can vary from about 18 to 30V, and the circuit can handle as much as approximately 10A with proper heat sinking of the FET.  The circuit flashes at a rate of about 100 flashes/minute, with a duty cycle of about 47%.  You can use this circuit as a solid-state flasher for vehicles with 24V nominal-power systems. __ Circuit Design by Navdhish Gupta, TDF Corp, Naperville, IL

Sound Triggered Night Light -  A while back, I received a schematic from a guy by the name of Karl.  He described a situation he and his wife found themselves in aboard a cruise ship in the Caribbean.  They were staying in a room toward the inside of the ship, which did not have any port holes, windows or a balcony. . . Circuit by David A. Johnson P.E.-August, 2013

Spark Detector Uses Proximity -  27-Nov-08 EDN Design Ideas:  Use a Hall-effect sensor to measure engine rpm with a voltmeter __ Circuit Design by Robert Most, Ferris State University, Big Rapids, MI

Spark gaps Provide ESD Protection -  09/01/97 EDN Design Ideas:  Using a spark gap fabricated as part of the conductor pattern of a pc board provide as significant protection against ESD damage to an interface circuit.  Working with inexpensive passive components, spark gaps can protect interface connector pins against repeated 25-kV discharges.  And if you position the spark gap under the connector body, no additional pc-board space is necessary. __ Circuit Design by Bill Ehlers, PSC Inc, Eugene, OR

Speaker Protection & Muting -  Protect speakers from turn-on and turn-off transients and amplifier faults    __ Designed by Rod Elliott  ESP

Stabilized Power Supply with Short Protection -  Here is an efficient 4-stage stabilized power supply unit for testing electronic circuits.  it provides well regulated and stabilized output, which is essential for most electronic circuits to give proper results.  The circuit provides an audio- visual indication if there is a short circuit in the PCB under test, so the power supply to the circuit ‘under test’ can be cut-off immediately to save the valuable components from damage.  __ 

Standby Power-Loss Preventer -  Electronic devices consume some power even in the standby mode, i.e., when they have been switched off using a remote handset but not the mains power switch.  For instance, when a...__ Electronics Projects for You

Switcher improves overvoltage-protection -  10-Jun-04 EDN Design Ideas:  Overvoltage-protection circuits often protect electronic devices from power-supply transients, such as a rise from plugging in batteries or an external power adapter.  Although these devices traditionally find use as hysteretic switching controllers, you can reconfigure the LM3485 (Figure 1) to provide a robust overvoltage-protection circuit __ Circuit Design by Jason Rubadue, National Semiconductor, Thornton, CO

Synchronize asynchronous reset -  01/06/00 EDN Design Ideas:  Synchronous reset and asynchronous reset are both common reset mechanisms for state machines, and the reset circuit in Figure 1 combines the advantages of each.  Synchronous reset has the advantage of synchronization between clock and reset signals, which prevents race conditions from occurring between the clock and the reset signal.  However,  __ Circuit Design by Willy Tjanaka

Thermal Shutdown/ Protection -  The thermal protection of amplifiers is always a concern, since overheating is a sure way to reduce the life of semiconductors and other components.    Where you don't want to use a fan (such as in Project 42 - Thermo-Fan for Amplifier Cooling) , then a complete shutdown can be performed.   __ Designed by Rod Elliott  ESP

Thermal switches provide disconnect -  09/04/03  EDN Design Ideas:  A single temperature sensor can provide an interrupt to a microcontroller when the measured temperature goes out of range.  You need multiple temperature sensors when you have to monitorthan one hot spot.  A microcontroller implements __ Circuit Design by Mark Cherry, Maxim Integrated Products, Sunnyvale, CA

Three- Phase Appliance Protector -  Many of our costly appliances require three-phase AC supply for operation.  Failure of any of the phases makes the appliance prone to erratic functioning and may even lead to failure.  Hence...__ Electronics Projects for You

Three-Phase Motor Driver Prevents Stall -  01/05/95 EDN Design Ideas:  The circuit in Fig 1 drives a small 24V, 50-Hz motor at about 30 to 40 Hz for use as a chopper motor.  The best starting speed for the motor is about half the final running speed.  Therefore, the circuit uses an intermediate speed to prevent a stall condition.  The circuit uses IC 1Ato count down two cycles after the selection of the intermediate speed.  IC 1B's Johnson divide-by-three counter and IC 2's gates generate the 1208 phase angle __ Circuit Design by PM Kirkby , Crumpsall Electronics, Surrey, England

Traffic Baton -  in small towns, there are no traffic lights and the police regulates the traffic with hand signals.  Since their hand signals may not be visible at night, it is necessary to...__ Electronics Projects for You

Transistors offer thermal protection for controller -  07/19/01 EDN Design Ideas:  When a switch-mode power-supply controller, such as On Semiconductor's NCP1200, operates at a high ambient temperature, you should protect the entire power supply against lethal thermal runaway.  The NCP1200 operates directly from the power mains without an auxiliary winding; therefore, the die in the IC dissipates power (Figure 1)  __ Circuit Design by Christopher Basso, On Semiconductor, Toulouse, France

Turn your old inverter into an emergency power system -  An inverter turned into emergency power system, which turns on when the mains supply fails, and more importantly doesn’t turn on when the main supply is available  __ Designed by Robin Chalana & Sani Theo

Two buttons provide safe start -  07/06/00 EDN Design Ideas:  The circuit in Figure 1 provide as a safety interlock that checks the actuation of two pushbuttons before enabling a relay.  When you push both buttons, the circuit actuates the relay.  At that point, you can release one of the switches without the relay' __ Circuit Design by Vincent Himpe, Alcatel Microelectronics, Desselgem, Belgium

Voltage Monitor Prevents Deep Discharge of Battery -  09/26/96 EDN Design Ideas:  To avoid the deep discharge that can destroy or shorten the life of a rechargeable battery, you must disconnect its load before the discharge is complete __ Circuit Design by Ron Clark and Larry Suppan, Maxim Integrated Products

Voltage Monitor with LED indicator -  This project is an accelerometer data acquisition system for automotive suspension analysis.  in other words it’s a low frequency spectrum analyzer based on Lanchpad TiVA Series from Texas Semiconductors.__ 

Voltage Protection -  Safety devices like fuses provide protection against excess current, but do nothing for transients and short duration spikes of high voltahe on the power supply lines.  This circuit uses the "crowbar" method and provides fast protection against transient voltage spikes __ Designed by Andy Collison

Watch-Dog for Telephones -  Most of the telephone security devices available in market are simple but quite expensive.  These devices provide blinking or beeping type line-tap/misuse indications.  Quite often they do not offer guaranteed protection against unauthor-ised operation.  A very simple and uni- que circuit of a telephone watch-dog to safeguard subscriber telephone lines against any fraud is described here.  This little circuit keeps continuous watch over the telephone lines and sounds an alarm in case of any misuse.  in addition it transmits a loud tone through the telephone lines to prevent further misuse.  __ 

Watchdog protects against loss of battery charger's control signals -  21-Jul-05 EDN Design Ideas:  Hardware circuit keeps software-based charging within limits __ Circuit Design by Andy Fewster, Maxim Integrated Products Inc, Hampshire, UK

Watchdog reset catcher aids embedded system Debugging  -  11/19/98 EDN Design Ideas:  NOTE: Multiple circuits included.  Scroll to find this one.   A simple "junk-box" circuit uses a 4013  CMOS flip-flop and a handful of passive components to determine whether random resets are the result of a blown stack or the result of the watchdog-reset circuit tripping (Figure 1).  You can also use this circuit to "grab" and hold __ Circuit Design by Scott Newell, PCSI, Fort Smith, AR

Watchdog Time-Out Is Independent Of Reset -  09/01/95 EDN Design Ideas:  Many embedded systems use µP supervisors with on-chip watchdog timers.  Some supervisors, such as the MAX691, allow you to select different watchdog and reset time-out periods, depending on how you connect pin 7 (Osc in] and pin 8 (Osc Sel].  Table 1 in the MAX691 data sheet indicates the available watchdog and reset time-out choices.  However, when you implement __ Circuit Design by Larry Buyan, Criticare Systems Inc, Waukesha, WI

Watchdog timer allows entry to test Mode -  07/19/01  EDN Design Ideas:  Manuals for microprocessor-based devices often include instructions for entering a "secret mode" in which you can test or reset the device.  These instructions typically ask you to depress and hold one or two switches for a minimum  __ Circuit Design by Greg Sutterlin and Larry Barnes, Maxim Integrated Products, Sunnyvale, CA, and Craig Gestler, Mining Safety Appliances Co, Mars, PA

Watchdog timer assumes varied roles -  02/01/01 EDN Design Ideas:  The MAX6369-74 series of pin-selectable watchdog timers are designed to superviseµP activity and indicate when a system is working improperly.  During normal operation, aµP should repeatedly toggle the WDI (watchdog input) before the selected watchdog-time-out period elapses to indicate that the system is properly executing code.   __ Circuit Design by Terry Millward, Maxim Integrated Products, Lambourn Hungerford, UK

Watchdog Timer Assumes Varied Roles -  The following App Note demonstrates alternative uses for the MAX6369-MAX6374 family of pinselectable watchdog timers.  Alternative uses include a power saving power-on LED indicator circuit, load connect/disconnect circuit and push-button reset circuit. (582) __ 

Watchdog Timer Reboots PC's -  06/05/97 EDN Design Ideas:  When you use a PC to control a process or collect data, it's often desirable to have a watchdog timer reboot the computer if it runs astray.  The circuit in Figure 1 uses a PIC 16C84.   __ Circuit Design by Charles Hamilton, Burr-Brown Corp, Tucson, AZ

Watchdog uses AC triggering -  08/16/01 EDN Design Ideas:  A dc-triggered reset of a watchdog circuit is prone to failure.  if the watchdog program hangs up, then the reset signal becomes activated continuously, and the microprocessor has no way to escape the situation.  We found that a simple solution uses an ac trigger to reset the watchdog circuit (Figure 1)  __ Circuit Design by Shyam Tiwari, Sensors Technology Private Ltd, Gwalior, India

Watchdog uses Leftover Gates -  08/01/96 EDN Design Ideas:  The reset and µP-controlled watchdog circuit in Figure 1 a makes good use of some unused inverter gates in IC 1.  The design is extremely simple.  The circuit is a continuously running oscillator with programmable high- and low-level pulse widths that have additional intervention-control input from the µP.  Because the circuit is a continuous running oscillator, the circuit generates __ Circuit Design by Shyam Sunder Tiwari, IGCAR, Kalpakkam, India

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