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 1 Electronics Forums / Electronic Projects Design/Ideas / Re: Transistor problem on: May 20, 2013, 07:31:52 PM When the PIC output goes high then Q2 turns on and supplies about +4V to R1. It turns on Q1.If your circuit does not do this then maybe you connected the pins on the transistors backwards. Check the pins on the datasheet.
 2 Electronics Forums / Projects Q/A / Re: 0-30V Stabilized Power Supply on: May 15, 2013, 03:02:51 PM Quote from: Big zee on May 15, 2013, 01:57:37 PMAnd use the same circuit?Caps trnsistiors and diodes ?What about the transformer ? And the bridge ?Make two completely separate circuits. Even separate transformers and separate bridge rectifiers.The first circuit can make 0V to +30V and the second circuit can make 0V to -30V.QuoteAnd the output +30 0 0 -30The 2 zeroes conected to same point ?+30 0 -30Not+30 0 0 -30Yes, you can connect the positive output of the second one to the 0V of the first one.
 3 Electronics Forums / Projects Q/A / Re: 0-30V Stabilized Power Supply on: May 15, 2013, 07:08:54 AM Quote from: Big zee on May 15, 2013, 05:06:48 AMhow can i make it the best PS by adding -30 volt to the circuit and dual linear pontesiometer for the voltageso it will be -30 . 0 . +30can the IC power the -30 to add IC4 ?There is no IC4 in the circuit.Nothing in the project is grounded.If you want a negative supply then use one of these projects and use the positive output as 0V. Then the "0V" output is the negative output.Then make a second project to produce the positive output voltage with its "0V" used normally as 0V and the positive output is the positive output.
 4 Electronics Forums / Projects Q/A / Re: 0-30V Stabilized Power Supply on: May 13, 2013, 06:57:27 AM Quote from: Big zee on May 13, 2013, 06:52:21 AMCan I double the 2N3055 and use the BD139 off the PCB?Yes, if each 2N3055 has its own 0.33 ohm emitter resistor.
 5 Electronics Forums / Projects Q/A / Re: 0-30V Stabilized Power Supply on: May 13, 2013, 06:36:44 AM Quote from: Big zee on May 13, 2013, 02:30:08 AMim working on the new one but i already did the old one 4 times can i still use the old one if i used lower volt like 20The calculations are simple:A 20VAC transformer might produce 22VAC without a load. Its peak voltage will be 22V x 1.414= 31V and the bridge rectifier will charge the positive main filter capacitor to +29.6V.The TL081 opamps have a maximum allowed total supply of 36V and they still need the negative -5.6V supply so their total supply will be 35.6V which is fine.The tiny old 2N2219 driver transistor will probably still overheat especially when its obsolete heatsink might not still be available. The pins and heatsink for a modern BD139 driver transistor will not fit on the original pcb.You can calculate how big the heatsink and fan for a single 2N3055 must be since its maximum dissipation will be very high at 79W.
 6 Electronics Forums / Projects Q/A / Re: 0-30V Stabilized Power Supply on: May 11, 2013, 06:35:03 AM Quote from: Big zee on May 11, 2013, 05:55:58 AMi couldn't find tle2141 or mc34071  is there other options ?The TLE2141 is made by Texas Instruments who is the largest semiconductor manufacturer in the world.The MC34071 is made by Motorola/Freescale Semi who is also a very large semiconductor manufacturer.They were chosen because their maximum total allowed supply is 44V and they have inputs that work at very low voltages so the negative supply voltage can be only -1.3V.Go to www.farnell.com and click on the flag of your country because they supply electronic parts all over the world.
 7 Electronics Forums / Projects Q/A / Re: 0-30V Stabilized Power Supply on: May 08, 2013, 09:03:10 AM Quote from: Big zee on May 08, 2013, 01:48:45 AMPicmaster, Redwire and a few other people designed the pcb for the improved version of this project.
 8 Electronics Forums / Projects Q/A / Re: 0-30V Stabilized Power Supply on: May 07, 2013, 08:20:52 PM Quote from: nida on May 07, 2013, 02:46:13 PMHi, I have build my PCB.I checked the circuit without load so I get 30V at the output.I have full wave transformer not centre tape 24VAC,5A.(Does it affect the circuit?)The transformer must be 28V or 30V for the output to be regulated at 30VDC.At 3A your output will be about 26V and will not be regulated because it will be full of ripple because the voltage from your transformer is too low.QuoteWhat is current limiting and how it works in this circuit?The circuit does not have simple current limiting. Instead it has accurate current regulation.R7 senses the load current and feeds the sense voltage to the (-) input of opamp U3. The current setting pot P2 sends its voltage to the (+) input of U3. Then U3 amplifies the difference to turn on Q3 and the LED to indicate that current regulation is reducing the output voltage through D9. The output voltage is reduced to the amount that accurately produces the current set by the current-setting pot. QuoteI have connected a load of 100ohms 10W so i get 23V and 0.23A at output so Is it correct?only if the output voltage is set to 23V and the current-setting is set higher than 0.23A, or if the voltage is set higher than 23V and the current-setting is at 0.23A.QuoteI get 11.8V at the output of U2U2, the driver transistor and the output transistors have a voltage gain of R12/R11 (plus one) that is changed a little by the voltage calibration pot. They amplify the 0V to 11.2V from the voltage setting pot up to 30.0V so the voltage gain should be 2.67857 times.[/quote]I get 28.2V at the output of U3.[/quote]When not regulating the current, the output of U3 should be higher than 11.2V. 28.2V is fine. Quotewhat voltages should be maintain at the inputs of ICS (U1,U2 and U3)?IC1 is an amplifier with a voltage gain of 2.0 and it amplifies the voltage of the 5.6V zener diode D8 so the output of U2 should be 11.20V.IC2 is an amplifier described above.IC3 is also an amplifier and it reduces the output voltage for current regulation.
 9 Electronics Forums / Projects Q/A / Re: 0-30V Stabilized Power Supply on: May 07, 2013, 11:56:20 AM Quote from: Big zee on May 07, 2013, 12:10:02 AMyes i did the original and no one says any thing in the original about the problemsThe original project is an old kit. DO NOT BUY THE KIT!Quoteso how can i  fix itwhere is the last updateLook in the list of topics in the forum for Projects Q/A for two or three threads about the fixed version.Quotecan i use the original PCB?Many parts are larger (so they do not overheat) and some wiring is different.Many people posted a revised pcb design in the forum.Here is the latest schematic and parts list:
 10 Electronics Forums / Projects Q/A / Re: 0-30V Stabilized Power Supply on: May 06, 2013, 05:52:15 PM Quote from: Big zee on May 06, 2013, 05:29:10 PMHi thereI tride to do it 4 timesOn 4 pcb but the dc gives me 33 voltAnd the transformer 25.1 volt and 1.1 ampThe 3rd tl081 gets hot and i hear some thing then i unblog itAfter tring that agin its sems fine but the volt still 33 voltAnd p1 and p2 and rv1 dosent chang the volt just the LED  All the parts are correct and there are no shorts at allIs thes fake or what ?Since you are using TL081 opamps and a 25V transformer then I guess you made the original project that has problems:1) Your transformer is probably 27V with no load then its peak voltage is 27V x 1.414= 38.2V and the bridge rectifier reduces it to 36.8V as the positive unregulated supply to the opamps. The opamps also have a negative 5.6V supply so the opamps are powered with a total of 36.8V + 5.6v= 42.4V. But their absolute maximum allowed total supply is only 36V so they fail soon.2) Many parts in the original project are overloaded and fail soon.I fixed the project as shown on many threads about it in the forum by using opamps that are rated for a 44V total supply and reducing the negative supply to -1.3V.Since your output is always 33V then maybe opamp U2 is destroyed by having a supply that is too high or the pins on the driver transistor or the output transistors (yes, the improved circuit users two output transistors to share the heat) are connected backwards so that the transistor that is connected wrong is simply a 5V zener diode from the positive supply voltage that is reducing the 38V to 33V.
 11 Electronics Forums / Theory articles / Re: can a pwm create a radio wave? on: April 30, 2013, 09:24:11 PM PWM switches the power supply to the load on and off, over and over. The duty-cycle of the on time to the off time determines the average power output.If the PWM switches on and off at a radio frequency then it will cause interference in a radio tuned to that frequency. If the PWM is modulated with audio then an AM radio will receive it.Yes, an astable multivibrator (or any oscillator) produces radio waves if its frequency is at a radio frequency.
 12 Electronics Forums / Projects Q/A / Re: 0-30V Stabilized Power Supply on: April 29, 2013, 11:31:00 AM The original circuit has many parts overloaded. Then the parts will fail soon.The transformer voltage and current are too low. Then the output will not be as high as 30V at 3A.The modified circuit corrected all the problems.
 13 Electronics Forums / Projects Q/A / Re: 0-30V Stabilized Power Supply on: April 26, 2013, 08:08:36 PM Quote from: nida on April 26, 2013, 07:18:31 AMI have replaced two 1N4148 diodes still it gives the same voltage.Then the diodes are connected backwards or are burned out again.Quote12000uF capacitor is not available here, so can i connect C1(10,000uF   63V) with a capacitor(1000uF 50V)?It will not make much difference since the total is only 10% higher.QuoteI bought 0.47ohm resistor but (10W0ohm47) is written on that and it is giving 0.9ohm resistance so can I connect these two resistors in parallel combination? power rating of both resistors is 10W.You are probably measuring the resistance of the wires on your multimeter. The 0.47 ohm resistor value is probably correct. QuoteI don't need 30V at output, 26V with 3A is enough for my project so still Do I need to replace my transformer?Then if your 24VAC transformer can deliver 4.24A AC (102VA) it will be fine.This and nearly ALL modern circuits probably will not work when built on a breadboard. A pcb is needed.
 14 Electronics Forums / Projects Q/A / Re: 0-30V Stabilized Power Supply on: April 26, 2013, 06:52:29 AM Quote from: nida on April 25, 2013, 06:27:19 PMI have checked my circuit again and resolved the wiring errors.The voltage across two 1N4148 diodes connected in series is -11.2V not -1.3V. why?The two diodes are supposed to conduct a small current which clamps the voltage to -1.3V.Maybe your diodes are connected backwards or maybe they are burned out.Quotevoltage across R3=14V thats why it gets burn.Why?R3 is fed a small current from rectifier D6 which has its current limited by R2. The other end of R3 is fed to the voltage-limiting diodes and the negative power supply pin 4 of U3 that draws only a couple of mA.The current in R3 is supposed to be low.QuoteCan I connect two 0.8ohm resistors in parrallel to make 0.4ohm(the one connected in series with load)?R7 is 0.47 ohms for the 3A version and is 0.27 ohms for the 5A version. Why do you want 0.4 ohms?QuoteI have C1 (10000uF,63V) so can i connect 1000uf,50V in parallel?Transformer is of 24VAC.A 24V transformer does not have enough voltage for this project to supply 30VDC at 3A. Your maximum output might be 26V at 3A and full of ripple.12,000uF is recommended with a 28V or 30V transformer.
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