I'm experiencing a voltage drop across a pretty simple circuit and don't understand why.
I have a L7812 setup to give my circuit a 12V DC power. The L7812 has bridge rectifier, caps, and transformer 120V to 15V. From the LM7812 I pass the current through a pnp transistor that is fully saturated. Looks like I get about 18-19V into the L7812 and when the motors (small pc fan motors) are off (pnp open) I see a stable ~12V.
I have a small resistor in series (out of motors to ground) with the motors (3 in parallel) to limit the current. The motors are expected to draw 100mA. So I expect to drop a bit over 300mA across the circuit. My transformer and L7812 are all spec for up to 1A. When I turn the motors on (pnp saturated) the voltage sags to near 9V pulling about 300mA. So I'm not too sure why I'm seeing the sag as I should be able to drive plenty of current and with my resistor in series of the current path there should be current limited.
Any ideas? Thank you.
I have a L7812 setup to give my circuit a 12V DC power. The L7812 has bridge rectifier, caps, and transformer 120V to 15V. From the LM7812 I pass the current through a pnp transistor that is fully saturated. Looks like I get about 18-19V into the L7812 and when the motors (small pc fan motors) are off (pnp open) I see a stable ~12V.
I have a small resistor in series (out of motors to ground) with the motors (3 in parallel) to limit the current. The motors are expected to draw 100mA. So I expect to drop a bit over 300mA across the circuit. My transformer and L7812 are all spec for up to 1A. When I turn the motors on (pnp saturated) the voltage sags to near 9V pulling about 300mA. So I'm not too sure why I'm seeing the sag as I should be able to drive plenty of current and with my resistor in series of the current path there should be current limited.
Any ideas? Thank you.
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