Sounds like you are using an unsuitable configuration of the switching transistor. We would usually utilize a PNP transistor (or a PMOSFET, as suggested) to switch a positive supply. Both will allow a very low (e.g. < 50 mV) voltage drop.
I designed the attached circuit to provide push-on/push-off/program-off for a microcontroller. You could use the Q1/Q2/R1/R2 circuit to switch power to other devices.
Ken
The attached is the minimum circuit, Q1 is a P-channel logic-level MOSFET with the Source (S) to the battery +. Q2 is an N-channel logic-level MOSFET with its Source connected to battery common (-). Drains (D) and Gates (G) are connected as shown. Control is a low (off) or high (on) from the microcontroller.
A high on Q2's gate turns on Q2 and pulls Q1's gate to common. This turns on Q1 and supplies battery power to its Drain and to you devices. A low on Q2's Gate turns Q2 off. That allows R1 to pull Q1's gate to B+ and turning it off. That cuts power to Q1's drain and to your devices.
Ken
You use a PNP transistor for Q1 and PNP for Q2, if you add base series resistors, e.g. 1 - 2 k for Q1 and 10 - 20 k for Q2.
Sorry, my fault. Should mean a NPN in place of Q2.Two PNPs ?
I designed the attached circuit to provide push-on/push-off/program-off for a microcontroller. You could use the Q1/Q2/R1/R2 circuit to switch power to other devices.
Ken
Your battery is backwards. The 2N7265 is not a logic-level Mosfet.
Ken
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