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Hackaday Prize Entry: A 7805 Replacement | Hackaday

tagsinductors electronic components

If you want an easy way to reduce the voltage to 5V, then the 7805 regulator is a good device. This is a three-pin, single-component solution that dissipates five volts and a lot of heat. Simple and not efficient. For [hackaday award] entries, [KC Lee]


Linear regulators like 7805 are great, but they are not very efficient. According to the input voltage, 

See an efficiency of 50%. When using a switching power supply, the efficiency is as high as 90%.

[KC Lee] To replace his substitute, is using

, A switching regulator, only a few additional parts can be turned into a replacement of 7805. You will need to set an upper limit on the input, but you should have put them in the circuit anyway, right?

So, are linear regulators efficient now? (There was a grammatical error in writing), this is a good idea, but it is already sold in the market in the same size.

The question is: how does it function?

Last year, I designed a similar product, which not only can work under a given voltage, but also is limited by current, so it can be used to drive LEDs or charge various batteries (lithium ion, NIMH, etc.).

This version is very large, but my version is smaller and only uses SMD components.

[IMG] http://i65.tinypic.com/25frtbq.jpg [/ IMG]

[IMG] http://i64.tinypic.com/13zb98n.jpg [/ IMG]

Anyone who makes a real (no additional components) switch replacement for the 7805 that we all love should win the Nobel Prize. Please note that these days they distribute these things casually.

I would rather win the Zobel Award-when my speakers stop oscillating, that is ;)

Nice one:) When I was a kid, all my diy amplifiers would receive igzobel awards for screaming oscillators. This topic alone is worth an entire article.

Find 7805SR-H

I don't want to be "that guy", but has it been a while? It's just that the 7805 drop in the Google search switch mode converter will spit out a lot of commercial products. There is no point in redesigning the wheels

Yes, they do exist. I have even seen no model that takes up more overall volume than the TO-220 package. Create your own good idea, but it will not solve any major problems.

one of:


They also have a 3.3V output version.

I made them specifically for my UPS project in 2008 (also on hackaday.io). I will also record several other types (reinforced, isolated) for UPS.

I also want the module to have plug pins for mating with DIN connectors because they need to be pluggable. The same design is also used for 12V modules. The input must be as high as 18V, but when the battery is low, I want the duty cycle to reach 100%, and the PMOS is in the exit mode of my application. Some chips with integrated NMOS switches may limit the duty cycle to 90% or 95% that requires charge pump operation. and many more

I have sample trays of pre-production TI/Power Trends parts (unfortunately 5V input parts), so I know them well. I built mine with parts on hand or recyclable parts (i.e. purchased for $0). Most of my earlier personal projects have such a budget. I decided to share, but not necessarily sell.

It is more aware of the "78xx only" that most people usually use since the 1970s, without thinking about their inefficiency. I did not propose a proof of concept to suspect that drugs can cure cancer or magical food replicators to save the world from hunger. Just do my best for more engineering and design.

Yes, there have been many alternative products:

The second paragraph: very "ineffective" and inefficient.

Nice technique.

In optimized custom packaging, direct replacement products for 7805 (and other voltages) can also be obtained commercially.

Take Murata's Okami series as an example.

I will be on the Okami line. Great product, and it's hard to exceed the price of $6 per piece. I have used them to power the sensitive video circuits in the ROV without using the more filtering function of the linear regulator, and they have done a good job. I believe the input can be up to 36V.

Thanks for the tip! top notch.

The price is already set! Check the following Recom R-78Exx modules:

I often use these Recoms and get very good results, although I usually choose the R-78C series to provide you with a larger current and a wider input voltage range with the same form factor.

The direct plug-in switch replacement for the 7805 has been around for more than 20 years. For example, one of my projects has a Power Trends 78SR105HC (date code 1992). Another example is Murata OKI-78SR-5/1.5-W36-C (Digikey#811-2196-5-ND).

The problem is not usability. This is the cost. The price of the 7805 is US$0.50, and the replacement price of the Murata switch mode is US$4.30. The price of LM3485 itself is $1.68 (use Digikey price for comparison). Except for a few customers who need more efficiency to solve the overheating problem and are willing to pay any fees, these switch mode replacement products are not sold, so the output remains low and the price remains high.

The cheapest switch mode controller chip I know of is MC34063 ($0.60). If you are trying to lower the price, maybe this is a better option?

Yes, murata parts are my favorite, I have used them in professional projects for many years. The price of the components is actually very high, but the 7805 plus radiator is not very cheap, and this does not include the labor of fixing the radiator on the housing/PCB and applying thermal grease.

The problem with MC34063 is that it needs an external current sense resistor, if the current is larger, they may become quite bulky... But this is a delicate and small IC, although it has been aging, but still not obsolete ...

Unless current limiting is required to prevent the chip or inductor from overloading, the current sensing resistor is not required.

If no current limit is required, the current sense resistor can be omitted. I have seen this configuration in devices that consume less than 500mA. They do not have a 0.22 or 0.33 ohm current sense resistor, but only a 0 ohm jumper.

Really silly CC mode controller has inherent advantages. What happens when you try to charge the large output capacitor at startup?

SMT resistors are very cheap and small. Many CC controllers also have a built-in current limiting function, and overall, this would be a better choice.

You mean like this

Or this


Well, mine is much smaller:

(Version 2.1 or even smaller) Well, it must be said that it can only provide 0.6 amperes of current, and the efficiency is not optimal, but hey-in most cases, the efficiency is higher than 78xx.

Excellent job, what kind of IC did you use? Thank you

Recom's R-78Exx is also a good alternative, and the unit price of Digikey is $2.84.

I use them all the time in projects and they are great. The data sheet says that even external capacitors are largely optional. Slightly more expensive than linear regulators, but for most projects, the additional cost is only a small part of the total cost.


I have used them too, they are cheap and cheap! highly recommended!

One of the advantages of linear regulators is that they do not introduce any additional noise on the output voltage. If your project contains sensitive analog circuits such as ADCs, you will not always want a switcher.

The noise of the linear regulator is smaller than that of the switch. They still make a lot of noise themselves.

Yes, linear regulators have output noise. But they also reduce the "input" noise seen, which is usually not available in switching regulators. Their own output noise usually comes from a bandgap reference, and multiple LDOs allow this noise to be bypassed, reducing the noise to a negligible level at the cost of a slower start-up time.

If/when you have to do this due to power limitations in real life, choose a switching frequency outside of the ADC band. If you are really concerned about the noise reflected from the switch back to the power supply, you can use an LC filter to attenuate it.

You can release a linear regulator, or you can release a noisy power supply with low noise, high PSRR (power supply rejection ratio) and high bandwidth LDO. Depending on the frequency range, there will be an attenuation of 50-70dB. Therefore, even a power supply with a switching noise of 100mV can be reduced to 100uV. With the PSRR of the ADC, this may be sufficient.

If it's really that simple...

Switching power supplies not only generate noise at a specific frequency-transients are broadband (the current will generate a large switching spike when the FET is turned on), so it is really difficult to filter. It is helpful to use LDO for post-adjustment, but to find the LDO up to 50+ dB to the MHz region, a lot of searching is required. Obviously, LDO reduces the overall efficiency.

Micrel (now owned by Microchip) has manufactured these beautiful LDOs. These LDOs are designed for switching power supply filtering (ripple blockers) and are most suitable for low-current point-of-load regulation (for example, for the RF part), and operate at up to 10 Maintain 50 dB at a frequency of MHz.

As Jim Williams (...of course, what problem did he not solve?) pointed out in "Linear Application Notes" a few years ago, other LDOs may require carefully selected ferrite beads. Attenuation transient.

The ringing when the MOSFET is off is at the resonant frequency of the parasitic capacitance of the diode and inductor. You can design a buffer in parallel with the diode to minimize the ringing frequency.

Linear Technology has also manufactured a soft-switching regulator that can effectively balance noise to solve this problem.

For mathematical information in buffer design, see here:

A snubber can reduce ringing, but the switching spike itself will almost certainly get caught up unless you have a very inefficient switch. Even if you suppress it strictly, you will still experience switching spikes.

(Compared with Figure 5) shows that the initial pulse is still there-this is certainly not surprising, because the frequency component of the pulse reaches MHz well, and the resonance frequency reaches kHz-and you will not be able to decay easily ~10- Frequency above 100 MHz. Of course, it can greatly reduce spikes, but it cannot reduce 50-60 + dB like a properly implemented LDO + filter stage.

Now, how much impact the spike will have is another question. It only depends on the food you are feeding.

Wow; there are many comments on this thread!

Buffer: Here is a simplified description of the buffer.

Data sheet: The "complete" data sheet is indeed gradually disappearing. But the Internet has a good memory, so they can still be found. The 3-terminal regulator *in any practical application* requires more parts. Input and output capacitors are almost always required. If there is a capacitor but no voltage at the input, there may be a diode between the output and the input.

Noise: One thing not mentioned is that these micro switches use unshielded inductors. They magnetically couple noise into any wiring or traces nearby. If noise is important, the inductor should be ring-shaped, pot-shaped or other shielded type.

Efficiency: Usually it doesn't matter, unless you use battery power or have heat issues. If you keep the load current low and minimize the input-output voltage difference, a linear regulator will do. The switcher is more complicated and can bring unpleasant surprises (noise, reliability, hard to find parts, etc.). Use them when you need them, but not because they are cheap or sound cool.

Price: Please also remember that the cost is not all. Those who buy goods based solely on cost usually lack the technical ability to make decisions in any other way. First, make it run normally. Then worry about the cost.

You can't just "select the switching frequency outside the ADC band." Any noise transient at a frequency that is not your phase-aligned sampling frequency will cause aliasing on the ADC.

That is the first step in the list of steps to minimize the impact, if only the PSRR of the ADC/amplifier is good enough, you still need to be sure.

Therefore, after filtering the power supply to 100uV and considering the PSRR of the ADC (which should be between 40dB and 70dB), is power supply noise still an issue?

I hope someone can raise this point. A friend of mine is a senior analog design engineer at National Instruments. He said that they still use 78xx/79xx in many applications because they still have excellent performance in terms of noise performance, better than many modern LDOs. For applications where low noise is more important than low efficiency (for example, analog audio), the classic linear regulator is still a good choice, where the switching converter will become a non-starter.

what is this? You have run out of games, so do you just play some things you did before? Enough competition!

The reason why these products are not so popular is that many people can judge whether they need a switch mode power supply from the beginning of the design, but just design it into the PCB.

I saw one on Tindie, and there is also a 3.3 version...6USD

I believe that in most places, even if it is not a 3-pin one-to-one replacement, you can only place one eBay dc/dc module. You can buy 10 firs at this price...

I have used RECOM plug-in before. It costs an arm and a leg because their entire production line has been approved for medical equipment, but they work like a charm!

Digi-Key USD 2.84:

Yes, switch-mode regulators are usually more efficient, while the efficiency of a good linear regulator (low quiescent current) is directly given by the ratio of output to input voltage. To achieve an efficiency of 50% or lower, Need to use 10V or higher input. Linear regulators are usually not as bad as the job description.

They still have a place, but once you need to drop from 12V to 5V, the efficiency is no problem... Moreover, you can make the switch mode can achieve both step-down and step-up, linear (obviously) has no chance...

Areas more gray than this.... Maybe you have some high-power devices with a 12V power supply and a miniature drawing that only requires a few mA @ 5V, you don't need high-cost smps.

Or maybe you have developed a product that can stay cool in cold weather and can be warmer.... The linear regulator will be perfect.

Based on the last few comments, I think you may not know the final application of this module. I am a person *specially* designing modules for my UPS application.

Yes, they are designed in this way due to my request.


For my application, the input voltage can be as high as 18V (from AC adapter) and 9.5V (from battery). Therefore, in my application, the efficiency of the linear regulator is 27%. The 12V module is better, reaching 67%. Since it is also a wall wart eliminator, it is my requirement to provide multiple output voltages from one DC voltage to my electronic device.


As for designing on the PCB, the 1.0 and 2.0 versions of my UPS have actually put them on the PCB. Unfortunately, it is very impractical to redesign the PCB every time the voltage demand changes, so they are plug-in modules. Yes, even the types of modules are different: buck/boost/isolated.

Once you fully understand your purpose of using them, modular equipment is needed there. But in a general application, the designer should know in advance what kind of trade-offs he must make. This is a very special application and you have to put things made in 7805 into it.

Just go back to [i]modern[/i] electronics (when transistors were new, I started to try this new technology (Oh! Give up my age!).) I don’t know if there are any everywhere Alternative products for linear regulators. Thank you for posting this content here with all other commenters.

I am working on a project that uses a 36V battery pack, and I have been looking for a way to power logic levels without having to design my own downconverter. thank you!

In fact, the rated voltage of this IC is only 35V, so it may be a problem for you. There are many parts there. The TI-National Simple Switcher series has some easy-to-use high-voltage components. They are also from China.

No switch mode replacement I have seen is LDO components. For a 5 volt regulator, you still need at least 7 volts. Therefore, if the efficiency you need is too poor, you may be looking for battery-powered products, and now you need to connect more batteries in series to power the switching regulator. Wash like this?

Actually this is fine. This is why I use this chip.

When the battery voltage is 5V or lower, the PMOS will turn on and the voltage drop will be reduced by tens of millivolts, but you have no regulations.

> PFET architecture also allows less component count and ultra-low voltage drop, 100% duty cycle operation.

If you need 3.3V from LiPo, you need a step-down converter.

If you need LiPo to provide 5V, you need a boost converter.

If you need 5V for 4x NiMH, you need a buck-boost converter, such as SEPIC, because the input can be higher or lower than the output.

I use KIS-3R33S, one of the MP2307-based modules. Not long ago, I got dozens of bulk goods from Ebay, all of which were below $0.50/ea. The process of modifying the 5V output is recorded in multiple places on the network. It does need to supplement the output capacitor to ensure stability, otherwise it will output the wrong voltage. Only 10uF SMD ceramic is enough.

Using this value, it will generate about 100mV switching noise that I measured on the oscilloscope. Noise will appear in the output of any switching regulator, but I was surprised by the amount, which affected the ADC reading. A larger capital letter or multiple parallel capital letters will make it smaller. For example, a 10uF SMD ceramic and a 100uF low ESR electrolytic drop noise are connected in parallel to 50mV. Larger/more caps produce diminishing returns.

So next I tried the Pi filter. Using 10uF SMD ceramics, 100uF low ESR electrolysis, and trying to randomly extract ferrite from my parts warehouse, the noise can be reduced to the range of 5-20mV. For the final design, I ordered a more suitable SMD ferrite and chose the core material to achieve the best filtering at 340khz and reduce it to 3-4mV (I forgot the exact ferrite Specifications, my notes are not convenient).

That might be better than what I actually need, so I just stopped there. Use 1x KIS-3R33 module, 1x resistor to change the voltage, 2x 10uF SMD ceramic as input/output capacitor, and 1x SMD ferrite and 1x low ESR electrolysis to complete the output Pi filter. The cost of each complete regulator is still Less than $1.

As a result, I no longer use linear regulators. They have become my special case. I did use one in a wireless car battery voltage monitor. Although when the MCU and transceiver are active, reducing 12V to 3.3V through the linear regulator will waste a lot of power, but the MCU is in sleep most of the time and the transceiver is not powered; making the average power consumption less than what I use The case of KIS-3R33S (quiescent current is about 10mA).

I reverse engineered them a long time ago. You can use them without opening the shell.

For voltages above 3.3V to about 10V, the resistance between pin 7 and ground.

For voltages lower than 3.3V, connect a resistor between pin 7 and Vout.

For 5V output, connect a 10K resistor from pin 7 to ground. For 1.2V, short pin 7 to Vout.

There is an overvoltage clamp zener at the output, the modification guide will tell you to remove it. Your schematic is missing.

I am not sure what the Zener voltage is. It is probably higher than the preset 3.3V. If so, and you increase the voltage without removing the diode, the diode will fail. If it fails to open, it’s okay, but if it fails to close, it’s another matter. Personally, I would rather not take risks, it will not take a long time to open the case, and it may also improve the heat dissipation effect.

Have you ever played with the voltage on the soft start pin? It adjusts the output linearly. For example, if the module is set to 5V output and the normal voltage (0.925V) on SS is halved, 2.5V output can be obtained. I have used it for current limiting, just discharge the SS capacitor until the current drops to an acceptable level.

I added a project log for this:

Unlike other web pages, no modification is required!

It's still cool to have a homemade one!

Now, what I want to see is the 7805-based drop of the 7805 replacement regulator.

The heat produced by the 7805 depends on the power dissipated. That will be the voltage drop times the current. If your input voltage is close to the output voltage and/or does not consume much current, you will not "generate a lot of heat".

As mentioned earlier, there is nothing new here, even for the specific circumstances specified by the designer, the product is easily available. As for those who mentioned all the designs, there is a buck/boost power supply on one of my boards, which can easily adapt to the 7805 pin size, Vin is 2.1v-12v, and the output 5v can reach 2.5 The efficiency of the amplifier is as high as 93% .

Is the 78 series regulator a single component? Well, it is unlikely. of course not. I have a Motorola data book (for your young people, a book is a series of pieces of paper organized in a smart way that you can touch and read at the same time. As books age, they emit a smell, And my smell is like the engineer is my mentor and likes to smoke cigars on his desk...wow! I also gave up my age).

Today, there is a severe lack of data tables in .pdf format. I suggest everyone read everything, I mean everything written by Bob Pease. Go to Google and enter Pease Porridge Electronic Design. This guy is a godsend gift once a month!

The correctly designed 78 series regulator is not, I mean it is definitely not a single component device. You have at least two input capacitors, two output capacitors and a diode. Without it, it may oscillate at a certain current or temperature. What will happen to the power supply when the 78 series is removed from the input power supply? It must go somewhere. Ask me how do I know...

That data book from the late 1970s is no longer in print, Motorola let... move with the wind... the phone... today... I will return to a burning building. Don’t get me wrong, I love mine. Child, but I am getting these data before booking in the picture. Believe it or not, young engineer, the value of an engineer used to be how many open data books he had on the bench.

Before PSpice, the bench was the road that rubber encountered, but then it went into the garbage and came out again. Lol, now i know i am showing my age. The data sheet was once made by engineers for engineers, and now it has become a marketing tool. Everyone knows what a "tool" is.

I dare to find a 78 series data manual, which has a clear and understandable schematic diagram of the inside of a real 78 series regulator. Bean counters are involved, and if they can get rid of transistors to save money and add a few cents to the bottom line, they will win.

Now, all you have to do is Google to think back and see what happens when an accountant beats an engineer. The Takata airbag recall is a good starting point.

I do like Hackaday and other sites, but if they don’t conduct due diligence, it will cause damage to them. The 78 series regulator is not a single component. Never, never.

You are right in most things, but I worry that things have changed:

TI is still keeping the old national data sheet:

They will show the smoke inside and tell you to use capacitors and diodes.

If you look at the internal structure, you will find that the old and the new are different.

The internal schematics and values ​​of all 3 links are slightly different. There are more details on On Semi, showing the transistor model they are using and the output trimming resistor network.

On Semi is separated from Moto. This is their data sheet, which shows the schematic:

Great, these guys even showed off all the feedback resistor networks on the chip. They may be able to make different versions with only one metal... Or hit with a laser?

eBay, USB charger for car lighters, $1, switch mode, 5V output.

eBay, $1, free shipping.

Check Traco can provide 1A output positive and negative regulators.

Can be purchased from Element 14 & RS

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