Problem regarding mje13007 transistor control circuit

[mpgmike]

NPN transistors and N-MOSFETs switch the Negative side of the circuit. If you want to control the Positive side, use a PNP transistor or P-MOSFET. With N- devices, the Gate or Base must be higher than the Source to get the Source/Drain Emitter/Collector to conduct. With P- devices, the Gate or Base must be lower than Source to get Source/Drain Emitter/Collector to conduct. You are attempting to use an N- type device to do the work of a P- type device.

[Charlie]

NPN transistors and N-MOSFETs switch the Negative side of the circuit. If you want to control the Positive side, use a PNP transistor or P-MOSFET. With N- devices, the Gate or Base must be higher than the Source to get the Source/Drain Emitter/Collector to conduct. With P- devices, the Gate or Base must be lower than Source to get Source/Drain Emitter/Collector to conduct. You are attempting to use an N- type device to do the work of a P- type device.

That's an over simplification, and technically wrong. While a PNP would be easier, there is no reason an NPN will not work if the base voltage is high enough to supply the required base - emitter current.