Fuente de 12 VDC Sin Transformador

7/30/2019 Fuente de 12 VDC Sin Transformador

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http://www.zen22142.zen.co.uk/Circuits/Power/tps.htm

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. Please

also read the Disclaimeron this site.

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 circuitsits 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.

Below is a project by Ron J, please heed the caution above and Ron's design

notes.

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 controlit, usually only require a few milliamps. Yet the low voltage power supply is
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frequently the largest part of the construction and a sizeable portion of the cost.

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, providedthat 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. 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 SupplySupport Materialprovides a complete circuit

description including all the calculations.
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Ron J

(http://www.zen22142.zen.co.uk)

Fuente de poder de 12 voltiosimplementada sin transformador. Sepuede alimentar de 110 o 220 VACcambiando slo dos elementos.

Circuito que permite obtener 12 VDC, con una entrada de voltaje en AC, sin

necesidad de untransformador.

Importante: Este circuito, por sus caractersticas, obliga a tener un cuidado

especial pues no existe aislamiento con la entrada de voltaje (VAC). No tocar las

salidas de la fuente (12 VDC).

Este circuito entrega aproximadamente 20 mA y no consume ms de 30 mA. Es

especial para circuitos y proyectos pequeos.

Para reducir elvoltajese utiliza una red RC (R1 y C1), crendose una reactancia

capacitiva que causa la cada de voltaje.

Los dosdiodos zener(ZD1 y ZD2) conectados en sentido opuesto reducen la seal
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AC a un mximo de +/- 16 voltios. Esta seal, AC de menor valor, es aplicada al

puente de diodos (pueden serdiodosrectificadores individuales) que funciona como

rectificador de onda completa. La salida de este es aplanada por elcapacitorC2 y

regulada a 12 voltios con ayuda del diodo zener ZD3 y delresistorR2.

Se puede reemplazar el conjunto ZD3 y R2 por unregulador monolticotipo 7812para obtener los 12 voltios DC.

Notas: C1 debe de ser del voltaje apropiado (ver el diagrama) especial para

conectar directamente a la tensin de entrada. (No tiene polaridad)

FR es un resistor fusible (fuse resistor). Protege al circuito contra picos de

corriente. Se puede utilizar en conjunto con elfusiblepara mayor seguridad, pero

no es obligatorio.

Verartculo original(en ingls)

Enlaces relacionados:

Fuente de poder. Diagrama de bloques

Regulador con diodo Zener

Circuito RC serie

Constante de tiempo

Condensador y la corriente alterna

Circuit : Andy Collinson

Email :

Description

This RF probe can be used at High Frequency (HF) or Ultra High

Frequency (UHF) on both 50 and 75 ohm coaxial cables. In

addition the RF voltage can be measured under load or no-load

conditions which allows the circuit to double as an RF Watt

meter. The RF probe can be used for oscillators and small

transistors for powers up to 2 Watts.
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Circuit NotesThe circuit is a simple half wave rectifier. In this circuit it works

at radio frequencies (RF) and converts any RF signal to a DC

voltage, in addition S1, allows a resistive load to be switched in

or out of circuit. S1 is a single pole, double throw switch with a

Centre off position. The centre position is no load, and left and

right positions1are for 50 and 75 ohm measurements. First, a

small section on measuring RF voltage, current and power, then

I'll describe how to use this simple test instrument.

Measuring RF Voltage

Digital and analogue multi meters can already measure AC

voltages so why can't they be used at radio frequencies? The

reason is that they can only measure with accuracy a limited

frequency range. My Maplin meter measures frequencies up to

400Hz with 1% accuracy, and up to 20KHz at 4%. This also

requires that the waveform is a sine wave. At frequencies above

20KHz, accuracy is not reliable.
http://www.zen22142.zen.co.uk/Circuits/Testgear/rfprobe.htm#1http://www.zen22142.zen.co.uk/Circuits/Testgear/rfprobe.htm#1http://www.zen22142.zen.co.uk/Circuits/Testgear/rfprobe.htm#1


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To measure radio frequencies (RF) a simple diode detectorcircuit is all that's needed. The detector in this probe is an OA91germanium diode, but any germanium diode will work.Germanium diodes have a low forward voltage drop (about

0.2V) and are preferred to silicon diodes which have a higher(0.6 - 0.7V) voltage drop. The diode rectifies the RF signal andconverts it to a DC voltage, which can be read by a multimeterwith good accuracy; the 1nF capacitor is there to smooth therectified DC signal presented to the meter.

RF Power, Voltage and Current

When measuring any AC or RF signal, the currents and voltages

are only in phase if the load is purely resistive. All transmitters

are tested with a dummy load which are resistive. This simplifies

the calculations and the pie chart forOhms's Law at ACcan now

be used.

Typical RF Voltages

For example, a 1 watt transmitter delivers an average power of

1 watt into a 50-ohm resistive dummy load. Transmitter power

is measured in RMS or root-mean-square. As power, P = V2/R,

then re-arranging, V(rms) = sqrt(P x R). Power is also foundfrom P = I2R and re-arranging in terms of current, I(rms) =

(P / R) Peak values are simply 1.414 x the RMS values.

So for a 1 W transmitter V(rms) = ( 1 x 50) = 7.071 Volts.and current, I(rms) = ( 1 / 50) = 0.141 Amps.

Power

Output

AC Volts

RMS

AC Amps

RMS

AC Volts

Peak

AC Amps

Peak

2 W 10 V 0.20 A 14.4 V 0.283 A

1 W 7.07 V 0.141 A 10.0 V 0.200A

0.5 W 5.0 V 0.100 A 7.07 V 0.141 A

0.2 W 3.16 V 0.0632 A 4.47 V 0.0894 A
http://www.zen22142.zen.co.uk/Theory/ohmac.htmhttp://www.zen22142.zen.co.uk/Theory/ohmac.htmhttp://www.zen22142.zen.co.uk/Theory/ohmac.htmhttp://www.zen22142.zen.co.uk/Theory/ohmac.htm


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0.1 W 2.24 V 0.0447 A 3.17 V 0.0632 A

RF Probe Functions

S1 allows a 50 or 75 ohm resistive load to be switched in and

out of circuit. This allows the probe to read loaded and no-loadvoltages. However as the load has a fixed resistance (50 or 75

ohm) then power delivered to the load can also be worked out.

Finally because the probe has a fixed resistance and can

measure loaded and no-load voltages then it is possible to

measure output impedance of a transmitter, see alsoMeasuring

Input and Output Impedancemay also be of assistance. The RF

probe has four functions:

1) Unloaded Transmitter Voltage

In all cases, connect the RF probe between the circuit under test

and the meter. The circuit under test could be a transmitter, RF

oscillator or other signal source. As the OA91 diode and 10n

capacitor are a half wave rectifier, the RF value measured will

be a peak value. As V(RMS) = V(peak)/ 2 then:

V(RMS) =Vpeak

= 0.7071 x Vpeak2

To measure unloaded RMS transmitter voltage switch S1 to off

and multiply the meter reading by 0.7071.

2) Loaded Transmitter Voltage

To measure a transmitter voltage under load switch S1 to either

50 or 75 ohm position. Normally this will be 50ohm, but for

Band II ( 87.5MHz - 108MHz) 75 ohm impedance should be

used.

To measure loaded RMS transmitter voltage switch S1 to either

50 or 75 ohm and multiply the meter reading by 0.7071.

3) Measuring Output Impedance

To measure the output impedance of an unknown circuit or

transmitter you first need to take two readings, one unloaded
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and then a reading under load at either 50 or 75 ohms. The

output impedance can be found from the following equation:

Z =R ( VNL - VL)

VL

where:

Z = output impedance of circuit in ohms

R = resistance of probe ( depending on S1 this is either 50 or

75 ohm)

VNL voltage RMS reading with S1 in centre position (no-load)

VL voltage RMS reading under load

4) Measuring Output Power

The output power in Watts can also be calculated. Output power

is the loaded (RMS) output voltage squared divided by

transmitter impedance:

P =VL

2

Z

where:

Z = output impedance of circuit in ohms

VL voltage RMS reading under load

Output Power and SWR

The output power as measured by the probe will not be exactly

the same as the radiated power by the antenna. This is because

there are losses in the antenna system and the Standing Wave

Ratio (SWR). When an antenna and feedline do not have

matching impedances, some of the electrical energy cannot be

transferred from the antenna cable to the antenna. Energy not

transferred to the antenna is reflected back towards the

transmitter. It is the interaction of these reflected waves with

forward waves which causes standing wave patterns. An SWR

meter can be used to measure the SWR ratio in order to obtain

the best match between antenna and the feedline.


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Important Note About Resistors

The components in the circuit are all readily available, however

there is one Important consideration. The resistors used Must be

carbon type and not wirewound types. The reason is that

wirewound resistors contain inductance due to the coiled wire,this is not normally important except at very high frequencies,

as in this circuit.

PCB or Veroboard Layout

A circuit this small with very few components is hardly worth the

trouble of producing a PCB. However because of its small size it

took me about 14 minutes, to draw the schematic and produce

the PCB in Kicad. The 3D rendered components are all createdby Renie S Marquet, more in the simulation section.

PCB 3D view

Enlarged Component Side


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Actual Size copper track view.

If you are thinking of using this PCB layout first printout the

actual size copper track view on paper, then you can match up

the components to see if they fit the pads. This is the same for

any PCB program. It does not matter if its open source or the

program cost several thousand pounds, the components that

you use must fit the footprints on the PCB board. As sizes of

components vary wildly then this is a problem for all PCB

layouts.

1 As drawn in the schematic.

Circuit : John Samin VK1EME

Email : [email protected]

Web :John's own website
http://www.mrx.com.au/http://www.mrx.com.au/http://www.mrx.com.au/http://www.mrx.com.au/


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DescriptionWhat can you use to test how effective your antennas are for

2.4 Ghz? Which antenna has the best gain or, how do you know

that there is any 2.4Ghz RF transmitted? Here are the details on

how to build a general purpose 2.4Ghz Radio Frequency Field

Strength Meter. This one was built using the microwave rated

diode from a MICROTEK solid state microwave leakage detector

(purchased from Dick Smith Electronics for around $24) these

diodes can be more expensive than that if purchased in single

units from electronics suppliers. There may be other suitable

diodes available. Electronics stores also sell Schottky Hot Carrier

Diodes that will probably also be suitable for this application.


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The antenna is a 2 element quad. I've orientated it in thediamond configuration so it should be effective for bothhorizontal and vertically polarised signals. You could build theantenna in the vertical or horizontal sense if you like. The

antenna was constructed on a right angled BNC connector,however I'm sure you could come up with a different sort ofplug setup that would still provide good results. Just keep thelead lengths to a minimum to reduce losses. I have used anattachment that allows the BNC connector to be inserted intomy Voltmeter. I switch the Voltmeter to Millivolts, point it at the2.4Ghz RF and read the result. The yellow plastic cylinder isused to keep the antenna separation at 10mm. I cut a channelinto the plastic to allow the wire to sit tight, and pushed someliquid nails into the hole to hold it. The bottom of the reflector

loop is held to the BNC connector with another dolop of glue.


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The detail of the antenna plugged into my Voltmeter.


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Above is the antenna plugged into the Volt meter. It workspretty well, pointing it at the SUN also gets a reading! Point it atthe microwave oven and it will exceed the Millivolt scale! With alittle work I'm sure you could build a radar detector... I tunedthe capacitor with a plasitc screwdriver to get maximum readingfrom a 2.4Ghz RF source. You should use a Wireless LAN card asthe source.


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Here is the schematic detail (not to scale), you should make theelements of the antenna as close to the correct size as possible.This will ensure maximum energy is absorbed at 2.4Ghz. Theelements should be spaced around 10mm apart. The antenna

will display some gain and uni-directionality, so point thesmaller antenna loop (driven element) towards the RF sourceyou wish to measure. I tried connecting the antenna directly toa microamp moving coil meter, however there was very littlemeter deflection from a Wireless LAN card. The electronicvoltmeter is far superior.

DIODE Update!The original diode in the Microwave detector has been hard to

find. I have found a supplier for the diodes.... Purchased here:


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http://www.xs4all.nl/~barendh/Cateng/Cateng_diode.htm

Site Main Page :http://www.xs4all.nl/~barendh/Indexeng.htm

This site has many GHZ rated Diodes you may want to checkout... Here is a quote from the website:

"Following point contact diode for Ghz usage are originallymarked units. Being detectors for frequencies up to 12GHzdepending upon type numbers these are also excellent noisesources, because of the extremely high cutoff frequency.Technical details are available on ordering. Stocked: 1N21B1N21D 1N23ER 1N416B 1N416E from $3.58"

Questions?

Email [email protected]
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Fuente de 12 VDC Sin Transformador