# Vref > Vin on comparator

M

Jan 1, 1970
0
Doing the ciruit suggested below, I was able to set 0.8 volts on the Vref. Currently my output is about 4.8 volts when the Vin > Vref. How can I get the HIGH output when Vref > Vin instead?

+----------+---+5V
| |
[100k] |
| |
+---------|+\
| | >--[<1N914]...
Vin>--|---------|-/
| |
[50k]<-+ |
| | |
+----+-----+---GND

which will get you your 0.8V point with the pot at adjusted to

W

#### William Hightower

Jan 1, 1970
0
You already have HIGH when VRef > Vin. If you want the inverse VRef < Vin,
then swap + and - pins of the circuit. I hope this helps.

Bill

J

#### John Fields

Jan 1, 1970
0
Doing the ciruit suggested below, I was able to set 0.8 volts on the Vref.
Currently my output is about 4.8 volts when the Vin > Vref.
How can I get the HIGH output when Vref > Vin instead?

+----------+---+5V
| |
[100k] |
| |
+---------|+\
| | >--[<1N914]...
Vin>--|---------|-/
| |
[50k]<-+ |
| | |
+----+-----+---GND

---
You're doing something wrong.

With the signal on the - input more positive than the signal on the
+ input, the output should be close to GND.

Conversely, with the + input more positive than the - input, the
output should be close to +5V.

BTW, if you want to see the circuit working, simulate it.

Go to:

http://www.linear.com/designtools/index.jsp

Version 4
SHEET 1 880 680
WIRE -416 384 -416 224
WIRE -416 544 -416 464
WIRE -304 384 -304 -32
WIRE -304 544 -416 544
WIRE -304 544 -304 464
WIRE -144 -32 -304 -32
WIRE -144 0 -144 -32
WIRE -144 256 -144 80
WIRE -144 384 -144 256
WIRE -144 544 -304 544
WIRE -144 544 -144 464
WIRE -80 224 -416 224
WIRE -80 256 -144 256
WIRE -48 -32 -144 -32
WIRE -48 208 -48 -32
WIRE -48 544 -144 544
WIRE -48 544 -48 272
WIRE 32 240 -16 240
WIRE 112 240 96 240
WIRE 112 240 112 224
WIRE 112 352 112 240
WIRE 112 416 112 352
WIRE 112 544 -48 544
WIRE 112 544 112 480
WIRE 240 -32 -48 -32
WIRE 240 0 240 -32
WIRE 240 128 240 80
WIRE 240 256 240 128
WIRE 240 400 240 256
WIRE 240 544 112 544
WIRE 240 544 240 480
WIRE 288 128 240 128
WIRE 288 352 112 352
WIRE 400 224 112 224
WIRE 400 256 240 256
WIRE 432 -32 240 -32
WIRE 432 208 432 -32
WIRE 432 544 240 544
WIRE 432 544 432 272
WIRE 528 128 368 128
WIRE 528 240 464 240
WIRE 528 240 528 128
WIRE 528 352 368 352
WIRE 528 352 528 240
WIRE 528 416 528 352
WIRE 528 544 432 544
WIRE 528 544 528 496
WIRE 528 608 528 544
FLAG 528 608 0
SYMBOL res -160 -16 R0
SYMATTR InstName R1
SYMATTR Value 100k
SYMBOL res -160 368 R0
SYMATTR InstName R2
SYMATTR Value 19k
SYMBOL voltage -304 368 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 5
SYMBOL voltage -416 368 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
WINDOW 3 24 104 Invisible 0
SYMATTR InstName V2
SYMATTR Value PULSE(+5 0 0 1 0 1 1 1)
SYMBOL res 224 -16 R0
WINDOW 0 -52 37 Left 0
WINDOW 3 -48 67 Left 0
SYMATTR InstName R3
SYMATTR Value 100k
SYMBOL res 224 384 R0
WINDOW 0 58 40 Left 0
WINDOW 3 64 69 Left 0
SYMATTR InstName R4
SYMATTR Value 100k
SYMBOL diode 96 224 R90
WINDOW 0 -51 32 VBottom 0
WINDOW 3 -41 34 VTop 0
SYMATTR InstName D1
SYMATTR Value 1N914
SYMBOL res 384 112 R90
WINDOW 0 -43 57 VBottom 0
WINDOW 3 -32 60 VTop 0
SYMATTR InstName R5
SYMATTR Value 22k
SYMBOL res 384 336 R90
WINDOW 0 -36 61 VBottom 0
WINDOW 3 -32 67 VTop 0
SYMATTR InstName R6
SYMATTR Value 100k
SYMBOL cap 96 416 R0
SYMATTR InstName C1
SYMATTR Value .2e-6
SYMBOL res 512 400 R0
SYMATTR InstName R7
SYMATTR Value 10k
SYMBOL Opamps\\LT1013 -48 176 R0
SYMATTR InstName U1
SYMBOL Opamps\\LT1013 432 176 R0
SYMATTR InstName U2
TEXT -450 554 Left 0 !.tran 1

I've substituted LT1013's for the LM324's, but that shouldn't make
any real difference in whether the thing runs or not.

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