Changing voltage in 24v 6A power supply

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SunLike
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Changing voltage in 24v 6A power supply

If anyone know which resistor I must change to change voltage? Now it is 23.63v, must be about 16.4v

ANSWER IS: U4, but minimum operation voltage is 18v, and I do not know how force it to work with 16.4v =(

I am going to use it as a fast charge with SunLike15M https://budgetlightforum.com/node/75377







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Edited by: SunLike on 11/24/2020 - 08:21
Quadrupel
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Yea, i read your mind and i think you looking for this

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Quadrupel wrote:
Yea, i read your mind and i think you looking for this

So, I must change R22?
It was my first idea, but lampman’s helper offer me to change U4

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I just tested R22 — NO

U4 — YES (2401=23.63v +100k=24.17v)

p.s. 3.6k ~16.5v and non operation voltage =(

pps. seems like 18v is minimum operation voltage =(

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kennybobby
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@Quad, you might want to replace that dented 1000uF capacitor?

@Sun, it appears that you are changing the base drive on the U4 transistor, which looks like some sort of feedback for the MB358 op amp. i think there is more to control of the transformer in the middle section, e.g. what is the part number of ic U1?

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drivin' around on fossil fuel,
until i saw what i was doin',
was drivin' down the road to ruin. --JT

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kennybobby wrote:
@Quad, you might want to replace that dented 1000uF capacitor?

@Sun, it appears that you are changing the base drive on the U4 transistor, which looks like some sort of feedback for the MB358 op amp. i think there is more to control of the transformer in the middle section, e.g. what is the part number of ic U1?


where is U1? I can not find it, I find only U2 and U3 marks

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kennybobby
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On the bottom layer, near the center in a block section marked with “14”

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drivin' around on fossil fuel,
until i saw what i was doin',
was drivin' down the road to ruin. --JT

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kennybobby wrote:
On the bottom layer, near the center in a block section marked with “14”

H2798o
really hard to read it

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[edit] U1: is some sort of switching voltage regulator chip but i can’t find that marking code.

U3 is a photodiode optocoupler.

U2 is the MB358 dual op amp.

U4 is a MB431A, a programmable precision voltage reference.

Now i used to think that i was cool,
drivin' around on fossil fuel,
until i saw what i was doin',
was drivin' down the road to ruin. --JT

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Were you measuring current (i.e. supply under load) with your voltage testing above?

Now i used to think that i was cool,
drivin' around on fossil fuel,
until i saw what i was doin',
was drivin' down the road to ruin. --JT

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kennybobby wrote:
Were you measuring current (i.e. supply under load) with your voltage testing above?

no, just voltage. With under 18v was some reload noise and not constant voltage

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Would you be able to read the markings on Q1 and D4(?), the ones that are attached to the heatsinks?

Can you double check the marking on U1—it is not coming up as any part? i use a silver sharpie pen to help bring out the digits, but white chalk or most anything light colored might help identify that component. It controls Q1 to switch the primary side of the transformer, and that is what you need to do to lower the output voltage.

Now i used to think that i was cool,
drivin' around on fossil fuel,
until i saw what i was doin',
was drivin' down the road to ruin. --JT

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kennybobby wrote:
Would you be able to read the markings on Q1 and D4(?), the ones that are attached to the heatsinks?

Can you double check the marking on U1—it is not coming up as any part? i use a silver sharpie pen to help bring out the digits, but white chalk or most anything light colored might help identify that component. It controls Q1 to switch the primary side of the transformer, and that is what you need to do to lower the output voltage.


U1:
H27988
08228(6?)9CP

q1 need remove with diode to read =( I will do it if it is necessary

d4:
ER1004CJ(7?)

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kennybobby
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i haven’t been able to find the U1 chip, but found this diagram that is very close to the primary side control on your device.

Now i used to think that i was cool,
drivin' around on fossil fuel,
until i saw what i was doin',
was drivin' down the road to ruin. --JT

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i have mostly traced out the board, but i can’t tell some of the connections for U2. Would you be able to check where these go?
Does the top of R31 go to pin 6?

Does the bottom of the “106” resistor go to pin 7?

Is there any connection to pin 2?

Now i used to think that i was cool,
drivin' around on fossil fuel,
until i saw what i was doin',
was drivin' down the road to ruin. --JT

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R31 goes to R27 (to top) and to R39, but in R39 there is no resistor

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kennybobby
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i need to verify all the connections to pins 2, 6 and 7, and the bottom of R30—there are hidden traces under the chip so you will need a meter to ring out where they go.

Is there a connection between R28 and pin 2?

Does the bottom of R30 go to pin 7?

Does the top of R31 connect to pin 6?

Now i used to think that i was cool,
drivin' around on fossil fuel,
until i saw what i was doin',
was drivin' down the road to ruin. --JT

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The U1 chip may be an FAN6604 Flyback Converter PWM Controller.

The transformer appears to have a primary and 2 secondary windings; one secondary is the power winding for the DC Output and the other is an auxillary winding to create a low level supply voltage for U1.

The 6604 requires 17V Vdd to start and has an UVLO that will turn it off if Vdd drops below 10V.

The duty cycle of the transformer (and thus the Output DC voltage) is controlled by several sources: the U4 chip and the U2 op amp pulsing the U3 opto coupler; and the current sense resistors (R4-R7) and U3 opto feedback into U1.

Now i used to think that i was cool,
drivin' around on fossil fuel,
until i saw what i was doin',
was drivin' down the road to ruin. --JT

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Here are the “?” areas since i can’t ring out the board over the Thanksgiving Staycation Holiday. Stuck at home, fun little project.

The U4 TL431 is being used as a single-side comparator looking at the Output DC voltage.

There is no current sensing on the Output DC, only on the transformer primary winding current, so some additional BMS or Li cell charging IC might need to be added to use this as a CC-CV charger.

Now i used to think that i was cool,
drivin' around on fossil fuel,
until i saw what i was doin',
was drivin' down the road to ruin. --JT