Ok, I have one of the protoboards all soldered up and finally have it programmed. After testing everything, it appears the MOSFET's will just not turn off Battery voltage is 12.8V. If the prop pin is off, the MOSFET output is 12.47V. If the pin is ON, the MOSFET output is 12.8V. Am I missing something here? I took Phil's advice and used the "recommended" resistors.
Measure the G-S voltage on the PFET in both cases.
in circuits like this, depending on the noise expected on the 12V side, you could add some gate-spike protection.
(Zener, G-S) - with no protection when the device is ON, the Vin becomes gate supply, and that is 20V max.
Currently, I have not measured any noise with my O-scope on this circuit as it is running from a 12V sealed battery on my bench and there are no spikes in the voltage going into the MOSFET or the entire circuit.
I recall a Dutch engineer, who used a workshop metal file, and ran the furry end of some stripped multi-core cable along the file, as his Noisy-Supply test. He even did this for mains supplies(!), which I thought was a little hairy, if dramatic to watch.
Hopefully, he still has a pulse...
Ok, let me get this right.... the Gate of the P channel Mosfet needs to be pulled HIGH in order to turn off. Once pulled low, then the output of the Mosfet should be HIGH? Maybe 2.2K is not a "stiff" enough resistor to pull the gate up enough? A resistor is needed there though, correct? I don't want to pop the NPN because it basically creates a direct short without the resistor.
Ok, let me get this right.... the Gate of the P channel Mosfet needs to be pulled HIGH in order to turn off. Once pulled low, then the output of the Mosfet should be HIGH?
Yes, but always measure Gate-Source and Drain-Source voltages with your meter. Removes any other variables.
Maybe 2.2K is not a "stiff" enough resistor to pull the gate up enough? A resistor is needed there though, correct? I don't want to pop the NPN because it basically creates a direct short without the resistor.
Some resistor is needed G-S on the P_FET, (it can be via the pullup), the FET gate leakage should be very low, so value should matter only for switching speed reasons.
Check with some load on the FET, to avoid measuring leakages.
Maybe 2.2K is not a "stiff" enough resistor to pull the gate up enough?
It's plenty stiff. The gate itself does not draw any current (except when switching, to charge/discharge the gate capacitance): it's strictly voltage-sensitive. I suspect there's something else that's wrong with your layout that's causing the pMOS transistor to stay on.
I am not sure if anything else is wrong just yet. I am still testing each function. So far, everything else seems to be working properly. The P Channel mosfet circuit is exactly how it is shown in the above picture. I have tried removing the 330ohm resistor and putting a jumper there which did not work either. The 2.2K's are still in place though.
The 10K resistor is now a 2.2K, the 4.7K is now a straight connection, and the 1K is now a 2.2K.
When measuring the voltage change from the NPN (Ground to testing pin), it reads 12.78V with the prop pin off that is connected to the base and 0.063V with the prop pin on. This is the same for both NPN's that control the PMOS. The voltage on the Gate of the PMOS with the NPN off is 12.78V and with it on, it drops to 0.063V.
Yes, 100% since I just got these boards in and I have triple check the current board and the other 2 that came in just to make sure there was no glitch. I even ensure the ground plane was properly connected and was not broken anywhere.
The link is broken I have also spent the last bit of my money on these boards and can't afford to be buying anything else for now. I was hoping to stick with what I am using, just get it working... if it is possible.
Yes, 100% since I just got these boards in and I have triple check the current board and the other 2 that came in just to make sure there was no glitch. I even ensure the ground plane was properly connected and was not broken anywhere.
What is the test load Fet -D to GND ?
If the FET is reverse connected, expect the Drain to drop some mV then ~600mV as the gate varies with a reasonable load.
I was using a 12V light, but then I tried a 0.37 Ohm electromagnet. Still does not toggle the power. I put in my code to toggle the output with a button press. The Gate toggled, but the PMOS did not.
Ok, with the electromagnet connected, the prop pin LOW, and the meter connected to the electromagnet High side, the voltage is 11.84V. The Gate is 12.8. When I turn the Prop pin to HIGH, the Gate voltage goes to 0.063 and the output goes to 12.8V from the PMOS.
EDIT : I just tested from the Tab to the lead on the right of the PMOS (Source) and there is a 0.66 volt change when the prop pin is toggled. I am guessing I have this connected backwards then huh?
I hope you did not really mean a 0.37 Ohm electromagnet ? (that's ~ 32A !)
Those numbers sound rather like the FET is backwards. Measure the current thru the fet, and if it warms check the Drop.
-ve tempco in 500mV-1V region, is a diode = reverse S-D connections.
If you measure D-S, what values do you get ?
See
Fig. 8 Diode Forward Voltage vs. Current
Fig. 1 Typical Output Characteristic
If you are not on either curve, then you have damaged the FET.
lol, it is 37.0 ohms.... sorry. It is late and I have been up WAY too long. I am really thinking I have this backwards now. the tab should be what is connected to the electromagnet, not the Source pin.... I guess that is one way to learn how not to hook up this mosfet....
EDIT : changed ohm reading....and heading off to bed. I can't think straight right now.....
Comments
Measure the G-S voltage on the PFET in both cases.
in circuits like this, depending on the noise expected on the 12V side, you could add some gate-spike protection.
(Zener, G-S) - with no protection when the device is ON, the Vin becomes gate supply, and that is 20V max.
Hopefully, he still has a pulse...
Yes, but always measure Gate-Source and Drain-Source voltages with your meter. Removes any other variables.
Some resistor is needed G-S on the P_FET, (it can be via the pullup), the FET gate leakage should be very low, so value should matter only for switching speed reasons.
Check with some load on the FET, to avoid measuring leakages.
-Phil
-Phil
-Phil
-Phil
The PMOS circuit is wired just like this : http://forums.parallax.com/attachment.php?attachmentid=104611&d=1382941193 which is in post #24
The 10K resistor is now a 2.2K, the 4.7K is now a straight connection, and the 1K is now a 2.2K.
When measuring the voltage change from the NPN (Ground to testing pin), it reads 12.78V with the prop pin off that is connected to the base and 0.063V with the prop pin on. This is the same for both NPN's that control the PMOS. The voltage on the Gate of the PMOS with the NPN off is 12.78V and with it on, it drops to 0.063V.
-Phil
http://www.mouser.com/ProductDetail/Infineon-Technologies/BTS452R/?qs=sGAEpiMZZMuCmTIBzycWfNaB4tqdZgjBmdjjHyJ3guk%3d
Repetitive short circuit current limit: 6A
What is the test load Fet -D to GND ?
If the FET is reverse connected, expect the Drain to drop some mV then ~600mV as the gate varies with a reasonable load.
Here is the datasheet on the PMOS : http://www.diodes.com/datasheets/DMP3010LK3.pdf
EDIT : I just tested from the Tab to the lead on the right of the PMOS (Source) and there is a 0.66 volt change when the prop pin is toggled. I am guessing I have this connected backwards then huh?
Those numbers sound rather like the FET is backwards. Measure the current thru the fet, and if it warms check the Drop.
-ve tempco in 500mV-1V region, is a diode = reverse S-D connections.
If you measure D-S, what values do you get ?
See
Fig. 8 Diode Forward Voltage vs. Current
Fig. 1 Typical Output Characteristic
If you are not on either curve, then you have damaged the FET.
EDIT : changed ohm reading....and heading off to bed. I can't think straight right now.....