Home Motor drivers Solar engines Type 1 (voltage) Zener-based FLED-based Mazibug3 1381-based "Miller" 1381 GBSE MicroPower VTSE DSSSE Chloroplast Vx2SE Type 2 (time) Type 3 (charge rate) Nocturnal Sensors Complete robots Misc. circuits   The BEAM Circuits Collection is a BEAM Reference Library site.		The GBSE (gate boost solar engine) Another Wilf Rigter design, described in his own words The Gate Boost SE uses a 1381, a 2N7000 MOSFET 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. The 2N7000 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 has triggered. 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 diode drops. This voltage is applied to the 2N7000 gate 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 voltage +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 gate, the MOSFET 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 main capacitor again. The result is an SE that applies a voltage of 2xV(trigger) to the MOSFET gate when triggered. That gate voltage decays to V (reset) in a few seconds and the cycle repeats. 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 voltage by 0.5V and shows inproved performance. But the rapid decay of the gate voltage to 0V make the marriage of a Miller SE and a MOSFET less than a happy one. Parts list for basic circuit Part Solarbotics Digikey Radio Shack Storage capacitor various various various 2.2 uF capacitor 0.22 uF capacitor Solar cell various N/A N/A 2N7000 MOSFET 2N3906 Transistor $0.15, #TR3906 $0.26, #2N3906-ND $0.07, #900-5457 100 KOhm Resistor 1 MOhm Resistor 1N4148 Diode 1381* IC 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 sheets. Wilf's original post of this material is here. If this page just doesn't whet your appetite for 1381-based solar engine designs, you ought to check out the Miller solar engine and VTSE pages.
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