digital output drive current help - Electronic Circuits Projects Diagrams Free

jllabs · 7th May 2009, 12:44 AM

I have a controller that has an unusual digital I/O. When using its digital output - the drive current is only 220 uA @ 2.7 Vdc (yes micro amps), the output high state is 3.3Vdc no load and low state is <0.9 Vdc for each channel. I cannot find a SSR that will work with such a low drive current. Ultimately I want to control several 12 Vdc solenoids that need approximately 60mA each.

I do have a circuit diagram attached (power switching without relay) that I used on another system where the drive current was 1.5 mA @ 4.5Vdc, the output high was 5 Vdc and low was 0 Vdc. Can the initial resister value be lowered (substantially) to make it work for the lower drive current? Is there a SSR available that will work with such low drive current and output high?

I am not an electronics guy but can put most anything together with proper guidance. Thanks in advance for any assistance offered.

jllabs · 8th May 2009, 03:12 PM

I was able to try one of the two circuits and got it to work as shown in the attached sketch. The second circuit I was not able to test as I do not have the second transducer. I did build the circuit in LTspice and it works. However, the control is triggering at about 0.6 V and the control low is rated as <0.9 V. It could, in theory, not open or close unpredictably. The measured low is 0.0 V but this is without anything else connected to the controller.

Anyone's input would be appreciated...

ericgibbs · 8th May 2009, 03:45 PM

Quote:

Originally Posted by jllabs

I was able to try one of the two circuits and got it to work as shown in the attached sketch. The second circuit I was not able to test as I do not have the second transducer. I did build the circuit in LTspice and it works. However, the control is triggering at about 0.6 V and the control low is rated as <0.9 V. It could, in theory, not open or close unpredictably. The measured low is 0.0 V but this is without anything else connected to the controller.

Anyone's input would be appreciated...

hi,
For driving the relay, look at this pdf for the Si1012R/X, very low Vgate/source.

ericgibbs · 8th May 2009, 03:50 PM

hi,
For higher currents, look at this dual FDS6898AZ, using low Vgs.

jllabs · 8th May 2009, 04:34 PM

Can you provide a sketch or describe where the MOSFET would be used.

ericgibbs · 8th May 2009, 05:19 PM

Quote:

Originally Posted by jllabs

Can you provide a sketch or describe where the MOSFET would be used.

hi,
The Si1012 N MOSFET would replace the 2N2222 in your diagrams, change the value of the resistor to say 47R.

Post a drawing showing N MOSFET and we can check it for you.

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7th May 2009, 12:44 AM	#1
jllabs	digital output drive current help I have a controller that has an unusual digital I/O. When using its digital output - the drive current is only 220 uA @ 2.7 Vdc (yes micro amps), the output high state is 3.3Vdc no load and low state is <0.9 Vdc for each channel. I cannot find a SSR that will work with such a low drive current. Ultimately I want to control several 12 Vdc solenoids that need approximately 60mA each. I do have a circuit diagram attached (power switching without relay) that I used on another system where the drive current was 1.5 mA @ 4.5Vdc, the output high was 5 Vdc and low was 0 Vdc. Can the initial resister value be lowered (substantially) to make it work for the lower drive current? Is there a SSR available that will work with such low drive current and output high? I am not an electronics guy but can put most anything together with proper guidance. Thanks in advance for any assistance offered. Attached Thumbnails

8th May 2009, 03:12 PM	#2
jllabs	Additional info I was able to try one of the two circuits and got it to work as shown in the attached sketch. The second circuit I was not able to test as I do not have the second transducer. I did build the circuit in LTspice and it works. However, the control is triggering at about 0.6 V and the control low is rated as <0.9 V. It could, in theory, not open or close unpredictably. The measured low is 0.0 V but this is without anything else connected to the controller. Anyone's input would be appreciated... Attached Thumbnails

8th May 2009, 04:34 PM	#5
jllabs	Can you provide a sketch or describe where the MOSFET would be used.