PRESS ON OFF SWITCH CIRCUIT

Simple soft press switch using an NPN transistor, N mosfets, and either a P mosfets or a relay depending on your load.

The soft press switch in this circuit is similar to our computer, monitor and some phone switches. I like it most because of its durability and nice look when fixed.

SOFT PRESS SWITCH CIRCUIT DIAGRAM

PRESS SWITCH CIRCUIT OPERATION

IRF5210 can be replaced with a 12V relay to control heavy loads. The relay is connect to point A and B. Connecting a 100uf capacitor across the relay coil will ensure better operation.

When an input voltage is applied, the circuit stays off until the switch S1 is pressed because Q8 has turned on and connected the base of Q10 close to ground.

Because U23 is not charging, it’s shorted, hence, pressing the switch S1 shorts the base of Q8 and connects it to ground through R30 and U23. This actions turns Q8 off to remove its latch and allows Q10 to turn on and Q9 or the relay is turned on and latched until the switch is pressed again.

As Q10 turns on, U23 is charged through R47 and R46 at time constant 2RC. When U23 is charged and the switch is pressed again, the voltage stored in capacitor U23 is connected to the base of the NPN transistor through the 220 ohms resistor and the circuit turns off again and stays off until next press or infinity.

Capacitor U21 ensures that the circuit operation is not affected by electrical noise.

 To let the circuit turn on automatically at DC in or power restored, remove U24 from the circuit. Else leave it as it is for the function explained above.

The circuit is tested and is in use.

INVERTER BATTERY CHARGER CIRCUIT

In inverter designing, one of the most required tasks is a good charging system. A good inverter charger will increase battery life span and will also increase the run time of the inverter. 

Many inverter chargers exist but one that will keep the battery always fully charges is the best. These type of chargers are known as float chargers. 


A float charger is a charger that keeps the battery always under its float voltage level or fully charged level without over charging it.

Many poor or basic chargers consists of relays that disconnects the power supply line when the battery reaches its full state. This is not best because the relay contacts may stack and the battery will be overcharged and even swell up.

Many home made inverter chargers also lacks current regulation and also make heavy humming noise during charging.

The circuit below shows an inverter charger circuit for all battery sizes. The circuit is based on Iron transformer, SG3524, Mosfets, fast switching diodes and filter capacitor.

INVERTER  CHARGER CIRCUIT FOR ALL BATTERY SIZES

CLICK TO ENLARGE

LEARN HOW TO MAKE INVERTER TRANSFORMER 

INVERTER  CHARGER CIRCUIT OPERATION

The power conversion technique employed here is bridgeless boost power factor correction (boost PFC).  This technique ensures minimum parts count and high reliability.

One adorable advantage of this circuit is that, a smaller transformer can charge a battery of any ampere hour (AH) rating.

The circuit is based on SG3524 PWM IC. The datasheet of the SG3524 can be downloaded from here.

The inverter float charger works by supplying 220V or110V AC to a step down transformer T1.

This produce a stepped down voltage at the secondary side of the transformer.

D1, D2, Q1 and Q2 forms a bridge circuit which is connected to the secondary side of the transformer. The secondary winding coil forms an inductor connected to the bridge circuit. This means that if we are able to switch Q1 and Q2 alternatively at a higher frequency, the circuit will behave as a boost converter which will boost the stepped down AC to a high voltage DC.

Example, if a 12V transformer is used, more than 36V DC can be obtained from the output. This means that, a small 12V transformer can be used to charge 24V battery bank or 36V battery bank.

Best practice is to use a transformer with half of your battery bank ratting for charging or little higher than half. That is select 6V-10V for 12V battery banks, 12V -18V for 24V battery banks, 28V to 19V -24V for 36V battery banks etc. 

D1 and D2 can be any fast switching diode which can handle your desired output current. 

Q1 and Q2 is any N-mosfet which can handle your maximum charging voltage and current. 

NB. the mosfet voltage should be higher than your floating voltage by minimum of half.

The duty of the SG3524 is to switch Q1 and Q2 alternatively at a frequency set by U4 and R12.

U4 is 103 fixed capacitor and R12 is 100K.  This set the operating frequency to f = (1.3/RtCt) where Rt =100k and CT = 0.01uf.

If the value for RT and CT does not work for you, you can use 104 capacitor and 4.7k

T2 is a current transformer which is used for setting the maximum charging current. The current transformer is done by removing all the secondary winding of any transformer (smaller ones preferred ) and using a cable to rewind the part you removed by 2 turns. After winding, connect it as shown in the diagram above.

The output from the current transformer is rectified using normal diodes and fed to pin 10 for current regulation. U3 is used for setting the charging current. PLEASE ENSURE THAT U3 IS CONNECTED BEFORE TESTING YOUR CIRCUIT IF NOT, THE HIGH VOLTAGE FROM THE CURRENT TRANSFORMER WILL CAUSE THE SG3524 TO FAIL.

U2 is used for setting the floating voltage or battery full level.

READ ALL MY POSTS FROM THE LINK BELOW

DSPIC30F2010 inverter with charger circuit

SG3524 INVERTER WITH CHARGER

MAKE FERRITE TRANSFORMER

MAKE INVERTER TRANSFORMER

https://manycircuits.blogspot.com/

SG3524 PWM INVERTER CIRCUIT

PWM Inverter circuit  with charger  using a single transformer. The circuit is based on SG3524 IC.

Inverters are electronic devices which converts battery power (DC) to alternating current (AC) which is clean enough to power our useful appliances.

Inverters can be expensive but going through this tutorial can give you enough ideas to build your own solar inverter at home without spending much.

Let’s go through the designing and construction of 100W to 6000W single phase PWM inverter or UPS with charger using a single transformer, since two transformer systems requires much money and also much space.


The PWM inverter circuit is made up of three sections:

1. Oscillator section

2. Power driver stage

3. Change over and charging stage

THE OSCILLATOR STAGE 

FOR PWM INVERTER CIRCUIT WITH CHARGER

Credits to Nick_Zouein of instructables.com who provided the driver stage. which was later updated by me base on testing.

This is the heart of the solar inverter design. The main inverting work is done by this section using pulse width modulation IC (SG3524 or KA3524) or similar. Below is a 12V inverter circuit but few components can be changed or added to work for 24V, 48V and 96V systems whiles the concept still remains unchanged.

In this design the oscillator section is powered by a nine volts regulator IC (LM7809) when switch S1 is closed. The output frequency of the inverter is determined by R22, R23 and U12 (104 fixed cap). Theoretically, total resistance values should be higher but practically these values works best without humming in inductive loads such as fans. The output of the inverter/UPS is regulated using U3 which is 10K variable resistor or pot. This ensure that the output is always stable or within accepted range when loaded.

POWER DRIVE STAGE FOR PWM INVERTER CIRCUIT WITH CHARGER

This stage switches the transformer on/off 50 times is a second. That is 50Hz frequency base on the output from pin 11 and 14 of SG3524. 
The main components used here are N-Channel mosfets connected in parallel to deliver the required current to the transformer as shown in the circuit. In my designs I always assume that each pair will switch 20A of DC current. So if I want to switch 1000W using 12V DC supply, I calculate the max current to switch, which is 1000/12 = 83.3A. I then divide 83.3 by 20A which is my assumed current for each pair of mosfets and get 4pairs as the number of Fets to use.

Another great function of this section is to act as a half bridge rectifier during charging. During inverter charging, pin 10 of SG3524 receives positive signal from optocoupler U17 and shut down the SG causing the mosfets to turn off. The internal body diode of the mosfets then acts as rectifier to achieve DC battery charging.

PWM Inverter circuit with charger

INVERTER CHARGING

Battery charging is controlled automatically by LM358. It is configured such that the output pin 1 goes high when the battery voltage drops from a set value using U19. The high output turns Q10 on, but since Q10 and Q11 are connected to form an AND gate, when optocoupler U16 senses the presence of 220V input, Q11 also turns on and relay U14 switches and charging begins. When the battery is full adjust U19 until the relay switches and the full indicator turns on to set battery full.

 Relay U15 provides output from the inverter as well as your nation grid for the inverter to work as UPS. Output is filtered using 335 by 400V capacitor. In some cases without filter some inductive loads will not run. The system is protected from power surge using NTC 8 ohms or better. You can add NTC in parallel when handling higher wattage. this will cause the NTC not to over heat.

How to wind PWM Inverter Transformer

The transformer secondary coil must be Thick enough to handle the high current at the DC side else undue voltage drop will occur when loaded with little load. A center tap transformer is to be used for this project with the following specifications:

SECONDARY: 12-0-12

24-0-24

48-0-48

PRIMARY: 0-220-250

0-110-140 for US

NB: use 0-200-250 secondary for places with low line voltages else charging won’t occur.

AWG for primary should be 11 and below depending on the wattage. (You can double AWG or use higher voltage design for high output power)

NB. You can lower or increase charging current by reducing the secondary turns and voltage. E.g. To lower 12-0-12 charging current…make it 11-0-11 and vice versa.

Feedback winding: this should be a separate winding on the same transformer in the range of 12V to 16v. Winding gauge should be smaller…AWG…..18 to 28.

SIMPLE DC TO DC CONVERTER 1

The DC to DC converter circuit below uses an N-mosfet to produce a variable output of 3V and above depending on your input voltage. The maximum output of the circuit will be little lower than the input voltage.

3A TO 5A DC TO DC CONVERTER CIRCUIT

 VARIABLE DC TO DC CONVERTER CIRCUIT EXPLANATION

 

Every mosfet is controlled by the level of voltage that enters its gate. The circuit above is a simple mosfet switch circuit. The more voltage the gate sees, the higher the voltage that will flow from Drain to source.

 R1 and U1 forms a variable voltage divider, whiles R2 reduces the gate current.  when input voltage is applied, the gate receives a divided voltage from R1 and U1 through U2. This voltage turns the mosfet on. As the mosfet turns on, part of the input voltage flows from drain to source and given as output. C1 serves as output filter. 

U1 is a 10k variable resistor. By adjusting it, the output voltage changes proportionally.  

U1 can be replaced by a fixed resistor of know value using a try and error approach.

 R1 is left as 10K for less than 24V input. Increase it by 10K or higher when handling voltages higher than 24V (two 12V batteries).

Any N mosfet will work. only make sure that its voltage rating is higher than your input voltage.

 

DC TO DC CONVERTER 2

DC to DC converter steps up low DC voltage or steps down high DC voltage to a more acceptable voltages to be used on control boards and other low voltage devices.
When I started working on electronic circuits during my basic school level  at Begoro Roman catholic School, my biggest problem was how to step down high voltages to applicable level for components operation.

Am therefore sharing this post so that many electronic hobbyists who are confronted with this same challenge even at their higher levels will be able to have their way through after reading this post.

  DC TO DC CONVERTER STEP UP STEP DOWN  (BOOST / BUCK) USING UC3845

Buck converter circuit is a DC to DC converter circuit that steps down a higher DC voltage to a lower DC voltage.

A boost converter on the other hand is a DC to DC converter circuit which produces a higher DC voltage from a lower DC voltage.

Both converters can only be achieved by using appropriate switching technique at a desired frequency. (20kHz. to 80kHz.)

UC3845 PWM DC TO DC CONVERTER IC

The UC3845 IC is a pulse width modulated IC with 50 percent duty cycle. The IC operates with a supply voltage of 8V to 32V DC but works best with 8V-14V. 

The output frequency of the IC is calculated with this formula:

frequency (f)=1.8/(Rt x Ct). Download UC3845 datasheet from here.

STEP UP STEP DOWN DC TO DC CONVERTER CIRCUIT

Click to enlarge

  DC TO DC CONVERTER Circuit operation

The circuit works with input voltage of 9V to 75V to produce either a stepped down DC voltage or Stepped up DC Voltage.

To set up the circuit:

• Set the operating voltage for the IC. The operating voltage is set by adjusting U3 until you get 10V to 14V on pin 7 or on capacitor C5. This should be done before inserting the IC.

•  T1 is ferrite ring transformer with turns ratio of 1:1. The ring transformer is wound by winding the primary and the secondary at the same time as shown below.
  
  though all ferrite rings will work, some works extremely well. That is iron powdered rings. they are mostly yellow.

TYPICAL WINDING TURNS FOR THE ABOVE DC TO DC CONVERTER CIRCUIT

12V input .........................8 turns

24V input ......................... 16 turns

36V input.......................... 24 turns

48V input..........................32 turns

72V input...........................46 turns 

 NB: increase the number of turns if coil heats.

NB: Thick gauge means high current but do not use one thick coil, but use many smaller ones put together to avoid skin effect at high frequency. 18 gauge or smaller is OK.

• The operating frequency is determined by U1 and R3.

 

• D1 is any fast switching diode which can handle your desired output current.

• C2 is the output filter capacitor. it can be increased when handling higher output current.

• U2 is 10k variable resistor which is used for setting output voltage level. Never power the circuit without the feedback connected. Doing that will produce very high output voltage.

•  R10  is a current sense resistor which provides short circuit and over current protection for the circuit. It can be reduced if higher output current is required.

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