LT1001 op-amp input current reads high in LTspice.

[Bill Bowden]

There seems to be excessive input current with this LR oscillator using the LT1001 op-amp. I measure the current through the bypass cap C1 at about 1.8 milliamps peak. I thought it would be more in the microamp or nanoamp range. I built this same circuit using a LM358 op-amp and it works fine without the cap. Very little voltage swing on the input pins with no bypass cap used.

-Bill


Version 4
SHEET 1 880 680
WIRE 16 0 -80 0
WIRE 96 0 16 0
WIRE 352 0 96 0
WIRE -80 32 -80 0
WIRE 16 32 16 0
WIRE 96 112 96 0
WIRE -80 128 -80 112
WIRE 16 128 16 112
WIRE 16 128 -16 128
WIRE 64 128 16 128
WIRE 352 128 352 0
WIRE 16 144 16 128
WIRE 160 144 128 144
WIRE 256 144 240 144
WIRE 320 144 256 144
WIRE 64 160 48 160
WIRE 464 160 384 160
WIRE 320 176 304 176
WIRE 96 192 96 176
WIRE 256 192 256 144
WIRE 352 208 352 192
WIRE -16 224 -16 128
WIRE -16 224 -80 224
WIRE -80 240 -80 224
WIRE 16 240 16 224
WIRE 256 288 256 272
WIRE 48 320 48 160
WIRE 464 320 464 160
WIRE 464 320 48 320
WIRE -80 336 -80 304
WIRE -16 352 -16 224
WIRE 304 352 304 176
WIRE 304 352 -16 352
FLAG 256 288 0
FLAG 352 208 0
FLAG 96 192 0
FLAG 16 240 0
FLAG -80 128 0
FLAG -80 336 0
SYMBOL Opamps\\LT1001 96 80 R0
WINDOW 3 -28 157 Left 0
SYMATTR InstName U1
SYMBOL Opamps\\LT1001 352 96 R0
SYMATTR InstName U2
SYMBOL ind 256 128 R90
WINDOW 0 5 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName L1
SYMATTR Value 100m
SYMATTR SpiceLine Rser=100
SYMBOL res 240 176 R0
WINDOW 0 -32 47 Left 0
WINDOW 3 -37 73 Left 0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res 0 128 R0
WINDOW 0 -59 41 Left 0
WINDOW 3 -64 66 Left 0
SYMATTR InstName R2
SYMATTR Value 10k
SYMBOL res 0 16 R0
WINDOW 0 41 40 Left 0
WINDOW 3 41 65 Left 0
SYMATTR InstName R3
SYMATTR Value 10k
SYMBOL voltage -80 16 R0
WINDOW 3 36 44 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value 9
SYMATTR InstName V1
SYMBOL cap -96 240 R0
WINDOW 0 -39 32 Left 0
WINDOW 3 -48 59 Left 0
SYMATTR InstName C1
SYMATTR Value 10ľ
TEXT -16 392 Left 0 !.tran .001

 

[Maynard A. Philbrook Jr.]

In article <02584722-0d8d-4d03-bd60-4c4291c99632@googlegroups.com>,
bperryb@bowdenshobbycircuits.info says...

There seems to be excessive input current with this LR oscillator using the LT1001 op-amp. I measure the current through the bypass cap C1 at about 1.8 milliamps peak. I thought it would be more in the microamp or nanoamp range. I built this same circuit using a LM358 op-amp and it works fine without the cap. Very little voltage swing on the input pins with no bypass cap used.

-Bill

As with many op-amps, there are back to back diodes between
the inputs inside. This prevents the input from getting over driven
between the inputs.

I took your sim and placed a 10k R inline to the (+) of U1.

You can go higher if you wish,.

Jamie

 

[Bill Bowden]

On Thursday, February 6, 2014 4:35:27 PM UTC-8, Maynard A. Philbrook Jr. wrote:

In article <02584722-0d8d-4d03-bd60-4c4291c99632@googlegroups,


There seems to be excessive input current with this LR oscillator using the LT1001 op-amp. I measure the current through the bypass cap C1 at about 1.8 milliamps peak. I thought it would be more in the microamp or nanoamp range. I built this same circuit using a LM358 op-amp and it works fine without the cap. Very little voltage swing on the input pins with no bypass cap used.

-Bill


As with many op-amps, there are back to back diodes between
the inputs inside. This prevents the input from getting over driven
between the inputs.

I took your sim and placed a 10k R inline to the (+) of U1.
You can go higher if you wish,.

Jamie

Yes, that helped out. The capacitor current dropped to about 200 microamps with the 10K installed. Thanks.

-Bill