2. black box electronics.pdf

8/10/2019 2. Black Box Electronics.pdf

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Active BJTsClass Awith four resistors

Class Awith negative feedback


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Drain to source resistance and/or current 1 / gate to source voltage. Zero gate current!

Operate in active region (analog), or saturation or cutoff (digital).

MOSFETs(Metal Oxide Semiconductor Field Effect Transistor)

Most common are N-channel for analog, both for digital.

Limited in current I D, voltage V DS and power P D.

Very very good saturation, R DS(on) .

Limited frequency range, capacitance dominates at high frequency.

Select for current, voltage, speed and R DS(on) if saturating.

Typical voltage V DS range 10V to 200V, extreme to 1.5KV.

Typical current I D range 100mA to 10A, extreme to 100A.


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Sample FET Transfer CurvesA general purpose 48A, 60V N-FET from Fairchild (Digikey.ca).http://www.fairchildsemi.com/ds/ND/NDP6060L.pdf


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NDP6060L Data Sheet Parametric Section


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Basic Q Switching

N-FET Good speed.

Very good saturation. One component.

(Note that Id is 0.1% of limit yet itworks well)

NPN BJT Good speed.

Poor saturation. Two components. Rule of thumb: I b Ic /10


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Sample Linear FET CircuitOpamp uses a N-FET to increase current driving capacity.

The opamp can supply only tens of mA but the laser needs ten times more.

1. The opamp can drive the Q1 FETfrom cutoff through to saturation.

2. All of the laser current goesthrough R2.

3. The opamp monitors the R2voltage.

4. The opamp adjusts the FET gatevoltage to control the FETconductance and therefore thelaser current.


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IGBT (Insulated Gate Bipolar Transistor)Less Common Active Parts

Thyristers: SCR (Silicon Controlled Rectifier) & Triac

Current allowed through collector to emitter is proportional to voltage

between gate and emitter. Voltage controlled like a FET, switches like a BJT. Used for power control such as motors. Pros: High voltage and current. Cons: slow, poor saturation.

Anode/MT1 connects to cathode/MT2 once gate current exceedsthreshold, stays on until anode/MT1 current drops below threshold.

SCR is unipolar, Triac is bipolar. Used for motor and lighting controls ( control). Pros: High voltage and current. Cons: slow, poor saturation.


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Three terminal linear device: 2 inputs & 1 output (plus 2 power).

Hard Rule: The output goes positive if the input is positive (where input is defined as +ve input relative to ve input).

OpAmps(Operational Amplifiers)

Limited input voltage range Finite input offset voltage Finite input currents Different input currents Phase shifting Finite quiescent supply current Temperature sensitivity and agingof all parameters

Finite open loop gain (GBW) Finite bandwidth (GBW) Limited output voltage range Limited output current Finite slew rate (output dV/dt) Unstable with capacitive load Noise generation

+

_

Soft Rule: The inputs and output can only range between the rails (thepositive and negative supply pins).

All else is imperfections


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Output is difference between the inputs.Taken from Analog Devices AD8605 data sheets, a very good device series.

Sample Difference Amp


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Hi-Z (impedance) inputs, difference out, very fast.Taken from Analog Devices AD8065-6 data sheets.

Sample Instrumentation Amp


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Current in, voltage out, used for photodiodes.Taken from Analog Devices AD8605 data sheets.

Sample TIA


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Active low pass filter of Sallen-Key design.Taken from Texas Instruments OPA2735 data sheets.

Sample Filter


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Some OpAmp Errors

Ib : Input bias current, fA to A. Io : Input offset current, ~10-50% of I b . Vio : Input offset voltage, 10s V to mV. Vn : Equivalent input noise, 1-1000nV/ Hz

Av: Open loop gain, usually 10 5-10 6. GBW, f: Gain bandwidth product, ranges 1KHz to 1GHz. Slew Rate, dV/Dt: Output slew rate, ranges 0.1V/S to 10KV/S. Iout : Output current limit, ranges 1mA to 10A.

Plus temperatures, supply, load, R in , drifts, aging, interactions,


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Basic OpAmp Amplifiers

Vout = 1 + R 3 / R 4 AV = -R 1 / R 2f-3dB = 1 / 2 R3 C2

In this example: Av = 1 + 100K / 10K = +11 f-3dB = 1 / 2 * 100K * 1nF = 1.59KHz 0V < V out < +5V 0V < V in < +5V if V ref = 0

f-3dB = 1 / 2 R1 C1

In this example: Av = -100K / 10K = -10 f-3dB = 1 / 2 * 100K * 1nF = 1.59KHz 0V < Vout < +5V Vin range depends on Vref


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The End

Next: 3. Digital Electronics4. Sample Circuits5. Simulations: Spice is your Friend6. Eagle hands on: If you can, bring a laptop with

Eagle loaded and the sample schematic and board.

Then: More in depth on anything? Suggestions?

2. black box electronics.pdf

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