The BEAM Circuits Collection is a
The GBSE (gate boost solar engine)
Another Wilf Rigter design,
described in his own words
The Gate Boost SE uses a 1381,
and a 2N3906
with a unique voltage
doubler to increase the voltage
applied to the gate
of the MOSFET.
Normally the 2.6V output of a 1381C
is barely able to turn on the 2N7000.
As a result the "on resistance"
of the MOSFET
is high and much power is wasted.
works very well with 5V or 6V gate
drive and then has an "on resistance
" of a few ohms.
The Gate Boost SE uses a voltage
doubler to pump up the voltage
of the 0.22 uF capacitor
after the 1381C
How it works
The action of the triggered 1381
is to internally connect the voltage
on the input pin to the output pin. The trigger voltage
is actually about 2.8V because of two aditional series
drops. This voltage
is applied to the 2N7000
and starts to turn on the MOSFET.
When the 2N7000
starts to turn on the voltage
across the motor increases and the base
of the 2N3906
turns on. As the 2N3906
turns on, the voltage
on the collector
rises to the capacitor
+V. That voltage
rise is capacitively coupled through the 2.2uF capacitor
to the midpoint of the two diodes.
As this point is initially +V-100mV, a step voltage
of +V-100mV is superimposed and turns on the lower diode
to charge the .22uF capacitor
to nearly double the trigger voltage
or about 5.6V. Since that capacitor
supplies the voltage
for the 2N7000
turns on hard and the motor is efficiently powered up.
Because of the low leakage current
of the 1381
(1 to 5uA), the voltage
on the .22uF capacitor
now decays towards the reset level of the 1381
at about 2.5V at which point the MOSFET
turns off and the whole SE resets and starts charging the
The result is an SE that applies a voltage
of 2xV(trigger) to the MOSFET
when triggered. That gate
decays to V (reset) in a few seconds and the cycle
Compare this with the action of a Miller
SE which applies only 1xV(trigger) to the gate
which then decays to 0V in a few seconds. According to some
reports, a photodiode
in series with the gate
increases the gate
by 0.5V and shows inproved performance. But the rapid decay
of the gate
to 0V make the marriage of a Miller
SE and a MOSFET
less than a happy one.
For more information...
1381s are great little ICs, but their availability
seems to be spotty. If you can't find 1381s
locally, you might have better luck finding its
European cousin, the TC-54 -- for details on both
of these, see their data
Wilf's original post of this material is
If this page just doesn't whet your appetite for
solar engine designs, you ought to check out the
Miller solar engine
and VTSE pages.