Triac Switch

Why Because I needed to switch a bank of five monitors (three flat-panels, two CRTs) from one switch. I originally used a 12-volt relay, but that turned out to be suboptimal; the inrush current for all five power supplies was so high the relay contacts tended to get welded together and occassionally required a swift tap to disconnect, gradually degrading until they had to be replaced. As solid-state devices tend to have much higher peak current capabilities, after wasting the third relay I decided to replace the whole design. What The unit is just a simple triac switch, with an optoisolator calculated to handle 5 to 12 volts. Future upgrade to USB control is thus possible without modification of parts values. The unit lacks a snubber. This was omitted due to the capacitive nature of the load. Transients on the mains may open the triac momentarily. The unit is however connected through a transient suppressor, and problems of this nature were not observed so far. TODO Snubber (if needed) Replace the K3021 with MOC3041 (or TLP3041) for zero-cross switching Replace the whole unit with six individually controlled sockets Images Outside view, topOutside view, sideOutside view, top-side

Inside viewInside viewLow-voltage part, detail

Smart Trailing SocketCircuit diagram:

Final del formulario

R1,R2_________100R 1/2W Resistors

C1____________100nF 630V Polyester Capacitor

D1 to D6_____1N5408 1000V 3A Diodes (See Notes)D7__________TIC225M 600V 8A Sensitive Gate Triac (See Notes)

A commercial trailing socket to be modified or a self-made box with several sockets.

Comments:This circuit consists of a Trailing Socket (also called Extension or Distribution Socket) or similar device where two, three or more sockets (depending on the box dimensions and on constructor's needs) will be powered only when a current flows in the Control Socket.For example: if an electric drill is connected to the Control Socket, the Switched Sockets will be powered each time the electric drill is running. In this case, a lamp could be connected to a Switched Socket and will illuminate when the drill is operating.Another example: a desk lamp could be connected to the Control Socket and a PC, a Monitor and a Printer could be connected to the Switched Sockets and will be running after the lamp is switched on. Switching off the lamp, all the above mentioned appliances will be automatically switched off.A further application is the control of a High Fidelity chain, plugging the Power Amplifier in the Control Socket and - for example - CD Player, Tape Recorder, and Tuner in the Switched Sockets. Usually, trailing sockets are placed to the rear of the appliances, often in places not easily reachable, so, even if the socket has a switch, it is much easier to switch on and off the High Fidelity chain from the main amplifier itself.The same consideration is valid for computer-monitor-printer chains etc. Nevertheless, in this case, the use of a table lamp plugged in the Control Socket is almost mandatory, as explained below.In fact, this very sensitive circuit works fine when appliances having full breaking switches like lamps, drills, most power amplifiers, old radios, old TV sets, fans, almost all electrical household appliances etc. are plugged in the Control Socket. This is because these devices have a switch that fully excludes the internal circuitry from the mains.Unfortunately, in modern devices like computers, monitors, CD players, recent radios and TV sets (usually powered by means of internal "switching" supplies), the power switch does not completely isolate the internal circuitry from the mains, as transient suppressors and other components remain on circuit. This causes a very small current to flow across the sensing circuitry, but sufficient to trigger the output Triac.Therefore, the switched devices will remain always on, no matter if the control appliance is on or off. This could also happen when devices connected to the mains by means of plug-in power supply adapters are used as control appliances, due to their lack of a mains switch.In spite of this restriction, the circuit can be still useful, due to the high number and variety of devices allowing impeccable performance when they are plugged in the Control Socket. Circuit operation:Six back-to-back power diodes are connected in series to the Control Socket. The current drawn by the device plugged into this socket when in the on state, flowing through the diode chain, causes a voltage drop of about 2V. This voltage, limited by R1, drives the Gate of the Triac D7 which, in turn, will switch the output sockets.C1 and R2 form a so called "Snubber network", helping to eliminate switching transients generated by inductive loads.

Notes: The circuit is sufficiently small to be embedded into some types of commercial trailing sockets, or a box with a number of sockets can be made at will. The diode types suggested in the Parts List for D1 to D6 will allow an appliance of up to about 500W power to be plugged in the Control Socket. Use BY550-800 diodes for up to 800 - 1000W. For less demanding appliances, 1N4007 diodes will allow up to 200W power. The Triac type suggested in the Parts List for D7 will allow a total power available to the Switched Sockets of more than 1000W. If you intend to drive loads of more than 500W total, please use a suitable heatsink. Wanting to drive less powerful loads, you can use for D7 a TIC216M (up to 800 - 1000W) or a TIC206M (up to 500 - 600W). Warning! The device is connected to 230Vac mains, so some parts in the circuit board are subjected to lethal potential! Avoid touching the circuit when the mains cord is plugged in!http://www.redcircuits.com/index.htmlModular Preamplifier Control Center

Circuit diagram:

Parts:Principio del formulario

Final del formularioP1______________47K Log. Potentiometer (twin concentric-spindle dual gang for stereo)

R1,R2,R4_______100K 1/4W ResistorsR3,R14_________560R 1/4W ResistorsR5_______________1K 1/4W ResistorR6,R7,R10_______10K 1/4W ResistorsR8,R9___________22K 1/4W ResistorsR11_____________68K 1/4W ResistorR12______________1K5 1/4W ResistorR13_____________12K 1/4W Resistor

C1_______________1F 63V Polyester CapacitorC2,C3__________100pF 63V Polystyrene or Ceramic CapacitorsC4______________47nF 63V Polyester CapacitorC5______________22nF 63V Polyester CapacitorC6_____________220pF 63V Polystyrene or Ceramic CapacitorC7,C10_________100nF 63V Polyester CapacitorsC8,C11___________47 25V Electrolytic CapacitorsC9,C12________2200F 25V Electrolytic Capacitors

IC1___________TL072 Dual BIFET Op-AmpIC2___________78L15 15V 100mA Positive Regulator ICIC3___________79L15 15V 100mA Negative Regulator IC

D1,D2________1N4002 200V 1A Diodes

SW1____________DPDT Toggle SwitchSW2____________2 poles 3 ways Rotary Switch

J1,J2,J3,J5____RCA audio input socketsJ4_____________Mini DC Power SocketComments:This is the first article of a five-part series describing a complete audio preamplifier formed by five Mini-Modules, namely: Control Center, Switching Center, Phono Preamplifier, Tone Control and Headphone Amplifier. A suitable Power Amplifier module is already available here: 45 Watt Class B Amplifier.The arrangement of these modules is similar to a late-1980's commercial production, the Thorens Restek Mini-Modules. Obviously, all the circuits of this Modular Preamplifier are original designs and have no relationship with the Thorens Modules.The modular arrangement allows the amateur to choose only the modules more suited to his requirements in order to build a chain one to five modules long.For the minimalist, the Control Center module described in this page will be most probably the only useful module, allowing the choice of two input sources, e.g. a CD player and an Aux input (Tuner or iPod etc.).The purist can also omit the Loudness control available there: the 2 poles 3 ways Rotary Switch used for this control (SW2) can be converted into a three-input selector switch. Therefore, the two-input selector SW1 at the center of the front panel, can be substituted by a 3mm stereo mini-jack socket, allowing, for example, the quick and easy plugging of an iPod.Each module, excepting the Switching Center that is a passive circuit, incorporates its own separate power supply rectifiers and regulators and requires only an external 15 - 18V ac (50mA minimum) Power Supply Adaptor.In a chain formed by several modules, the use of a series of Power Supply Adaptors may be considered excessive. In such cases, the dual 15V dc stabilized supply can be carried from a main module to the others by means of a three-wire cable and suitable connectors. Or the ac output of a single Power Supply Adaptor can be routed to several modules by using two Mini DC Power Sockets in each module wired in parallel, allowing to use a two-wire cable interconnection.Each electronic board can be fitted in a standard enclosure: Hammond extruded aluminum cases are well suited to host the boards of this preamp. In particular, the cases sized 16 x 10.3 x 5.3 cm or 22 x 10.3 x 5.3 cm are the more appropriate and can be stacked with advantage.Control Center circuit description:This circuit features two high-level inputs switched by SW1, followed by the unity-gain high input impedance buffer IC1A. The output of this buffer drives the passive network Loudness circuit. Its control switch SW2A allows the choice of two different frequency compensation curves (see graph below) to be used when the sound programme is reproduced at low levels. Curve I should be used with low to mid reproduction levels, in practice when the volume control knob is set around the second quarter of its travel. Curve II is best suited to very low levels, i.e. when the volume control knob is set around the first quarter. To obtain a perfectly flat frequency response, the Loudness control must be set in the OFF position.The following Op-Amp (IC1B) provides all the gain required by the preamplifier, featuring 166mV RMS input sensitivity at 1.5V RMS output with very low distortion. Therefore it is capable of driving low input sensitivity power amplifiers.The dual rail power supply necessary for this circuit is drawn from the single 15 - 18V ac voltage provided by a suitable external Power Supply Adaptor. D1 and D2 rectify respectively the positive and the negative half wave in order to obtain a dual opposite polarity rail voltage referred to ground. IC2 and IC3 provide a well regulated 15V dc supply to the Op-Amps.Notes: The circuit diagram shows the Left channel only and the power supply. Some parts are in common to both channels and must not be doubled. These parts are: P1 (if a twin concentric-spindle dual gang potentiometer is used), IC2, IC3, C7, C8, C9, C10, C11, C12, D1, D2, SW1, SW2 and J4. This module requires an external 15 - 18V ac (50mA minimum) Power Supply Adaptor.

Technical data:Input sensitivity:166mV RMS for 1.5V RMS outputMaximum output voltage:9.5V RMS into 10K loadFrequency response:flat from 20Hz to 23KHzTotal harmonic distortion @ 1KHz and 10KHz:less than 0.002% at all levels up to 9.5V RMS (0.0017% typical)Loudness Frequency Response:

A possible arrangement of the front and rear panels of this Module

Simple Capacitance Meter

Operates in conjunction with a voltmeter1pF to 22F in six Ranges - 9V Battery supply

Circuit diagram:

Parts:Principio del formulario

Final del formularioP1_____________470R Linear Potentiometer

R1 to R6________47K 1/2W Cermet or Carbon TrimmersR7______________10K 1/4W ResistorR8_____________100R 1/4W Resistor

C1_______________1nF 63V Polyester or Polystyrene Capacitor 5% Tolerance or betterC2______________10nF 63V Polyester or Polystyrene Capacitor 5% Tolerance or betterC3_____________100nF 63V Polyester Capacitor 5% Tolerance or betterC4_______________1F 63V Polyester Capacitor 5% Tolerance or betterC5______________10F 25V Electrolytic Capacitor (See Notes)C6______________47F 25V Electrolytic Capacitor

IC1____________4093 Quad 2 input Schmitt NAND Gate ICIC2___________78L05 5V 100mA Regulator IC

SW1____________2 poles 6 ways Rotary SwitchSW2____________SPST Toggle or Slide Switch

J1,J2__________1 or 2mm. chassis sockets (See Notes)J3,J4___________4mm Output sockets

B1_______________9V PP3 Battery

Clip for PP3 BatteryComments:A Capacitance Meter can be an useful tool for the electronics amateur, mainly to measure the value of capacitors obtained after dismantling old radios, PC cards and other electronics appliances.Good quality capacitors can be found frequently, but often their capacitance value is unknown because the lettering on the case is hardly readable: in some cases being partially or completely erased.This device can measure capacitors in the 1pF to 22F range with good accuracy if low tolerance capacitors are used for C1 - C5, and is even more appealing as it requires a common digital or analog Multimeter set to 2V dc voltage range to clearly and cheaply display the unknown capacitor value.This test tool can be useful also when a more tight value is required for a capacitor: selecting it from a batch will become much easier.Circuit Operation:In conjunction with a voltmeter, this circuit gives a direct reading of capacitance. IC1A and IC1B form an oscillator and buffer, the frequency being set by R1 to R6 trimmers and C1 to C5 capacitors switched by SW1A and B in six different ranges. Output goes to IC1D, one of whose inputs is inverted and delayed by the unknown component by time proportional to its value. At the output of IC1D, normally high, a negative-going pulse with a width proportional to the capacitance appears, the duty cycle of the output and, therefore, the average voltage indicating the value of capacitance.Supply voltage stability is required for accuracy: therefore, a small 5V voltage regulator IC was added.Circuit Calibration:To calibrate, set the dvm to its 2V range and remove CX, adjusting P1 for a zero reading (a very narrow pulse is present in this condition due to the inherent delay of IC1C). For ranges 2 to 6 (2nF to 20F) connect a capacitor of the same value and tolerance of C2 to C5 in the CX position, set the frequency switch and adjust R2 to R6 trimmers for reading the correct value on the Multimeter display.Obviously, this operation must be repeated five times, connecting the correct capacitor in the CX position and adjusting the corresponding Trimmer for each range.To calibrate the first range (200pF) set the frequency switch in the first position and connect a 100pF low tolerance polystyrene capacitor in the CX position. Then adjust R1 for a reading of 100 on the display.Notes: P1 must be adjusted for a zero reading (Cx removed) whenever the range is changed. A +100% - 20% tolerance value is very common for electrolytic capacitors. Therefore, C5 should be a low tolerance type or a 1F or 2.2F polyester capacitor, 5% tolerance or better, can be used in the CX position to calibrate the last range. Wiring from the circuit board to J1 and J2 must be kept as short as possible to avoid stray capacitance. As described in the Parts List, J1 and J2 can be chassis sockets of 1 or 2mm diameter, or even two short leads ended with crocodile clips, but perhaps the best solution is to use a 2 way spring loaded, lever action, quick connection loudspeaker terminal.Originally developed for terminating loudspeaker leads, these terminals have found numerous uses in applications requiring quick interconnection between equipment. The spring loaded lever allows wires to be easily inserted into the terminal where they are firmly trapped once the lever is released, giving a reliable connection. Total current consumption is 3.5mA. This is a modified version of an original circuit by Rae Perl, Helsinki, Finland. Simple Frequency Meter 10Hz - 200kHz in three rangesOperates in conjunction with a Digital Multimeter

Circuit diagram:

Parts:Principio del formulario

Final del formularioR1_______________2K2 1/4W ResistorR2______________10M 1/4W ResistorR3_____________100K 1/4W ResistorR4,R5__________330K 1/4W ResistorsR6,R7,R8_______100K 1/2W Cermet or Carbon Trimmers

C1,C2,C3_______220nF 63V Polyester CapacitorsC4,C8__________100nF 63V Polyester CapacitorsC5______________10nF 63V Polyester CapacitorC6_______________1nF 63V Polyester CapacitorC7_____________100F 25V Electrolytic Capacitor

IC1____________4011 Quad 2 input NAND Gate CMos ICIC2___________78L06 6V 100mA Regulator IC

D1___________1N4148 75V 150mA Diode

Q1____________BC547 45V 100mA NPN Transistor

SW1____________2 poles 3 ways Rotary SwitchSW2____________SPST Toggle or Slide Switch

B1_______________9V PP3 Battery

Clip for PP3 BatteryCircuit operation:A digital voltmeter or (with a bit less precision) an analog one, can be used for frequency measurements up to 200kHz using this circuit. The design is based on an original idea of Rae Perl, Helsinky, Finland.The frequency to be measured is amplified by Q1, but the input signal is limited to a maximum of about 2V peak-to-peak by R1, D1 and D2.The ac input of the logic gate IC1A is biased towards the switching point by resistors R4 and R5. In this way, the gate switches at a significantly lower input voltage than would otherwise be needed and changes its output voltage each time the input voltage passes the half supply voltage threshold.IC1A controls gates IC1B and IC1D. Gate IC1D output voltage is reversed and delayed by a capacitor (C4, C5 or C6) relative to gate IC1A's output. One input of gate IC1B is fed with the output voltage of IC1A and in the other input with the delayed voltage from gate IC1D. Output of gate IC1B comprises a negative pulse with a duration equal to the time it takes for gate IC1D to falling from its high state to its low state. Pulses from gate IC1B are then inverted in gate IC1C. These pulses are always similar in shape, independent of the amplitude and shape of the original input voltage.The mean value of gate IC1C's output voltage can then be measured by a digital multimeter with its 200mV dc voltage range selected.Three frequency measuring ranges (2kHz, 20kHz and 200kHz) are selected by SW1A, which connects a suitable capacitor to gate IC1D's output, and SW1B which in turn connects a trimmer for each range to gate IC1C's output.In this way the meter reading can be adjusted so that the voltage reading directly represents the unknown input frequency.The circuit requires a 6V regulated power supply, obtained from IC2 and a 9V battery, with a total current drawing of 2.5mA.Circuit Calibration:The circuit can be easily calibrated using tones of known frequency, centered for each range at 1kHz, 10kHz and 100kHz respectively. These tones can be easily obtained from sine or square wave generators, computer software (many free or shareware programs: simply type "tone generator software" on Google), or directly downloaded from the web as sound files of the desired frequency (type "audio tone files" or "test tone files" on Google).With the multimeter set to 200mV dc and an input signal of 1kHz, trim R6 to read 1000. Common 3 1/2 digits multimeters will display 100.0 but please forget the point.Trim R7 to read always 1000 with an input signal of 10kHz: in this case, the least significant digit of 10000 is not displayed but even in this range forget the point.Trim R8 to read 100.0 with an input signal of 100kHz: in this range the point is displayed correctly. Technical data:Input Sensitivity:2.5mV RMS from 100Hz to 20kHz7mV RMS at 100kHz10mV RMS at 15Hz and 200kHzTotal Current Drawing:2.5mANote: If an input sensitivity of about 280mV RMS is considered sufficient, Q1, R2, R3 and C2 can be omitted and the junction of R1, D1 and D2 can be connected to C3.

These are the original diagrams that led me to think of such a circuit. Typical dimmer circuit...

How to use a sensitive triac to control a power triac...

How to calculate the limiting resistor value...

I could not resist the temptation to use the off the shelf dimmer. I can buy the whole circuit for the control less than the parts. Its nice to have a mounting plate also. Whenever I build the 240 volt ones, I replace the pot and the cap. The off the shelf ones are not rated high enough on the capacitors. I tried it with disasterous results. The caps exploded and stank the place up really bad.

Triac regulator

Why Sometimes a mains-powered device needs lower than full power. To adjust it, a triac regulator can be used. The power of heating elements, lightbulbs, or the rotational speed of commutator motors can then be easily adjusted by turning a knob. What The regulator is built as a compact unit for laboratory purposes and ad-hoc setups. The input power connector is the IEC 60320 socket, the output is a standard European power socket. An off-the-shelf KPZ12 box was used for the housing. A third-party brush motor regulator was used as the base schematics. It was however rather poorly specified at some points, e.g. the type of the triac was omitted; it was apparently different than the BT138 one used here, necessitating changes of values of some components. Regulator circuitry The regulator itself is a standard circuit for a triac switch, using a DIAC to make the switching more symmetrical for both positive and negative half-wave. The resistor-capacitor network provides timing; when the capacitor reaches breakdown voltage of the DIAC, the DIAC switches and dumps the energy from the capacitor into the triac's gate and opens it for the rest of the half-wave. The moment the triac switches therefore depends on the value of the series resistor. The regulator potentiometer should work from zero to full scale. The series and parallel fixed resistors are therefore necessary to fine-tune the operation range. The 2M2 resistor was chosen to eliminate the dead space on the left side of the pot scale where the triac was not switching on at all (by reducing the resistance of the pot when on max), the series 1k resistor sets the full-scale limit (by addition to the pot resistance when it is on min). The exact values depend strongly on the triac and diac used. The high-current path in the schematics is emphasized with thicker lines. Snubber circuit and filtering The 100nF capacitors with one parallel resistor act as a snubber network, filtering out the transients (present especially when inductive load is being regulated) that could cause trouble like false triggering of the triac or excessive EMI. The choke in series with the rest of the circuit serves to filter out the EMI from the triac switching. Its value turns out to not be mission-critical, at least for the low-hundred-watts motors and tens-of-watts lightbulbs used as test loads. Original schematics suggested 200 H; such value was not readily available for high enough current, a choke from a reusable-parts bin was therefore chosen and turned out to be satisfying. Indicators Two neon bulbs are used as indicators. One shows the power being present on the input connector, the other one is connected across the load and shows the relative power available by its brightness (and has full brightness across the scale when there is no load). For rough measuring of the current flowing through the load, a low-cost ammeter was fashioned from an extra-cheap VU meter. Its full-deflection voltage was measured and a suitable shunt resistor was made from a length of resistive wire, with assistance of a milliohmmeter. To make it work with the AC current, a diode bridge was employed. TODO Labels on the box Scale for the ammeter Images Inside viewInside viewAmmeter detailTriac board detail

Triac board detailBoth halves of the boxOutside viewOutside view

Outside viewOutside, side viewOutside, top view

Master/Slave Switch In this age of enlightenment any sort of relationship that could be described as master/slave would be questionable but for the purposes of this circuit it gives a good idea of how it functions. The circuit senses mains current supplied to a master device and switches slave equipment on or off. This feature is useful in a typical hi-fi or home computer environment where several peripheral devices can all be switched on or off together. A solid-state relay from Sharp is an ideal switching element in this application; a built-in zero crossing detector ensures that switching only occurs when the mains voltage passes through zero and any resultant interference is kept to an absolute minimum.Circuit diagram:

All of the triac drive circuitry (including optical coupling) is integrated on-chip so there are very few external components and no additional power supply necessary. This makes the finished design very compact. Diodes D1, D2, D3 and D4 perform the current sensing function and produce a voltage on C2 when the master equipment is switched on. A Schottky diode is used for D5 to reduce forward voltage losses to a minimum. The circuit is quite sensitive and will successfully switch the slave even when the master equipment draws very little mains current. The RC network formed by R1 and C1 provides some protection for the solid-state relay against mains-borne voltage transients.

Warning:This circuit is connected to the mains. it is important to be aware that the chip has lethal voltages on its pins and all appropriate safety guidelines must be adhered to! This includes the LED, for safety it must be fitted behind a transparent plexiglass shield.Author: Karl Kckeis - Copyright: Elektor July-August 2004