Spy Camera Solar Power Box

Battery life has always been a critical consideration for most of the electronic gadgets and equipment. When we talk about spy  cameras,  which  normally  function  round-the-clock, they often run out of power within a few days.  Many spy cameras (CCTV cameras) are powered by 9V PP3 type batteries that offer five times more energy  than the regular 9V alkaline battery.

Mini CCTV cameras also accept 6-12V DC supply from AC mains adaptor through the DC IN jack. AC mains adaptor for the camera increases the capacity of the 9V PP3 battery but is bulky and noisy. Whether disposable  or rechargeable batteries, making frequent replacement or recharging them is a cumbersome job. The unique solar power box described here serves an alternative solution to the problem.

Spy Camera Solar Power Box Circuit Diagram 

The circuit of the solar power box is simple. It contains a  battery charger and a battery health indicator and  a few other components.  As shown in the circuit,  DC supply available from  the solar panel (SP1) is  directly applied to the in-put of the circuit through  a protection diode (D1).  This diode is used to pre-vent  the  reverse  current  flow from the battery to  the  solar  panel  during  night. Thus, D1 allows  the current to flow from the solar panel  to the battery only. Low-voltage-drop  type 1N5817 diode is perfect for the  job. 

At the heart of the circuit is an integrated current source, realised using a  popular 3-pin adjustable voltage regulator LM317T(IC1). This IC is designed  to adjust its internal resistance between  the In (pin 3) and Out (pin 2) terminals  to maintain a constant voltage of 1.25V  between the Out (pin 2) and Adj (pin 1) terminals. Here, a 9V, 280 mAh  rechargeable PP3 type Ni-MH battery  (BATT) is used as reservoir. Normally,  a charging current of about 10 per cent  of  ampere-hour  rating  is  safe  for  the  battery. Resistor R1 (39-ohm, 0.5W),  connected between pin 1 and 3 of IC1,  limits  the  charging  current  to  about  30 mA. DC output from the battery is  available at output jack J2. Red LED  ( LED1) is used as a battery ‘health’  indicator. Switch S1 is used to start the  charging while S2 is used for connect-ing the load. Note that suitable heat  sink should be used for the IC1.

The proper selection of solar panel  is important but not critical. A miniature 12V type solar panel with a cur-rent output of about 100 mA can be  used. Even if you have a solar panel  with  higher  voltage  rating,  it  will  not  create a problem as the circuit ensures  that the charging current cannot exceed  the predetermined value.

The circuit can be easily assembled  on a general-purpose PCB and housed  in a small plastic cabinet.

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LED Volt Meter Circuit

Here is a Simple LED Volt meter to Monitor the charge level in Lead Acid Battery or Tubular battery. The terminal voltage of the battery is indicated through a four level LED indicators. The nominal terminal voltage of a Lead Acid battery is 13.8 volts and that of a Tubular battery is 14.8 volts when fully charged. 

 LED Volt Meter Circuit Diagram

The LED voltmeter uses four Zener diodes to light the LEDs at the precise breakdown voltage of the Zener diodes. Usually the Zener diode requires 1.6 volts in excess than its prescribed value to reach the breakdown threshold level. When the battery holds 13.6 volts or more, all the Zener breakdown and all LEDs light up. When the battery is discharged below 10.6 volts, all the LEDs remain dark. So depending on the terminal voltage of the battery, LEDs light up one by one or turns off.

Author: D. Mohan Kumar Copyright: electroschematics.com

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Sensitive Audio Power Meter

As a follow-up to the simple audio power  meter described in [1], the author has developed a more sensitive version. In practice,  you  rarely  use  more  than  1 watt  of  audio  power in a normal living-room environment.  The only time most people use more is at a  party when they want to show how loud their  stereo system is, in which case peaks of more  than 10 W are not uncommon. With this circuit, the dual LED starts to light up  green at around 0.1 watt into 8 ohms (0.2 watt  into 4 ohms). Naturally, this depends on the  specific type of LED that is used.

 
Circuit diagram:

 

Sensitive Audio Power Meter Circuit Diagram

 

Here it is  essential to use a low current type. The capacitor is first charged via D1 and then discharged via the green LED. This voltage-doubler effect  increases the sensitivity of the circuit. Above a level of 1 watt, the transistor limits the current through the green LED and the red LED con ducts enough to produce an orange hue.The red colour predominates above 5 watts. Of course, you can also use two separate ‘normal’ LEDs. However, this arrangement cannot generate an orange hue. For any testing that may be necessary, you should use  generator with a DC-coupled output. If there is a capacitor in the output path, it can cause misleading results.

Reference: Simple Audio Power Meter, Elektor July & August 2008.

Author : Michiel Ter Burg - Copyright : Elektor Electronic

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Automatic Bicycle Light

T his  automatic  bicycle  light  makes cycling in the dark much  easier (although you still need  to pedal of course). The circuit  takes  the  ambient  light  level  into account and only turns on  the light when it becomes dark.  The light is turned off when no  cycling has taken place for over  a minute or if it becomes light  again. The biggest advantage of  this circuit is that it has no manual controls. This way you can  never ‘forget’ to turn the light  on or off. This makes it ideal for  children and those of a forgetful  disposition.

Bicycle Light Image :

To detect when the bicycle is  used (in other words, when the  wheels turn), the circuit uses a  reed switch (S1), mounted on  the frame close to the wheel.  A small magnet is fixed to the  spokes (similar to that used with  most  bicycle  speedometers),  which  closes  the  reed  switch  once for every revolution of the  wheel. Whilst the wheel turns,  pulses are fed to the base of T1  via C1. This charges a small electrolytic capacitor (C2). When it is  dark enough and the LDR there-fore has a high resistance, T2  starts conducting and the lamp  is turned on. With every revolution of the wheel C2 is charged  up again. The charge in C2 ensures that T2  keeps conducting for about a minute after  the wheel stops turning. Almost any type of  light can be connected to the output of the  circuit.

Circuit diagram :

Automatic Bicycle Light Circuit Diagram

Part List :

Resistors
R1 = 1MΩ (SMD 0805)
R2,R4 = 100kΩ (SMD 0805)
R3,R6 = 1kΩ (SMD 0805)
R5 = LDR e.g. FW150 Conrad Electronics # 183547
Capacitors
C1 = 1µF 16V (SMD 0805)
C2 = 10µF 16V (SMD chip type)
C3 = 100nF (SMD 0805)
Semiconductors
T1 = BC807 (SMD SOT23)
T2 = STS6NF20V (SMD SO8)
Miscellaneous
S1 = reed switch (not on board) +
2-way right angle pinheader
BT1 = 3–12V (see text)

With a supply voltage of 3V the quiescent  current when the reed switch is open is just  0.14 μA. When the magnet happens to be in  a position such that S1 is closed,  the current is 3 μA. In either case  there is no problem using batteries to supply the circuit. The  supply voltage can be anywhere  from 3 to 12 V, depending on the  type of lamp that is connected. Since it is likely that the circuit  will be mounted inside a bicycle light it is important to keep  an eye on its dimensions. The  board has therefore been kept  very compact and use has been made of SMD components. Most  of them come in an 0805 pack-age.  C2 comes in a so called  chip version. The board is single sided with the top also acting as the solder side.

The print outline for the LDR (R5)  isn’t exactly the same as that of  the  outline  of  the  LDR  mentioned  in  the  component  list.  The outline is more a general one  because there is quite a variety  of different LDR packages on the  market. It is therefore possible  to use another type of LDR, if for  example the light threshold isn’t  quite right. The LDR may also be  mounted on the other side of the  board, but that depends on how  the board is mounted inside the  light. For the MOSFET there are also many alternatives available, such as the FDS6064N3 made  by   Fairchild ,  the  SI4864 DY  made by  Vishay Siliconix , the IR F74 0 4 made by IR F or the NTMS 4N01R 2G  made by ONSEMI. The reed switch also  comes in many different shapes and sizes; some of them are even waterproof and come with the wires already attached.

For the supply connection and  the connection to the lamp you  can either use PCB pins or solder the wires directly onto the  board. The soldered ends of the  pins can be shortened slightly so that they  don’t stick out from the bottom of the board.  This reduces the chance of shorts with any metal parts of the light. Do take care when you use a dynamo  to  power the circuit the alternating voltage must first be rectified! The same applies to  hub dynamos, which often also output an  alternating voltage.

Sourced By : circuitsproject.blogspot.com

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Simple Acoustic Sensor

This acoustic sensor was originally developed for an industrial application (monitoring a siren), but will also find many domestic applications. Note that the sensor is designed with safety of operation as the top priority: this means that if it fails then in the worst-case scenario it will not itself generate a false indication that a sound is detected. Also, the sensor connections are protected against polarity reversal and short-circuits. The supply voltage of 24 V is suitable for industrial use, and the output of the sensor swings over the supply voltage range.

Circuit diagram :

Simple Acoustic Sensor Circuit Diagram

The circuit consists of an electret micro-phone, an amplifier, attenuator, rectifier and a switching stage. MIC1 is supplied with a current of 1 mA by R9. T1 amplifies the signal, decoupled from the supply by C1, to about 1 Vpp. R7 sets the collector current of T1 to a maximum of 0.5 mA. The operating point is set by feedback resistor R8. The sensitivity of the circuit can be adjusted using potentiometer P1 so that it does not respond to ambient noise levels. Diodes D1 and D2 recitfy the signal and C4 provides smoothing. As soon as the voltage across C4 rises above 0.5 V, T2 turns on and the LED connected to the collector of the transistor lights. T3 inverts this signal.

If the microphone receives no sound, T3 turns on and the output will be at ground. If a signal is detected, T3 turns off and the output is pulled to +24 V by R4 and R5. In order to allow for an output current of 10 mA, T3’s collector resistor needs to be 2.4 kΩ. If 0.25 W resistors are to be used, then to be on the safe side this should be made up of two 4.7 kΩ resistors wired in parallel. Diode D4 protects the circuit from reverse polarity connection, and D3 protects the output from damage if it is inadvertently connected to the supply. 

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Transformerless Power Supply Circuit

This circuit will supply up to about 20ma at 12 volts. It uses capacitive reactance instead of resistance; and it doesn't generate very much heat.The circuit draws about 30ma AC. Always use a fuse and/or a fusible resistor to be on the safe side. The values given are only a guide. There should be more than enough power available for timers, light operated switches, temperature controllers etc, provided that you use an optical isolator as your circuit's output device. (E.g. MOC 3010/3020) If a relay is unavoidable, use one with a mains voltage coil and switch the coil using the optical isolator.C1 should be of the 'suppressor type'; made to be connected directly across the incoming Mains Supply.

They are generally covered with the logos of several different Safety Standards Authorities. If you need more current, use a larger value capacitor; or put two in parallel; but be careful of what you are doing to the Watts. The low voltage 'AC' is supplied by ZD1 and ZD2. The bridge rectifier can be any of the small 'Round', 'In-line', or 'DIL' types; or you could use four separate diodes. If you want to, you can replace R2 and ZD3 with a 78 Series regulator. The full sized ones will work; but if space is tight, there are some small 100ma versions available in TO 92 type cases. They look like a BC 547. It is also worth noting that many small circuits will work with an unregulated supply.

Transformerless Power Supply Circuit Diagram

You can, of course, alter any or all of the Zenner diodes in order to produce a different output voltage. As for the mains voltage, the suggestion regarding the 110v version is just that, a suggestion. I haven't built it, so be prepared to experiment a little. I get a lot of emails asking if this power supply can be modified to provide currents of anything up to 50 amps. It cannot. The circuit was designed to provide a cheap compact power supply for Cmos logic circuits that require only a few milliamps. The logic circuits were then used to control mains equipment (fans, lights, heaters etc.) through an optically isolated triac.

If more than 20mA is required it is possible to increase C1 to 0.68uF or 1uF and thus obtain a current of up to about 40mA. But 'suppressor type' capacitors are relatively big and more expensive than regular capacitors; and increasing the current means that higher wattage resistors and zener diodes are required. If you try to produce more than about 40mA the circuit will no longer be cheap and compact, and it simply makes more sense to use a transformer. The Transformerless Power Supply Support Material provides a complete circuit description including all the calculations.

Web-masters Note:

I have had several requests for a power supply project without using a power supply. This can save the expense of buying a transformer, but presents potentially lethal voltages at the output terminals. Under no circumstances should a beginner attempt to build such a project.

Important Notice:

Electric Shock Hazard. In the UK,the neutral wire is connected to earth at the power station. If you touch the "Live" wire, then depending on how well earthed you are, you form a conductive path between Live and Neutral. DO NOT TOUCH the output of this power supply. Whilst the output of this circuit sits innocently at 12V with respect to (wrt) the other terminal, it is also 12V above earth potential. Should a component fail then either terminal will become a potential shock hazard.

MAINS ELECTRICITY IS VERY DANGEROUS.

If you are not experienced in dealing with it, then leave this project alone. Although Mains equipment can itself consume a lot of current, the circuits we build to control it, usually only require a few milliamps. Yet the low voltage power supply is frequently the largest part of the construction and a sizeable portion of the cost.

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USB Converter

Does this sound familiar: you buy a small piece of equipment, such as a programming & debugging interface for a microcontroller, and you have to use a clunky AC wall adapter to supply it with power? It’s even worse when you’re travelling and there’s no mains socket anywhere in sight. Of course, you can use the USB bus directly as a power source if the supply voltage is 5 V. If you need a higher voltage, you can use the USB converter described here. This small switch-mode step-up converter can generate an output voltage of up to 15 V with a maximum output current of 150 mA.

 

The LM3578 is a general-purpose switchmode voltage converter. Figure 1 shows its internal block diagram. Here we use it as a step-up converter. The circuit diagram in Figure 2 shows the necessary components. Voltage conversion is achieved by switching on the internal transistor until it is switched off by the comparator or the current-limiting circuit. The collector current flows through coil L1, which stores energy in the form of a magnetic field. When the internal transistor is switched off, the current continues flowing through L1 to the load via diode D1. However, the voltage across the coil reverses when this happens, so it is added to the input voltage. The resulting output voltage thus consists of the sum of the input voltage and the induced voltage across the coil.

 USB Converter Circuits Diagram 1

The output voltage depends on the load current and the duty cycle of the internal transistor. Voltage divider R5/R6 feeds back a portion of the output voltage to the comparator in the IC in order to regulate the output voltage. C5 determines the clock frequency, which is approximately 55 kHz. Network R4, C2 and C3 provides loop compensation. The current-sense resistor for the current-limiting circuit is formed by three 1-Ω resistors in parallel (R1, R2 and R3), since SMD resistors with values less than 1 Ω are hard to find. The output voltage ripple is determined by the values and internal resistances of capacitors C11, C8, C7 and C6.

 
 USB Converter Circuits Diagram 2

 

The total effective resistance is reduced by using several capacitors, and this also keeps the construction height of the board low. L2, C1, C9 and C10 act as an input filter. Ensure that the DC resistance of coil L2 is no more than 0.5 Ω. Use a Type B PCB-mount USB connector for connection to the USB bus.  A terminal strip with a pitch of 5.08 mm can be used for the output voltage connector. Of course, you can also solder a cable directly to the board. Two additional holes are provided in the circuit board for this purpose. As we haven’t been able to invent a device that produces more energy than it consumes, you should bear in mind that the input current of the circuit is higher than the output current. As a general rule, you can assume that the input current is equal to the product of the output current and the output voltage divided by the input R5 and R6 for other output voltages:

6V:	R5 = 47k, R6 = 9,1k
12V:	R5 = 110k, R6 = 10k
15V:	R5 = 130k, R6 = 9,1k

voltage and divided again by 0.8. Specifically, with an output current of 100 mA at 9 V, the input current on the USB bus is approximately 225 mA. Finally, Figure 3 shows a small PCB layout for the circuit. All of the components except the connector and the terminal strip are SMDs.

Parts List:

(for UO = 9 V)

Resistors

R1,R2,R3 = 1Ω

R4 = 220kΩ

R5 = 82kΩ

R6 = 10kΩ

Capacitors

(SMD 1206)

C1 = 100nF

C2 = 2nF2

C3 = 22pF

C4 = 100nF

C5 = 1nF5

(tantalum SMD 7343)

C6 = 68μF 20V

C7 = 68μF 20V

C8 = 68μF 20V

C9 = 47μF 16V

C10 = 47μF 16V

C11 = 68μF 20V

Inductors

L1 = 820μH (SMD CD105)

L2 = 47μH (SMD 2220)

Semiconductors

D1 = SK34SMD (Schottky)

IC1 = LM3578AM (SMD SO8)

Miscellaneous

K1 = 2-way PCB terminal block, lead pitch 5mm

(optional)

K2 = USB-B connector

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Single-cell Power Supply

Many modern electronic devices and micro-controller based circuits need a 5 V or 3.3 V power  supply. It is important  that  these voltages are constant and so a regulator of some kind is essential, including in battery powered devices. The simplest approach is to select a (perhaps rechargeable) battery whose voltage is rather higher than that required by the circuit and use an ordinary  linear voltage regulator. Unfortunately this solution is rather wasteful of precious energy and space: for a 5 V circuit at least six NiCd or NiMH cells would be required.

Both these disadvantages can be tackled using a little modern electronics. A good way to minimise energy losses is to use a switching regulator, and if we use a regulator with a step-up topology then we can simultaneously reduce the number of cells needed to power the circuit. Fortunately it is not too difficult to design a step-up converter suitable for use in portable equipment as the semi-conductor manufacturers make a wide range of devices aimed at exactly this kind of application. The Maxim MAX1708 is one example. It is capable of accepting an input voltage anywhere in the range from 0.7 V to 5 V, and with the help of just five external capacitors, one resistor, a diode and a coil, can generate a fixed output voltage of 3.3 V or 5 V. With two extra resistors the output voltage can be set to any desired value between 2.5 V  and 5.5 V.

Circuit diagram :

Characteristics

• Input voltage from 0.7 V to 5 V
• Output voltage from 2.5 V to 5.5
• Maximum output current 2 A
• Can run from a single cell

The technical details of this integrated circuit can be  found on the manufacturer’s website [1], and the full datasheet is available for download. An important feature of  the device is that it includes an internal reference and integrated power switching MOSFET, capable of handling currents of up to 5 A. It is, for example, possible to convert 2 V at  5 A at the input to the circuit into 5 V at 2 A at the output, making it feasible to build a 5 V regulated supply powered from just two NiCd  or NiMH cells. With a single cell the maximum possible current at 5 V would  be reduced to around 1 A.

The example circuit shown here is configured for an output voltage of 5 V. The capacitor connected to pin 7 of the IC  enables the ‘soft start’ feature. R2 provides current limiting  at slightly more than 1 A. For maximum output current R2  can be dispensed with. Pins 1 and 2 are control inputs that allow the device to be shut down. To configure the device  for 3.3 V output, simply connect pin 15 to ground.

The coil and diode need to be selected carefully, and depend on the required current output. To minimise  losses D1 must be a Schottky type: for a 1A output current the SB140 is a suitable choice.

For L1 a fixed power inductor, for example from the Fastron PISR series, is needed. A fundamental limitation of the step-up converter is that the input voltage must be lower than the output voltage. For example, it is not possible to use a  3.7 V  lithium-polymer cell (with a terminal voltage of 4.1 V fully charged) at the input and expect to be able to generate a 3.3 V output, as diode D1 would  be  permanently conducting. On the other hand, there is no difficulty in generating a 5 V  output from a lithium-polymer cell.

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Micropower Voltage Regulator

This circuit was developed to power an AVR microcontroller from a 12 V lead-acid battery. The regulator itself draws only 14 µA. Of course, there are dedicated ICs, for example from Linear Technology or Maxim, which can be used, but these can be very hard to get hold of and are frequently only available in SMD packages these days. These difficulties are simply and quickly avoided using this discrete circuit.

Circuit diagram :

The series regulator component is the widely-available type BS170 FET. When power is applied it is driven on via R1. When the output voltage reaches 5.1 V, T2 starts to conduct and limits any further rise in the output voltage by pulling down the voltage on the gate of T1. The output voltage can be calculated as follows:

UOUT = (ULED + UBE) × (R4 + R2) / R4

where we can set ULED at 1.6 V and UBE at 0.5 V. The temperature coefficients of ULED and UBE can also be incorporated into the formula. The circuit is so simple that of course someone has thought of it before. The author’s efforts have turned up an example in a collection of reference circuits dating from 1967: the example is very similar to this circuit, although it used germanium transistors and of course there was no FET. The voltage reference was a Zener diode, and the circuit was designed for currents of up to 10 A. Perhaps our readers will be able to find even earlier examples of two-transistor regulators using this principle?

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Isolated Fuse Fail Indicator

This circuit uses standard components and shows a method of indicating the fuse status of mains powered equipment while providing electrical isolation from the mains supply.

Circuit diagram:

Isolated Fuse Fail Indicator Circuit Diagram

A standard miniature low power mains transformer  (e.g. with an output of around 6 V at 1.5 VA) is used as a ‘sense’ trans-former with its primary winding (230 V) connected across the equipment’s input fuse so that when the fuse blows, mains voltage is applied to the transformer and a 6 V ac output volt-age appears at the secondary winding. The 1N4148 diode rectifies this voltage and the LED lights to indicate that the fuse has failed.

The rectified voltage is now connected to an RC low-pass filter formed by the 10 kΩ resistor and 100 nF capacitor. The resulting positive signal can now be used as an input to an A/D converter or as a digital input to a microcontroller (make sure that the signal level is within the microcontroller input voltage level specification). The 1 MΩ resistor is used to discharge the capacitor if the input impedance of the connected equipment is very high.

As long as the fuse remains intact it will short out the primary winding of the ‘sense’ transformer so that its secondary out-put is zero.

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0-30 Volt Laboratory Power Supply

The linear power supply, shown in the schematic, provides 0-30 volts, at 1 amp, maximum, using a discrete transistor regulator with op-amp feedback to control the output voltage. The supply was constructed in 1975 and has a constant current mode that is used to recharge batteries.

Circuit diagram :

0-30 Volt Laboratory Power Supply Circuit Diagram

With reference to the schematic, lamp, LP2, is a power-on indicator. The other lamp (lower) lights when the unit reaches its preset current limit. R5, C2, and Q10 (TO-3 case) operate as a capacitor multiplier. The 36 volt zener across C2 limits the maximum supply voltage to the op-amps supply pins. D5, C4, C5, R15, and R16 provide a small amount of negative supply for the op-amps so that the op-amps can operate down to zero volts at the output pins (pins 6). A more modern design might eliminate these 4 components and use a CMOS rail-to-rail op-amp. Current limit is set by R3, D1, R4, R6, Q12, R10, and R13 providing a bias to U2 that partially turns off transistors Q9 and Q11 when the current limit is reached. R4 is a front panel potentiometer that sets the current limit, R22 is a front panel potentiometer that sets the output voltage (0-30 volts), and R11 is an internal trim-pot for calibration. The meter is a 1 milliamp meter with an internal resistance of 40 ohms. Switch S1 determines whether the meter reads 0-30 volts, or 0-1 amp.

A more modern circuit might use a single IC regulator, such as the MC78XX, or MC79XX series, immediately after the half wave rectifier, to replace approximately 30 components, or at least a high precision zener diode to replace D10 as the voltage reference. The LM4040 is one such voltage reference and has excellent stability over temperature. IC regulators such as the MC78XX series may eventually become obsolete as newer IC regulators are designed, however, discrete transistors, op-amps, and zeners are more generic, have a longer production lifespan, and allow the designer to demonstrate that he understands the principles of linear regulated power supply operation.

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Power Supply with High Voltage Isolation

Occasionally you come across some unusual  situations when setting up measurement  systems. The author once had to set up a system to register the vibrations and strain supposed to be  present in a contactor that operated at a voltage of 25 kVAC.

One of the biggest problems with this project turned out to be the power supply for  the measurement system. Since it required  a power of about 30 W it wasn’t possible to  use batteries since the system had to operate  for many hours at a time. A logical solution  would seem to be to use an isolating trans-former, but still.25 kVAC means a peak volt-age approaching 40 kV, and on top of that  you would have to include a safety margin. In  addition, everything that is connected to high  voltage lines should also be able to withstand  lighting strikes!

Circuit diagram :

 

Power Supply with High Voltage Isolation Circuit Diagram

Consequently the isolation should be able to  cope with a test voltage of 150 kV, which is a  lot to ask of the isolating material.

After extensive research no supplier could be  found for a transformer rated at 50 W, 230 V  primary, 12 V secondary and an isolation of  25 kVAC. Because of this, a dynamic system  had to be used that unfortunately suffers a  bit from wear and tear. This system consists  of a 50 W 3-phase motor connected up via an  isolating drive-shaft to a 30 W generator (a  3-phase servo motor that was used as a generator), which provides the power for the data  logger and associated electronics.

Because a 3-phase generator was used, the  voltage obtained after full-wave rectification (via D1 and D4 to D8) already looked good,  also because the revs of the generator was  fairly high. The secondary supply can there-fore remain fairly simple. The main supply of 9 VDC is stabilised by IC3, an LM317T. From  there it is fed to a few small DC/DC modules  (IC1, IC4, IC5), which supply voltages of +5 V,  +30 V and -9 V, which are required by the other parts of the circuit. IC2 (LM566, a volt-age controlled oscillator) makes LED D2 flash  when the supply voltage is present.

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Regulator for Three-Phase Generator

This regulator was designed for use with a  generator with a higher output voltage. This  type of generator can be found on some boats  and on vehicles for the emergency services.  They are really just an adapted version of the  standard alternator normally found in cars.  The field winding is connected to the 12 V  (or 24 V) battery supply, whereas the generator winding is configured for the AC grid  voltage (230 V or 115 V). This AC voltage now  has to be kept stable via the 12 V field winding. Although it’s perfectly possible to use a  switching regulator for this, we deliberately  chose to use the old and trusted 723.

Circuit diagram :

Regulator for Three-Phase Generator Circuit Diagram

The generator is a three-phase type, with the  field winding rated for 12 VDC. The output voltage of the generator depends on its revs  and the current through the field winding.  Since the output voltage is relatively high, it  is fed via opto-couplers to the 723, which is  used in a standard configuration.  The output is fed via driver T1 to two  2N3055’s, connected in parallel, which sup-ply the current to the field winding. In the prototype we used TLP620 opto-couplers. These are suitable for use with alternating voltages because they have two anti-parallel LEDs at the input. The regulation works  quite well with these, with the output volt-age staying within a small range across a wide  range of revs.

However, the sensitivity of the two internal  LEDs can differ in this type of opto-coupler,  since it’s not always possible to ensure during  the manufacturing process that the distance  between each LED and the phototransistor is  exactly the same. For a more precise regulation it would be better to use two individual  opto-couplers per phase, with the inputs connected in anti-parallel and the outputs connected in parallel.

In order to ensure that there is sufficient isolation between the primary and secondary side  you should make a cutout in the PCB underneath the middle of each opto-coupler. Instead of a BD136 for T1 you could also use  a TIP32 or something similar. For T2 and T3  it’s better to use a type with a plastic casing,  rather than a TO3 case.

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Monolithic Step-Down Switching Regulator

L4962 is a monolithic step-down  switching regulator. It provides  output voltage of 5.1V to maxi-mum 40V, delivering current up to  1.2A to 1.5A, depending on the type  and package. The theoretical internal  functions are almost the same. The  heart  of  the  device  is  the  regulation  loop  consisting  of  a  saw  tooth  oscillator, error amplifier, comparator and  source-sink output stage.

Circuit diagram :

 Fig. 1: Circuit of switching regulator

An error signal is produced by  comparing  the  output  voltage  with  a precise 5.1 volt on chip reference  (which is zener zap trimmed to ±2  per cent). This error signal is then  compared  with  the  saw  tooth  signal  to generate the fixed frequency pulse  width  modulated  pulses  which  drive the output stage.

Fig. 1 shows circuit diagram of  the regulator. The gain and frequency  of the loop can be set by RC network  connected to IC pin 11. When the loop  is  closed  directly  by  connecting  the  supply output to the feedback input  IC pin 10, an output voltage 5.1 volt is  produced. Higher output voltages are  obtained by inserting a voltage divider  in this feedback path. the outputs over current errors generated  at  the  on  switch  are  prevented  by  the  self-start  function.  The  error  amplifier  output is initially  clamped  by  the  external  capacitor ‘Css’ of pin15,  and  is  allowed  to  rise  linearly  as  this  capacitor  is  charged  by  a  constant  current  source.

Output overload protection is pro-vided in the from of a current limiter.  When the load current exceeds a preset  threshold, this comparator sets a flip-flop, which disables the output stage  and discharges the soft start capacitor. Another internal comparator resets  the flip-flop when the voltage across the soft capacitor C3 falls  to 0.4V. The output is thus  re-enabled  and  the  volt-age  rises  under  the  control of soft start network.  If overload condition is  still  present,  the  limiter  will  trigger  again  when  the  threshold  current  is  reached.  The  average  short-circuit is limited to a  safe value by the dead time introduced  in the soft start network. The thermal  overload circuit disables circuit operation when the junction temperature is  about 150°C and has hysteresis to  prevent instability. Frequency is about  100 KHz with parallel RC network connected to this terminal.

Assemble the circuit on a general-purpose PCB by using two connectors one  for  the  input  and  the  other for the output. You can also use  a  DC-DC  converter  circuit  in  place  of  the  linear  regulator  to  avoid  the  use  of transformer and also to reduce dissipation. Finally, short-circuit protection is provided for all of the auxiliary  outputs by clips, internal current limiter and thermal protection circuit.  It is a ferrite torroid core T-18  with a small 20 turns of 27 SWG enameled copper wire.

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Linear RF Power Meter Circuit

The National Semiconductor LMV225 is a linear RF power meter IC in an SMD package. It can be used over the frequency range of 450 MHz to 2000 MHz and requires only four external components. The input coupling capacitor isolates the DC voltage of the IC from the input signal. The 10-k? resistor enables or disables the IC according to the DC voltage present at the input pin. If it is higher than 1.8 V, the detector is enabled and draws a current of around 5–8 mA. If the voltage on pin A1 is less than 0.8 V, the IC enters the shutdown mode and draws a current of only a few microampères. The LMV225 can be switched between the active and shutdown states using a logic-level signal if the signal is connected to the signal via the 10-kR resistor.

Circuit diagram:

 Linear RF Power Meter Circuit Diagram

The supply voltage, which can lie between +2.7 V und +5.5 V, is filtered by a 100nF capacitor that diverts residual RF signals to ground. Finally, there is an output capacitor that forms a low-pass filter in combination with the internal circuitry of the LMV225. If this capacitor has a value of 1 nF, the corner frequency of this low-pass filter is approximately 8 kHz. The corner frequency can be calculated using the formula fc = 1 ÷ (2 p COUT Ro) where Ro is the internal output impedance (19.8 k?). The output low-pass filter determines which AM modulation components are passed by the detector.

The output, which has a relatively high impedance, provides an output voltage that is proportional to the signal power, with a slope of 40 mV/dB. The output is 2.0 V at 9 dBm and 0.4 V at –40 dBm. A level of 0 dBm corresponds to a power of 1 mW in 50 R. For a sinusoidal wave-form, this is equivalent to an effective voltage of 224 mV. For modulated signals, the relationship between power and voltage is generally different. The table shows several examples of power levels and voltages for sinusoidal signals. The input impedance of the LMV225 detector is around 50 R to provide a good match to the characteristic impedance commonly used in RF circuits.


The data sheet for the LMV225 shows how the 40-dB measurement range can be shifted to a higher power level using a series input resistor. The LMV225 was originally designed for use in mobile telephones, so it comes in a tiny SMD package with dimensions of only around 1 × 1 mm with four solder bumps (similar to a ball-grid array package). The connections are labelled A1, A2, B1 and B1, like the elements of a matrix. The corner next to A1 is bevelled.

Author: Gregor Kleine Copyright: Elektor Electronics

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Green USB switch

Green USB switch Circuit Diagram. According to the Energy Saving  Trust, if you add up all the current drawn in standby mode by items such as stereos, TVs, VCRs and DVDs over a year in the UK alone, it amounts to 3.1 million tonnes of CO2 released into the atmosphere.This is without factoring in the current drawn by all the PCs,laptops and their associated peripherals left in standby mode. 

Circuit diagram :

Green USB switch Circuit Diagram

It  is  not  necessary  to  spend  a  great deal of money or time to  make a difference on a personal  level. The circuit described here  is designed for use by laptop or  notebook computers. It will automatically switch off all mains  powered peripheral equipment  including monitor, printer, scanner, TV tuner and USB hub etc  when it detects that the notebook  is switched off. The circuit is quite  straightforward; in addition to an  optocoupler it requires a 12 V  double-pole  relay  with  mains  rated contacts and a small power  supply  for  the  optocoupler.  When the laptop is switched on  5 V appears at the USB socket,  activating the relay and switching  through  the  mains  supply  on K3 and K4. The notebook’s  USB socket is still available to be  used as normal but it’s worth remembering that the optocoupler  takes a few milliamps from the  USB supply and this may cause a  problem if a high-current device  is plugged into the USB socket.  In the case where the laptop has  more than enough USB sockets it may be worthwhile us-ing one of them solely for this  circuit, the extension USB connector K2 would then not be  required. 

The circuit is mounted into a  mains plug enclosure which  provides a socket where the  mains extension strip will be  plugged into. With any luck  there will be sufficient space  to fit the entire circuit into the  mains extension strip enclosure and save the need for a  separate enclosure. The slow-blow 6.3-A fuse (F1) protects  the equipment plugged into  the strip. 

In  addition  to  the  optocoupler  and relay the circuit also has a  ‘freewheel’ diode D1 and a relay  driver formed by T1 and its base  bias voltage divider network R2/ R4. The two ‘snubber’ networks  C1/R3 and C2/R5 reduce the  possibility of arcing which can  occur  when  the  relay  contacts  open (especially with inductive  loads). Capacitors C1 and C2  must be class X2 types which  can handle mains voltage plus any  spikes.  The  power  supply  consists of a small mains trans-former  (12 V,  50 mA),  bridge  rectifier and smoothing capacitor C3. 

The laptop’s mains adaptor itself  can also be switched by this circuit when the laptop is fitted with  its rechargeable battery which  allows the computer to boot up  without a mains supply. The en-tire USB switch circuit draws cur-rent even when it is off but this value  is  tiny  compared  to  the  combined standby current of all  the peripherals. 

Note that parts of this circuit are  connected to the (potentially lethal) mains supply voltage; it is  essential to provide protection  to ensure that nothing can accidentally make contact with these  parts of the circuit. It is also important to observe correct separation between parts of the circuit carrying low voltage and  those carrying the high volt-age. Please observe the electrical Electrical Safety guide-lines which are reprinted in  Elektor  Electronics  several  times a year. 

The  circuit  is  less  suitable  for use with desktop PCs be-cause  the  majority  of  these  machines supply 5 V over the  USB socket even though they  have been shut down via soft-ware. The only way to turn off  in this case is to reach around  the back of the machine and  switch off at the main switch. 

Author : Wolfram Winfera - Copyright : Elektor

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