Design of a Constant Current Source

This article will explain the way a simple transistor based current source is designed, this will give an idea on how some components can be used in a practical way to make the circuit do some function, the objective is not design but to become familiar with the basic ideas.

Requirement.

We need a fixed current around 20mA for a voltage variation of 10V to 20V to drive a LED flasher circuit.

Component Selection. The transistor should handle 20V * 2 = 40V and a current of 20mA * 5 = 100mA. We have to overrate the components for long term reliability and make the design rugged. Chosen MPSA92 PNP-300V-500mA which is good for this job. Look at the pin details of MPSA92 in the bottom view given in the right of this page in its TO-92 package, it has a beta of 25 . The Power dissipation of MPSA92 can be upto 650mW , our requirement may be a max of 20V*20mA = 400mW which is just within limits.

Now we need a voltage reference a low cost voltage reference is a LED which has a 1.6V forward drop. As the circuit is a not an accurate one CFR 5% resistors are fine.

From my Tutorials on Basics and Instrumentation Electronics

Circuit design.

The LED at 40mW will last long, some energy emits as heat and some as light. 40mW / 1.6V = 25mA. so let us choose 20mA max LED current as a thumb rule.

In this circuit the LED is used as a reference so to keep it cool a 2.2K is chosen. (20V – 1.6V) / 2.2K = 8.3mA on the high side and when voltage is 10V the current will be 3.8mA min. .

You should know that the LED forward drop can change with ambient light as it is photo sensitive and will vary with temperature.

Look at the circuit in the right, the LED has a forward drop of 1.6V which is applied across the resistor R4 and the base-emitter diode. That means 1V across R4 as a diode drop is around 0.6V. The base-emmiter now gets forward biased and a small base current Ib flows . The Ic or collector current is 1V / 50E = 20mA. The Ib = Ic / beta, That means 20mA / 25 = 0.8mA which flows thru R4 and R5.

The Load Resistor R6 represents the LED flasher circuit that consumes 20mA, even on short circuit of R6 the current is limited to 20mA.

When more current flows in R6 the voltage at emitter falls, the voltage at base is 20V – 1.6V =18.4V, and the voltage at emitter should be 18.4 + 0.6V = 19V for bias and Ibto flow. When Ic increases the Ib reduces to that extent as only to maintain emitter voltage at 19V, this way Ic is kept constant, if Ic reduces the voltage at emitter builds up to rise Ibwhich in turn builds up Ic. so we made a current regulator.

Circuit Improvement.

The circuit can be improved by using a zener in place of the LED or better still a temperature compensated reference like LM336.

The circuit on the right will be more stable, but still the forward drop on base-emmiter junction is temperature sensitive. The base current will also introduce an error, so you can get a 8 bit stability, that means around 255 counts on an A-D converter. If you need a more stable current source you should design with FET and opamps.

LM336-2.5 pdf details, It has a 2.5V drop. A LM336-5.0 pdf version is also available for 5V. these are from National Semiconductor.

Operating Current of LM336 is 400uA to 10mA, 20V The max. voltage 20V / 3.3K = 6mA. so within limits. Then you can compute the rest, wire it up to see if your design works.

“If all parts are working, connected in proper polarities and there are no dry solders and loose connections then any circuit well designed ought to work. ”
Solderman 1702

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Read more at Instrumentation and Measurement Circuits

Toshiba – Advanced Electronic Technology

Toshiba, a world leader in high technology, is a diversified manufacturer and marketer of advanced electronic and electrical products, spanning information & communications equipment and systems, Internet-based solutions and services, electronic components and materials, power systems, industrial and social infrastructure systems, and household appliances.

Toshiba – Advanced Electronic Technology

1875 -Hisashige Tanaka opened a telegraph equipment factory in Shimbashi, Tokyo.
1890 – Ichisuke Fujioka and Shoichi Miyoshi established Hakunetsu-sha & Co., Ltd. in Kyobashi, Tokyo. Manufactured Japan’s first electric incandescent light bulbs.
1895 – Produced Japan’s first induction motors.
1930 – Manufactured Japan’s first electric washing machines and refrigerators.
1978 – Launched medium-sized experimental broadcast satellite, Yuri. Released the first Japanese word processor.

Toshiba : History

Piggyback40 Toshiba

Piggyback40 Toshiba

Ceramic DIL Package, 40 Pins + 14pin Socket, Toshiba TLCS90-TMP90G840E, 1988

Toshiba is organised into four business groupings: the Digital Products Group, the Electronic Devices Group, the Home Appliances Group and the Social Infrastructure Group. In 2010,

Toshiba Corporation – Wikipedia

Toshiba Vacuum Tube

Toshiba Vacuum Tube

Toshiba Electronic Components

Toshiba Electronics Europe (TEE) offers a wide IC and discrete product range. high-end memory, microcontrollers and ASIC. Optoelectronic Semiconductors include Light Emitting Diodes (LEDs) and Photocouplers.

Toshiba Electronic Components

Toshiba Electronics Europe (TEE) offers a wide IC and discrete product range. high-end memory, microcontrollers and ASIC. Optoelectronic Semiconductors include Light Emitting Diodes (LEDs) and Photocouplers.

Toshiba Electronic Components

Toshiba InGaAlP LED-devices feature high brightness as it employs four-element LED chip technology (InGaAlP). Higher Visibility, Low Power and Reliable LEDs for Lighting.

Toshiba News n-channel power MOSFET

Toshiba expands family of semi power devices with new n-channel power management MOSFET. – Toshiba News n-channel power MOSFET

Also see this page What’s Fuel Cell ? – “Fuel Cell is not a battery but a generator. The principle is the reverse of “electrolysis of water”

More –

Toshiba has a wide and very diverse range of components and advanced materials technologies.

Infineon Technologies – Advanced Semiconductors

They have chip and system solutions for automotive and industrial electronics. They also specialized semiconductor IC for chip card and security applications.

Infineon Technologies – Advanced Semiconductors

Industrial, Lighting, Wireless Communications are other areas. The Industrial Power Control (IPC) Division have solutions for electrical drives and energy generation components in solar or wind power plants.

Products Include Consumer Electronic ICs, Fiber Optics, Microcontrollers, Power Semiconductors for Automotive, Power Semiconductors, Chip Card + Security ICs, Trusted Computing, Sensors, Small Signal Discretes.

Infineon XMC4500 ARM Cortex-M4F Demo

The modular design kit for the XMC4500 series. Up to three additional application boards – for actuators and sensors (top), for human-machine interface (HMI) functions (right), and for communication with other systems (left) – can be connected to the basic design board with XMC4500 (middle), depending on the respective application requirements.

Infineon XMC4500 ARM Cortex-M4F Demo

This page documents a demo application that uses the FreeRTOS GCC ARM Cortex-M4F port. It targets the Infineon XMC4000 Hexagon Development Kit CPU board, which is populated with an XMC4500 microcontroller.

Infineon Technologies – Wikipedia

Infineon Technologies was founded in April 1999 when the semiconductor operations of parent company, Siemens AG, were spun off to form a separate entity.

Infineon Technologies
Am Campeon 1-12 Neubiberg, M√ľnchen, 85579, Germany.

Renesas Technology – Semiconductors

Development, design, manufacture, sales and servicing of system LSIs, including microcomputers, logic and analog devices, discrete devices and memory products, including flash memory and SRAM.

Renesas Technology – Semiconductors
.
Renesas Technology was established April 1, 2003 as a joint venture of Hitachi, Ltd. and Mitsubishi Electric.

YRPBRL78L12 For RL78/L12
The Renesas Promotion Board is pre-programmed to work with the GUI provided on the included DVD to demonstrate the key low power capabilities of the RL78/L12 device family along with it’s direct drive LCD functionality.

YRPBRL78L12 For RL78/L12

The RPBRL78L12 includes RL78/L12 CPU board with custom segment LCD integrated, On Chip Debugger (OCD), Eclipse based e2studio (a Integrated Development Environment), Free of charge GNU compiler and Example embedded code, extensive documentation.

Renesas Electronics Corporation
2801 Scott Boulevard Santa Clara, CA 95050-2554, USA

Vectron International – RF-Microwave Components

Products include crystals and crystal oscillators; frequency translators; clock and data recovery products; SAW filters and other components.

MD-010 Disciplined Oscillator Module - Vectron

Vectron International – RF-Microwave Components

“The MD010 is a Vectron standard platform module that provides 1 pps TTL,10 MHz sine wave and 10 MHz square wave outputs that are disciplined to an external 1pps reference. Internal to the module is a Vectron oscillator, ranging from a TCXO to a double oven OCXO, dependent upon performance requirements.”

MD-010 Disciplined Oscillator Module

Vectron International is A Dover Company
267 Lowell Road Hudson, New Hampshire 03051, USA

ROHM – Electronic Components

ROHM – Electronic Components

“ROHM Co. Ltd. was established in Kyoto, Japan, in 1958. ROHM designs and manufactures semiconductors, integrated circuits and other electronic components. These components find a home in the dynamic and ever-growing wireless, computer, automotive and consumer electronics markets…..”

1954 – Toyo Electronics Industry established. Carbon film resistors developed and marketed.
1967 – Transistors and switching diode developed and marketed.

Company History Rohm

  • Discrete Semiconductors
  • Opto Electronics
  • LED / LCD Drivers
  • Sensor ICs
  • Laser Diodes
  • Contact Image Sensor

High speed Switching – High Voltage Resistance MOSFET Series

“ROHM expands its widely used lineup of high speed switching, high voltage resistance MOSFETs for PFC circuits in switching power supplies and main switch circuits with a variety of package types.”

High speed Switching - High Voltage Resistance MOSFET Series