Power Supply Circuit for PMDC Motor Controller-28V-4A

This circuit is the part of a bigger project – 3 Speed PMDC Motor Controller without using a micro-processor.

PMDC means Permanent Magnet DC Motor. PMDC Motors can deliver high starting and acceleration torque and predictable motor speed. It’s compact in size and highly energy efficient. The application ranges from battery powered wheel chair, power tools, conveyors, door controllers, welding & X-Ray equipment, tomography systems, pumping equipments and numerous other applications.

Most of the PMDC Motors are rated at 12V or 24V, and some Motors are rated at 36V DC. The Power supply circuit is an integrated unit to supply 12V-28V (adjustable) for Motor supply, 12V DC for control circuit and +5V DC for Logic Circuits.

electronics15.com_circuit_28V-4A_dc power suplly

 A 30V / 5A transformer delivers 30V AC to a 10A Bridge Rectifier block. The output of the bridge rectifier will be about 34/35V DC and is smoothened by a 3300MFD / 50V electrolytic capacitor to get pure DC Voltage at the Input of the LM1 – 317T Regulator.

LM1 is a TO-225 package variable voltage regulator whose output can be adjusted to get 12V to 28V DC (as may be required) by P1 (5K Trimpot). The output of LM1 passes through a TO-3 Transistor 2N3055 to boost the current to 5Amps. The output is available at the emitter of T1 which is the input of LM2 – LM317T. LM2 is a TO-3 package regulator and supplies 12V DC for the control relay circuit. The output of LM2 is the input of LM-3 which is a  TO-3 Package 7805 regulator. The LM-3 output is +5V DC for the control logic circuit.

Regulator Package details and pin connections are provided in the circuit diagram.

Here is the Bill of materials (BOM) for the above circuit:


The above circuit is designed and tested by Sonu Perito. If this circuit is useful to you, please provide a feedback.

What Are Flexible Printed Circuit Boards?

The world has seen a major digital technology revolution in the past two decades. The phenomenal success stories of personal computer, laptop, tablets and smart-phones have made these equipment a part of our daily lives.

Engineers designed complex flexible printed circuit boards to make these equipment reliable and user friendly. The traditional wire harnessing, costly and complicated wired assemblies were replaced by the much simpler and significantly cost-effective flexible circuits. Interconnection methods were revolutionized through the advent of Flexible printed circuit boards.

Flexible Printed Circuit Boards is made by bonding conductive traces on a flexible substrate. Flexible PCB is also called flexible circuits, flex circuits, flexible printed circuits or just flex. Flex circuits are printed circuit board that has the ability to flex or bend. The design, fabrication process and some other functional parameters will vary depending on the end use.

Fig-1 below shows a flexible PCB used in Hitachi TravelStar Portable Hard Drive. (Wikimedia Commons).



Electronic design engineers are able to create innovative products due to the advent of Flexible Printed Circuit Boards. Flexible circuit boards will improve connectivity, add circuit density and enhance life of the electronic equipment and gadgets.

Types of Flexible Printed Circuit Boards:

(1) Single Sided Circuit – This type of flexible PCB has a single layer of the conductive metal traces bonded to on one side of a dielectric layer.

(2) Double Sided Circuit – This type of flexible PCB has the conductive metal layers on both sides of a single dielectric layer.

(3) Multi-layer Circuit – It is a flexible PCB in which several copper layers (conductive metal layer) are separated and enclosed by dielectric layers.

(4) Rigid Flex Circuits – They are multi-layer circuits which comprise layers that are hard board and flexible circuit.

Composition of Flexible PCB:

Flexible PCB is designed with a metallic layer of traces being bonded to a dielectric layer. Copper is one of the conductive materials used in the construction of a flexible PCB. However, other types of conductive materials can be used. The thickness of the conductive material used ranges from thin (<0.001”) to thick (>0.010). The dielectric layer which the conductive material is bonded to can either be polyamide or polyester in nature. The thickness of the dielectric layer is between 0.005” to 0.010”. Adhesives and vapour deposition is used to bond the conductive material to the dielectric layer.

Copper, which is commonly used as the conductive material in the construction of flexible printed circuit board, is usually coated with a protective layer. This is because the metal has the ability of oxidizing when exposed. The metal that is commonly used for this coating purpose is gold (due to its conductivity and durability in the environment). The dielectric material can also be used to prevent oxidation and electrical shorting in non-contact areas.

Numerous types of materials are used in the construction of flexible printed circuits. The decisive factor that determines the types of the materials to be used in the fabrication process includes:

  • Chemical and mechanical resistance requirement
  • Current capacity of the flex pcb.
  • Capacitance
  • Temperature
  • Nature of Flexing

What Are the Advantages of Flexible Printed Circuit Design?

Flexible printed circuit boards have a number of advantages over rigid PCBs.

Ease of Use: Design limitations are negligible. PCBs can be designed to fit any device shape. Range of motion allows Printed Circuit Boards to suit nearly any application. Less mass reduces risk in environments with regular vibrations. The errors that are found in standard PCB assemblies are reduced in flexible PCB. It also reduces weight through the elimination of additional wires, cables and connectors.

PCB Size is drastically reduced: Thinner and more lightweight than their rigid alternatives. It’s durable against motion and bending. HDI allows for the miniaturization of devices.

Rigid-flex PCBs: Blends flexible and rigid PCBs. Commonly formed with flexible circuits connecting several rigid flex boards.

HDI for Flex: Smaller package size increases the need of HDI. It allows additional space for other features on the PCB.

Cost Reduction: Total cost of installation is reduced. Flex circuits eliminate several steps within the production process and thus reduce overall manufacturing time and also reduces cost.

We’ll discuss more about Flexible Printed Circuit Boards in coming articles.

career help

Scope of an electronic engineer in large industries and corporate sectors.

 What jobs can you do with an electronic engineering degree?

Let’s take a tour to the relevant industries where electronic engineer has good prospects. The obvious choice may be the companies which produces electronics product. In my opinion, this may not be the only choice. Your selection should be guided by pay package, job stability, and reputation of the company and scope of learning.

Welcome to electronics15.com_your Career help

                                            Fig-1- Scope of electronic engineer in industries

Look at the image above (Fig-1), and you will find that the options are much broader both within the engineering industries and outside the electronics industries.

It’s obvious that each industry will have will have typical requirements for electronics engineers. This blog will focus on these typical requirements and prepare you to face the challenges during interview and also during your professional career. Let’s find out this typical job requirements for different industries.

1. Electronics Sector:

Here an electronics engineer has two major roles:

(a) Design Engineer: To design a Product or prototype of a Product or designing a component prior to launch. Product design requires in-depth knowledge & experience in electronics and this may not be suitable for a fresh graduate engineer.

(b) Application Engineer:  any fresh graduate engineer can become an application engineer (supporting a product for its entire life) after successful completion of installation & commissioning training on the products.

2. Automotive Industry:

Electronics is an significant division in Automobiles. Today, engine control systems, dashboard indicators, sensors, air-conditioning, safety systems and info-attainment systems in automobiles are designed by electronics engineer. This website will deal with electronics in automobile engineering in great details.

3. Defense Sector:

Electronics plays a vital role in manufacturing and application of Defense Products. Here an electronics engineer has to operate in cross-discipline like a mixture of mechanical, electronics and electrical engineering knowledge. Sensors, actuators and automation are some of the important areas in defense sectors. Electronics15.com will cover all the above to a large extent.

4. Power Generation Engineering:

The job openings are mainly as maintenance engineer. Here electronics engineer has to maintain Instrumentation & control systems in plant and adequate knowledge of SCADA, DCS, Instrumentation engineering, Telephony and Data Networks are necessary. This website will cover all the requirements in power generation sector.

5. Railways Engineering Sector:

Electronics engineers are involved in Signaling systems, Advanced Rail movement & controls, Safety Control equipment and advanced Telecom and Networks. The Magelv Bullet Train has opened up a new job prospect for electronic engineers. The train uses state-of-the-art  technology to propel by magnetic force and hover above the track at very high speed.

6. Elevator & Escalator:

The elevator world is changing rapidly. Our sweet mother earth has limited space at ground level and that too cannot be increased. The only way is to go up and up and build skyscrapers to accommodate a living space / office space for everyone.

A tower like Burj Khalifa in Dubai is 828 meter high. Engineers have to build a high speed elevator which travels at a speed of 36km/hr or 10m/sec to match the tower height. This elevator is a Double Decker elevator and fastest in its class. The elevator built for the skyscraper Taipei101 is faster and travels at a speed of 60km/hr or 16.83m/sec.

These high speed and ultra-high speed elevators are built with advanced technology to take care of the elevator speed, passenger comfort at such a high speed and above all the safety of the passenger.

Electronics engineers have tremendous scope in elevator and escalator engineering. We’ll extensively cover this subject.

7. Food and Beverages sector:

Automation and Robotic Integrations are finding extensive applications in Food & Beverages sector. Electronics engineers are playing very important roles in these sectors. This website will completely cover this sector.

Fig-2 below is an example of fully automatic plant controls in a modern biscuit factory.

welcome to electronics15.com_modern automatic biscuit plant

                                          Fig-2 – Automatic Biscuit Manufacturing Plant

  1. Petro-chemicals, Oil & Gas Sector:

Electronics engineers having a sound knowledge of Instrumentation engineering, Sensor Engineering and Automation technology will be hired by this sector at a comfortably high salary level.

9. Aerospace Industry:

The insertion of power electronics in aerospace technologies is becoming widespread. The application of semiconductor devices and electronic converters are used in the International Space Station, satellite power system, and motor drives. Advanced electronics technology is applied to aircraft, starter/generators and reusable launch vehicles. Flywheels, servo systems embodying electro-mechanical actuation, and spacecraft on-board electric propulsion are being used. Electronics engineers have enormous scope here.

10. Pharmaceutical, Cosmetics and Medical Industry:

These industries have to avoid bare hand contact and so Automation and Robotics are an integral part in manufacturing processes in these industries. Electronics engineers have tremendous scopes in designing and implementation of automatic process control equipment.

11. Ship Building Industries:

Modern ships have sophisticated on-board automatic electronics equipment and automatic ship controls including navigational gadgets. Ship building companies are hiring electronics engineers to bring up to date controls and automation in ships.

Electronics Engineers has scopes in the following industries: Construction, Solar & Wind Energy, Transport, Energy, Machine Building and Building Automation.

We have listed scopes of an electronics engineer in large industries and corporate sectors. Should you require any help during job search or job interview, please click “contact us” and send your requirement, we will help you as much as possible.

Sonu Perito – Profile


  • B.Tech (Hons) in Electronics and Electrical Communication Engineering from the premier engineering college – IIT, Kharagpur, India.

Over 30 years of professional experience as Design Engineer.

Internet based design engineer for:

  • electronic product design
  • pcb design
  • contract manufacturing

Professional Experience:

He has more than 30 years of electronic design engineer experience in India & USA, boosted by a degree in electronics and electrical communication engineering from the premier institute – Indian Institute of Technology, Kharagpur, India.

He has wide design engineer experience in automaton systems, elevator engineering, robotic technology, industrial automation, electronics weighing systems and electronic product design and is acclaimed by Industry Experts.

He undertakes design in a wide spectrum of electronic products and pcb design – right from 2 layers to 14 Layers, flexible and HDI Multilayer PCB.

The challenge to efficiently handle complex design jobs is fulfilled by acquiring latest tools and design knowledge.

TEN Perfect designs which are highly acclaimed by Sonu Perito Clients:

  1. Electronic product design (developed from concept stage) – A PIC Micro-controller based Door Drive Controller for Elevator Center Opening Door for 36V D.C. / Built-in Encoder PMDC Motor. The system is designed by PWM technology which tracks International Standard Speed Curve for Elevator Doors.
  2. Electronic product design (developed from concept stage) – A 10 channel auto-triggered pre-programmed Voice Announcer for Elevator use.
  3. Complete development of a product (4 Layer PCB) ready for manufacturing by client – A recipe based Automatic Check Weighing System for a Food Manufacturing Company.
  4. Electronic product design (developed from concept stage)- Fully Automatic Murukku making Machine using Archimedean Spiral principle of Motion Technology.
  5. Complete development of a product (Double sided PTH PCB) ready for manufacturing by client – Dot Matrix Scrolling Display for Elevators.
  6. Prototype Development (developed from concept stage) – A fully automatic G+19 Elevator Controller.
  7. Prototype Development (developed from concept stage) – Automatic sliding glass Door Drive suitable for PIR Motion Sensor.
  8. Prototype Development (developed from concept stage) – Robotic Truck Loading System using unique Matrix Loading technique.
  9. Electronic product design including pcb design ready for manufacturing by client – Elevator LCD Display Card to drive Dot Matrix LCD Module.
  10. System engineering design – A Robotic system integration for automatic Pick & Place Conveyor Loading of Aluminum Castings.

Sonu Perito will be glad to interact with anyone and ready to answer questions on relevant subjects. Please visit “contact us” page to establish a no-obligation contact with Sonu Perito.

Just click the links below to find out electronic engineering design services provided by Sonu Perito.