Can anybody tell me what is the maxium negative voltage I can apply on the power supply pins

I think that is pin 4 right

Was gonna use the MAX232 to give me the negative voltage..

Kinda confused on if VCM means that the max negative volts that can be applied?? since it is only - 1.5 volts -2 volts.

Max postive is +32 volts is max neagtive -32 volts.

It doesn't look like that amp is designed to run from a split supply. Tie pin 4 to GND.

You can acutally run them from split is says in manual and was also looking at how to use a input clamp diode because the negative on the signal input is only 0.3v

If anybody can tell me what the negative would be to run this in split supply, is it -1.5 VCM?

Mr Smith:)

hmm well it says so for the LM158 but the manaul I have is for all lm258 and lm358 and lm2904.. it does not say if the lm358 can or can not

Guess I got my answer -3 to -32 :)

These devices consist of two independent, high-gain, frequency-compensated operational amplifiers designed to operate from a single supply over a wide range of voltages. Operation from split supplies also is possible if the difference between the two supplies is 3 V to 30 V (3 V to 26 V for the LM2904 and LM2904Q), and VCC is at least 1.5 V more positive than the input common-mode voltage. The low supply-current drain is independent of the magnitude of the supply voltage.

input common-mode voltage??

Input is 20mv so if I am using MAX232 to give me negative and positive supply of 5v for the LM358 I should be cool because I have at least 4.8 more volts right??

or does it mean the postive needs to be 1.5 volts more than the negative volts

5 v positive and then 3.5 on negative

I found a different datasheet from NI that says:

So I stand corrected - it looks like it can run from a dual supply at up to ±16V.

I think in this instance common mode voltage means that both inputs shouldn't go below the supply voltage on pin 4.

What can I use as a input clamp diode when powering it from battery with regulators, it says to add a input clamp diode to power supply only I think to protect against a negative voltage drop of -0.3v, would it be nessary to add some to the input if I am only using a 20mv electric mic.

Still trying to find how I am supposed to add a diode and resistor to protect against a -0.3v negative voltage drop found these schematics Don't think I can use the 1N5817 because it will then act as a rectifier for the DC power??

I got my triple inverters mixed up with my rectifiers, can I use the 1N5817 or a Schottky Barrier.. for the -0.3v voltage drop how do I tell which one to buy.

I found this one :)

F1 is a PTC polyfuse. Generally rated 2x above my max planified current.

D1 is a Zener, with breakdown voltage a bit below the absolute maximum rating of the weakest part

D2 is a Schotky with the lowest possible VForward. I'm usually using Toshiba CMS01 with 0.3V forward.

Now, the explanation: Let's say you plug the thing straight: the PTC won't trigger and do not dissipate much heat.

If the circuit short, or a big undesired current draw happens: F1 will climb it's resistance value and contain the problem.

If someone plugs the thing backward: D2 will let the current flow, and F1 will activate to lower the max current flowing trough the loop. Since D2 has a VF of 0.3V, the circuitry will have to resist to -0.3V, and most of today's chip does.

Then, if overvoltage happens, D1 will clamp the voltage to an acceptable value, and if it stays that way for too long, F1 will activate too.

Complete protection that won't cost you too much of your precious power input.

Thought I add the sites where I got most information

http://www.societyofrobots.com/electronics_negative_voltages.shtml

http://www.sparkfun.com/news/220

Anybody know how to apply methods such as these without distortion,

specifically, I was gonna use a zener diode to protect the mbed ADC input pin.. but the distortion is not good??

And schotky for the LM358AN -0.3 but the distortion.

You can offset the input of the LM358 with a simple two resistor divider network at the - input, it will influence the load on the signal input as you feed the signal in with a 100k series resistor. If it is an AC signal you can insert a series capacitor too.

All in all, with that 100k series you will not going to blow up anything as long as your input voltages stay within +/- 50 Volts or so.

I am not so concerned about blowing it up I am concerned about reverse polarity protection the LM358 can only go -0.3V in reverse:)

I have not fully taken in what you have said above, but will that cover me for reverse polarity protection.

Also I am only gonna be using a 20mv electric microphone.

Some googling brought me this:

It is a non inverting electret microphone amplifier. The 16k and 8k resistors offset the input to about 3 Volts (in fact a bit lower because of the parallel 5.6k resistor) so the input signal can swing up and down 3 Volts before hitting 'ground'. With you 20 mV Signal that will never happen. The electret microphone is phantom powered by the 2.2k resistor. only the AC signal of the microphone gets through the 0.01u capacitors. The opamp can be powered from a single supply. The diodes connecting to MCU 5 Volt can be left out or connected to the 3.3 Volt of the mbed.

The amplification factor is (if I am correct) 10k/56 = 178 so 20 mV in will give about 3.5 Volts out max.

Gert

The thing is the two Didode will cause distortion you end up with a square wave instead of a sine wave and also how can this protect any of the amplifiers inputs from a reverse polarity of -300mv.

The amplifier input is lifted from ground by the 16k and 8k resistors, you can calculate the (bias) voltage at the + input by doing the math. Whatever voltage you present at the microphone output only the ac part will be added to this 'bias' voltage of about 3 Volt (that is with your microphone +/-20mV max) either 3-0.02 or 3+0.02 and will never go beneath zero. Both inputs of the opamp will be at the same DC level of about 3 Volts.

The 1N914 diode at the bottom will only become active if the output goes more than 0.6V below zero (never), the other when the output becomes more than 0.6 V above 5V (or 3.3V if you connect it to the +3.3V of the mbed) and even then the current is limited by the 1k resistor to harmless values.

So if your output signal stays below these thresholds the diodes are not influencing the output signal.

To limit the amplification reduce the 10k resistor to e.g. 6k8 and it will not go beyond 3 Volts with maximum microphone signal of 20mV. Just breadboard the circuit and put a scope on the output and make as much noise at the microphone as you can :-) If the output jumps above 3 Volts, reduce the 10k resistor.

Gert

So that means it can swing 3 volts from positive to negative + - their is no reverse polarity protection, on the op amps inputs.. The microphone is power by 9v above ,where does the 9volts go, something can go wrong and that 9v can go straight into the op amp.

I am just gonna use a regulator outputting about 200mv and a Mosfet anyway when I can work out how Mosfet transistor are use for reverse polarity protection.

Maybe this:)

Replaces a Power Schottky Diode Internal 20mΩ N-Channel MOSFET 0.5μs Turn-Off Time Limits Peak Fault Current Operating Voltage Range: 9V to 26.5V Smooth Switchover without Oscillation No Reverse DC Current

http://www.linear.com/product/LTC4358

http://www.solarbotics.net/library/circuits/misc_switching.html

Also as soon as you put any diode on the circuit connected to ground it changes the wave form distortion, and like I said it outputs in a square wave.

Oh and the circuit you posted does not even work, like most of the stuff I have found so far on the net:)

The circuit is quite standard, can't imagine why it should not work. Have you checked the DC levels on the in and output ?

You need to increase the value of the 16k resistor to get the default output level beyond 3 Volt, probably to about 1.5 to make the output swing between 0 and +3 Volts. The 16 and 8 k resistors build a divider chain. Leave out the bottom 5k6 and replace the 16k with a 40k (default E12 range 8k2 and 39k will do).

Check the output DC level of the opamp and the DC level of the inputs, they should all be around 1.5 Volts with 9 Volts as supply. It is all rather basic opamp and ohms law stuff.

Build your circuit step by step:

Set your power supply to a stable 9 Volts, if it has a current limit set it to 100 mA max, build the resistor divider and measure the voltage on the bottom resistor (the 8k one) is it 1.5 Volts ? If so, connect the opamp, pin 4 to ground, pin 8 to +9 Volts. Connect the divider chain to the + input, connect the 10k resistor from output to the - input. Check the DC levels after switchon, they all should be around 1.5 Volts (+ input, - input and the output) then add the other components.

The micrpophone in this circuit is an electret one which gets its power through the output pin, the resistor will limit the DC current and the voltage to the microphone, the 0.01u capacitor will block this 9 Volts to the rest of the circuit.

Also remember that the LM358 is a DUAL opamp, so inputs and outputs all are on the same side for each of the two opamps inside. Connect the inputs of the unused opamp to gnd, leave the unused output open.

Gert

Thankyou Mr HOROWITZ!!! :)))

Just remember taht the LM393 is NOT an opamp.. It is a comparator (meaning the output does only high or low) Input protection is the same as in your original circuit (the noisy alternator)

Then stormed my creations.. it not finished yet so don't criticize.. thanks:)