Linear regulator based on op amp

Linear regulator based on op amp

Linear regulator based on op amp

Why DIY?

There are two reasons, the first is the market on the three-terminal regulator does not meet the requirements, either performance is not good, or not enough power.

Second, the market also has a single show, excellent performance of the regulator, but they are expensive,

For example, Ling Linear Technology's lt1581,13 dollars/piece, buy a bunch of components. Or they are uniquely packaged and cannot be easily interchanged with ordinary three-terminal ICS.

How does a linear regulator work?

This reading of the electricity book to go, here is not translated.

In short, a negative feedback loop, the sample output voltage change, and the reference voltage comparison,

The error signal is enlarged to control the current of the adjusting tube, and then the pressure drop on it is adjusted to achieve the purpose of voltage regulation.

A slightly more complex start: Sulzer Regulators

The circuit, as shown above, is published in the February 1980 audio Enthusiasts magazine. Several highlights of this circuit are:

1. The NE5532 is used faster than before.

2. Input is filtered first through R3 and C3,C4, and the output of the Zener diode is filtered through R4 and C5.

3. Large capacitance C1 filter out most of the high-frequency components, so that they are not amplified by the error amplifier, thereby reducing the amplifier bandwidth, improve system stability.

The performance of this circuit goes beyond the ordinary LM317, because the LM317 internal error amplifier performance and μa741 is a level.

If a better amplifier is used, the performance of the circuit can be further improved.

Sulzer Derivative series

In the January 1981 Audio Amateur magazine, Sulzer released its sequel,

This article is no more than the new self-design that was brought about in the previous article, and more like some of the changes made in some of the people's piecemeal opinions.

Since there will be a better version of the Sulzer circuit later, the specific circuit diagram is not given here.

The new ideas it brings are:

1. Use LM317 to do pre-level voltage regulation

2. Replace the Zener diode with a precision voltage reference

3. The adjustment tube uses the Darlington structure, improves the output current drive ability

In the January 1983 Audio Amateur magazine, the Sulzer circuit and its improved version have been extensively tested and researched,

In contrast to the lm317/lm337, the result, as one might expect, is that if the error amplifier uses μa741 in the Suzler circuit, its performance is similar to LM317,

If a better op amp is used, its performance goes beyond LM317.

When using LM317 to do pre-level regulation, the results are not as people imagine, it only brings a small amount of performance improvement.

Sulzer-borbely Voltage Regulator

In the January 1987 issue, the prolific designer Erno Borlely published an improved Sulzer regulator with the following circuits:

Compared to Sulzer and Breakhall's article, its biggest improvement lies in the front-level regulator LM317 circuit to do a more in-depth thinking

What I think is the fallacy of design:

A voltage reference LM336 with Gap reference is used instead of an embedded Zener diode (buried Zener Diode).

In contrast, the noise of the scattered particles with a gap reference is large, and the buried Zener diode is much less noisy.

Jung Super Regulator

It was published in the first two issues of the 1995 TAA magazine. The circuit is as follows:

Its improvement is: the use of better adjustment tube, improved adjustment tube Drive mode, better op amp, op amp input protection, precision reference power supply.

On the drive of the adjustment tube, the Jung uses a better driving mode, Q2, D1, R5 constitute a constant current source, which is partly used to supply the adjustment tube, part of the op-amp absorption,

This forces the op-amp AD797 output stage to work in the deep-class condition, avoiding possible cross-over distortion.

On the other hand, it also restricts the large current----caused by accidental short-circuit at the output, and does not exceed the β-times of constant current source.

In this circuit, the op amp is filtered by R3, C3, C2, and the adjustment tube is connected directly to the power input.

On the one hand it reduces the input resistance of the adjustment branch, improves the voltage regulator's large current output capability,

On the other hand, the op amp is protected from fluctuations in the output current.

Jung 2000 Regulator

The circuit appeared on the April 2000 audio Electronics (TAA's successor).

I used to collect and label components of the same name as much as possible to build circuits to compare with the 1995 circuit.

A very important change is the power connection of the error amplifier, please note that its v+ is connected to the voltage output of the adjustment tube.

The error amplifier's power supply is the "clean output" of the regulator, not the unstable power supply after a mild filter.

The output diode of the error amplifier is also replaced by a 6.8V Zener diode.

It makes the voltage regulator start more reliable.

In other forms of the original Jung circuit, you may also need this zener diode, but here, Jung says, it is required.

If you use a normal diode, the output of the OP amp is locked at a level close to the negative supply (i.e. 0 level) at startup.

--------This is mainly due to the change of the OP amp Point, now it takes power from the output, if only one diode is used, the output of the OP amp must be close to the supply voltage,

This causes the op-amp to go into a non-linear state and lose its adjustment (positive or negative), and when the circuit starts, the output is zero, and the op amp output is locked to zero level.

The circuit now uses Ad825,jung to say that AD797 work in an environment with a strong RF interference will be problematic,

The output of the op amp becomes unstable because it is rectified by the input stage of the RF interference input. Op-amp with FET input is not very sensitive to this,

Emitter-degenerated Bipolar transistors are also considered to be feasible. Jung recommended AD817.

Choose other models of the chip, you need to choose the speed of the relatively fast op amp, output level of the driving capacity is also an important factor.

........ (omission)

The LEDs as well as the shot-level resistors have been modified according to Gary Galo's recommendations, which Gary says will reduce the voltage drop of the regulator.

However, Jung did not mention this point. -------This comparison, replaced by 2.0V pressure drop LED,

has made constant current source transistor into a mild saturation, the individual thought to reduce pressure drop, rather than with low on-voltage LED.

Now, the LM317 of the preamplifier is much smarter than the Sulzer and borbely, and it is changed to a floating connection.

The output and sample ends of the LM317 are wound on the output adjustment tube, so that the output voltage clamp is at a higher level than the voltage regulator outputs a fixed value.

The figure resistor gives a voltage difference of about 2.3V, which is sufficient to allow the adjustment tube to output 1.5A current without affecting the output voltage (saturation).

The pre-regulator removes most of the ripple components that should be handled by the error amplifier, which reduces the power dissipation of the (most) adjustment tubes by reducing a small portion of the error signal through the current source.

Personal commentary:

LM317 the additional benefit of this connection is that the power to adjust the dissipation of the tube becomes fully controllable, only the maximum output current of the circuit is known, regardless of the input voltage fluctuation range;

Of course, as with all two-stage regulated circuits, the power adjustment rate has become very good, because here the adjustment tube sees the input voltage ripple becomes very low, most of the output voltage changes are borne by LM317.

In addition, the circuit is slightly modified, it is convenient to make a high output current,

High-quality power supply, the method is to use any method to LM317 the expansion of the same time to select a larger output current adjustment tube,

While this can lead to a deterioration in the LM317 of the voltage regulator, it is not a problem in this circuit because we also have a second-level regulator circuit.

This circuit also has a debatable part, such as C4, R7 value, because op amp work in open loop State,

Must be particularly sensitive to input noise, and the reference is a well-known source of good noise,

So the value of the R7 is too small, because the op amp is the Jeft input, from the input point to see the past voltage reference output resistance is not very important,

For C4, it is difficult to require very low ESR in this capacity.

Linear regulator based on op amp