The same power supply can drive multiple laser diodes if they are connected in series, but they must never be connected in parallel. Series connection means a side by side connection. Two series-connected diodes with reverse bias: In practice, the $v-i$ characteristics for the same type of diodes differ due to tolerances in their production process Under forward-biased. simulate this circuit – Schematic created using CircuitLab Your schematic indicates that you're connecting two 8V linear regulators to an 8V power supply. Powered by 12 volts, 1 amp wall wart. All light, but some brighter, some.
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