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Topic: 2.3" 16 segment common anode LEDs, HT16K33 and ULN2803 (Read 1 time) previous topic - next topic

This looks correct, it will pull high when the gate goes low.
Take a close look at your led/display and see if you have done something wrong there.

Remember: You have to put some data into the HT16K33 to make the other drives do something.

MitchSF

I'm using two red LEDs connected in series, not the alphanumeric display. The HK16K33 is connected to an ESP32 displaying segments in a loop. I verified that by connecting a smaller display directly to the HK16K33.

MitchSF

I've switched to a max626 MOSFET driver, and everything appears to work up to it's output. The Arduino is running a blink sketch on every pin and I see the PWM output on the scope showing 0v - 5v,  following an LED connected directly to the HK16K33 so I know that part is working.

When the output of the max626 is connected to the gate of the NDP6020P, the LED stays on. I appreciate any help on this. Thanks.


When the output of the max626 is connected to the gate of the NDP6020P, the LED stays on. I appreciate any
The driver must be supplied with the same voltage as the MOSFET, i.e. 12V

MitchSF

Thanks for the reply. The output of the max626 is now at 0v and 12v, but the LEDs are dimly lit. They are on full brightness before the sketch starts when the gate is at 0v.


There was also something with a pullup resistor to 5V on the COM pins.

Grumpy_Mike

#67
Aug 27, 2019, 07:38 am Last Edit: Aug 27, 2019, 07:39 am by Grumpy_Mike
From the data sheet of the NDP6020P
Quote
Absolute Maximum Ratings
V GSS Gate-Source Voltage - Continuous  ±8 V
You seem to be putting 12 volts between gate and source when the FET is on.


MitchSF

That's why I originally put 5v on VCC for the Max626.

I thought the pullup resistor was only necessary when the 74HC04 was used. I'm not sure where to go from here.

That's why I originally put 5v on VCC for the Max626.
That does not work when the MOSFET is powered from 12V.

I thought the pullup resistor was only necessary when the 74HC04 was used.
The HT16K33 output is a pulldown output, it always needs something to pull it up.


I'm not sure where to go from here.
Find another mosfet that can take 20V over Gate Source, you do not need a logic level one.

MitchSF


Grumpy_Mike

#71
Aug 27, 2019, 04:14 pm Last Edit: Aug 27, 2019, 04:16 pm by Grumpy_Mike
I thought the pullup resistor was only necessary when the 74HC04 was used. I'm not sure where to go from here.
You add another 1K resistor between your FET's gate and your driver, that means your gate only drives to -6V and not -12V, which as I pointed out is too much for that FET.

Quote
That's why I originally put 5v on VCC for the Max626
Yes but that still put -12V on the gate when you pulled it down, with the added disadvantage that it would not pull it up high enough to turn off your FET anyway.

I don't know but maybe your FET is damaged it is never wise to exceed absolute maximum values.

The whole circuit seems to be a sledge hammer to crack a nut.

MitchSF

Quote
The whole circuit seems to be a sledge hammer to crack a nut.
Probably true!

I'll try that when we return from our travels, but maybe I'll just find an EE to do some consulting on this, to get it done right.


You add another 1K resistor between your FET's gate and your driver, that means your gate only drives to -6V and not -12V, which as I pointed out is too much for that FET.
I forgot that resistor, it is not needed with a the MOS driver chip and a MOSFET that can handle the voltage.

Grumpy_Mike

Quote
it is not needed with a the MOS driver chip and a MOSFET that can handle the voltage.
Well it is not the driver chip it is the FET. The whole thing about the driver chip seems silly as you are not trying to pull amps out of the FET so why not simply use an NPN transistor here? That will save a lot of money.

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