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Isnin, Julai 29, 2013

12VDC to 20VDC converter (Suatable for audio amplifier)


ATTENTION Keep in mind that THIS IS NOT A PROJECT FOR A BEGINNER, IT CAN BE VERY DANGEROUS IN CASE OF PROBLEMS, NEVER BRIDGE, BYPASS OR AVOID FUSES THESE WILL SAVE YOUR BACK FROM FIRE RISK.


Circuit diagrams



The limitation of car supply voltage (12V) forces to convert the voltages to higher in order to power audio amplifiers.

In fact the max audio power x speaker (with 4 ohm impedance) using 12V is (V supply +- V supply-)^2/(8*impedance) 12^2/32 = 4.5Watts per channel, that is laughable...
For powering correctly an amplifier the best is to use a symmetric supply with a high voltage differential. for example +20 - -20 = 40Volts
in fact
40^2/32 = 50 Watts per channel that is respectable.
This supply is intended for two channels with 50W max each (of course it depends on the amplifier used). Though it can be easily scaled up or the voltages changed to obtain different values.

Overview - How it works
It is a classic push-pull design , taking care to obtain best symmetry (to avoid flux walking). Keep in mind that this circuit will adsorb many amperes (around 10A) so take care to reinforce power tracks with lots of solder and use heavy wires from the battery or the voltage will drop too much at the input.
The transformer must be designed to reduce skin effect, it can be done using several insulated magnet wire single wires soldered together but conducting separately. The regulation is done both by the transformer turn ratio and varying the duty cycle. In my case i used 5+5 , 10+10 turns obtaining a step up ratio of 2 (12->24) and downregulating the voltage to 20 via duty cycle dynamic adjust performed by the PWM controller TL494.
The step-up ratio has to be a little higher to overcome diode losses, winding resistance and so on and input voltage drop due to wire resistance from battery to converter.

Transformer design
The transformer must be of correct size in order to carry the power needed, on the net there are many charts showing the power in function of frequency and core size for a given topology. My transformer size is 33.5 mm lenght, 30.0 height and 13mm width with a cross section area of 1,25cm^2, good for powers around 150W at 50khz.
The windings , especially the primary must be heavy gauged, but instead of using a single wire it is better to use
multiple wires in parallel each insulated from the other except at the ends. This will reduce resistance increase due to skin effect. The primary and secondary windings are centertapped, this means that you have to wind 5 turns, centertap and 5 windings again. The same goes for the secondary, 10 turns, centertap and 10 turns again.
The important thing is that the transformer MUST not have air gaps or the leakage inductance will throw spikes on the switches overheating them and giving a voltage higher than expected by turn ratio prediction, so if your voltage output (at fully duty cycle) is higher than Vin*N2/N1 - Vdrop diode, your transformer has gap (of course permit me saying you that you are BLIND if you miss it), and this is accompanied with a drastical efficiency reduction. Use non-gapped E cores or toroids (ferrite).

Output diodes, capacitors and filter inductor
For rectification i preferred to use shottky diodes since they have low forward voltage drop, and are incredibly fast.
I used the cheap 1N5822, the best alternative for low voltage converters (3A for current capability).
The output capacitors are 4700uF 25V, not very big, since at high frequency the voltage ripple is most due to internal cap ESR fortunately general purpose lytics have enough low esr for a small ripple (some tens of millivolts). Also at high duty cycle they are feed almost with pure DC, giving small ripple. The filter inductor on the secondary centertap furter increases the ripple and helps the regulation in asymmetrical transients

Power switch and driving
I used d2pak 70V 80A 0.004 ohms ultrafets (Fairchind semiconductor), very expensive and hard to find. In principle any fet will work, but the lower the on-resistance, the lower the on-state conduction losses, the lower the heat produced on the fets, the higher efficiency and smaller the heatsinks needed. With this fets i am able to run the fets with small heatsinks and without fan at full rated power (100W) with an efficiency of 82% and perceptible heating and with small heating at 120W (some degrees) (the core starts to saturate and the efficiency is a bit lower, around 75%)
Try to use the lowest resistance mosfet you can put your dirty hand :-) on or the efficiency will be lower than rated and you will need even a small fan. The fet driver i used is the TPS2811P, from Texas instruments, rated for 2A peak and 200ns. Is important that the gate drive is optimized for minimal inductance or the switching losses will be higher and you risk noise coupling from other sources. Personally i think that twisted pair wires (gate and ground/source) are the best to keep the inductance small. Place the gate drive resistor near the Mosfet, not near the IC.

Controller
I used the trusty TL494 PWM controller with frequency set at around 40-60 Khz adjustable with a potentiometer. I also implemented the soft start (to reduce powerup transients). The adjust potentiometer (feedback) must be set to obtain the desired voltage. The output signals is designed with two pull-up resistors on the collector of the PWM chip output transistor pulling them to ground each cycle alternatively. This signal is sent to the dual inverting MOSFET driver (TPS2811P) obtaining the correct waveform.

Power and filtering
How i said before the power tracks must be heavy gauged or you will scarify regulation (since it depends of transformer step up ratio and input voltage) and efficiency too. Don't forget to place a 10A (or 15A) fuse on the input because the car batteries can supply very high currents in case of shorts and this will save you face from a mosfet explosion in case of failture or short, remember to place a fuse also on the battery side to increase the safety (accidental shorts->fire, battery explosion, firemen, police and lawyers around). Input filtering is important, use at least 20000uF 16V in capacitors, a filter inductor would be useful too (heavygauged) but i decided to leave it..

Final considerations
This supply given me up to 85% efficiency (sometimes even 90% at some loads) with an input of 12V because i observed all these tricks to keep it functional and efficient. An o-scope would be useful, to watch the ripple and gate signals (watching for overshoots), but if you follow these guidelines you will avoid these problems.
The cross regulation is good but keep in mind that only the positive output is fully regulated, and the negative only follows it. Place a small load between the negative rail and ground (a 3mm led with a 4.7Kohm resistor) to avoid the negative rail getting lower then -20V. If the load is asymmetric you can have two cases:
-More load on positive rail-> no problems, the negative rail can go lower than -20V, but it is not a real issue for an audio amplifier.
-More load on negative rail-> voltage drop on negative rail (to ground) especially if the load is only on the negative rail.
Fortunately audio amplifiers are quite symmetrical as a load, and the output filter inductor/capacitors helps to maintain the regulation good during asymmetrical transients (Basses)

FOR FIRST TESTING USE A SMALL 12V power supply and use resistors as load monitoring switches heat and current consumption (and output) and try to determine efficiency, if it is higher then 70-75% you are set, it is enough. Adjust the frequency for best compromise between power and switching losses, skin effect and hysteresis losses

Bill Of Materials
=================
Design: 12V to 20V 100W DC-DC conv
Doc. no.: 1
Revision: 3
Author: Jonathan Filippi
Created: 29/04/05
Modified: 18/05/05

Parts
2 R1,R2 = 10
4 R3,R4,R6,R7 = 1k
1 R5 = 22k
1 R8 = 4.7k
1 R9 = 100k
2 C1,C2 = 10000uF
2 C3,C6 = 47u
1 C4 = 10u
3 C5,C7,C14 = 100n
2 C8,C9 = 4700u
1 C12 = 1n
1 C13 = 2.2u
1 U1 = TL494
1 U2 = TPS2811P
2 Q1,Q2 = FDB045AN
4 D1-D4 = 1N5822
1 D5 = 1N4148
1 FU1 = 10A
1 L1 = 10u
1 L2 = FERRITE BEAD
1 RV1 = 2.2k
1 RV2 = 24k
1 T1 = TRAN-3P3S



Credit

6VDC to 12VDC Converter


This inverter circuit can provide up to 1A of 12V power from a 6V supply. For example, you could run 12V car accessories in a 6V (British?) car. The circuit is simple, about 70% efficient and quite useful. By changing just a few components, you can also modify it for different voltages.


Circuit diagram



Parts
R1,    R4 2.2K 1/4W Resistor
R2,    R3 4.7K 1/4W Resistor
R5    1K 1/4W Resistor
R6    1.5K 1/4W Resistor
R7    33K 1/4W Resistor
R8    10K 1/4W Resistor
C1,   C2 0.1uF Ceramic Disc Capacitor
C3    470uF 25V Electrolytic Capcitor
D1    1N914 Diode
D2    1N4004 Diode
D3    12V 400mW Zener Diode
Q1,   Q2, Q4 BC547 NPN Transistor
Q3    BD679 NPN Transistor
L1     See Notes
    MISC Heatsink For Q3, Binding Posts (For Input/Output), Wire, Board

Notes
1. L1 is a custom inductor wound with about 80 turns of 0.5mm magnet wire around a toroidal core with a 40mm outside diameter.
2. Different values of D3 can be used to get different output voltages from about 0.6V to around 30V. Note that at higher voltages the circuit might not perform as well and may not produce as much current. You may also need to use a larger C3 for higher voltages and/or higher currents.
3. You can use a larger value for C3 to provide better filtering.
4. The circuit will require about 2A from the 6V supply to provide the full 800mA at 12V.

500W Inverter, 12VDC to 220VAC







Attention: This Circuit is using high voltage that is lethal. Please take appropriate precautions



This circuit you can convert the 12VDC into 220VAC. The 4047 IC is use to generate the square wave of 50hz.



Circuit diagram





How to calculate transformer rating

The basic formula is P=VI and between input output of the transformer we have Power input = Power output. 

For example if we want a 220W output at 220V then we need 1A at the output. Then at the input we must have at least 18.3A at 12V because: 12V*18.3A = 220V*1A, when P1 is 12V*18.3A and P2 is 220V*1A. 
So  if you have to wind the step up transformer 12V to 220v but input winding must be capable to bear 20A.

For this project to produce 220VAC with 500W, we find.

Output power is P2 = Output voltage x output current
        Output current = 500W/220V
                                = +- 2.272A

most importance is primary current
                           P1 = 12V x current
                      500W = 12V x current (I1)
                          I1        =  500W/12V
                                 = 41.67A

So your transformer to must be capatable to support primary current at lease 41.67A and don't forget for 2N3055 max current 15A . At lease 4 pcs for both side, total 8 pcs of 2N3055. 

try DIY


Rabu, Julai 17, 2013

Hyper fast robot line following

Free Electronic/electric Circuit diagram for many electronic project, electrical project and electromachanical.


Hyper fast robot line following 1


Hyper fast robot line following 2



Simple colour detector circuit for line tracking robots.

The given circuit is tested by myself in NCE Robotics Club ( www.facebook.com/ncerobotics ) many times with various modifications, the given circuit works very effectively.

Figure: Verified circuit diagram of color detector
The circuit can detect two different colors comparing the light reflecting capacity of those colors. As we know the light reflecting capacity of brighter color is higher than dark one, thus the different intensity of light reflected by different color surface will cause the different value of resistance in LDR ( Light Dependent Resistor ) sensor, which is converted into voltage levels by implementing LDR and a fixed resistor in voltage divider arrangement (but as fixed resistor we use preset to change the sensitivity as our desire and required level).

In above circuit, 100 ohm resistor is used to light LED1 safely with high intensity, The LDR and a preset is used as voltage divider and gives the primary output of sensor which will changes as the color of reflecting surface changes. Two 10 k ohm resistors gives the fixed ( reference) voltage to the negative terminal of comparator which is compared with the input from sensor primary output in non-inverting terminal. when the sensor primary output is below the reference voltage the sensor gives low output ( indicator is off ) and when the sensor primary output is above the reference voltage the sensor gives high output ( indicator is on). In this way the above circuit detects the colors.

For example in case of white and black color the sensor gives high output for white color and low output for black color. This logic can be altered by altering the inputs to the comparator.

By arranging these sensors in different numbers and applying as input to the micro-controller for further process we can make a line following robots easily as I have mentioned in earlier posts.

Khamis, Julai 11, 2013

Astable 555 Multivibrator




Astable 555 Multivibrator  


freq  Hzperiod Secduty cycle
Power
Ra 

   


Rb 

   


Ct 

   



LED1




LED2






Above in Gadget form, Astable 555 Multivibrator Gadget , for your Webpage or Google Home Page.
These are the formulae used by 555 and same is used in javascript without any change.

T1 = 0.693 (Ra + Rb) * Ct   charge time of Ct 

T2 = 0.693 (Rb * Ct)  discharge time of Ct

T = T1 + T 2    total period in seconds

F = 1 / T = 1.44 / ((Ra + (2 * Rb)) * Ct)   Frequency in Hertz

D = T 2 / T  duty cycle, multiply by 100 to get %.

Ct in farads and Ra-Rb in ohms.
The max power dissipation of 555 is 700mW so overload of more than 200mA will damage the device, connecting the battery in the reverse or wrong polarity will also damage device, ensure also Ra and Rb do not go less than 2.2K (use 4.7K minimum) as it may damage the discharge transistor at pin 7. The supply voltage can go upto 18V. For CMOS 555 like 7555 see the datasheet they are different.
the above circuit in pdf format  del00018.pdf
the cadsoft eagle source of the circuit  del00018.zip




datasheet of LM555 here pdf.
pdf links may take time to load in the browser, save file target to your disk is better.
If LEDs are not lighting up, refresh the page. Tested in Mozilla 1, Opera 5 and IE5 with javascript and images enabled.



Press the Red button below to turn on the circuit press it again to turn off. The 555 can source (LED2) or Sink (LED1) upto 200mA. It can even drive a small motor or lamp with diodes added to protect from inductive kickback.
Vary Ra, Rb and Ct with the controls given and see the change of frequency, period and duty cycle.


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