Mains Voltage monitor using LM3914

This Circuit helps in the monitoring of mains supply voltage. It does not use a isolation step down transformer. This has to be constructed only by skilled people with knowledge of safety requirements.

C1 limits the current and drops most of the voltage. The zener regulated supply is for the chip. C2 can be raised to 220uF or more if required. The bar mode display may consume more power.

Mains Voltage Power Transformers 

R2-R3-R5-R6 form a voltage divider to get a sample of the input voltage, D11-C3 get the DC value.

Adjust R5 preset with a log Plastic tweaker to get the 5th led to just turn on when input voltage is at 138V AC. This has to be done after PCB is put in a sealed fire-retardant-plastic or epoxy box. drill a hole in box for plastic tweaker.

National LM3914 – Dot Bar Display Driver
This Circuit is Not a Tested Design. It is an Idea for study

Mains Voltage monitor using LM3914

Warning : This Circuit is Mains Operated without Isolation Transformer and will give lethal electric shock if touched when the circuit is turned on. Test circuit only with DC 9V Bench Power Supply to try it out. Do not use 230V AC.

Regulated High Voltage Power Supply

The Circuit below is a paper design and not tested. It can be used for education and information, this can help you make your own design. Please do not just wire it up and expect it to work.

Regulated High Voltage Power Supply

Now let me see if i can explain the circuit, This is a regulated AC power supply. This circuit uses the Mosfet to turn off when voltage goes beyond a reference point. That means it just chops the Sine wave above a point, that also implies that the output may not be pure sine and may have harmonics. The Transformer if well designed may smoothen the chops. Even a Series Inductor or Resonant Circuits may reduce harmonics.

The opto coupler 4N50 Provides isolation and good Current Transfer Ratio. That may mean you may not get a shock and that even a small current signal in Opto-LED will give a saturated or Low Impedance in Opto-Transistor. The Mosfet is used like a Impedance Control switch turned On-Off by Opto. The Optocoupler diode is controlled by the Opamps which work Closed loop. The transformer output is compared with reference to drive opto-led.

This Circuit is based on Teledyne Solid State data book application note. They may not be making these parts anymore but they are available from others.

Regulated High Voltage Power Supply – del20032

Single Polarity Power Supply

This circuit uses a PNP Power Transistor TIP2955, you can use any other according to your current and voltage requirement.

Look at R2 a 10 Ohm resistor, when the current in your load to the power supply is less than 70mA the voltage across R2 is less than 10E * 70mA = 700mV right. The base emitter junction of Q1 will be biased or turned on around 700mV, less than 700mV the transistor just does nothing.

Single Polarity Power Supply

When the current in your load goes over 70mA the voltage across R2 goes above 700mV and a small base current Ib flows from emitter to base of Q1 turning on the transistor. Now a collector current Ic flows from emitter to collector and then to your load supplying the excess demand. The Ic = Ib * hfe where hfe or beta is the DC gain value.

From my Power Electronic Circuits

Some transistors will have only AC gain specified which is lower than DC gain. TIP2955 has a gain of 20 so for an Ib of 50mA the Ic will be 1 Amp which saves the regulator from heating up or shutting down as the main current flows thru the transistor. Q1 should be provided with a good heatsink.

Mains Voltage Indicator with a LED

This is a mains 230V AC voltage indicator and is a LIVE CIRCUIT, so take care. The Resistor has to be a fusible ceramic wire wound and the capacitor 630V AC or higher capacity.

More at my Home Made Circuits.

Mains Voltage LED Indicator

This circuit has been drawn from my memory and i have not tried it out again, just see if it is ok and then try. You should use the fuse of 100mA a slow blow if you want but it is very important. This circuit has to be enclosed in a plastic sealed enclosure to avoid contact.

Mains Current Indicator with a LED

This is a mains 230V AC load current indicator and is a LIVE CIRCUIT, so take care. The Resistors have to be a fusible ceramic wire wound.

More at Mains Voltage and Power Circuits

Mains Current LED Indicator

This circuit has been drawn from my memory and i have not tried it out again, just see if it is ok and then try. You should use the fuse of 1A a slow blow if you want but it is very important. You can design the shunt R3 and Fuse rating as required by your load.

Note that this circuit is to be put in series with the load like an ammeter. If you put it across the supply like a voltmeter it will fuse out or burn out. This circuit has to be enclosed in a plastic sealed enclosure to avoid contact.

Solid-State Stabilizer Step up 110V AC

The circuit uses opto-coupler MOC3041 of Motorola and the Triac BTA16-600 of STMicro as a solid state switch or relay. Four Switches boost or buck the mains voltage, keeping output within limits.

Power Electronics Design Methods

It also uses the LM324 quad opamp from National Semiconductor which is low power and single supply. As the MOC3041 switches the Triac at zero crossover there is no inter-winding short of transformer on crossover hopefully, the control circuit is designed in such a way that more than one triac will not be turned on at a time, i would like you to give feedback.

555 multivibrator like power oscillator

This circuit is a design concept, not tested by me and i did it just to explain some ideas.

Solid-State Stabilizer Step up 110V AC

The triac will switch at zero cross over because of MOC3041, hence no problem of an interwinding short, but then control circuit may fail or malfunction, so use fuse as shown . Also a snubber made of a 47E resistor and 0.02uF 630V pl cap in series must be placed across each triac.


Battery and Energy Management

Use heatsinks for all parts that heat, air circulation. Use Presets with series resistor as required so that you can test or calibrate. This Stabilizer should not be used with Inductive loads like motors or solenoids it may be ok for lighting and small electronics. If input voltage is 230V put the two 110V windings in series in proper polarity. BTA16600 is a ST part, metal tab is electrically insulated, 16A and 600V.

All mains wiring and connections should be designed for high voltage and current, They should be isolated visually from control circuits by 10 mm or more.

Stabilizer Step up 110V AC to 230V AC 500VA

It can Stabilize Mains voltage to around +/- 10% . It can be used for both 110V AC or 220V AC inputs with modifications. The Output is 220V AC. There is an overload, under voltage and over voltage trip circuit.

Mains Stabilty and Supply Regulation

U2A and U2B are two comparators which controls relays K2 and K3 Respectively. One Boosts the voltage (Step-up) when mains supply is low. The other Bucks the voltage (Step-down) when mains voltage goes beyond a limit.

UPS Power Inverter and DC to AC

U2C and U2D work like a window comparator to trip the unit above and below certain preset limits. This circuit is clubbed with a Mains control relay K1 which can be Turned ON-OFF with two pushbuttons.

Stabilizer Step up 110V AC to 230V AC 500VAThis circuit is a design i did, not tested by me as yet.With some tweaks and modifications it might work.

Put a 0.1uF 1KV pl cap across all relay contacts to avoid sparking. Relay current paths should be large and direct to supply, or when relay operates ground will lift and cause malfunction.All mains wiring and connections should be designed for high voltage and current, They should be isolated visually from control circuits by 10 mm or more. If input voltage is 230V put the two 110V windings in series in proper polarity.

Electric double layer capacitor an eFlywheel

Put one LED with resistor for boost and buck indication if required. Use Presets with series resistor as required so that you can test or calibrate. The 1M dead band or hysteresis resistor can be varied from 330K to 10M as performance demands, this resistor stops oscillation or chattering of relays.