Problem regarding mje13007 transistor control circuit

[Tarsha]

For npn MJE13007 transistor (https://www.utmel.com/components/mje13007-npn-bipolar-power-transistor-equivalent-datasheet-and-pinout?id=723), I connect the collector to the 24V relay, the other end of the relay to 24V positive, the emitter to negative, and the base to the 1K resistor to the optocoupler output. The microcontroller outputs a high level signal every second, and the relay works normally.
But I connect the collector to the positive pole, the emitter to one end of the relay, and the other end of the relay to 24V negative, and the base is input high, the relay just doesn't work. .
Master, where is the problem with my line? Theoretically speaking, it is impossible for a triode to control only the negative electrode but not the positive electrode.

Does anyone know why? Thanks for the help!

[Ioannis]

How much high is the high on base of transistor? Remember you said 24V on Collector, so are you sure that base has at least 23 volts through a resistor?

Ioannis

[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.