Understanding output regulation with multiple output power supplies

Specifying which low wattage, multiple output power supply to use can be complex if the user does not fully understand how output loading affects the product’s regulation characteristics.

An application powering a single board with fixed loads is fairly simple. The power supply is turned on, and the output voltages are monitored to ensure that they are delivering the correct voltage for the circuit card operation.

If the power supply is being used in a system with multiple cards, particularly when the end product is configurable for different user options, trying to predict output voltage changes requires more care and testing.

The block diagram of a traditional, low cost triple output is shown in figure 1.

Figure 1

The power supply control circuitry senses the output voltage of the +5V output, and if the voltage changes, it will compensate accordingly. The two other outputs, +V and –V, are not part of the control loop and are classed as semi regulated.

There are three types of conditions which will cause the voltages to vary.

Line regulation

This is the change in output voltage due to variations in the AC input, usually specified from minimum to maximum AC (90-264Vac). When the AC input is reduced, the power supply’s control loop will compensate accordingly by increasing the pulse width of the switching section. The actual line regulation on all three outputs will be quite small, just a few mV.

Load regulation

This is the change in output voltage due to variations in output load. A change in the +5V load will again be a few mV as the control loop will compensate. On the +V & -V, because they are semi regulated, the voltage regulation will be much higher, in the order of +/-360mV for the +/-12V outputs. Most manufacturers will also stipulate a minimum load condition for the regulation, sometimes as high as 25%. A point to note is that if the minimum load is not applied, the power supply will not be damaged, but the change in output voltage becomes much greater.

Cross regulation

When the 5V load is changed, the control circuitry adjusts the pulse width of the switching section as before, but this significantly alters the +V and –V output voltages. Even with a minimum load of 25%, voltage changes of 700mV can be expected.

If the +5V has a trim potentiometer to adjust the output voltage, then the +V & -V outputs will rise or fall by a similar percentage.

For systems that cannot tolerate such large variations, or if minimum loading requirements are not desired, there is a solution available. TDK-Lambda’s CUT75 triple output power supply utilises a two converter topology, one to power the 5V output and one to power the +12V & -12V outputs. The block diagram is shown in figure 2.

Figure 2

The result is a dramatic improvement over a one converter solution. Measured line and load regulation on the +/-12V outputs is only 300mV for a 0-100% load change.

  • The two converter approach also has other benefits:
  • No minimum loading requirements
  • No cross regulation from +5V to the +/-V outputs
  • The 5V can be adjusted up to 5.25V to compensate for cable drops, without affecting the +V & -V output voltage levels
  • The +V and –V outputs are electrically isolated (tested to 500Vac) from the 5V, allowing them to be connected in series as one output. For example, the dual +/-12V can be configured to provide an isolated 24V output.
  • The two transformer design also allows lower profile magnetics to be used, giving the CUT75 a height of only 38mm.

Traditionally post regulators are used in low power multiple output designs to improve regulation performance. In the CUT75 these have been eliminated with a novel passive circuit. This gives the CUT75 an efficiency rating of 85%, enabling the series to operate without the need for forced air cooling.

More details on the CUT75 can be found on this link www.uk.tdk-lambda.com/cut.

May26

Employees team together to improve workplace efficiency

TDK Corporation is pleased to announce that teams of TDK-Lambda UK employees have received accreditation, after participating in a LEAD (Lean Education And Development) programme, which, in total, saved the company £15,000.

The LEAD course provides invaluable hands-on experience in developing various skills by involving the teams in real-life business improvement projects. The overall aim of the projects is to reduce cost by applying theory into real practice on the production line.

“Our manufacturing plant’s success is based on many ‘lean’ initiatives,” says Phil Scotcher, General Manager, TDK-Lambda UK. “We strive for continuous improvement – reducing or eliminating any activity that consumes resources without adding value.”

The 3 teams worked on various production improvement projects at TDK-Lambda’s power supply manufacturing facility in Ilfracombe, which included evaluating one piece manufacturing flow, reducing process scrap and applying the 5S workplace organisation method.

“Upon completion the teams presented their success stories to the LEAD Group and, after validation, were presented with several nationally accredited qualifications,” adds Tim Puttick, Production Manager, TDK-Lambda UK. “Overall, the total savings achieved were £15,000 and gave all those involved a greater sense of ownership for their work place areas”.

May21

Full Size Simulator

EFE400M - medical AC-DC digital power supply

Industrial simulators are widely used across a wide range of test applications ranging from aerospace to automotive. To minimise equipment size, the design of the test rack is usually carefully tailored to meet the end need. TDK-Lambda’s Power + Solutions team was called upon by a simulator designer, who in addition to selecting Genesys™ programmable power supplies, needed a custom enclosure to house 24V output EFE400 power supplies. A 19” rack was developed and delivered with a suitable paint finish, matching the other components in the system.

www.uk.tdk-lambda.com/efe

May21

Small diameter electrolytic capacitors in power supplies

There has been a great deal of emphasis recently on power supply electrolytic capacitor life. No more apparent than with the launch of several new products, like TDK-Lambda’s ZMS100 series to the market, where life-time is stated as a major competitive differentiator. Many customers recognise e-cap life-time as a key reliability factor and will ask for capacitor temperatures and calculated lifetimes before they even test a sample.

Many engineers, both customers and power supply designers alike, focus on the larger sized capacitors. In particularly, the “bulk” capacitor that provides the hold-up energy and the output capacitors that reduce the output ripple and improve transient load response. Unfortunately, the smaller capacitors that are associated with the housekeeping circuit and start up circuitry are often overlooked and considered relatively unimportant.

Looking at one of the major capacitor manufacturer’s datasheets for a long-life capacitor, it can be seen that for a 10mm diameter capacitor, the life is stated at 10,000 hours. The life for a 6.3mm diameter capacitor at 105oC though is only 6,000 hours. If run at 24 hours a day, 365 days a year, that equates to only 250 days. At that point the datasheet says the capacitance can be 25% less. After a couple of years that will be significantly reduced further, but unless the power supply suffers a loss of input power, it might go un-noticed.

Electrolytic capacitors are also notoriously sensitive to temperature. A change in ambient temperature from 40 to 0oC can reduce the capacitance value by up to 10% and double the impedance.

A recent incident in the home of one of our technical marketing team members revealed the effect of this combination. His central heating system was being upgraded and the 7-year old gas boiler had been turned off for 2 days. When the boiler was switched on, it failed to start. The heating technician was baffled and an additional cost of £200-300 was mentioned, along with a two day delay. As it had been snowing, our team member was reluctant to wait for spare parts and asked to see the boiler. Examining the power supply, he applied heat to the small diameter electrolytic capacitors and 20 seconds later the boiler started up.
When questioned how he knew what the fault was by the suitably impressed technician, he answered “poor power supply design; aged electrolytic capacitors and freezing temperatures!”

During the initial development stage of the ZMS100 series of 100W open frame power supplies, TDK-Lambda received similar customer feedback of large scale field failures with a competitor product. The Engineering team designed the start-up circuitry using a longer-life ceramic capacitor in place of commonly used electrolytic. Ceramic capacitors do not contain liquid electrolyte which over time will dry out and cause a loss of capacitance and an increase in ESR. This known failure mechanism can lead to failures and power supply start-up problems.

www.uk.tdk-lambda.com/zms

May19

Cyclists ride from John O’Groats to Land’s End for Cancer Research

TDK Corporation is pleased to announce that two TDK-Lambda UK employees will be embarking on a charity cycle ride from John O’Groats to Land’s End. Starting on June 19th 2015, the two riders aim to complete the 916 mile endeavour in nine days. All money raised will go to Cancer Research UK.

TDK-Lambda’s Richard Davey (Product Quality Development Engineer) and Paul Dyer (Trainee Electronics Technician) are riding the entire distance without the accompaniment of a support vehicle. Richard and Paul are both very keen cyclists, who regularly participate on many routes, sportives and fund raising events.

“Cancer is a disease that will somehow affect everyone, so we set ourselves a target to raise one thousand pounds to help the research in fighting the disease. Any donations are gratefully received with thanks from both of us” the pair stated on their sponsorship page www.justgiving.com/Paul-Dyer-Richard-Davey.

With just over a month to go the pair are reaching the halfway mark with 39% of their target met, with donations coming from friends, family and co-workers.

Cancer Research UK is the world’s leading charity dedicated to beating cancer through research.

For information about TDK-Lambda power supplies, please call TDK-Lambda directly on +44 (0)1271 856600 or visit the TDK-Lambda website at: www.uk.tdk-lambda.com

May13

Laser Cutting

An industrial cutting laser requires a very stable voltage that can be pulsed to control the depth and size of the cut. A laser cutting equipment manufacturer selected the 2400W Genesys™ 20V 120A programmable power supply not only for its ability to handle pulsed loads, but for the product’s 1U (43.6mm) height and local technical support.

www.uk.tdk-lambda.com/genesys

May12

Gas Analysis Equipment

The benefits to having portable gas analysis equipment is that it can be temporarily located in areas or atmospheres that are hazardous to humans. When designers of one such piece of equipment approached TDK-Lambda looking for a lightweight, but unusual combination of outputs, they were offered the NV300 open frame configurable power supply with 24V, 5V and 12V outputs, none of which required any minimum load.

www.uk.tdk-lambda.com/nv

May05

3D Printer

LS Series AC-DC Power Supply

The prices for 3D printers have dropped rapidly since their initial introduction. As many R&D facilities now depend on these printers for rapid prototyping, any equipment downtime can dramatically impact Engineering schedules. Realising this, a manufacturer of large printer chose TDK-Lambda’s LS200-24 for both quality and cost effectiveness.

www.uk.tdk-lambda.com/ls

Apr28

Tissue Ablation

Tissue ablation is widely used in a number of surgical procedures ranging from neurosurgery to cosmetic surgery. Next generation products are now focused on ease-of-use to allow the surgeon to focus on the patient rather than the operation of the equipment. TDK-Lambda’s technical support also made it easy for the customer to solve his power supply needs! A 650W Vega modular power supply was quickly configured to provide +/-48V, 12V and 24V outputs complete with medical certification.

www.uk.tdk-lambda.com/vega

Apr21

Small diameter electrolytic capacitors in power supplies

There has been a great deal of emphasis recently on power supply electrolytic capacitor life. No more apparent than with the launch of several new products, like TDK-Lambda’s ZMS100 series to the market, where life-time is stated as a major competitive differentiator. Many customers recognise e-cap life-time as a key reliability factor and will ask for capacitor temperatures and calculated lifetimes before they even test a sample.

Many engineers, both customers and power supply designers alike, focus on the larger sized capacitors. In particularly, the “bulk” capacitor that provides the hold-up energy and the output capacitors that reduce the output ripple and improve transient load response. Unfortunately, the smaller capacitors that are associated with the housekeeping circuit and start up circuitry are often overlooked and considered relatively unimportant.

Looking at one of the major capacitor manufacturer’s datasheets for a long-life capacitor, it can be seen that for a 10mm diameter capacitor, the life is stated at 10,000 hours. The life for a 6.3mm diameter capacitor at 105oC though is only 6,000 hours. If run at 24 hours a day, 365 days a year, that equates to only 250 days. At that point the datasheet says the capacitance can be 25% less. After a couple of years that will be significantly reduced further, but unless the power supply suffers a loss of input power, it might go un-noticed.

Electrolytic capacitors are also notoriously sensitive to temperature. A change in ambient temperature from 40 to 0oC can reduce the capacitance value by up to 10% and double the impedance.

A recent incident in the home of one of our technical marketing team members revealed the effect of this combination. His central heating system was being upgraded and the 7-year old gas boiler had been turned off for 2 days. When the boiler was switched on, it failed to start. The heating technician was baffled and an additional cost of £200-300 was mentioned, along with a two day delay. As it had been snowing, our team member was reluctant to wait for spare parts and asked to see the boiler. Examining the power supply, he applied heat to the small diameter electrolytic capacitors and 20 seconds later the boiler started up.
When questioned how he knew what the fault was by the suitably impressed technician, he answered “poor power supply design; aged electrolytic capacitors and freezing temperatures!”

During the initial development stage of the ZMS100 series of 100W open frame power supplies, TDK-Lambda received similar customer feedback of large scale field failures with a competitor product. The Engineering team designed the start-up circuitry using a longer-life ceramic capacitor in place of commonly used electrolytic. Ceramic capacitors do not contain liquid electrolyte which over time will dry out and cause a loss of capacitance and an increase in ESR. This known failure mechanism can lead to failures and power supply start-up problems.

Apr16