Showing posts with label current. Show all posts
Showing posts with label current. Show all posts
Thursday, April 9, 2009
4-20mA Current Loop Receiver with Input Overload
Protection circuit
The RCV420 is a precision current-loop receiver designed
to convert a 4–20mA input signal into a 0–5V
output signal. As a monolithic circuit, it offers high
reliability at low cost. The circuit consists of a premium
grade operational amplifier, an on-chip precision
resistor network, and a precision 10V reference. The
RCV420 features 0.1% overall conversion accuracy,
86dB CMR, and ±40V common-mode input range.
FEATURES
-COMPLETE 4-20mA TO 0-5V CONVERSION
- INTERNAL SENSE RESISTORS
-PRECISION 10V REFERENCE
- BUILT-IN LEVEL-SHIFTING
- ±40V COMMON-MODE INPUT RANGE
- 0.1% OVERALL CONVERSION ACCURACY
- HIGH NOISE IMMUNITY: 86dB CMR
A current-sensing circuit derives its power from the
to convert a 4–20mA input signal into a 0–5V
output signal. As a monolithic circuit, it offers high
reliability at low cost. The circuit consists of a premium
grade operational amplifier, an on-chip precision
resistor network, and a precision 10V reference. The
RCV420 features 0.1% overall conversion accuracy,
86dB CMR, and ±40V common-mode input range.
FEATURES
-COMPLETE 4-20mA TO 0-5V CONVERSION
- INTERNAL SENSE RESISTORS
-PRECISION 10V REFERENCE
- BUILT-IN LEVEL-SHIFTING
- ±40V COMMON-MODE INPUT RANGE
- 0.1% OVERALL CONVERSION ACCURACY
- HIGH NOISE IMMUNITY: 86dB CMR
A current-sensing circuit derives its power from the
4-20-mA current loop.
4-20mA Current Loop Receiver with fault protection and
digital-signal recovery circuit
digital-signal recovery circuit
Figure shows one form of flexible fault protection for the 24VDC
power supply of a 4-20mA loop. Also included is circuitry for recovering
a digital signal superimposed on that loop. U1 (a high-side current-
sense amplifier with comparator and reference) senses the loop current
in R1 as an 8-40mV voltage and amplifies it by 100, producing an
output-voltage range of 0.8V to 4V. That output (VOUT) can directly
drive external meters, strip-chart recorders, and A/D converter inputs.
More pdf
power supply of a 4-20mA loop. Also included is circuitry for recovering
a digital signal superimposed on that loop. U1 (a high-side current-
sense amplifier with comparator and reference) senses the loop current
in R1 as an 8-40mV voltage and amplifies it by 100, producing an
output-voltage range of 0.8V to 4V. That output (VOUT) can directly
drive external meters, strip-chart recorders, and A/D converter inputs.
More pdf
4-20mA Current Loop Receiver with Input Overload
Protection circuit
The RCV420 is a precision current-loop receiver designed
to convert a 4–20mA input signal into a 0–5V
output signal. As a monolithic circuit, it offers high
reliability at low cost. The circuit consists of a premium
grade operational amplifier, an on-chip precision
resistor network, and a precision 10V reference. The
RCV420 features 0.1% overall conversion accuracy,
86dB CMR, and ±40V common-mode input range.
FEATURES
-COMPLETE 4-20mA TO 0-5V CONVERSION
- INTERNAL SENSE RESISTORS
-PRECISION 10V REFERENCE
- BUILT-IN LEVEL-SHIFTING
- ±40V COMMON-MODE INPUT RANGE
- 0.1% OVERALL CONVERSION ACCURACY
- HIGH NOISE IMMUNITY: 86dB CMR
A current-sensing circuit derives its power from the
to convert a 4–20mA input signal into a 0–5V
output signal. As a monolithic circuit, it offers high
reliability at low cost. The circuit consists of a premium
grade operational amplifier, an on-chip precision
resistor network, and a precision 10V reference. The
RCV420 features 0.1% overall conversion accuracy,
86dB CMR, and ±40V common-mode input range.
FEATURES
-COMPLETE 4-20mA TO 0-5V CONVERSION
- INTERNAL SENSE RESISTORS
-PRECISION 10V REFERENCE
- BUILT-IN LEVEL-SHIFTING
- ±40V COMMON-MODE INPUT RANGE
- 0.1% OVERALL CONVERSION ACCURACY
- HIGH NOISE IMMUNITY: 86dB CMR
A current-sensing circuit derives its power from the
4-20-mA current loop.
4-20mA Current Loop Receiver with fault protection and
digital-signal recovery circuit
digital-signal recovery circuit
Figure shows one form of flexible fault protection for the 24VDC
power supply of a 4-20mA loop. Also included is circuitry for recovering
a digital signal superimposed on that loop. U1 (a high-side current-
sense amplifier with comparator and reference) senses the loop current
in R1 as an 8-40mV voltage and amplifies it by 100, producing an
output-voltage range of 0.8V to 4V. That output (VOUT) can directly
drive external meters, strip-chart recorders, and A/D converter inputs.
More pdf
power supply of a 4-20mA loop. Also included is circuitry for recovering
a digital signal superimposed on that loop. U1 (a high-side current-
sense amplifier with comparator and reference) senses the loop current
in R1 as an 8-40mV voltage and amplifies it by 100, producing an
output-voltage range of 0.8V to 4V. That output (VOUT) can directly
drive external meters, strip-chart recorders, and A/D converter inputs.
More pdf
Tuesday, April 7, 2009
The XTR117 is a precision current output converter designed
to transmit analog 4-20mA signals over an industry-standard
current loop. It provides accurate current scaling and output
current limit functions.
to transmit analog 4-20mA signals over an industry-standard
current loop. It provides accurate current scaling and output
current limit functions.
The on-chip voltage regulator (5V) can be used to power
external circuitry. A current return pin (IRET) senses any
current used in external circuitry to assure an accurate
control of the output current.
FEATURES
_ LOW QUIESCENT CURRENT: 130 uA
_ 5V REGULATOR FOR EXTERNAL CIRCUITS
_ LOW SPAN ERROR: 0.05%
_ LOW NONLINEARITY ERROR: 0.003%
_ WIDE-LOOP SUPPLY RANGE: 7.5V to 40V
_ MSOP-8 AND DFN-8 PACKAGES
0-5V To 4-20mA Current-Loop Transmitter Circuit
The AM422 is a low cost monolithic voltage–
to–current converter specially designed for
analog signal transmission. The AM422 is
available in a 3– or 2–wire version, which allows
applications with flexible input voltage
ranges to be used for a standard output current.
Output current range and current offset level
are freely adjustable by external resistors. The
IC consists of three basic sections: an operational
amplifier input stage for single ended
input signals (0.5–4.5V, 0–10V, or other), a
programmable 4.5 to 10V reference for transducer
excitation, and a current output, freely
adjustable in a wide current range (4–20mA,
0–20mA, other). With the broad spectrum of
possible input signals the AM422 is a flexible
and multipurpose voltage–to–current converter
for single ended transducers or voltage transmission.
FEATURES
- Wide Supply Voltage Range: 6...35V
- Wide Operating Temperature Range: –40°C...+85°C
- Adjustable Voltage Reference:4.5 to 10V
- Operational Amplifier Input:0.5...4.5V, 0...5V, other
- Adjustable Offset Current
- Available as Three– (0/4...20mA) or Two–Wire Version (4...20mA)
- Adjustable Output Current Range
- Protection Against Reverse Polarity
- Protected Current Output
AM422 datasheet pdf
to–current converter specially designed for
analog signal transmission. The AM422 is
available in a 3– or 2–wire version, which allows
applications with flexible input voltage
ranges to be used for a standard output current.
Output current range and current offset level
are freely adjustable by external resistors. The
IC consists of three basic sections: an operational
amplifier input stage for single ended
input signals (0.5–4.5V, 0–10V, or other), a
programmable 4.5 to 10V reference for transducer
excitation, and a current output, freely
adjustable in a wide current range (4–20mA,
0–20mA, other). With the broad spectrum of
possible input signals the AM422 is a flexible
and multipurpose voltage–to–current converter
for single ended transducers or voltage transmission.
FEATURES
- Wide Supply Voltage Range: 6...35V
- Wide Operating Temperature Range: –40°C...+85°C
- Adjustable Voltage Reference:4.5 to 10V
- Operational Amplifier Input:0.5...4.5V, 0...5V, other
- Adjustable Offset Current
- Available as Three– (0/4...20mA) or Two–Wire Version (4...20mA)
- Adjustable Output Current Range
- Protection Against Reverse Polarity
- Protected Current Output
AM422 datasheet pdf
The XTR117 is a precision current output converter designed
to transmit analog 4-20mA signals over an industry-standard
current loop. It provides accurate current scaling and output
current limit functions.
to transmit analog 4-20mA signals over an industry-standard
current loop. It provides accurate current scaling and output
current limit functions.
The on-chip voltage regulator (5V) can be used to power
external circuitry. A current return pin (IRET) senses any
current used in external circuitry to assure an accurate
control of the output current.
FEATURES
_ LOW QUIESCENT CURRENT: 130 uA
_ 5V REGULATOR FOR EXTERNAL CIRCUITS
_ LOW SPAN ERROR: 0.05%
_ LOW NONLINEARITY ERROR: 0.003%
_ WIDE-LOOP SUPPLY RANGE: 7.5V to 40V
_ MSOP-8 AND DFN-8 PACKAGES
0-5V To 4-20mA Current-Loop Transmitter Circuit
The AM422 is a low cost monolithic voltage–
to–current converter specially designed for
analog signal transmission. The AM422 is
available in a 3– or 2–wire version, which allows
applications with flexible input voltage
ranges to be used for a standard output current.
Output current range and current offset level
are freely adjustable by external resistors. The
IC consists of three basic sections: an operational
amplifier input stage for single ended
input signals (0.5–4.5V, 0–10V, or other), a
programmable 4.5 to 10V reference for transducer
excitation, and a current output, freely
adjustable in a wide current range (4–20mA,
0–20mA, other). With the broad spectrum of
possible input signals the AM422 is a flexible
and multipurpose voltage–to–current converter
for single ended transducers or voltage transmission.
FEATURES
- Wide Supply Voltage Range: 6...35V
- Wide Operating Temperature Range: –40°C...+85°C
- Adjustable Voltage Reference:4.5 to 10V
- Operational Amplifier Input:0.5...4.5V, 0...5V, other
- Adjustable Offset Current
- Available as Three– (0/4...20mA) or Two–Wire Version (4...20mA)
- Adjustable Output Current Range
- Protection Against Reverse Polarity
- Protected Current Output
AM422 datasheet pdf
to–current converter specially designed for
analog signal transmission. The AM422 is
available in a 3– or 2–wire version, which allows
applications with flexible input voltage
ranges to be used for a standard output current.
Output current range and current offset level
are freely adjustable by external resistors. The
IC consists of three basic sections: an operational
amplifier input stage for single ended
input signals (0.5–4.5V, 0–10V, or other), a
programmable 4.5 to 10V reference for transducer
excitation, and a current output, freely
adjustable in a wide current range (4–20mA,
0–20mA, other). With the broad spectrum of
possible input signals the AM422 is a flexible
and multipurpose voltage–to–current converter
for single ended transducers or voltage transmission.
FEATURES
- Wide Supply Voltage Range: 6...35V
- Wide Operating Temperature Range: –40°C...+85°C
- Adjustable Voltage Reference:4.5 to 10V
- Operational Amplifier Input:0.5...4.5V, 0...5V, other
- Adjustable Offset Current
- Available as Three– (0/4...20mA) or Two–Wire Version (4...20mA)
- Adjustable Output Current Range
- Protection Against Reverse Polarity
- Protected Current Output
AM422 datasheet pdf
Monday, April 6, 2009
Constant Current Battery Charger
Simple Power Supply and Charger Circuits
Figure 4 shows a simple power supply circuit. I have tested with KABO,
it works fine. For those who have a big capacity rechargeable battery,
the resistance value of R can be selected for approx. 10% output
charging current. DC in can be higher if your battery voltage higher than
8.4V, say. To ensure the output current is within the value calculated by
R, measure DC current before. The maximum supply for LM317 is ~35V.
A Simple Peak-detecting Nicad Charger
The circuit consists of two parts, a constant current generator using
a PNP power transistor (Q2), and a peak-detecting shutoff circuit
using a high-gain opamp (IC1). To start the charge cycle, switch
SW1 is momentarily closed, causing C1 to discharge. As IC1's
inverting input is now higher than its non-inverting input, its output
goes low, turning on Q1. This lights the red "charge" LED (D2) and
provides about 80mA through R6 and R7 to turn on Q2, which starts
charging the battery. Charge current flows through R8 on its way to
the battery. When the voltage across R8 exceeds about 0.6V, Q3
starts to turn on and robs current from the base of Q2. This regulates
the output current to an amount determined by the value of R8.
Constant Current Battery Charger
Simple Power Supply and Charger Circuits
Figure 4 shows a simple power supply circuit. I have tested with KABO,
it works fine. For those who have a big capacity rechargeable battery,
the resistance value of R can be selected for approx. 10% output
charging current. DC in can be higher if your battery voltage higher than
8.4V, say. To ensure the output current is within the value calculated by
R, measure DC current before. The maximum supply for LM317 is ~35V.
A Simple Peak-detecting Nicad Charger
The circuit consists of two parts, a constant current generator using
a PNP power transistor (Q2), and a peak-detecting shutoff circuit
using a high-gain opamp (IC1). To start the charge cycle, switch
SW1 is momentarily closed, causing C1 to discharge. As IC1's
inverting input is now higher than its non-inverting input, its output
goes low, turning on Q1. This lights the red "charge" LED (D2) and
provides about 80mA through R6 and R7 to turn on Q2, which starts
charging the battery. Charge current flows through R8 on its way to
the battery. When the voltage across R8 exceeds about 0.6V, Q3
starts to turn on and robs current from the base of Q2. This regulates
the output current to an amount determined by the value of R8.
Saturday, April 4, 2009
The HIP5600 can supply a 450 A (20%) constant current.
It makes use of the internal bias network.
See Figure 27 for bias current versus input voltage.
With the addition of a potentiometer and a 10 F capacitor the
HIP5600 will provide a constant current source. IOUT is given
by Equation 13 in Figure 16.
With the addition of a potentiometer and a 10 F capacitor the
HIP5600 will provide a constant current source. IOUT is given
by Equation 13 in Figure 16.
FIGURE 16. ADJUSTABLE CURRENT SOURCE
1.5A ADJUSTABLE CURRENT SOURCE Circuit
1.5A ADJUSTABLE CURRENT SOURCE Circuit
The LM317 is an adjustable 3−terminal positive voltage regulator
capable of supplying in excess of 1.5 A over an output voltage
range of 1.2 V to 37 V. This voltage regulator is exceptionally
easy to use and requires only two external resistors to set the
output voltage. Further, it employs internal current limiting,
thermal shutdown and safe area compensation, making it
essentially blow−out proof.
The LM317 serves a wide variety of applications including
local, on card regulation. This device can also be used to
make a programmable output regulator, or by connecting a fixed
resistor between the adjustment and output, the LM317 can be
used as a precision current regulator.
Features
-Output Current in Excess of 1.5 A
-Output Adjustable between 1.2 V and 37 V
-Internal Thermal Overload Protection
-Internal Short Circuit Current Limiting Constant with Temperature
-Output Transistor Safe−Area Compensation
-Floating Operation for High Voltage Applications
-Available in Surface Mount D2PAK−3, and Standard 3−Lead
Transistor Package
-Eliminates Stocking many Fixed Voltages
-Pb−Free Packages are Available
capable of supplying in excess of 1.5 A over an output voltage
range of 1.2 V to 37 V. This voltage regulator is exceptionally
easy to use and requires only two external resistors to set the
output voltage. Further, it employs internal current limiting,
thermal shutdown and safe area compensation, making it
essentially blow−out proof.
The LM317 serves a wide variety of applications including
local, on card regulation. This device can also be used to
make a programmable output regulator, or by connecting a fixed
resistor between the adjustment and output, the LM317 can be
used as a precision current regulator.
Features
-Output Current in Excess of 1.5 A
-Output Adjustable between 1.2 V and 37 V
-Internal Thermal Overload Protection
-Internal Short Circuit Current Limiting Constant with Temperature
-Output Transistor Safe−Area Compensation
-Floating Operation for High Voltage Applications
-Available in Surface Mount D2PAK−3, and Standard 3−Lead
Transistor Package
-Eliminates Stocking many Fixed Voltages
-Pb−Free Packages are Available
The HIP5600 can supply a 450 A (20%) constant current.
It makes use of the internal bias network.
See Figure 27 for bias current versus input voltage.
With the addition of a potentiometer and a 10 F capacitor the
HIP5600 will provide a constant current source. IOUT is given
by Equation 13 in Figure 16.
With the addition of a potentiometer and a 10 F capacitor the
HIP5600 will provide a constant current source. IOUT is given
by Equation 13 in Figure 16.
FIGURE 16. ADJUSTABLE CURRENT SOURCE
1.5A ADJUSTABLE CURRENT SOURCE Circuit
1.5A ADJUSTABLE CURRENT SOURCE Circuit
The LM317 is an adjustable 3−terminal positive voltage regulator
capable of supplying in excess of 1.5 A over an output voltage
range of 1.2 V to 37 V. This voltage regulator is exceptionally
easy to use and requires only two external resistors to set the
output voltage. Further, it employs internal current limiting,
thermal shutdown and safe area compensation, making it
essentially blow−out proof.
The LM317 serves a wide variety of applications including
local, on card regulation. This device can also be used to
make a programmable output regulator, or by connecting a fixed
resistor between the adjustment and output, the LM317 can be
used as a precision current regulator.
Features
-Output Current in Excess of 1.5 A
-Output Adjustable between 1.2 V and 37 V
-Internal Thermal Overload Protection
-Internal Short Circuit Current Limiting Constant with Temperature
-Output Transistor Safe−Area Compensation
-Floating Operation for High Voltage Applications
-Available in Surface Mount D2PAK−3, and Standard 3−Lead
Transistor Package
-Eliminates Stocking many Fixed Voltages
-Pb−Free Packages are Available
capable of supplying in excess of 1.5 A over an output voltage
range of 1.2 V to 37 V. This voltage regulator is exceptionally
easy to use and requires only two external resistors to set the
output voltage. Further, it employs internal current limiting,
thermal shutdown and safe area compensation, making it
essentially blow−out proof.
The LM317 serves a wide variety of applications including
local, on card regulation. This device can also be used to
make a programmable output regulator, or by connecting a fixed
resistor between the adjustment and output, the LM317 can be
used as a precision current regulator.
Features
-Output Current in Excess of 1.5 A
-Output Adjustable between 1.2 V and 37 V
-Internal Thermal Overload Protection
-Internal Short Circuit Current Limiting Constant with Temperature
-Output Transistor Safe−Area Compensation
-Floating Operation for High Voltage Applications
-Available in Surface Mount D2PAK−3, and Standard 3−Lead
Transistor Package
-Eliminates Stocking many Fixed Voltages
-Pb−Free Packages are Available
Friday, April 3, 2009
Booster Constant-Current Circuit
Constant-current circuits can be configured to take
advantage of the fact that CMOS regulators consume
a very low current.
If you wish to set constant current value io to a
larger value, PNP transistor Tr1 and resistor R1 can be
added, as seen in Figure 5. This will improve the
input/output voltage characteristics, allowing you to
increase the said current value as a result.
Consequently, under the same conditions as stated
above, that is, an input voltage VIN of 3 V and a
device voltage VO higher than 1V, for example, the
drive capacity will rise from 10 mA (typ.) to 100 mA
(typ.).
Figure 4. Booster Constant-Current Circuit
Constant Current Battery Charger Circuit
Constant Current Battery Charger Circuit
The resistors R1 and R2 determine the final charging voltage
and RSC the initial charging current. D1 prevents discharge
of the battery throught the regulator.
The resistor RL limits the reverse currents through ther
regulator (which should be 100 mA max) when the battery
is accidentally reverse connected. If RL is in series
with a bulb of 12 V/50 mA rating this will indicate incorrect
connection.
Transistor constant current Circuit
This is a schematic of the smoke circuit regulator. This is a
constant current regulator. The two 1.5 ohm resistors sense
the current in the smoke elements. If the smoke element
current increases, the base voltage of the 2N3904 increases
and it in turn drags down the base of the TIP122 pass transistor
which reduces the voltage and therefore the current of the
smoke elements. The circuit regulates the current to about 1 amp.
The resulting voltage across the elements is about 6 volts. The
most significant internal voltages are shown in red referenced to
the (-) side of the bridge.
and RSC the initial charging current. D1 prevents discharge
of the battery throught the regulator.
The resistor RL limits the reverse currents through ther
regulator (which should be 100 mA max) when the battery
is accidentally reverse connected. If RL is in series
with a bulb of 12 V/50 mA rating this will indicate incorrect
connection.
Transistor constant current Circuit
This is a schematic of the smoke circuit regulator. This is a
constant current regulator. The two 1.5 ohm resistors sense
the current in the smoke elements. If the smoke element
current increases, the base voltage of the 2N3904 increases
and it in turn drags down the base of the TIP122 pass transistor
which reduces the voltage and therefore the current of the
smoke elements. The circuit regulates the current to about 1 amp.
The resulting voltage across the elements is about 6 volts. The
most significant internal voltages are shown in red referenced to
the (-) side of the bridge.
Constant Current for Sensor Excitation Circuit
Abstract:
The MAX1464 can be easily configured to generate constant
current excitation for sensors that is ratiometric to the power supply
voltage for resistive transducer applications. Applications utilizing
sensing elements with high temperature coefficients, TCR, such as
piezo resistive bridges, RTDs, etc. are typically implemented with
constant current excitation. This application note suggests a simple
resistive network that can be implemented to provide a ratiometric
current source for sensor excitation.
Transistor constant current source Circuit
The current source shared by the two transistors is also shown in the
figure. Due to the fact that the forward biased diodes have fixed
voltageVd = 0.7V, the base voltage of the transistor is also fixed at 2.1V
, so is the current Icc, i.e., the circuit can be used as a constant current source
Booster Constant-Current Circuit
Constant-current circuits can be configured to take
advantage of the fact that CMOS regulators consume
a very low current.
If you wish to set constant current value io to a
larger value, PNP transistor Tr1 and resistor R1 can be
added, as seen in Figure 5. This will improve the
input/output voltage characteristics, allowing you to
increase the said current value as a result.
Consequently, under the same conditions as stated
above, that is, an input voltage VIN of 3 V and a
device voltage VO higher than 1V, for example, the
drive capacity will rise from 10 mA (typ.) to 100 mA
(typ.).
Figure 4. Booster Constant-Current Circuit
Constant Current Battery Charger Circuit
Constant Current Battery Charger Circuit
The resistors R1 and R2 determine the final charging voltage
and RSC the initial charging current. D1 prevents discharge
of the battery throught the regulator.
The resistor RL limits the reverse currents through ther
regulator (which should be 100 mA max) when the battery
is accidentally reverse connected. If RL is in series
with a bulb of 12 V/50 mA rating this will indicate incorrect
connection.
Transistor constant current Circuit
This is a schematic of the smoke circuit regulator. This is a
constant current regulator. The two 1.5 ohm resistors sense
the current in the smoke elements. If the smoke element
current increases, the base voltage of the 2N3904 increases
and it in turn drags down the base of the TIP122 pass transistor
which reduces the voltage and therefore the current of the
smoke elements. The circuit regulates the current to about 1 amp.
The resulting voltage across the elements is about 6 volts. The
most significant internal voltages are shown in red referenced to
the (-) side of the bridge.
and RSC the initial charging current. D1 prevents discharge
of the battery throught the regulator.
The resistor RL limits the reverse currents through ther
regulator (which should be 100 mA max) when the battery
is accidentally reverse connected. If RL is in series
with a bulb of 12 V/50 mA rating this will indicate incorrect
connection.
Transistor constant current Circuit
This is a schematic of the smoke circuit regulator. This is a
constant current regulator. The two 1.5 ohm resistors sense
the current in the smoke elements. If the smoke element
current increases, the base voltage of the 2N3904 increases
and it in turn drags down the base of the TIP122 pass transistor
which reduces the voltage and therefore the current of the
smoke elements. The circuit regulates the current to about 1 amp.
The resulting voltage across the elements is about 6 volts. The
most significant internal voltages are shown in red referenced to
the (-) side of the bridge.
Constant Current for Sensor Excitation Circuit
Abstract:
The MAX1464 can be easily configured to generate constant
current excitation for sensors that is ratiometric to the power supply
voltage for resistive transducer applications. Applications utilizing
sensing elements with high temperature coefficients, TCR, such as
piezo resistive bridges, RTDs, etc. are typically implemented with
constant current excitation. This application note suggests a simple
resistive network that can be implemented to provide a ratiometric
current source for sensor excitation.
Transistor constant current source Circuit
The current source shared by the two transistors is also shown in the
figure. Due to the fact that the forward biased diodes have fixed
voltageVd = 0.7V, the base voltage of the transistor is also fixed at 2.1V
, so is the current Icc, i.e., the circuit can be used as a constant current source
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