Low Power Voltage Doubler Circuit Diagram

All miniature electronic devices operate off batteries. Some of them need higher than the standard battery voltages to operate efficiently. If the battery of that specific voltage is unavailable, we are forced to connect additional cells in series to step up the DC voltage. Thus, the true meaning of miniaturisation is lost. A simple way to overcome this problem is to employ a voltage doubler, if the device under consideration can operate at a small current.

Here we present a low-power voltage doubler circuit that can be readily used with devices that demand higher voltage than that of a standard battery but low operating current to work with. The circuit is quite simple as it uses only a few components. Yet, the output efficiency is 75 to 85 percent along its operating voltage range. The available battery voltage is almost doubled at the output of the circuit.

Here IC1 is wired as an astable multivibrator to generate rectangular pulses at around 10 kHz. This frequency and duty cycle of the pulses can be varied using preset VR1. The pulses are applied to switching transistors T1 and T2 for driving the output section, which is configured as a voltage-doubling circuit. The doubled voltage is available across capacitor C5. During each cycle of the pulse occurance, the high level drives T1 into its saturation, keeping transistor T2 cut off.

Circuit diagram:

Low-Power Voltage Doubler Circuit Diagram

So transistor T1 charges capacitor C4 via the path formed by diodes D2 and D1 to a voltage level slightly lesser than the supply. But during the low period of the pulse, transistor T1 is cut off while transistor T2 is driven into saturation. Now, transistor T2 raises the charge on the negative pole of capacitor C4 by another step equal to the supply voltage. Therefore an equal amount of charging is built up on capacitor C5 via diode D3.

This doubling action increases the total voltage across capacitor C5 to almost double the input voltage. If the output of the pulse generator is maintained with a high enough amplitude and frequency, the output voltage and current remain constant and cater to the needs of the load. Even with the half-wave function, this circuit is almost free of ripple voltage. If the connected load doesn’t require a high current, the efficiency can be expected in the upper 90 percentranges.

Since the input voltage is doubled, the current drain from the input power supply is also doubled at the input but halved at the output. One point of caution is that if the multivibrator’s frequency is fairly high, the output may suffer with the interference imposed over the DC voltage. In this case, the frequency must be set favorably by trials and actual load connection procedure. This tiny circuit can be assembled on the general-purpose PCB. If all of the components are surface-mount type, the whole module can be genuinely miniaturized.

EFY Lab note. During testing with input of 8V and 1.25mA load current the output voltage was found to be around 13V.

Author :M.K. Chandra ,Mouleeswaran And A.N. Vadivudai Naayaki

 

 

Source

Wiring Diagram Protection For Telephone Line

However, if
you have the good fortune to live in the countryside in a building
served by overhead telephone lines, there’s an obvious risk of very high
voltages being induced on the lines during thunderstorms. While we
have lost count today of all of the modems, fax machines and other
telephones that have been destroyed by a ‘bolt of lightning’,
surprisingly you only have to invest a few pounds to get a remarkably
efficient protection device like the one we are proposing here.

During
a storm, often with lightning striking near a telephone line, the line
carries transient voltages up to several thousands of volts. Contrary
to the HV section of television sets or electrical fences, on which
practically no current is running, in the case of lighting striking
current surges of thousand of amps are not uncommon. To protect oneself
from such destructive pulses, traditional components are not powerful
or fast enough.

As you can see on our drawing, a (gas-filled)
spark gap should be used. Such a component contains three electrodes,
insulated from each other, in an airtight cylinder filled with rare gas.
As long as the voltage present between the electrodes is below a
certain threshold, the spark gap remains perfectly passive and presents
an impedance of several hundreds of MW. On the other hand, when the
voltage rises above this threshold, the gas is very rapidly ionized and
the spark-gap suddenly becomes a full conductor to the point of being
able to absorb colossal currents without being destroyed.

The
one we are using here, whose size is of the same magnitude as an
ordinary one watt resistor, can absorb a standardized 5,000 amps pulse
lasting 8/20 ms! Since we are utilizing a three-electrode spark gap, the
voltage between the two wires of the line or between any wire and
ground, cannot exceed the sparking voltage, which is about 250 volts
here. Such protection could theoretically suffice but we preferred to
add a second security device made with a VDR (GeMOV or SiOV depending on
the manufacturer), which also limits the voltage between line wires to
a maximum of 250 volts.

Even if this value seems high to you,
we should remember that all of the authorized telephone equipment,
carrying the CE mark must be able to withstand it without damage. This
is not always the case however with some low-end devices made in China,
but that’s an entirely different problem. Since pulses generated by
lightning are very brief, the ground connection of our assembly must be
as low-inductance as possible.

It must therefore be short, and
composed of heavy-duty wire (1.5 mm2 c.s.a. is the minimum). If not, the
coil, composed of the ground connection, blocks the high frequency
signal that constitutes the pulse and reduces the assembly’s
effectiveness to nothing. Finally, please note that this device
obviously has no effect on the low frequency signals of telephones and
fax machines and it does not disturb (A)DSL signals either.

On/Off Infrared Remote Control

Therefore,
the first one you find allows you to turn off the light and enjoy your
movie in the best possible conditions. The infrared receiver part of
our project is entrusted to an integrated receiver (Sony SBX 1620-52)
which has the advantage of costing less than the components required to
make the same function. After being inverted by T1, the pulses
delivered by this receiver trigger IC2a, which is nothing other than a D
flip-flop configured in monostable mode by feeding back its output Q
on its reset input via R4 and C3. The pulse that is produced on the
output Q of IC.2A makes IC.2B change state, which has the effect of
turning on or turning off the LED contained in IC3.

This
circuit is an opto triac with zero-crossing detection which allows our
setup to accomplish switching without noise. It actually triggers the
triac T2 in the anode where the load to be controlled is found. The
selected model allows us to switch up to 3 amperes but nothing should
stop you from using a more powerful triac if this model turns out to be
insufficient for your use. In order to reduce its size and total cost,
the circuit is powered directly from the mains using capacitor C5 which
must be a class X or X2 model rated at 230 volts AC.

This type
of capacitor, called ‘self-healing’, is the only type we should use
today for power supplies that are connected to ground. ‘Traditional’
capacitors, rated at 400 volts, do not really have sufficient safety
guarantees in this area. Considering the fact that the setup is
connected directly to the mains, it must be mounted in a completely
insulated housing. A power outlet model works very well and can easily
be used to inter-space between the grounded wall outlet and that of the
remote control device.

Based on this principle, this setup
reacts to any infrared signal and, as we said before, this makes it
compatible with any remote control. On the other hand, it has a small
disadvantage which is that sometimes it might react to the ‘normal’
utilization of one of these, which could be undesirable. To avoid that,
we advise you to mask the infrared receiver window as much as possible
so that it is necessary to point the remote control in its direction
in order to activate it.