# Precise line regulation using linear voltage regulators

I am trying to build a linear 24/12V power supply. One of the requirement for it is for the line regulation to be very precise (an error of 0.0005 V is considered acceptable). I wanted to use a linear regulator Ic, but I haven't found any that fit my needs.

What can I use to build such a supply?

Thanks!

• You're asking for +/-20ppm. Why? What do you know about precision analog design? Line regulation wouldn't mean much if it shifts with temperature, would it? – Spehro Pefhany Nov 24 '16 at 0:59
• How much current do you want to pull from this thing? And does it need to sink current as well as source it? – ThreePhaseEel Nov 24 '16 at 1:08
• Well, you certainly can't use any existing regulators. As Spehro has pointed out, your requirement is quite extreme. Are you aware that a fairly normal resistor tempco is 100 ppm/deg C? – WhatRoughBeast Nov 24 '16 at 2:09
• Please specify: (1) the load current; (2) the output voltage: is it 12 V, or 24 V, or both? (3) temperature stability requirements. – Master Nov 24 '16 at 8:51
• @Master The load current is 250 mA max. The output voltage is 12V. temerature stability is as follows: 20C - 12.0198 V 25C - 12.0195 V 40C - 12.0190 V – Egor Tamarin Nov 26 '16 at 12:24

## 1 Answer

From what you're saying, it sounds like you want to do this from ac wall power? Please clarify. Although you say you want to use a linear voltage regulator, I would caution against that. It may be better to combine a transformer, a full bridge rectifier, and a switching power buck (or boost) power supply that meets your quality requirements.

Linear voltage regulators will have ripple, and because many things don't use them anymore, they aren't subject to the kind of innovation that switching supplies get. Linear power supplies remove power as heat. This can be calculated by the equation (Vin - Vout) * I = Heat (in Watts). It is because of this wasted power that most higher voltage things don't use linear supplies. Of course, arduino boards use them because the draw very low current, and it much less space consuming.

If your goal is less supplying power and more a precise voltage, consider a precision voltage reference. These can be as cheap as $5 if you're willing to buy from china. In conclusion: • Linear power supplies step down voltage with considerable ripple based on many factors, like supply voltage, and also produce heat • This heat makes them a poor choice for situations requiring high voltage, long battery life, or both. • A switch mode power supply may be good if you can find one with that precision if you still want efficiency • Also, consider a precision voltage reference if you need very high precision. • Sorry for not clarifying. I am trying to do it from a 24V DC. I'm a student, and I ahve a project underway where I have to build both a switching supply and a linear one - I myself would have built a second switching one if only the task allowed me to do that. – Egor Tamarin Nov 26 '16 at 12:21 • Ok. Egor, is that precision required? And you say you must make both a linear and switching supply on your own/from scratch? I would assume with this new info that a precision voltage reference would not work - you are trying to specifically make power supplies. Is that precision really necessary? – Bobdabiulder Nov 26 '16 at 12:59 • I read the above comments. This sounds like a very hard task. Is there any more info you can provide? – Bobdabiulder Nov 26 '16 at 13:01 • Well, I asked the project supervisor and he said that no IC's will do the job. Yes, the precision is required. Additional info: For line regulation the specs are: Vin 15 V - Vout 12.0188V Vin 17 V - Vout 12.0182 V Vin 20 V - Vout 12.0185 V at Iout = 125 mA For load regulation at 17 V: Vout = 12.0215 V - Iout = 0mA Vout 12.0185 V - Iout 125mA Vout 12.0155 V - Iout 250mA – Egor Tamarin Nov 26 '16 at 14:56 • Huh. Maybe a voltage divider with hugh precision resistors. You can get 600 +/- 1% resistors of 30 different values for$5 from china, but you might need more precision than that. – Bobdabiulder Nov 26 '16 at 15:07