* In this presentation definitions and examples from Wikipedia, HowStaffWorks and some other sources were used
Lecturer: Dr. Samuel Kosolapov

• Dual Powering Problem with Arduino
• Usage of DC Voltage Inverter
• Single Supply OA
• Examples
2

Two standard 9V batteries can be used to get
+9V and a 9V.
Problem:
Bulky, Expensive, sophisticated power ON switch
3

http://www.intersil.com/en/products/power-management/isolated-power/charge-pumps/ICL7660.html
Possible Solution: tiny integrated circuit ( ICL7660 ) that acts as a voltage inverter
4

LM386 Single Supply
Low Voltage Audio Power Amplifier.
Basic Properties
The LM386 is a power amplifier designed for use in low voltage consumer applications.
Low distortion: 0.2% (Av = 20, Vs = 6V, Rload = 8
W
, Pout =125mW, f = 1kHz)
The gain is internally set to 20
Addition of an external resistor and capacitor between pins 1 and 8 will increase the gain to any value from 20 to 200.
The inputs are ground referenced.
The output automatically biases to one-half the supply voltage.
The quiescent power drain is only 24 milliwatts when operating from a 6 volt supply,
 LM386 is ideal for battery operation.
Applications
AM-FM radio amplifiers
Portable tape player amplifiers
Intercoms
TV sound systems
Line drivers
Ultrasonic drivers
Small servo drivers
Power converters
5

LM386 Low Voltage Audio Power Amplifier. Circuits and Pins
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LM386 Low Voltage Audio Power Amplifier. Parameters
Supply Voltage Vs: Min: 4 V Max 12V
Quiescent current Iq: Typical 4 mA (for Vs=6V, Vin = 0)
Output Power ~ 300 mW (for Vs = 6V, Rload = 8 Ohm)
Voltage Gain Av: 26 dB (for Vs = 6V, f = 1 kHz) 26 dB
46 dB ( 10 uF between pin1 and pin 8)
Input Resistance Rin: 50 k
Input Bias Current Ibias: 250 nA
Bandwidth (BW) : 300 kHz (Pins 1 and 8 open)
Total Harmonic Distortion (THD): 0.2%
(for Vs = 6V, Rload = 8 Ohm, Pout = 125 mW; f = 1 kHz, Pins 1 and 8 open)
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LM386. Default Gain = 20 two pins (1 and 8) are provided for gain control.
With pins 1 and 8 open the 1.35 kOhm resistor sets the gain at 20 (26 dB).
8

LM386. With Capacitor Gain = 200 two pins (1 and 8) are provided for gain control.
With pins 1 and 8 open the 1.35 kOhm resistor sets the gain at 20 (26 dB).
If a capacitor is put from pin 1 to 8, bypassing the 1.35 kOhm resistor, the gain will go up to 200 (46 dB).
9

LM386. Gain = 50 two pins (1 and 8) are provided for gain control.
With pins 1 and 8 open the 1.35 kOhm resistor sets the gain at 20 (26 dB).
If a resistor is placed in series with the capacitor, the gain can be set to any value from 20 to 200.
10

LM386. Variable Gain Control two pins (1 and 8) are provided for gain control.
With pins 1 and 8 open the 1.35 kOhm resistor sets the gain at 20 (26 dB).
Gain control can also be done by capacitively coupling a resistor ( or FET ) from pin 1 to ground.
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LM386. Amplifier with Bass Boost
Small Speaker typically has poor bass response
12

LM386. Audio Power Amplifier
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LM386. Input Bias
Both inputs are biased to ground with a 50 kOhm resistor.
The base current of the input transistors is about 250 nA, so the inputs are at about 12.5 mV when left open.
If the dc source resistance driving the LM386 is higher than 250 kOhm it will contribute very little additional Offset
(about 2.5 mV at the input, 50 mV at the output).
If the dc source resistance is less than 10 kW, then shorting the unused input to ground will keep the offset low
(about 2.5 mV at the input, 50 mV at the output).
For dc source resistances between these values we can eliminate excess offset by putting a resistor from the unused input to ground, equal in value to the dc source resistance.
Of course all offset problems are eliminated if the input is capacitively coupled.
14

https://lowvoltage.wordpress.com/2011/04/23/lm386-audio-amplifier/
Can be used to drive small speaker.
Unfortunately this simple circuit is not practical: high noise
15

https://lowvoltage.wordpress.com/2011/04/23/lm386-audio-amplifier/
Pins 1 and 8 control gain.
When not connected (NC), the amplifier gain is 20.
Adding a 10uF capacitor between them gives a gain of
200.
Intermediate values are also possible, (see datasheet).
16

https://lowvoltage.wordpress.com/2011/04/23/lm386-audio-amplifier/
Pins 2 is the negative input –
GND in our case.
Pin 3 is the positive input – i.e. the actual signal to be amplified.
There is a 10K potentiometer before it, which adjusts the input signal level, acting as a volume control.
17

https://lowvoltage.wordpress.com/2011/04/23/lm386-audio-amplifier/
Common way of dealing with power supply noise is adding a small
(100nF) capacitor C5 to the IC power pins
Depending on the exact wiring and on the power source, you may also need another larger capacitor C6 (100uF)
Pins 4 (GND) and 6 (Vcc) connected to supply voltage
(For example, 4*1.25V ~ 5V)
Pin 5 is the output. It is biased to 1/2 of the Vcc.
This biased voltage
Is GOOD is Pin 5 is connected to A0 pin of Arduino but biased voltage cannot be fed directly to a speaker.
The 250uF electrolytic capacitor filters out the DC component and the remaining
AC goes to the speaker.
18

https://lowvoltage.wordpress.com/2011/04/23/lm386-audio-amplifier/
The 0.05uF capacitor and 10 ohm resistor pair from pin 5 to ground used to to damp high frequency oscillations that might occur in the absence of loads at high frequencies
(“Boucherot cell” or “Zobel Network” )
Boucherot cell correcting loudspeaker impedance
19

http://www.ti.com/product/lm358 http://www.ti.com/lit/ds/symlink/lm358.pdf
Consist of two independent, high-gain frequency-compensated operational amplifiers designed to operate from a single supply . (3V to 32 V)
Applications:
Blu-ray Players and Home Theaters
Chemical and Gas Sensors
DVD Recorder and Players
Digital Multimeter: Bench and Systems, Handhelds
Field Transmitter: Temperature Sensors
Motor Control: AC Induction, Brushed DC Brushless DC, High-Voltage,
Low-Voltage Permanent Magnet, and Stepper Motor
Oscilloscopes
TV: LCD and Digital
Temperature Sensors or Controllers
Weigh Scales
20

http://www.ti.com/product/lm358 http://www.ti.com/lit/ds/symlink/lm358.pdf
21

http://www.ti.com/lit/ds/symlink/lm358.pdf
Supply Voltage Vcc Min -0.3 V; Max 32 V. Recommended: Min 3V Max 30 V
Differential Input Voltage Vin: Min – 32 V Max 32 V
Duration of output short circuit to ground: Unlimited
Operating free air temperature: LM358 : 0 to 70
LM158: -40 to 125
Storage temperature: -65 to 150
Input Offset Voltage: ~ 3 mV
Input bias Current: ~ 20 nA
Avdiff = 100 V/mV = 1E5
CMRR: 80 dB
Slew rate: 0.3 V/mks
Unity Gain Bandwidth: 0.7 MHz
Equivalent Input Noise Voltage 40 nV/sqrt(Hz) (for Rs = 100 Ohm, f = 1 kHz, Vi = 0)
22

http://www.ti.com/lit/ds/symlink/lm358.pdf
23

http://www.ti.com/lit/ds/symlink/lm358.pdf
24

http://www.ti.com/lit/ds/symlink/lm358.pdf
A typical application for an operational amplifier
I s an inverting amplifier
The supply voltage must be chosen such that it is larger than the input voltage range and output range.
For instance, this example will scale a signal of ±0.5 V to ±1.8 V.
Setting the supply at ±12 V is sufficient
RF and RI: Choosing a value in the kilohm range is desirable because the amplifier circuit will use currents in the milliamp range.
This ensures the part will not draw too much current.
This example will choose 10 kΩ for RI which means 36 kΩ will be used for RF.
25

http://www.ti.com/lit/ds/symlink/lm358.pdf
RI= 10 kΩ ; RF =36 kΩ
26

http://www.ti.com/lit/ds/symlink/lm358.pdf
27

http://www.ti.com/product/lm358
The LM358 does not have a true rail-to-rail (0V to VCC) output
The datasheet specifies an
“output voltage swing 0V to (VCC – 1.5V)”.
This means that when VCC = 5V, the largest possible analog reading is in the 715 – 750 range.
In order to get an wider output range, a better op-amp should be used.
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In 1821 Thomas Johann Seebeck discovered that a small voltage is produced when two different metals are joined together and the junction is heated.
That difference increases with temperature, and is between 1 and 70 micro volts per degree Celsius
(uV / degree C) for various metal combinations.
Typical thermocouple produces a voltage of around 30 mV
Thermocouples are used at much higher temperatures than thermistors, which change resistance with change in temperature, and don't produce a voltage at all.
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Build Your Own
INSTRUCTIONS: Twist one end of the iron wire together with one end of the copper wire.
Set your voltmeter to its most sensitive range and connect it to the terminals where the wires attach.
The meter should indicate nearly zero voltage.
What you have just constructed is a thermocouple: a device which generates a small voltage proportional to the temperature difference between the tip and the meter connection points.
Light a candle and insert the twisted wire tip into the flame.
You should notice an indication on your voltmeter.
Remove the thermocouple tip from the flame and let cool until the voltmeter indication is nearly zero again
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Voltage from a thermocouple is small  it is difficult to measure.
Working and tested thermocouple amplifier using a Lm358 single voltage dual opamp.
The gain is from 50 to about 150 depending on the adjustment of R3.
My test thermocouple (a commercial unit) put out a maximum voltage of 20 mV produced 3.8 volts output
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• What have I learned ?
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1. TBD
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