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Nominal power supply voltage
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You can use? q3.8. Pl dont again say + /- All the best.? On Fri, 3 Apr 2020, 12:56 pm Christopher Miller, <djmalak2k6@...> wrote:
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Ian Reeve
¿ªÔÆÌåÓý
I use 12 volts but a higher voltage can be delivered to just the PA feed to boost the rf output.
Get
From: [email protected] <[email protected]> on behalf of Christopher Miller <djmalak2k6@...>
Sent: Friday, April 3, 2020 8:26:22 AM To: [email protected] <[email protected]> Subject: [BITX20] Nominal power supply voltage ?
Hello,
I am currently feeding 12 volts in to my v3 uBitx. I was wondering if I should be using 13.8 volts. Will that blow up the 5 volt regulator?
Thanks,
Chris KF4FTR
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Sorry. I sm withdrawing my statement.? V3, the TDA2822 WILL LIKELY GET DAMAGED AT HIGHER VOLTAGE.? LIMIT TO 12.? After all you can reduce 13.8 to 12 by some pot on the psu.? On Fri, 3 Apr 2020, 1:05 pm Mvs Sarma, <mvssarma@...> wrote:
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Ian Reeve
¿ªÔÆÌåÓý
In the v3 the audio output chip is at its limit with 12 volts,the PA can be run from say 15. or a bit more for increased rf output
Get
From: [email protected] <[email protected]> on behalf of MVS Sarma <mvssarma@...>
Sent: Friday, April 3, 2020 8:37:51 AM To: [email protected] <[email protected]> Subject: Re: [BITX20] Nominal power supply voltage ?
Sorry. I sm withdrawing my statement.? V3, the TDA2822 WILL LIKELY GET DAMAGED AT HIGHER VOLTAGE.?
LIMIT TO 12.?
After all you can reduce 13.8 to 12 by some pot on the psu.?
On Fri, 3 Apr 2020, 1:05 pm Mvs Sarma, <mvssarma@...> wrote:
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Thanks, I was lucky enough to be given a complete transceiver I don¡¯t want to mess with cutting traces and modifying it until I have everything set up. I just wanted to make sure I didn¡¯t need to increase the voltage. Chris On Fri, Apr 3, 2020 at 12:38 AM Ian Reeve <ian.radioworkshop@...> wrote:
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On the v3 I have found a slight but noticeable decrease in the sound quality when I have increased the voltage to the receiver. I suspect that the op amp is being overdriven. The easiest way to limit the voltage to the receiver was to forward bias a diode or two in series with the power input connector.? The finals can handle much higher voltage.? You don't need to touch directly on the board.??
Touch the 2822 chip after the radio has been picking up strong signals for a while. If it is warm consider making a change in the input voltage to the receiver. Unless you know exactly what you want to do don't go modifying anything on the board. Nearly every uBITX that I have repaired had some modification done by an owner who really did not grasp what they were doing. Repair mostly involves undoing what they "improved", including repairing traces. 73 Dave |
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Christopher,
The LM7805? 5 volt regulator can take up to 35 volts, The regulator issue with the higher voltage is the thermal power dissipation goes up as the input voltage goes up.? The stock display with no other mods would be within the thermal capabilities, though it will run "hot".? If you add other things to the 5 volt rail, like a graphic display, then the device might shut down and cause strange things to happen.? Adding a heatsink to the regulator helps, and I have done this when a 2.4" Nextion was added. As Dave said, the main issue with the v3 at higher input voltage levels is the audio output device, a TDA2822.? The increased power that the TDA2822 can produce goes beyond the thermal dissipation system (none) that is in the stock build.? the datasheet states that the maximum input voltage is 15, so just the higher voltage would not destroy it, the increased power at high volume levels has in the past per posts on this board. If you already have a good 12 volt 2.5 amp or better supply, then there is not really any need to go to 13.8 volts.? The slight increase in power output is not really noticeable on the receive side.? With that understanding, you CAN split off the power amp (PA) without cutting any traces.? The power connector on the board has three pins: ground, mainboard, and PA.? What some have done is to put diodes between the PA and mainboard to drop the voltage to the mainboard.? Each diode would provide about 0.6 volts forward voltage drop, so for 13.8 volts two diodes should do it.? I would do this (and have for my v4) only if I did not have a 12 volt 2.5 amp supply for the v3.? The other versions do not have the audio IC issue. Dave's advice on making sure you know what, and how, to make a given modification is sound.? It is a rig that was built with tinkering in mind, however, you should study up on what you are going to do and be prepared to fix the results if it doesn't go as plan.? That is the learning experience in this kit. 73 Evan AC9TU |
¿ªÔÆÌåÓýThe max voltage for a TDA2822 is 15 volts, according to the datasheet.? A car battery charging voltage is between 13.4 and 13.8 volts, usually 13.8.? A fully charged battery will be higher than 12 volts (if I remember right, ~13.4).? Look it up and look at the max ratings (which appear to have a bit of a safety factor built in), as well as the Quescent Current graph.?If it was that sensitive to voltage over 12, it would not be usable in a mobile setting.? 13.8 should be fine. Bob N4FBZ On 4/3/20 3:37 AM, MVS Sarma wrote:
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Perhaps datasheet is correct. But with multiple manufacturers , the situation changes. Mist of these are made for pocket fm and tape recoders. They work well at 3 to4.5v.? Hence many of us have changed 12v supply to tda2822 alone as 8 or 9v.? Many suffered damages plugging mono plugs on earphone socket.? ?Thus i advised to work woth safety margin.? On Fri, 3 Apr 2020, 7:53 pm Robert D. Bowers, <n4fbz@...> wrote:
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¿ªÔÆÌåÓýA simple solution is to add heat sinks - no changing the board (a little bit of metal as a fin works great)!? (You can add them to the top of chips!)? Also, a tiny fan to move air through the radio is a good idea - that's what I did to my old BitX20 V3b (with the airflow crossing the board and being pulled out near the finals).A good rule of thumb is "If you're comfortable, your electronic equipment is also!"? The only difference is when you have something like an oscillator that needs thermal regulation to not drift, such as a VFO. On 4/3/20 8:43 AM, Evan Hand wrote:
Christopher, |
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Hi,
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I do not want to diss anybody who has reported the loss of the audio IC in a V3 due to using supply voltage above 12.00 volts. I recall that some of the ICs were not up to spec and those probably all died. I have been using sealed lead-acid batteries with my "12 volt" gear including my V3 uBitX. That means I apply voltages only very slightly under 14 volts with fresh fully charged batteries. That voltage quickly drops to around 13.5 to 13.8 volt but stays at those levels for quite a while. One of the posts mentioned the higher power dissipated in that audio chip with the higher voltages. I do not drive a loudspeaker with mine. Using the cans requires less audio power AND the volume control is backed down, too. If mine does fail I will replace it with something more robust :) Now what did I do with those 6V6 vacuum tubes? 73, Bill KU8H On 4/3/20 10:20 AM, Robert D. Bowers wrote:
The max voltage for a TDA2822 is 15 volts, according to the datasheet. A car battery charging voltage is between 13.4 and 13.8 volts, usually 13.8.? A fully charged battery will be higher than 12 volts (if I remember right, ~13.4).? Look it up and look at the max ratings (which appear to have a bit of a safety factor built in), as well as the Quescent Current graph. --
bark less - wag more |
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For general information of the group:???? The electrical datasheet for my 2011 Chevy Silverado shows 5 Battery Charging Modes of Operation.? Generator Output Voltages?range from 13.9 Volts to 15.6 Volts.?? The instrument panel is commanded to display a WARNING if it detects a voltage greater than 16 Volts. GM Document ID 2614222 Bob WB8BEL From: "Robert D. Bowers" <n4fbz@...> To: [email protected] Sent: Friday, April 3, 2020 10:20:45 AM Subject: Re: [BITX20] Nominal power supply voltage If it was that sensitive to voltage over 12, it would not be usable in a mobile setting.? 13.8 should be fine. Bob N4FBZ On 4/3/20 3:37 AM, MVS Sarma wrote:
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Cristian Radulescu
Hi all. While working on the Tulip SDR I had the same problem supplying TDA2822 with more than 12 V. As a matter of fact, many of the "alternate producers" warrant the device to a max. of 12 V supply voltage. Searching the data sheets I found the NJM2073 to be pin-to-pin compatible with a little lower gain. Try this solution as it doesn't generate any cost. 73's de YO3IAZ,Cristian |
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=Vic='s suggestion of a three-terminal regulator to drop the voltage from the PA voltage is a good one, as long as you follow the specs for the regulator.? An LM7812 would be one choice as long as the PA voltage will be over 14.5 volts (the spec says a minimum of 2 volts for dropout, but the output voltage specs 14.5 as a minimum).
Others have used buck/boost regulators.? That removes the requirement on the PA minimum voltage.? The disadvantage is finding one that has a low noise figure or adding filtering and shielding (mounting outside of a metal case that houses the uBiTx). Since I am using a 13.8 volt ham base supply from TekPower, I have installed 2 diodes in series to reduce the voltage to the mainboard.? 73 Evan AC9TU |
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I am using a 7812 in mine, and even with supply voltages of closer to 12v, the output is still around11v, which is plenty for the uBitX main board, so don't be concerned if you have low supply voltage. It is there in mine as sort of an insurance policy against high voltages...I see around 14.4v in a car that is running at times, but has not been adversely affected by running on a partially discharged Lithium power pack at under 12v.
=Vic= |
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Ok, I just wanted to ask because I had a commercial rig and for a while I couldn¡¯t make contacts. I had to set the voltage from my supply to 13.8 volts. I just wanted to be sure that I wasn¡¯t making the same mistake.? I will probably get a small amp, but I don¡¯t plan on running the radio hot. It¡¯s working and I don¡¯t want to break anything. Chris? |
_Dave_ AD0B
Vic WA4THR
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