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buck/boost converter problem..advise appriciated

Discussion in 'General Electronics Discussion' started by von, Sep 6, 2015.

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  1. von


    Sep 6, 2015
    I set 2 buck/boost converters (see specs below) powered by a small ~12 volt solar/battery/ regulator system.
    2 x 80watt pv's, 1 X12v batt, 1 x 10 amp regulatory.
    The 2 buck/boost converters - 1 used & set at 10v output for a laptop (solid circuit, no rotating disc) ~2.2A.
    - 1 used & set @ 14v for an led 22" monitor, 2.3A.
    Both had 2amp fuses on the + lead into the buck/boost converters.
    (So the buck/boost converters replaced the transformers & the correct voltage & polarity was set & used to power my laptop & Monitor.)

    RESULT; The buck/boost converter powering the laptop (Laptop battery in place, so via its battery) powered the battery & laptop, but made a slight buzzing sound coming from the laptop, I adjusted the buck/boost converter to slightly higher voltage output which seemed to quiet it (mostly). Note I have used an Auto laptop converter in the pass with no buzzing & it worked fine, I figured the buck/boost converter would be exactly the same, but perhaps my circuit is missing a component (present in the Auto laptop converters).

    The LED Monitor worked but intermittently would go dark for a second, then the image would reappear. I disconnected the laptop buck/boost converter, but the monitor still malfunctioned in the same way.
    I disconnected the buck/boost converter from the monitor & reconnected it again with the same multifunctional result. On the 3rd attempt in as many minutes < 3 min usage total, the buck/boost converter died & output < 1v.

    Any ideas what I did wrong?

    /boost converters ;
    This module is a LM2577 DC-DC Automatic Buck or Boost Converter 3-35V to 2.2-30V LM2596 Voltage Step-Down Power Supply. IN+ is for positive voltage input. IN- is for negative voltage input.
    That means after you set the output voltage, it can output your desired voltage no matter the input voltage is LESS or GREATER than your desire voltage.
    Step-up or Step-down action is automatic.

    Great for solar panel supply, solar panel input voltage is not constant. Therefore it can output constant voltage

    Module properties: Non isolated, Automatic Buck-Boost (SEPIC)
    Rectifier type : Non synchronous rectifier
    Input voltage : 3V-35V
    Output voltage: 2.2V-30V
    Output current: 2A MAX
    Conversion efficiency: 92% ( highest)
    Switching frequency: 50KHz
    Output ripple : 40mV MAX
    Load regulation rate: ± 0.5% Voltage regulation rate: ± 0.5%
    Working temperature: - 40C to +85C
    Dimension:48 x 24 x 14mm

    Typical output, do not need heatsink (reference)

    Input 12V----Output 12V/2A; 24W
    Input 12V----Output 5V/3A; 15W
    Input 12V----Output 13.8V/1.8A; 25W
    Input 5V----Output 3.3V/3A; 9.9W
  2. Alec_t


    Jul 7, 2015
    Welcome to EP!
    Converter :-
    Monitor :-
    Do you see the problem there?
    von likes this.
  3. von


    Sep 6, 2015
    Thanks for your reply, I should add my understanding of electronics is very very basic, but keen to develop, so I probably need things spelt out at my fledgling position :)
    So are you suggesting that my amps may be too low? 1.8A which should be 2.3A.
    I didn't measure the Amps (worried about shorting the circuit) Ironically the monitor is rated to run at 12v to 14v. I do have 1 spare buck/boost converter, I could sacrifice it. But even Input 12V----Output 12V/2A; 24W is not 2.3A. So I guess that won't work either?
    So not having enough Amps kills the buck/boost converter (for the monitor)? I would have expected the monitor to just not work, or does the low amps represent a short to the Input buck/boost converter? Again I would have expected the 2A fuse on the + input line to blow first.

    So the higher the buck/boost converter voltage output the lower the Amps?
  4. Alec_t


    Jul 7, 2015
    You've sussed it. Your monitor needs more current than the converter can provide. You need a higher power rated converter.

    Correct. You can't get more power out than the rated value without cooking something. Power(W) = current(I) x volts(V),
    There's a well-known saying: "the transistor is there to protect the fuse" ;). Transistors can be destroyed in milliseconds, whereas fuses are comparatively sluggish.
    von likes this.
  5. AnalogKid


    Jun 10, 2015
    Can you post a datasheet on the converter module or a link? The 2577 is typically used as a bock only converter, not buck-boost?

  6. von


    Sep 6, 2015
    "the transistor is there to protect the fuse" ;).

    Big thanks, Makes total sense now. I should be able to id the 1 of 3 transistors & replace the cooked 1.
    So I could also be able to wire the output of 2 of the
    DC DC Buck - Boost Modules
    in series?
    If each Buck - Boost Module is set at 7volts output - the combination would give me 14v.
    However I'm guessing that would probably give me ~2.5A + ~2.5A = ~5A which would probably kill the led monitor & my wattage would be in the 70's more than the monitor's required 22W.
  7. von


    Sep 6, 2015
    Thanks AnalogKid
    My posting spec's above were from my own notes from early searches.
    Below is the info provided from the seller (the most accurate I think), & below that the same item from another vendor;

    Technical parameters: DC DC Buck - Boost Module

    Model Specification DSN6000AUD Automatic Buck module
    Module Properties:Non- isolated boost (BOOST)
    Rectification:Non- Synchronous Rectification
    Input Range:3.8V ~ 32V
    Output Range:1.25V ~ 35V
    Input Current:3A ( max ) , no-load 18mA (5V input , 8V output , no-load is less than 18mA. Higher the voltage , the greater the load current . )
    Conversion efficiency:< 94% ( greater the pressure , the lower the efficiency )
    Switching frequency:400KHz
    Output Ripple:50mV ( the higher the voltage , the greater the current , the greater the ripple )
    Load Regulation:± 0.5%
    Voltage Regulation:± 0.5%
    Operating Temperature:-40 ? ~ +85 ?
    Dimensions:48mm * 25mm * 14mm ( L * W * H )

    2nd vendor (I think the above description is the most accurate, but again its new to me so maybe there is a lot of variations available)
    This neat little power supply board is super useful for your gadgets drawer.

    What makes them so handy is that they are a SEPIC, otherwise known as a Buck-Boost, or Step-Up Step-Down DC-DC converter.

    That means that once you set the output voltage, your input voltage can be lower, or higher than the output, and the output stays the same.

    Input: 3 to 35v
    Output: 1.25 to 30v
    Maximum output power: 12w without heatsink, 20w if you slap a nice heatsink on the bottom of the board (not included)
    Maximum current (either end): 2 Amp but remember the power limit above.

    Especially useful for little power harvesting and alternative energy projects like solar where your panel will produce wildly different voltages depending on the available sunlight, hook one of these babies up to stabilise that voltage.

    Based on the LM2577, usage is simple, connect your input voltage on one end, and take your output from the other, the trimpot adjusts the output. So just use your multimeter to set it as required.

    They are pretty high efficiency - varies by the input/output ratio up to around 92% in the best conditions but you are more likely to see around 80 to 84%, still vastly better than a linear regulator!

    3rd vendor
    Hard to find decent specs on them.This is the specs from .alibaba (close as I can get to their manufacture)note the coils? have #407 on them, mine & the above vendors have #101

    XL6009 400KHz 4A switching current booster module

    Baby Description:

    Auto start voltage will be pulled down to 7V less or smaller engine at high speed when the voltage up to 15V or higher. For 12V electrical work hard at work, this automatic buck module solves this problem, regardless of the input voltage is 5V or 12V or 32V, the output can be stabilized at 12V.

    Wide input voltage 5V ~ 32V;

    Wide Output Voltage 1.25V ~ 35V (with automatic buck, scope of work, any voltage inputs can be arbitrarily regulated voltage output);

    Built-4A efficient MOSFET switches enable efficiency up to 94%; (LM2577 current is 3A)

    high switching frequency of 400KHz, the ripple is smaller and smaller. (LM2577 frequency only 50KHz)


    Car regulator, solar photovoltaic, wind power and other applications of voltage instability.

    Technical parameters: Wouldn't copy for me, see their link above.
    Last edited: Sep 6, 2015
  8. Alec_t


    Jul 7, 2015
    I doubt it. The spec says they're non-isolated, which presumably means the output and input share a common ground.
    von likes this.
  9. von


    Sep 6, 2015
    Thanks, (I have made errors in the above threads 1st error I meant connecting the buck/boost in Parallel, & by coils I meant inductors)

    so still searching for a solution.
    Correct (I) Amp output (& voltage) is necessary & A x V = W (so Watts will be correct if the A & V output values are correct.
    So I need a module with adjustable A (aswell as V).

    Would Connecting in series, 2 (A&V) adjustable modules work? Or is the common ground an issue? If so - anyway I get get around that?
    In this case a boost (1st) & then a buck (2nd) to drop the v down to 14v

    Here's the specs of the 2 modules I have in mind;
    1st - DC DC boost converter Constant Current Mobile Power supply 250W 10A LED Driver

    Input Voltage: 8.5V-48V (48V maximum)
    Input Current: 10A (max) if exceeds 8A please include heat dissipation
    Quiescent current: 10mA
    Output Voltage: 10-50V (adjustable)
    Output Current: 10A (max) if exceeds 6A please include heat dissipation
    Output Power: Approx. 250W
    Operating Temperature: -40 to 85 degrees
    Operating frequency: 150kHz
    Dimension: 36 (L) x 70 (W) x 13 (H) mm
    Weight: 50g

    This Boost converter has overcurrent protection (input exceeds 13A) and reverse polarity protection capability.

    & 2nd - This is a non-isolated step-down, non-synchronous DC DC switch mode converter module.

    This module uses high-quality and high efficiency ICs, in conjunction with the original TI op amp to control the output current to produce very stable output. The module also uses low ESR Sanyo original filter capacitor which reduces the ripple voltage to as low as 50 mV.

    -Normal blood pressure modules
    -Battery Charger
    - High-power LED constant current driver module
    - Any applications that requires constant current constant voltage

    Input voltage: 5V - 32V
    Output voltage: 0.8V -30V
    Output Current: 5A maximum (Adjustable)
    Efficiency: up to 95%
    Switching frequency: 300KHz
    Output ripple: 50mV (maximum)
    Load Regulation: ± 0.5%
    Voltage Regulation: ± 2.5%
    Operating temperature: -40 ? to + 85 ?
    Size: 51mm (L) x 26.3mm (W) x 14mm (H)
    Overcurrent protection capability :Yes

    if more than 3A or 35W is used, please include fan or heat sink for heat dissipation purposes

    Last edited: Sep 7, 2015
  10. BobK


    Jan 5, 2010

    I think you have some misunderstanding of how power supplies work.

    First of all, what you need is a power supply that can supply the needed voltage and more than the needed current. You do not have to set the current, the device you are powering takes only as much current as it needs. So, if your device needs 12V at 2.3A, using a power supply that is rated at 12V 3A is good. Using one that supplies 12V 2A is bad (as you found out). Using one that supplies 12V at 10A will not harm anything, and there will be less stress on the power supply making it run cooler and probably last longer.

    Secondly, you cannot set both the voltage and current on a power supply. They have two modes of operation:

    1. Constant voltage. The voltage is set and the load (powered device) decides how much current to draw.

    2. Constant current. The current is set, and the power supply adjusts the voltage such that the load draws that amount of current.

    You need 1, the constant voltage supply.

    Also, if you have a device that can take a range of voltages, the current will vary with the voltage you give it, but it is not easy to predict how. It depends on how the device works internally. If there is no further regulation inside the device, it will probably draw more current at a higher voltage. But, if the device itself includes a switching converter, it will be the opposite, it will take more current at a lower voltage in order to provide the same amount of power.

    My advice: Get a buck / boost converter that can put out 3A or more, and add the heat sink if it is required, or even close to being required.

    Hope this helps.

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