I purchased a photovoltaic panel from maplin, maximum voltage output of 18.5 volts. I need to use a step up/down voltage regulator, I think this should be sufficient. I need to limit the maximum voltage that reaches the regulator to a maximum of 11 volts per the specification. Would this be best done with a zener connected between positive and ground before the regulator, this then links to a shutdown FET? This would of course only allow the regulator to operate when the panel is less than nominal.
My favourite option is attached, though I have doubts over it's functionality, dissipation and plausibility. Z1 has a breakdown of 11 volts, U1 is a simple voltage regulator of probably about 5 volts, but alternatively this could be replaced with a few diodes, totaling a voltage drop of 8 volts. The hatched box is a dc-dc converter, the same as I have linked to above. MOSFET1 is a P channel depletion (had to look that up, normally on/off at negative/positive/zero voltages, difficult to remember). The gate is connected to the output of the zener, so when this circuit section is activated, the direct connection is disconnected, protecting the adjustable converter from the raised voltages. D1 and D2 are blocking diodes, I am unsure whether this is necessary, but I could raise the voltage to compensate.
Whether diodes or a regulator would be used where vreg is on the diagram, both would present problems. The fixed regulator becomes inefficient at low loads and the diodes drop the voltage to a minimum of 4 volts, which will drop the efficiency of the adjustable regulator at high loads (as shown in the diagrams supplied on the polulu page). So mostly it is a case of whether the output would drive a high load or a low load. I find it more likely that it would be a low load.
Or would all of this be too complex and instead should locate a converter with an improved voltage spec?
Thanks,
My favourite option is attached, though I have doubts over it's functionality, dissipation and plausibility. Z1 has a breakdown of 11 volts, U1 is a simple voltage regulator of probably about 5 volts, but alternatively this could be replaced with a few diodes, totaling a voltage drop of 8 volts. The hatched box is a dc-dc converter, the same as I have linked to above. MOSFET1 is a P channel depletion (had to look that up, normally on/off at negative/positive/zero voltages, difficult to remember). The gate is connected to the output of the zener, so when this circuit section is activated, the direct connection is disconnected, protecting the adjustable converter from the raised voltages. D1 and D2 are blocking diodes, I am unsure whether this is necessary, but I could raise the voltage to compensate.
Whether diodes or a regulator would be used where vreg is on the diagram, both would present problems. The fixed regulator becomes inefficient at low loads and the diodes drop the voltage to a minimum of 4 volts, which will drop the efficiency of the adjustable regulator at high loads (as shown in the diagrams supplied on the polulu page). So mostly it is a case of whether the output would drive a high load or a low load. I find it more likely that it would be a low load.
Or would all of this be too complex and instead should locate a converter with an improved voltage spec?
Thanks,
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