Current Sense

Current Mirror sense

Simple Current Sensor Features Galvanic Isolation

 Applications that require a simple, low-cost current sensor with galvanic isolation can employ the circuit described here. 
If used as drawn, it's possible to sense currents up to 10 A with high precision (usually within %) and wide bandwidth (more than 500 kHz). 
The use of optocouplers provides 3000 V of isolation between the primary and secondary and 50 dB of CMRR. 
Transistors T1 and T2 form a coupled pair in current-mirror configuration that's unbalanced by the current (I) to be measured. 
Once this happens, transistor in OP1 balances the current-mirror biased by T3 that also biases OP2, making 
 its transistor conduct the same current that balances the current-mirror. 
Because the balancing current is directly proportional to the current being measured, a direct measurement is achieved. 
It can be easily shown that the gain in current is given by the ratio of the sensing resistor (RS) and R1, 
producing a proportional voltage drop at the Output terminals.

For the circuit to work properly, it's important that the coupled transistors which form the current mirror
 share the same substrate and that the optocoupler be a dual version, in order to have matching characteristics. 
Variations on this idea may lead configurations that can be used in a wide range of applications, 
such as sensing current in a ground line (inverting the operating idea of the current-mirror using npn transistors) 
or offering different conditioning at the output (increasing voltage with increasing current). 
The power supplies needed can be implemented using Zener diodes since only a small amount of power is required—usually less than 50 mW.

Dimitrov, Mitev

• Novel current mirrors application in high side current sensing in multichannel power supplies

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SLUA066

• High-Side Current Sensing With Benchmarq’s Fast-Charge Control ICs

Zetex

ZDS1009 at digikey

price brakes
1	2.57000	
10	2.20500	
100	1.80080	
250	1.61700	
500	1.39    

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NXP

• NPN dual transistor PMP4201

• PMP4201Y,115 at Digikey

Price Breaks	
1	0.46000	
10	0.38700	
25	0.33920	
100	0.29050	
250	0.25192	
500	0.21338	
1,000	0.16450

• PMP4201V115 at Mouser

1: 	0,157 € 	
25: 	0,14 € 	
100: 	0,139 € 	
250: 	0,133 € 	
500: 	0,114 € 	
1.000: 0,109 €

• BC847BS Dual NPN at Mouser

1: 	0,07 € 	
25: 	0,061 € 	
100: 	0,058 € 	
250: 	0,052 € 	
500: 	0,045 € 	
1.000: 0,039 € 	
3.000: 0,038 € 	
6.000: 0,033 €

• BC857BS Dual PNP at Mouser

1: 	0,07 € 	
25: 	0,061 € 	
100: 	0,058 € 	
250: 	0,051 € 	
500: 	0,045 € 	
1.000: 0,038 € 	
3.000: 0,036 € 	
6.000: 0,034 €

Wilson Current mirror

Wilson Current mirror at Wikipedia

ANALOG DEVICES

AD737 At Digikey Low Cost, Low Power, True RMS-to-DC Converter

1	8.24000
25	6.75440
100	6.09530
250	5.60108

MAXIM

• Delta-Sigma ADCs Replace Integrating ADCs for Panel Meters

• MAXIM Current-Sense Amplifiers (CSAs)

• Automotive Current-Sense Amplifier with Reverse-Battery Protection
• MAX9937 at Digikey
• MAX9937 datasheet

adjustable gain

• MAX4073 Low-Cost, SC70, Voltage-Output, High-Side Current-Sense Amplifier
• MAX4073F at Digikey

Three Gain Versions Available
+20V/V (MAX4073T)
+50V/V (MAX4073F)
+100V/V (MAX4073H)

Microchip

AN788 Numerical-Integration Techniques Speed Dual-Slope A/D Conversion

Using Delta-Sigma Can Be As Easy As ADC

• 5 articles from Dave Van Ess to electronics design magazine

• part1
• part2
• part 3
• part 4
• part 5

Multimeter resolution is 20 bits

TI

• ADS1000 Low Cost 12-bit ADC with I2C Interface
• ADS1000 at Digikey
• ADS1000 Datasheet

• TI Delta-Sigma Converter Basics video
• Delta-Sigma ADCs
• ADS1110 Tiny, low power, 16-bit ΔΣ ADC with onboard reference and PGA (G=1, 2, 4, 8) in SOT: 2.048V ±0.05% accuracy, 5ppm/ºC drift
• ADS1226 Low-cost, easy-to-use 24-bit ΔΣ ADC: dedicated START pin, 100SPS data rate, 4µVRMS low noise
• ADS1232 Ideal for weigh scales: 24-bit ΔΣ ADC, up to 23.5 effective bits, onboard PGA (G = 1, 2, 64, 128), 10SPS or 80SPS data rates
• ADS1256 Best-in-class 23-bit, noise-free ΔΣ ADC: 8 channels, 30kSPS and programmable digital filter (averaging)
• ADS1258 Fastest channel cycling, 24-bit, 125kSPS ΔΣ ADC: Measure all 16 channels in <675µs
• ADS1278 Widest bandwidth, simultaneous sampling: 24-bit, 8-channel ΔΣ ADC, 128kSPS, 106dB SNR, ±0.0003% INL
• ADS1281 Ultra-low distortion 24-bit ΔΣ ADC: 130dB SNR and –122dB THD while consuming only 12mW of power, ±0.00006% INL
• ADS1610 Fastest 16-bit ΔΣ ADC: 10MSPS, 86dB SNR, 5MHz wide and flat bandwidth
• DDC232

TI AMC1024

MSP430

• MSP430F2013 with SD16

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• MSP430AFE232 with SD24

• 24-TSSOP
• product page
• datasheet
• MSP430AFE232 at Digikey price $4.6 @ 1pc, $2.25 a 250 pcs

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• SLAA104 An MSP430F11x1 Sigma-Delta Type Millivolt Meter

INA139

• INA139 High-Side Measurement Current Shunt Monitor, Current Output

• at Digikey

1	$2.39000	
100	$1.74000

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• Flytron Ultralight 50A Current Sensor

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INA169

• Attopilot Compact DC Voltage and Current Sense PCB with Analog Output at sparkfun

• example Arduino sketch

• TI product page
• at digikey

1	$3.03000
100	$2.20400

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ALLEGRO

ACS756

• Flytron 50A Current Sensor For SimpleOSD

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ACS712

• Sparkfun ACS712 Low Current Sensor Breakout
• schematic

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• OPA734 0.05uV/degC (max), Single-Supply CMOS Zero-Drift Operational Amplifier Product page

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• at digikey

1	1.66000	
100	1.20640

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ST

TSC1021 High side current sense amplifier

File:Current sense-20.jpg File:Current sense-21.jpg

• TSC1021 product page
• Data Sheet

The TSC1021 has been specifically designed to deal with automotive conditions: 
 load-dump protection up to 60 V, 
 reverse-battery protection up to -32 V, 
 ESD protection up to 4 kV and
 internal filtering for EMI performance.

• Low current consumption: ICC max = 300 μA
• -40 to 125°C operating temperature range
• Internally fixed gain: 20 V/V, 50 V/V
• TSSOP-8 only
• At Digikey $2.38@1pc, $1.088@1000pcs

1	$1.91000	 
10	$1.72800	 
25	$1.54800	 
100	$1.39200	 
250	$1.23600	 
500	$1.08000	 
1,000	$0.89400

LPV521

• Nanopower, 350 nA, 1.6 V RRIO Single, CMOS input op amp
• Datasheet, section 8.2.3 High-Side Battery Current Sensing