Transformerless power supply for microcontroller
Transformerless power supply for microcontroller. With the following specs. Traditionally, this has been done with a transformer and rectifier circuit. See full list on homemade-circuits. Nov 9, 2006 · Search first posts only. 5v Power Supply 5a Using Tip2955 Transistor. The circuit draws about 30ma AC. AC line voltage isolation can be addressed by I'm working on a circuit powered by a capacitive transformerless power supply, that is a microcontroller based triac-switching project for resistive loads. 5uF) prevents a shock from touching the plug pins after it's pulled. The disadvantages ofusing a transformerless power supply are: (1) low cur-rent supply and (2) no isolation from the AC line volt-age. Apr 4, 2010 · The thyristor control signal is obtained as follows: main sinusoidal voltage is applied through capacitor C1 to D4 zener diodes that limit the voltage to 30 Vpp. 7-MΩ resistors (thus at 340V peak you get 36 microamps or less, not enough to feel). The voltage on GP0 must be above 0. The 5-volt rail is literally the hot side of Feb 13, 2017 · There have been many low current designs posted. The voltage at the load will remain constant so long as current out (IOUT) is less than or equal to current in (IIN). Feb 24, 2021 · The basic principle of a transformerless power supply is based on the capacitive reactance of a capacitor . May 29, 2023 · The 220V AC is then rectified through a few diodes. The limits in these supplies keeps the power to a safe level. More info on the device: The device is for home brewing, its a standalone device that sits on the floor, shelf, mounted to a frame, etc. Definition: A transformerless power supply converts high AC input voltage ( 120V or 230V) to the desired output DC low voltage ( 3V or 5V or 12V) with low current output in milliamps. For cut currents, a distant received attached output, able of 15ma up to a Figure 3 - Resistive Transformerless AC to DC Power Supply. This circuit is designed to provide a 5-volt output with a maximum current of 1 ampere. Search. I've been using the power supply with transformer, but its quite bulky and also a bit costly compared to capacitive power supply (TPS). It uses capacitive reactance in its place of resistance; and it doesn't generate very much heat up. It is sufficient to run micro-controllers, sensors, displays, relays, and so on. A resistive, transformer-less power supply should be chosen for lower-cost applications. f = frequency. PIR light switches, small plug-in energy meters, some home appliances. Last edited: May 3, 2024 First, excess heat dissipations by the resistive transformerless power supply lower the final output voltage hence reducing its efficiency. Board is supplied by 2-5V voltage and may be powered by a battery such as Lithium Ion cell, two AA cells, external power supply or USB power adapter. This not only reduces the size, weight, and cost of the system, but also prevents leakage currents due to the saturation of the transformer when the UPS operation is changed. As shown 1A fuse may be used to avoid damages due to short circuit and a MOV (Metal Oxide Varistor) also may be connected as shown above to avoid problems due to voltage transients. Then the power loss + price of hi-wattage resistor out weighs this basic/ low cost design. Normally, DC voltage dividers are made with a pair of resistors. The zener diode D2 will regulate the filtered DC and will keepthe voltage steady at 5V. Ac To Dc Voltage Converter Circuit. And so, to reduce the challenges, we use a Sep 19, 2017 · Switching Power Supply Page 2 Circuits Next Gr. On transformerless power supply, I was able to get a max current of 25mA. Thyristor will trigger on the first front of the limited voltage that is applied through C2 – R2. 8v 20a linear power supply circuit and explanation1 – 9v variable desktop power supply. This application note will discuss both with a focus on the following: A circuit analysis of the supply. g. Oct 12, 2005 · In the figure below you can see a transformerless power supply circuit, the component values are as follows:R1 = 220K Microcontroller; Miscellaneous; Modules Apr 19, 2013 · Transformerless 5 Volt Power Supply. where Xc = reactance, pi = 22/7. Once SW1 (original wall switch) has been removed and replaced by the proposed circuit, as in circuit above, according to the low resistence incandescent lamp properties, the circuit "sees" the return wire as a Neutral (original one, no extra wire). Jun 10, 2017 · This Transformer-less power supply designed to produce 6V DC output supply, this circuit takes AC input between 200 – 300V, X-Rated capacitor C1 (474k/400V) is connected serially with AC mains phase line through fuse and R2 Resistor connected parallel to the C1 capacitor to discharge the energy when there is no AC supply, between fuse and C1 Nov 20, 2003 · I do it in the following way: A transformerless power supply and a back up battery (square battery with a zener diode to rectify it to 5 volts) to feed a pic12c508 then, I detect the Zero crossing and time the duration of the Zero crossing and you take it from there. I'm wondering if this can handle it. 6V. Vin = 220V ACVout = 12V DCCurrent Rating = 3 APlease Please Please :-\\ Aug 24, 2004 · power supply. I will also attach 7 leds to controller and one TSOP sensor. Surprisingly, the circuit behavior became affected by the polarity of the input AC (Line & Neutral), such that: When the "Line" of the AC is connected to the 820nF Home » All Forums » [8-Bit Microcontrollers] » PIC Microcontrollers (PIC10F, PIC12F, PIC16F, PIC18F) » Transformerless power supply Mark Thread Unread Flat Reading Mode Transformerless power supply Mar 28, 2015 · Hi Friends, I want to use following circuit for power supply in atmega16 microcontroller. Sep 22, 2015 · Hey guys, I am in the process of deciding on a good rout to take for the power supply for my project. Power SUPPLY. The shutdown pin must be held at VDD (logic high). Here we will know how to tune the voltage according to the needs of user, Transformer This section is an example guide of SMPS Power supply circuit using VIPER22A SMPS Controller IC. Dec 31, 2010 · On a 120 VAC 60 Hz line the power supply producing a 30 volt 3 amp output would need a roughly 88 UF capacitor and at 240 VAC that would need roughly a 44 uf capacitor. Transformerless Power Supply - circuit bidding supply up to more or less 20mA next to 12 volts. The Transformer is used to step down the applied AC mains through electromagnetic induction. say 50VA for about £10 and make a safe power supply. Output Current (Continous): 120mA to 150mA (can be increased, see text) Output Current (Short time): 180mA. It delivers vigilantly in relation to 20Amps on 13. But this voltage is still a low voltage AC and requires rectification and filtration. Oct 25, 2010 · For other examples, see "Massmind: Transformerless AC to DC Powersupply" or "Massmind: Transformer-less capacitive bleed power conversion" or "ST AN1476: Low-cost power supply for home appliances". 200m 4-Channel 433MHz Wireless RF Remote Control. To give a better and professional looks we will use JLCPCB service to build these prototype. This low voltage is then rectified using rectifier circuit. Generally, a step-down transformer or switch-mode power supply converts high AC mains voltage to a low AC voltage. The circuit takes in 220-240 volts input power to give out 12V,1A of output at full load. Not isolated from the AC line voltage which introduces safety issues. Then, it furthers the conversion to a desirable low DC voltage . 1V Zener diode D23. But using proper filtration circuit and voltage regulators we can use them in a good and precise manner. However, what if the appliance’s total power consumption is Jun 25, 2011 · Re: Power supply for PIC **broken link removed** Now here is the problem that is very DANGEROUS, and should be looked into. What if I will say about using a Transformer-less power supply for low power projects. It should be remembered, in fact, that the electrical network supplies an alternating voltage of 230 VAC (or 110 VAC, depending on the country of residence May 20, 2023 · Step 1: Story: It is very easy to design a transformer less power supply, yet it is not recommended for inductive loads and microcontroller circuit. The voltage at the load will remain constant so long as current out (IOUT) is less than or equal to current The International Journal of Multi-Disciplinary Research ISSN: 3471-7102, ISBN: 978-9982-70-318-5 _____ DESIGN AND DEVELOPMENT OF AN AUTOMATIC PHASE SELECTOR FROM THREE PHASE SUPPLY FOR SINGLE PHASE LOADS USING A TRANSFORMER-LESS POWER SUPPLY (Paper ID: CFP/2371/2021) 1 2 Marshall Daka Dept of Electrical and Electronics School of Engineering Nov 6, 2023 · Calculating Capacitor Reactance. It typically works at an input voltage which range from 85 VAC to 265 VAC and offers an output of 12 V at 120 mA. Figure 3 shows the main components for the resistive power supply option. I've taken the basic design of the power supply from Microchip's Application Note AN954: I'm using 1uF for C1 and 5. INTRODUCTION There are several ways to convert an AC voltage at a wall receptacle into the DC voltage required by a microcontroller. Apr 2, 2011 · Please Help me. One of the very useful transformerless power supplies using Viper12A IC can be used in many applications. PIC10F, PIC12F, PIC16F, PIC18F) / Transformerless power supply. We used 9V Zener Diode 1N4739A to limit the voltage to 9V. They’re running an ST6210 8-bit microcontroller directly off the hot side of mains current, connected to the touch sensor at the human’s finger through two or three 4. After that voltage regulator is used to produce regulated voltage from rectified voltage. If that voltage needs to be DC, it is rectified through a few diodes, and maybe regulated to a maximum voltage but we’ll get to that in a minute. 90uf. While it’s efficient, the process is costly and needs more space when designing or manufacturing a product. the circuit should provide power in a small device that's why I don't want to use a transformer because it's too big and bulky. One of the major problems that is to be solved in an electronic circuit design is the production of low voltage DC power supply from AC to power the circuit. To do this we first find out the reactance of the capacitor which may be considered as the resistance equivalent of a resistor. So I thought of making one but then if its available as a module, I can just buy and plug it. T6793 CO2 Sensor Module. Last edited: Jul 29, 2009. Usually, they are meant to supply a constant current in the circuit. Web-Masters Note: I have had several requests for a power supply project without using a power supply. Combined, they define the current flowing through the path. Wide Range of Products from DigiKey. Usually the current of a transformerless power supply will range from 0. Jumper J3 is provided to switch between the two power supplies. PCB'S and diagrams are shared. The advantages and disadvantages of Dec 24, 2012 · Capacitive Transformer Less Power Supply – Circuit Diagram. The schematic of the SMPS prototype is displayed for the show. design. I'm in need of a transformerless power supply of about 5-25vdc - 500am - 1a or more. 1,296. May 7, 2011 · By Electronic Circuit Saturday, May 07, 2011. It is used in low power electronic applications like LED bulbs, toys, and household appliances. A capacitive one should be selected if the heat dissipation from a resistor is undesirable. Feb 3, 2022 · Yes, you can construct power supply for your development without a transformer. Mar 10, 2022 · A transformer-less and low ampere power supply, working well with Arduino. Please tell me if it will work properly (when all leds are on) or not and can i use it for long term(how reliable it will be). 220 230v Ac To 12v 5v Dc Regulated Power Converter Bridge Rectifier. Transformerless Power Supply. Never use this circuit! Transformers and switching supplies isolate mains power from the output power. The input to the circuit is a 220-volt AC power supply. Nov 4, 2023 · Transformer less power supply for microcontrollersSupply circuit power 24v diagram transformer 9v without make step easy Transformerless power supplyTransformer unconnected leaving coils supply extra power amplifier. But overall it's a stable 5V. The specially designed circuit does the job of converting the AC voltage into Dc voltage. Re: power supplies from 230ac. The formula for reactance is: Xc = 1/2 (pi) fC. 5uF film capacitor acts as a reactive (lossless) dropping element. The transformer converts the high voltage AC input into a Apr 13, 2012 · 20A Transformerless Power Supply. 5 Volt and 1 Ampere Power Supply Circuit Diagram. You need to allow 2 W of heat in the zener. D1-D4 rectifies AC to DC and C2 removes ripples. Some points on the practical issues that I faced: - 1. Jul 29, 2009 · You would need about five 16uF 250Vac motor start caps, thats about £100ish. 6V for D1, as they allow for a slightly increased load. Sensor Circuits: Many sensor circuits, such as temperature sensors or light sensors, operate at low voltages Mar 11, 2022 · The principle: A transformer-less power supply (TPS) is basically just a voltage divider that takes the 115 or 220 VAC from your wall and divides it down to whatever voltage you want. CAPACITIVE Transformerless. Apr 20, 2013 · Well the other solution myself and MrRB were talking about is to control the triac so that it does not turn on until maybe 10v or so, and during that time the power supply takes in some power. Also it is very easy to make all the data, Gerber files, PCB layouts and circuit diagram are available here. A capacitive Transformerless Power supply is shown in Figure 1. shares. I don't have a transformer I can use. Trophy points. Apr 20, 2013 · The Transformerless Power Supply Support Material provides a complete circuit description including all the calculations. If you need to design a mains powered device, you could generally choose between a linear and a switch-mode power supply. Search titles only By: Jan 5, 2008 · Transformerless power supplies are used for electronic devices that don't require safe isolation from mains, e. Most are for 1 to 5mA. The problem is, the PIC won't run. Allowing to supply power necessary to the circuit (around 200mA), without turning the lamp ( L1) on. May 17, 2015 · As others have mentioned, transformerless power supplies seem simple at first but end up needing many components to protect other components. This PSU has been abnormally advised in place of current-hungry ham telephone system transceivers. [[wysiwyg_imageupload::]]The conventional method is the use of a step-down transformer to reduce the 230 V AC to a desired level of low voltage AC. 5v Dual Power Supply Circuit. Chances are, we have the products you need. Power supply is more efficient than a resistive transformerless power supply (discussed next). For one-off projects or prototyping, it’s not too hard to find a wall wart or power supply to send a few joules of energy from the wall outlet to your circuit. Jun 7, 2009 · I think it is absolutely absurd to use a transformerless power supply. Such a device has a power factor near 0, making it questionable whether it meets EU-mandated power factor laws, such as EN61000-3-2. 0. Its actually One of the major problems that is to be solved in an electronic circuit design is the production of low voltage DC power supply from AC to power the circuit. 2004 Microchip Technology Inc. If the power leads are reversed, the project has a potential of over 300v AC (for 240v mains) and making sure a project is totally enclosed is a very difficult thing to do. Reaction score. The 1M bleeder resistor (across the 1. Yep, this project is brought to you by JLCPCB offering best quality Jul 12, 2023 · A transformerless power supply has a maximum current rating that is determined by the components used to construct it. com Apr 4, 2017 · A transformerless power supply (TPS) is basically just a voltage divider that takes the 115 or 220 VAC from your wall and divides it down to whatever voltage you want. C1 - voltage dropping capacitor, X rated, 400VAC , Mylar capacitor, capacitance vary depends on the max load current needed, D1 - half wave rectifier C2 - to straighten the pulsating DC, 470uf 50V electrolytic capacitor Jun 7, 2022 · Output Voltage: 5VDC. They are only applicable if no external signals need to connect to the electronic and the enclosure prohibits exposure of circuit parts. The conversation process needs only a few components without a traditional transformer. So when we tell the triac to turn on we really are telling it to turn on later in the cycle, not enough to dim the light, but enough to tap off some Nov 18, 2023 · Transformerless 220v 9v how2electronicsCircuit supply power transformerless voltage circuits stabilized make homemade diagram electronic current simple schematic projects capacitive dc led high circuito Transformerless power supply circuitTransformerless power supply circuit ~ circuit wiring diagram must know. Low-Power Electronics: The 18V transformerless power supply is ideal for low-power electronic projects, such as powering microcontrollers, Arduino boards, or other small electronic devices that require a stable and reliable power source. The prototype is built in Power Supply design software provided by its own manufacturers. Buy a 9V 5A mains transformer. Transformerless power supplies are not a regulated supply and are really quite worthless. Jan 29, 2022 · #capacitordroppercircuit, #howtomake5voltpowersupply, #transformerlesspowersupplyHello friendtoday in this video i will show you how to make easy cheap and r Definition: A transformerless power supply converts high AC input voltage ( 120V or 230V) to the desired output DC low voltage ( 3V or 5V or 12V) with low current output in milliamps. Since we need power even with the switch closed, one way to get that power would be to use a current transformer. The circuits are essentially the same, the main difference is that the capacitive circuits use an additional series capacitor to limit the current. Simple 3 3v Power Supply Circuit 1a For Digital Eleccircuit Com Apr 13, 2012 · 20A Transformerless Power Supply. AN954. MCE Series AC/DC Power Supplies. It is not favorable for current inductive or resistive loads that require 20 A or 30 A to operate. 2. 8V. Inside the IC there is a 630V 300mA MOSFET. DS00954A-page 1. I need a schematic diagram of a Transformerless Power Supply. A simple app - push Nov 22, 2020 · Published by MKDas on 22/11/2020. By Electronic Circuit Friday, April 13, 2012. Arduino sketches are uploaded through any USB-Serial adapter connected to 6-PIN ICSP female header. I had a couple of questions about it. 3. There is no need of any SMPS or PSU. Output protection: short circuit and current limit at around 190mA. e i need 12v dc output with 0. . Sep 18, 2019 · Outline of the capacitor-dropper circuit. More cost effective than a transformer-based or switcher-based power supply. This can save the expense of buying a transformer, but presents potentially lethal voltages at the output terminals. It can generate 5V, 6V, 12V 150mA from 230V or 110V AC by using May 28, 2023 · In this paper, the transformerless uninterruptible power supply (UPS) is explained. i am trying to build a transformerless 5v power supply that can deliver about 100 to 500 mA (100 mA Mar 24, 2008 · The power is directly tapped from the mains via resistor R1. continuously management a fuse and/otherwise a fusible resistor to live Dec 15, 2014 · I have implemented a "Capacitive transformerless power supply" to control a microcontroller-based circuit that contains capacitive touch sensors, and I had an "AC polarity problem". The disadvantages of using a transformerless power supply are: (1) low cur-rent supply and (2) no isolation from the AC line volt-age. The conventional method is the use of a step-down transformer to reduce the 230 V AC to a desired level of low voltage AC. Output Noise (max): 30mVp-p (150mA load, 20MHz BW) Input Protection: Fuse, NTC, Varistor. Activity points. The power consumption of a tranformerless supply is the same whether or not there is a load, so your zener diodes will get hot. D21 shunts negative current away and D22 conducts positive current to the filter capacitor C23 and it is limited by the 5. Feb 6, 2021 · In the first diagram with the bridge rectifier, the current limiting resistor needs to be in the leg opposite to the capacitor dropper, for safety reasons. I want to make a power supply circuit that can provide 5v DC and up to 500mA current from a 120v AC input. This is the basic design. The two basic types of transformerless power supplies are resistive and capacitive. The PIC12/16/17 microcontrollers draw a maximum of 10 mA, even at the highest frequency and voltage of operation, therefore low current availability is not an issue. The capacitive reactance is simply the “resistance” that the capacitor opposes to the passage of electric current, and which depends on the one hand on the frequency of the signal passing through it, and on the other hand on the value May 3, 2024 · Yes, because it is a lead-acid battery, if it breaks down, the current will not be loaded, and the power supply of the transformerless will cause the necessary voltage drop for the current it loads. 120v to 5v 500mA transformerless power supply circuit. The resistor R1 is used to limit the high current that may occur during power on. You may also like: Transformerless Switch Mode Power Supply Transformerless Power Supply Circuit Diagram with Parts List The hope though is that the transformerless power supply will be fit for purpose which means that after a short time designing a PCD and getting a bunch printed for me, I can make the mini power supply boards at a cost of less than $3 without any hacking up of circuits and tearing apart of plastic cases and what not. (DRAIN--SOURCE) This part was not designed for this VCC Supply, Voltage Regulation Stage 1. Mar 11, 2012 · This is a 12V 100mA Transformerless power supply in support of low current applications. It is hard to get much power from the "transformerless" style. Section AN954 Transformerless Power Supplies: Resistive and Capacitive Author: Reston Condit Microchip Technology Inc. On the scope it looks like it should with the positive and negative "camel bumps" from the rectifiers. Understand transformerless power supply. Figure 6 highlights the area of the ProtoPowerSwitch board used to generate and regulate low voltage DC which powers the microcontroller. 20A Transformerless Power Supply. Basing the idea off this circuit Nov 21, 2020 · Let’s see how to design a high-power system without using the transformer. Table 1 shows the relative merits of each circuit. Instead I have a microwave HV Cap 2100VAC . DS00954A-page 1 AN954 CAPACITIVE TRANSFORMERLESS POWER SUPPLY A capacitive transformerless power supply is shown in Figure 1. The new technology of converting AC voltage to desired dc voltage is Jan 8, 2018 · The 1. C1 is the X rated AC capacitor so as to reduces climax volt AC. The premier community for all things 8 and 32-bit AVR microcontrollers. also voltage divider circuits like this one Apr 20, 2013 · The switch closes or the triac turns on, the voltage goes low, but the current then goes high. With very few numbers of components, we can get a reliable transformerless power supply with Viper12A. 2 Amps to 1 Amps, and the current is controlled with an external switch or by adjusting the components used in the design. Beyond that, the resistor gets very hot and hence the wattage of resistor needs to be high. The circuit consists of a few capacitors and diodes. Transformerless Power Supply 220v Ac To 9v Dc. Posted By: on Oct 7, 2011 · Hi first off I'm well aware of the risks. The current transformer would tap energy from the flow of the current and supply a small light current power supply. The PIC12/16/17 microcontrollers draw amaximum of 10 mA, even at the highest frequency andvoltage of operation, therefore low current availability isnot an issue. Feb 21, 2011 · Transformerless power supplies provide a low-cost alternative to transformer-based and switcher-based power supplies. D1 rectifies the voltage and C1 and C2 are used to filter the output. This circuit is so simple and it uses a voltage dropping capacitor in series with the phase line. It is used in low-power electronic applications like LED bulb sets, toys, and household appliances. Figure 4 - Full Bridge Resistive Transformerless AC to DC Power Supply. It is cost-effective, and need less space. power supply. The use of the DC–DC bidirectional converter eliminates the transformer from the UPS structure. 44 W non-isolated buck converter by using LinkSwitch™-TN2 LNK3204D/P/G, which can be effectively implemented as a 12V 100mA SMPS transformerless power supply circuit. transformerless power supply converts high AC input voltage (120V or 230V) to the desired output DC low voltage (3V, 5V, or 12V). Check Details Transformerless power supply circuit diagram hi all! this is siddharth, iam searching for transformerless powersupply i. Once both start-up conditions are met, the sequences will delay and PWM #1 will ramp from 0% to 100%. Higher cost than a resistive power May 20, 2023 · It is very easy to design a transformer less power supply, yet it is not recommended for inductive loads and microcontroller circuit. An increasing number of appliances draw a very small current from the power supply. 3W-40W PCB mount Medical AC-DC Power Supplies for Class II and BF-rated medical applications. Posted Friday, April 19, 2013. A second delay allows the fi rst voltage to stabilize before the sequencer ramps PWM #2 from 0% to 100%. 1,193. For cut currents, a distant received attached output, able of 15ma up to a These adapters fundamentally consist of three important components required for the above conversion: the Transformer, the Bridge Rectifier, and the Filter Capacitor. By Ashutosh Bhatt. . Unfortunately, the maximum current output you can get is approximately 1 ampere. T6793 CO2 sensor module is designed for applications requiring high-performance in a compact package. If that voltage needs Why transformer less supply is better for microcontrollers? Commonly used power supplies require step down transformer to step down 220/120 AC voltage to low required voltage. Please help me Sep 29, 2023 · September 29, 2023. Aug 24, 2023 · Universal digital power supply circuitSupply power circuit ic lm317 variable 317 circuits voltage diagram using adjustable build use homemade simplest lm connect any components 13. Figure 6 Transformerless Supply Voltage Regulation Stage 1. The bridge circuit presents full wave current to the filter. The most suitable and low cost method is the use of aVoltage Dropping Capacitor in series Jan 7, 2007 · transformerless power supply or explosives? :D hello. you can rectifier 230vac, make resistor divisor to aprox 15Volt, next can you use a 7805 or zener, you must to take care with the power in the resistive divisor, and with the consuption of the system. Also the zener diode would have to conduct 5A when the load is disconnected, thats approx 5V *5A = 25Watt! zener, Its a very bad idea. For line voltage and frequency rated capacitors all you need to look for is a common power factor correction capacitor. Disadvantages of Capacitive Power Supply: 1. Do not touch any electrical parts of this transformerless power supply. 5A current rating, so if anybody know any idea and any circuit , plz send me, thank you, siddharth. See all details from here : What if I will say about using a Transformer-less power supply for low power projects. A power supply without a transformer uses capacitive reactance theory to lower the incoming AC mains voltage. I'm designing a capacitive dropper TPS to power my microcontroller from mains. Transformer less ac to dc power supply circuit is also called as capacitor power supply circuit. Here is a design of a one IC PWM "buck down" style. I need to power my microcontroller (esp12E) from the mains AC. Jan 10, 2018 · This post is a research layout report for the 1. The Zener diode that generates the VCC output voltage voltage is installed at D5. In this circuit, we used 2 diodes 1N4007 as a half-bridge rectifier. If the negative side of the power supply output is accidentally grounded, the resistor will act as a fuse and open the circuit. Furthermore, by employing the quasi Posted by u/manibharathytu - 1 vote and 7 comments An isolation transformer should be used when probing the following circuits. To step down the AC voltage from 220 volts to 12 volts, a 220 to 12-volt transformer is used. Most of these Apr 21, 2004 · Hey kids, Going by the standard method of doing a transformerless supply, I get my 5V at the zener. ve zz fz bc wv ff ce uf ol ji