Electrical – Comparator (lm2903) help

comparatorvoltage

I have a 9v source driving a comparator with a 5v source that is pulsing with 1s intervals, and a 2.5v constant source. with a pull up resistor of 10K to get make my vout 9v when my pulsing source is greater than 2.5v. This is working as expected. However, I'm trying to push the 9v vout into my 13ohm load which requires to be grounded. Is there anything I can do to keep the 9v vout switching and also use my grounded load? Any help is much appreciated. He is a rough design of what I'm looking at in LT Spice.

enter image description here

In the picture (R4) is the load that I want to get the 9v to go to.

Best Answer

If you want to drive a ground-referred load with a high side driver and waste as little power as possible you'll need to use a PMOS FET and reverse the sense of the inputs to the comparator, like this:

The diode's in there just in case the 13 ohm load is a relay or a horn...

enter image description here

Here's the LTspice circuit list just in case yuou want to play with the circuit:

Version 4
SHEET 1 880 680
WIRE 352 0 64 0
WIRE 448 0 352 0
WIRE 576 0 448 0
WIRE 448 32 448 0
WIRE 352 112 352 0
WIRE 176 128 160 128
WIRE 320 128 176 128
WIRE 576 128 576 0
WIRE 448 144 448 112
WIRE 448 144 384 144
WIRE 528 144 448 144
WIRE 288 160 256 160
WIRE 320 160 288 160
WIRE 576 240 576 224
WIRE 576 240 496 240
WIRE 576 256 576 240
WIRE 624 256 576 256
WIRE 576 272 576 256
WIRE 64 288 64 0
WIRE 160 288 160 128
WIRE 256 288 256 160
WIRE 496 288 496 240
WIRE 64 400 64 368
WIRE 160 400 160 368
WIRE 160 400 64 400
WIRE 256 400 256 368
WIRE 256 400 160 400
WIRE 352 400 352 176
WIRE 352 400 256 400
WIRE 496 400 496 352
WIRE 496 400 352 400
WIRE 576 400 576 352
WIRE 576 400 496 400
WIRE 64 464 64 400
FLAG 64 464 0
FLAG 176 128 VIN
FLAG 624 256 VOUT
FLAG 288 160 VREF
SYMBOL Comparators\\LT1017 352 144 R0
SYMATTR InstName U1
SYMBOL res 432 16 R0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL pmos 528 224 M180
SYMATTR InstName M1
SYMATTR Value FDS4465
SYMBOL res 560 256 R0
SYMATTR InstName R2
SYMATTR Value 13
SYMBOL voltage 64 272 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 9
SYMBOL voltage 160 272 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value PULSE(0 5 500m 1ms 1ms 500m 1s)
SYMBOL voltage 256 272 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value 2.5
SYMBOL schottky 512 352 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D1
SYMATTR Value MBRS1100
SYMATTR Description Diode
SYMATTR Type diode
TEXT 78 432 Left 2 !.tran 5
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