help with low cost current detector

ZXCT1009FCT

1 0.98000 $0.98 25 0.84160 $21.04 100 0.77150 $77.15

?name=ZXCT1009FCT-ND

Or

FAN4010IL6X_F113CT

1 0.86000 0.86 25 0.64760 16.19 100 0.48560 48.56

?name=FAN4010IL6X_F113CT-ND

1% resistor 0.25w RHM.22MCT-ND 10 for $1.5

?name=RHM.22MCT-ND

Hi TT_Man,

LM311 is your friend. You can tune the offset to a few mV in your most wanted direction, so you need only a milliohm resistor in the ground loop

A cheaper way may be a 1N4001 as high side shunt device parallel to a pnp-transistors BE diode that switches on a LED with resistor in series to ground.

Have a nice day

Marte

"TT_Man" skrev i en meddelelse news:pr%ak.180465$ snipped-for-privacy@newsfe17.ams...

How about a reed relay?

Wind the charger lead around it until it is "enough" to close it. You could adjust the current threshold by adding/removing turns.

If you have enough voltage to spare (open ckt - battery voltage), you can go real low-tech and put a 1-2 amp rated auto lamp in series. It should glow with .5 amps. If you short the charger terminals it will light up very brightly, but protect your charging circuitry. It is pretty reliable! You should be able to get one at any decent auto store or garage. The filament has a non-linear v vs. i characteristic, that should give you lower than expected voltage drop.

-Paul

"TT_Man" wrote in message news:pr%ak.180465$ snipped-for-privacy@newsfe17.ams...

Following is an LTspice ASCII file of a simple indicator which detects current over about 350 mA. The 2 ohm resistor will dissipate 1/2 watt at

500 mA. As current increases, some of it is shared by the BE junction of the transistor, so the resistor will see no more than about 1 watt. You can add a base resistor to eliminate this. You can use a different value sense resistor for other current ranges. A germanium transistor will allow even smaller sense resistors, but they are rare.

Actually, Mouser stocks a variety of SiGe transistors at about $1 each, but all are NPN and they are 60 GHz devices, and I did not see any forward voltage spec for Vbe:

You can also use a MOSFET with a low Vto, such as the Si4467DY (which is in the LTspice library), and is available from Mouser for about $2. But the FDC604P is only $0.36 each, and has typical Vto of 0.7 V, so it should work well.

I made a Spice circuit for that but it is identical except for the MOSFET.

Paul

==============================================================================

Version 4 SHEET 1 880 680 WIRE -16 0 -48 0 WIRE 112 0 48 0 WIRE 192 0 112 0 WIRE 112 48 112 0 WIRE -48 96 -48 0 WIRE 192 112 192 0 WIRE 112 160 112 128 WIRE 128 160 112 160 WIRE 112 176 112 160 WIRE 64 192 -160 192 WIRE -160 208 -160 192 WIRE 192 224 192 208 WIRE -48 272 -48 176 WIRE 112 272 112 256 WIRE 192 320 192 288 WIRE -160 416 -160 288 WIRE -48 416 -48 352 WIRE -48 416 -160 416 WIRE 64 416 64 240 WIRE 64 416 -48 416 WIRE 112 416 112 352 WIRE 112 416 64 416 WIRE 192 416 192 400 WIRE 192 416 112 416 WIRE 192 464 192 416 FLAG 192 464 0 SYMBOL res 96 32 R0 SYMATTR InstName R1 SYMATTR Value 2 SYMBOL LED 176 224 R0 SYMATTR InstName D2 SYMATTR Value QTLP690C SYMATTR Description Diode SYMATTR Type diode SYMBOL res 176 304 R0 SYMATTR InstName R2 SYMATTR Value 470 SYMBOL voltage 112 256 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 6 SYMBOL voltage -48 256 R0 WINDOW 3 29 91 Left 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value 12 SYMBOL res -64 80 R0 SYMATTR InstName R3 SYMATTR Value 12 SYMBOL diode -16 -16 M90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName D4 SYMATTR Value MURS120 SYMBOL pnp 128 208 M180 SYMATTR InstName Q1 SYMATTR Value 2N2907 SYMBOL sw 112 272 M180 WINDOW 0 -51 100 Left 0 WINDOW 3 -150 54 Left 0 SYMATTR InstName S1 SYMATTR Value MySwitch SYMBOL voltage -160 192 R0 WINDOW 3 -341 113 Left 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V3 SYMATTR Value PWL(0 0 .1 0 .101 14 .2 14 .201 0) TEXT -82 440 Left 0 !.tran .5 startup TEXT -880 352 Left 0 !.model MySwitch SW(Ron=.1 Roff=1Meg Vt=0 Vh=-.5 Lser=10n Vser=0)

How about...

(Scale resistors to match your input voltage.)

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
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I suppose you could run an operating point solution, Ib=10uA, Vce 3.3v with small inductive load. You should use all of the model values.

I could not find any more information on the SiGe transistors, except that they are super high frequency (up to 350 GHz), and very low voltage, wuth a combination of bipolar and CMOS operating as low as 1.2 V. But I don't know what the input characteristic is. It might be worth a dollar to order one of these beasts and check it out, although I don't do much with RF, and it's probably easy to blow out a device that has a BVceo of 3.5 volts. Here is some interesting info:

It's probably a CMOS gate with about 0.5-1 volt threshold.

Paul

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Voltage, current values would be nice. A transistor would do fine. pass the charging current through the base-emitter junction. Led- resistor between collector and supply return.