Hey all, first time on this wonderful site. I've looked around quite a bit and can't seem to find anything that points out an obvious answer to this issue I'm having...
I'm trying to create a power switch to some external circuitry. The external circuitry is run off of a 12Vdc supply and draws around 200 mA, peaking around 300 mA for short bursts (~1ms) when operating, but is brought down to roughly 1mA with small spikes of 100mA when I bring it to shutdown.
I must control this switch through a digital output pin, setting it 1 turning the circuitry on, and 0 for off.
After looking through The Art of Electronics, I decided to employ the circuit attached below as my power switch.
It is supposed to utilize an NPN BJT employed as a current sink from my digital output pin to control the voltage present at the gate of the PMOS, thus allowing current to flow through the 12V supply or stop it completely (or at least drop it to roughly 10nA consumption)...
The load is inductive, and the 12V power supply (once past the PMOS), is fed into this step-down buck converter here:
http://www.ti.com/lit/ds/symlink/tps54229e.pdf
(There is a transient voltage suppressor included in the load that is wired from 12V (just after the Drain of the PMOS) to ground)
The circuit runs perfectly when switched on- Vg is dropped down to roughly 4V, allowing for current to sink to the load.
I'm getting very odd results when trying to switch the circuit off though- Vg is .65 volts... so current is still allowed to sink.
Any help would be MUCH appreciated, and feel free to criticize and ask questions. Fresh undergrad here that's still trying to learn all the tricks!
~William
I'm trying to create a power switch to some external circuitry. The external circuitry is run off of a 12Vdc supply and draws around 200 mA, peaking around 300 mA for short bursts (~1ms) when operating, but is brought down to roughly 1mA with small spikes of 100mA when I bring it to shutdown.
I must control this switch through a digital output pin, setting it 1 turning the circuitry on, and 0 for off.
After looking through The Art of Electronics, I decided to employ the circuit attached below as my power switch.
It is supposed to utilize an NPN BJT employed as a current sink from my digital output pin to control the voltage present at the gate of the PMOS, thus allowing current to flow through the 12V supply or stop it completely (or at least drop it to roughly 10nA consumption)...
The load is inductive, and the 12V power supply (once past the PMOS), is fed into this step-down buck converter here:
http://www.ti.com/lit/ds/symlink/tps54229e.pdf
(There is a transient voltage suppressor included in the load that is wired from 12V (just after the Drain of the PMOS) to ground)
The circuit runs perfectly when switched on- Vg is dropped down to roughly 4V, allowing for current to sink to the load.
I'm getting very odd results when trying to switch the circuit off though- Vg is .65 volts... so current is still allowed to sink.
Any help would be MUCH appreciated, and feel free to criticize and ask questions. Fresh undergrad here that's still trying to learn all the tricks!
~William
Attachments
-
388.1 KB Views: 65