diagram circuit

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:

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.
Source: EFY Mag