Transformerless Power Supply
 
Transformerless Power Supply


 

Transformerless Power Supply

 


Simple, low cost and easy to build power supply. Ideal for applications that doesn’t require too much power. It can provide power to circuit that uses less than 100mA without any problem. The disadvantage of this circuit is the danger of an electrical shock, so it cannot be used if the circuit is in contact with the user. The voltage supplied by this is determined by the zener diode.


Transformerless Power Supply

Disclaimer: These circuits use dangerous HV AC. Use at your own risk. We don't guarantee the accuracy of this information. In addition, we make no claim as to the conformity of these circuits to UL regulations.

It's often necessary to power a low voltage circuit such as a microcontroller with HV AC line current. For example, most fire alarms are powered this way. In these situations, a transformer is both bulky and expensive especially if the device is a consumer product. The solution is to use a reactance to limit the current, rectify the voltage with a diode, regulate the voltage with a zener, and use a large electrolytic capacitor to filter out the ripples.

The main disadvantage of transformerless supplies is that they don't offer issolation from the HV line and present more of a safety issue.

We present four circuits which use this principle and a calculator which determines the power capability for the circuit. These circuits are based on the www.microchip.com App Note AN954. See the application note for the equations upon which the calculator is based.

Capacitive Transformerless AC to DC Power Supply

Figure 1 - Capacitive Transformerless AC to DC Power Supply, with common Hot.

Capacitive Transformerless AC to DC Power Supply, with common Neutral

Figure 2 - Capacitive Transformerless AC to DC Power Supply, with common Neutral.

Resistive Transformerless AC to DC Power Supply

Figure 3 - Resistive Transformerless AC to DC Power Supply.



Full Bridge Resistive Transformerless AC to DC Power Supply

Figure 4 - Full Bridge Resistive Transformerless AC to DC Power Supply.



The circuits are essentially the same, the main difference is that the capacitive circuits use an additional series capacitor to limit the current. The bridge circuit presents full wave current to the filter. Table 1 shows the relative merits of each circuit.


Supply Type Pros and Cons
Capacitive Higher cost than resistive, more efficient than resistive. The zero crossing is delayed.
Resistive Lowest cost, least efficient. The zero crossing is not delayed.
Bridge Highest cost, but highest current capacity and efficiency. The output voltage isn't referenced to line or neutral so TRIAC control isn't possible.

Use a class X2 capacitor for C1 with voltage double the line rating. Double the returned power values for each component to give sufficient power margin.


Transformerless Power Supply


Transformerless Power Supply





Accurate LC Meter Capacitance Inductance Meter with 16F628 and LCD
Volt Ampere Meter with 16F876 Microcontroller and LCD display
 
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Build your own Accurate LC Meter (Capacitance Inductance Meter) and start making your own coils and inductors. This LC Meter allows to measure incredibly small inductances making it perfect tool for making all types of RF coils and inductors. LC Meter can measure inductances starting from 10nH - 1000nH, 1uH - 1000uH, 1mH - 100mH and capacitances from 0.1pF up to 900nF. The circuit includes an auto ranging as well as reset switch and produces very accurate and stable readings.
PIC Volt Ampere Meter

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50MHz 60MHz Frequency Meter / Counter with 16F628 & LCD
1Hz - 2MHz XR2206 Function Generator
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1Hz - 2MHz XR2206 Function Generator

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BA1404 HI-FI Stereo FM Transmitter
USB IO Board PIC18F2455 / PIC18F2550
BA1404 HI-FI Stereo FM Transmitter

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RF Remote Control 433MHz Four Channel
100m 4-Channel 433MHz Wireless RF Remote Control
 
200m 4-Channel 433MHz Wireless RF Remote Control

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100m 4-Channel 433MHz Wireless RF Remote Control

Four button RF remote is used to turn ON / OFF four different devices independently. Any of the four outputs can be configured to work independently in either toggle or momentary mode. Outputs are buffered by BC549 NPN transistors and can drive low voltage devices directly or be connected to either 5V or 12V relays (or motors) to control appliances that use 110V / 220V mains voltage or any voltage of your choice. Multiple remote systems can be used independently to control more than four appliances in the same location by changing the address code on 433MHz receiver and remote. It is also possible to use several remotes to control the same appliance such as garage door.
 

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