juanpmoron1
- Feb 9, 2004
- 26
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- Feb 9, 2004
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- 26
I connected a switch power supply (with MC34063 IC) with 24V of this power supply and the 10uF cap in the out explode
???
???
juanpmoron1
- Feb 9, 2004
- 26
- Joined
- Feb 9, 2004
- Messages
- 26
I connected a switch power supply (with MC34063 IC) with 24V of this power supply and the 10uF cap in the out explode
???
???
audioguru2
- Apr 6, 2004
- 12,026
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Juan,
If you are referring to C7 in this project, check its polarity. Polarized capacitors make spectacular explosions if connected backwards.
If you are referring to C7 in this project, check its polarity. Polarized capacitors make spectacular explosions if connected backwards.
juanpmoron1
- Feb 9, 2004
- 26
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- Feb 9, 2004
- Messages
- 26
[Excuse me for my bad english! 
]
Yes the cap is the C7 and its polarity is ok, but when I connect the circuit, C7 vibrate producing sound and heat it up.
]Yes the cap is the C7 and its polarity is ok, but when I connect the circuit, C7 vibrate producing sound and heat it up.
juanpmoron, C7 is just a bypass cap on the output. Most likely, you have either connected it wrong or you are using a capacitor with too low of a voltage rating. Was it a used capacitor? What do you have connected to the output that audioguru thinks might cause your problem? In an earlier post you mentioned a problem with another part failing. You should check your circuit with the schematic.
MP
MP
audioguru2
- Apr 6, 2004
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Good news, Guys,
I found a high-voltage, readily available and inexpensive replacement opamp for U2 and U3, which are operating in this project with a supply voltage beyond the maximum specified ratings of the original TL081 opamp. It is ONSemi (formerly Motorola) part number MC34071AP. Its maximum supply voltage rating is 44V (this project gives 38V plus).
MP,
Do you recall that a couple of years ago, Chinese electrolytic capacitors were very unreliable? Maybe Juan got some. I know some techs who made a fortune relacing defective computer capacitors.
ONSemi is not recommending the TL081 for new designs (will soon be obsolete).
Please see ONSemi's spec sheet for Juan's MC34063, where they say that maximum ratings are not to be used continuously nor simultaneously. Their wording for the TL081 is the same as TI's (just a copy) which is very confusing.
Juan,
A-HA, I saw your other post about the 24V to 12V switching power supply that is heating too much when powered by this project. My suspicions are correct that C7 is too small physically (low ripple-current rating) and value (not enough storage to provide high-current pulses that are drawn by the switcher). Hopefully, a big C7 will solve both problems.
I found a high-voltage, readily available and inexpensive replacement opamp for U2 and U3, which are operating in this project with a supply voltage beyond the maximum specified ratings of the original TL081 opamp. It is ONSemi (formerly Motorola) part number MC34071AP. Its maximum supply voltage rating is 44V (this project gives 38V plus).
MP,
Do you recall that a couple of years ago, Chinese electrolytic capacitors were very unreliable? Maybe Juan got some. I know some techs who made a fortune relacing defective computer capacitors.
ONSemi is not recommending the TL081 for new designs (will soon be obsolete).
Please see ONSemi's spec sheet for Juan's MC34063, where they say that maximum ratings are not to be used continuously nor simultaneously. Their wording for the TL081 is the same as TI's (just a copy) which is very confusing.
Juan,
A-HA, I saw your other post about the 24V to 12V switching power supply that is heating too much when powered by this project. My suspicions are correct that C7 is too small physically (low ripple-current rating) and value (not enough storage to provide high-current pulses that are drawn by the switcher). Hopefully, a big C7 will solve both problems.
audioguru2
- Apr 6, 2004
- 12,026
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Mastrila,
Your variac, isolation transformer and rectifier diodes probably are not made to have a low voltage drop during the brief but HUGE current surge when the filter capacitor, C1, is re-charged. Therefore the voltage across C1 (at the lowest point of its ripple) probably is too low. Let's call this voltage, V+. V+ must be more than the project's output voltage by at least the total amount of voltage-drops that follows:
1) The base-emitter voltage of Q4. (0.9V)
2) The base-emitter voltage of Q2. (0.8V)
3) The voltage-drop across R15. (1.0V)
4) The output-high voltage of U2. (1.2V)
With the project providing 3A, voltage drops above add up to 3.9V.
Therefore if you want 30V output, V+ must be at least 33.9V.
A 24VAC transformer, low-current rectifiers and a low-value for C1, supplying 3A, won't give you this. What do you measure across C1?
Your variac, isolation transformer and rectifier diodes probably are not made to have a low voltage drop during the brief but HUGE current surge when the filter capacitor, C1, is re-charged. Therefore the voltage across C1 (at the lowest point of its ripple) probably is too low. Let's call this voltage, V+. V+ must be more than the project's output voltage by at least the total amount of voltage-drops that follows:
1) The base-emitter voltage of Q4. (0.9V)
2) The base-emitter voltage of Q2. (0.8V)
3) The voltage-drop across R15. (1.0V)
4) The output-high voltage of U2. (1.2V)
With the project providing 3A, voltage drops above add up to 3.9V.
Therefore if you want 30V output, V+ must be at least 33.9V.
A 24VAC transformer, low-current rectifiers and a low-value for C1, supplying 3A, won't give you this. What do you measure across C1?
concerning REPLY#26
I believe you will need a power supply which is isolated from the voltage which you are measuring for the panel meter to work (ie:the power source should be a 9v battery per manufacturer). This is causing me problems as I have 25 students encountering this problem (we added a panel meter to their project this year).
Does anyone have any suggestions/ alternatives to the 9v battery other than adding a transformer.
thanks
I believe you will need a power supply which is isolated from the voltage which you are measuring for the panel meter to work (ie:the power source should be a 9v battery per manufacturer). This is causing me problems as I have 25 students encountering this problem (we added a panel meter to their project this year).
Does anyone have any suggestions/ alternatives to the 9v battery other than adding a transformer.
thanks
EIST, the solution of using a battery would be a simple solution. As you have stated, the alternative is to use a transformer. The voltmeter needs a different source than the voltage which it is measuring.
If you could describe something about the rest of the project, maybe we can come up with another alternative. It sounds as if the project has some voltage in it to be measured. Perhaps there is a place where you can tap some of it.
MP
If you could describe something about the rest of the project, maybe we can come up with another alternative. It sounds as if the project has some voltage in it to be measured. Perhaps there is a place where you can tap some of it.
MP
HI
I AM NEW TO EL-LAB
I READ ABOUT 0-30V POWER SUPPLY I AM ALSO INTRESTED TO MAKE IT
1st OF ALL TRANSFORMER SHOULD HAVE1.6 TIMES HIGHER CURRENT RATING THEN SPASIFIED (NOT 3A IT SHOULD BE 3.6 A) HEATSINKING OE 2N2219 IS NOT EASY. IT SHOULD BE REPLACED BY TO-220 TYPE OF TR . DIODES OF BRIDGE RECTIFIER SHOULD ALSO BE CHANGED TO 4A TYPES. THE FILTRING CAP SHOULD ALSO BE CHANGED TO 1OOO MF TO HANDEL LARGE CURRENT SURGES.
I AM NEW TO EL-LAB
I READ ABOUT 0-30V POWER SUPPLY I AM ALSO INTRESTED TO MAKE IT
1st OF ALL TRANSFORMER SHOULD HAVE1.6 TIMES HIGHER
CURRENT RATING THEN SPASIFIED (NOT 3A IT SHOULD BE 3.6 A) HEATSINKING OE 2N2219 IS NOT EASY. IT SHOULD BE REPLACED BY TO-220 TYPE OF TR . DIODES OF BRIDGE RECTIFIER SHOULD ALSO BE CHANGED TO 4A TYPES. THE FILTRING CAP SHOULD ALSO BE CHANGED TO 1OOO MF TO HANDEL LARGE CURRENT SURGES.
audioguru2
- Apr 6, 2004
- 12,026
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- Apr 6, 2004
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Hi Zia, welcome to our forum. About this power supply:
1) We have already determined that the transformer's 3A rating is too low because the output of the power supply is 90VA (30V X 3A).
If you use a much higher current rated transformer, then its voltage won't sag as much during rectifier conduction, and its voltage won't rise as much with no load. Maybe a 5A rating is good.
2) I don't remember if the heatsink problem with the little 2N2219 was discussed, but I agree with you that a T0-220 would be much better.
3) We also determined that using a higher current bridge rectifier instead of those little diodes will reduce losses and allow for a heatsink.
4) We have had many suggestions for the size of the filter capacitor. In order to reduce loss due to ripple voltage, make it really large, such as 10,000uF.
5) As you have read here, the minimum and maximum voltages at the filter capacitor are crutial:
a) A minimum voltage of at least 33.9V when the project has a 30V, 3A load.
b) A maximum voltage of less than 36.4V when the project has no load, when using the 44V replacement opamp.
If you include a 10% mains voltage variation then these voltages are impossible. Perhaps this project should be rated to only 25V output, and when using changes as above should perform very well with a 24V/4A or 5A transformer.
1) We have already determined that the transformer's 3A rating is too low because the output of the power supply is 90VA (30V X 3A).
If you use a much higher current rated transformer, then its voltage won't sag as much during rectifier conduction, and its voltage won't rise as much with no load. Maybe a 5A rating is good.
2) I don't remember if the heatsink problem with the little 2N2219 was discussed, but I agree with you that a T0-220 would be much better.
3) We also determined that using a higher current bridge rectifier instead of those little diodes will reduce losses and allow for a heatsink.
4) We have had many suggestions for the size of the filter capacitor. In order to reduce loss due to ripple voltage, make it really large, such as 10,000uF.
5) As you have read here, the minimum and maximum voltages at the filter capacitor are crutial:
a) A minimum voltage of at least 33.9V when the project has a 30V, 3A load.
b) A maximum voltage of less than 36.4V when the project has no load, when using the 44V replacement opamp.
If you include a 10% mains voltage variation then these voltages are impossible. Perhaps this project should be rated to only 25V output, and when using changes as above should perform very well with a 24V/4A or 5A transformer.
Hello All I have built this power supply but I got a problem. As soon as I switch it on, the volt meter reads 23.5v and then I try to vary the Volt Pot, it goes up to 35v! In other words, my PSU is only variing from 23.5v to 35v !! I have changed the op amps twice and even tried the TL071 (which is better acording to a friend of mine who read the datasheets) Could anyone help me PLEASE?
thanks a lot
thanks a lot
