power supply question

[karombal]

yung application ko po kasi nangangailangan ng power supply na 5V..
so transformer - bridge rectifier - capacitor filter - voltage regulator (7805)

bale tumingin-tingin ako para makabili ng transformer.. kasi kailangan ko sa application ko ng power supply.. nakita ko yung mga transformer 220V to 9V... pero may 200mA, 750mA, etc... ano po ang kaibahan nito at paano sila gamitin?

ang problema ko po.. yung gamit ko 200mA.. pero nung kinabit ko na yung supply sa application ko na PIC.. umiinit po mashado yung 7805.. at kung op amp bias lang naman kinabitan ko nung same supply hindi naman sha umiinit.. ano po kaya ang principle na magagamit dito para masolusyonan ko ang problema?

[mArKhAo]

baka may mali sa circuit mo sa pic interface.. ?  check mo baka may shorted... delikado PIC mo baka masira

[marcelino]

yung application ko po kasi nangangailangan ng power supply na 5V..
so transformer - bridge rectifier - capacitor filter - voltage regulator (7805)

bale tumingin-tingin ako para makabili ng transformer.. kasi kailangan ko sa application ko ng power supply.. nakita ko yung mga transformer 220V to 9V... pero may 200mA, 750mA, etc... ano po ang kaibahan nito at paano sila gamitin?

ang problema ko po.. yung gamit ko 200mA.. pero nung kinabit ko na yung supply sa application ko na PIC.. umiinit po mashado yung 7805.. at kung op amp bias lang naman kinabitan ko nung same supply hindi naman sha umiinit.. ano po kaya ang principle na magagamit dito para masolusyonan ko ang problema?

check ko lang.,.. 220Vac - 9Vac.. then rectifier. ~9V yan kung walang capacitor. however, kung may capacitor na Vout= ~1.414*9V = 12.7V (nearly 13V).
at that voltage, 7805 ic regulator really create lots of heat. but don't worry 5V pa din ang out nyan.

ganito ang explanation sa akin ng mga master dyan. sabihin na natin na 13V na yung output nung power supply mo. therefore, [12-5], you will have an excess of 7V. after that, 7V times the current consumed = the heat dissipated on the 7805 (in watts). kung gusto mong di yan iinit, lower the input voltage.

ang ginagawa ko nyan ay maglagay ng isang rectifier diode/s sa unahan... BTW, ang bench power supply ko ay ATX power supply from PC. so, 12V lagi.






sa unang image, maaring inputan ng AC. and another thing, dalawang rectifier diode ang dinaanan. meaning ~1.4V na ang nawala...

sa pangalawa, nagwowork to saakin. at di na umiinit ang 7805. perhaps, most atx power supply is actually, less than 12V (yellow wire), minsan 11.8V lamang. kapag nabawasan ng .7, magiging around 10V nalang. siguro, at 10V ok na ang 7805. but, really, wala nang init sa 7805 saakin. check mo nalang sa datasheet.

nga pala, it is good to add 100nF ceramic disk on the input (to the ground) ng 7805. 

[karombal]

maraming salamat bossing..

^ ngunit nagdedepende po ba ang pag-init nung 7805 sa nakakabit sa output nito?
kasi kapag hindi naman PIC ung su-supply-an ko.. hindi sha umiinit..

and then ano difference ng mga current rating ng transformer? (200mA, 750mA, 1A)
para malaman ko ano mas bagay gamitin sa aking application..

[marcelino]

^ ngunit nagdedepende po ba ang pag-init nung 7805 sa nakakabit sa output nito?
kasi kapag hindi naman PIC ung su-supply-an ko.. hindi sha umiinit..

kung ganito ang case, may short sa board mo...

nga pala ano pang nakakabit sa board mo? sa tingin mo kaya, mag-eexceed sa 1A?

and then ano difference ng mga current rating ng transformer? (200mA, 750mA, 1A)
para malaman ko ano mas bagay gamitin sa aking application.. Smiley

yan yung mga current na pwedeng ibigay ng transformer. meaning, di ka na pwedeng mag-exceed sa mga currents na yan. pweden masunog yan. mahahalata mo kung malapit ka na sa mga current na yan yung consumption mo, umiinit na ang transformer.

[Mayalin22]

some good practice to remember before applying voltage to the board.. as much as posible remove first the IC's or Micro before powering the board... then check the vdd and gnd pin of each IC's or Micro if it is on the correct level. Once confirmed then power down the board and put the IC's or Micro.  

[marcelino]

some good practice to remember before applying voltage to the board.. as much as posible remove first the IC's or Micro before powering the board... then check the vdd and gnd pin of each IC's or Micro if it is on the correct level. Once confirmed then power down the board and put the IC's or Micro.  

well said...

pero, most of the time, di ko to nagagawa. excited eh! eheheh

[blackfin]

Kapag na check mo na wala kang shorted pins, etc.  yung PIC microcontroller mo ang nag dradraw ng more than nominal current. Check mo yung code mo baka meron kang loop na walang break or meron kang maling gamit ng port feedback.

[Mayalin22]

well said...

pero, most of the time, di ko to nagagawa. excited eh! eheheh

in fairness... pag medyo kabisado mo na di ko rin nagagawa pwera na lang pag maraming involve na chips he he he  

[TinTopHack]

maraming salamat bossing..

^ ngunit nagdedepende po ba ang pag-init nung 7805 sa nakakabit sa output nito?
kasi kapag hindi naman PIC ung su-supply-an ko.. hindi sha umiinit..

and then ano difference ng mga current rating ng transformer? (200mA, 750mA, 1A)
para malaman ko ano mas bagay gamitin sa aking application..

Ang paginit ng 7805 will depend on the current drawn by the load. The more current drawn by the load the higher will be the power dissipated by the 7805, the more na iinit sya. For this reason pag malaki ang load current mo, dapat maka heatsink ang 7805.

Transformer current rating - ito yung max current na kaya i-supply ng transformer. Depende sa load mo pwede na less than the rating ng transformer ang kukunin nyang current. For example: 200mA transformer
tapos your load needs only 100mA - 100mA lang ang higupin nya from the transformer. This means pwede mo pa dagdagan ang load mo. Pero if your load needs more than 200mA, di kaya ng transformer mo, iinit ang transformer mo at possibleng masira. Kelangan mo palitan ng transformer with higher rating.

Suggestion:

First remove your PIC IC from the board. Apply power to the board from your 7805. Dapat hindi sya iinit kasi dapat maliit lang ang current consumption under this condition. Pero kung uminit na sya at this time, me problema ka sa board mo. If this is the case then turn power off and using an ohmeter measure the resistance between the ground and +5 terminal on the board. Normally you can expect a resistance of 1K or more depende sa components on the board. If below 1K or below 100 ohms talagang me partial short ka somewhere on the board.

It might help if you can post your schematics here so we can help you further.

[karombal]

Ang paginit ng 7805 will depend on the current drawn by the load. The more current drawn by the load the higher will be the power dissipated by the 7805, the more na iinit sya. For this reason pag malaki ang load current mo, dapat maka heatsink ang 7805.

Transformer current rating - ito yung max current na kaya i-supply ng transformer. Depende sa load mo pwede na less than the rating ng transformer ang kukunin nyang current. For example: 200mA transformer
tapos your load needs only 100mA - 100mA lang ang higupin nya from the transformer. This means pwede mo pa dagdagan ang load mo. Pero if your load needs more than 200mA, di kaya ng transformer mo, iinit ang transformer mo at possibleng masira. Kelangan mo palitan ng transformer with higher rating.

salamat po sa accurate answers..

wala po akong short dun sa application circuit ko.. mashado lang po lang talaga ata maraming drawn current.. bale supply ng PIC, LCD, at mga LEDS...

actually hindi ko pa kasi alam kung pano magpost ng images dito.. >_<

[Mayalin22]

gano kalaki LCD mo at ilang LED gamit mo?

[karombal]

gano kalaki LCD mo at ilang LED gamit mo?

eto na lahat ng apps ko:
20x4 na lcd w/ backlight..
tapos may 3 LED na control ng PIC..
gamit ko rin yung 8 inputs na analong-ins..
at 2 pushbuttons na naka pullup (kung nakapinindot mapupunta sa ground)..

sabi ng kaibigan ko gamit daw ako ng pass transistor dun sa supply circuit hehe..

[marcelino]

20x4 na lcd w/ backlight..                = kunyari 300mA
tapos may 3 LED na control ng PIC..  = kunyari uli 10mA each (malaki nga to),times 3 =  30mA
at 2 pushbuttons na naka pullup (kung nakapinindot mapupunta sa ground)..... = maaring magresult to less than 1mA each kapag pinindot.

di pa yan 500mA....

ano ba ang load ng 8 inputs sa ADC?

nagawa mo na ba yung procedure na sinabi ni tintophack?

[TinTopHack]

Tama si Marce.  Ang LCD mo with backlight will at least draw 300mA.

Are you connecting your LCD backlight directly to 5V? If yes lalong malaki ang current consumption yan. Most 20x4 LCD display modules has a LED backlight and the forward voltage drop for the LED backlight is 4.1 to 4.6V and a forward current of 280mA. The most common mistake made is to connect the LED backlight directly to 5V kasi konti lang ang difference. BUT this will draw a large current >500mA from your 5V supply and will shorten the life of your LED backlight. I hope you did not commit this mistake.

Usually I put a 4.7-ohm 2W resistor in series with the backlight to make sure the current drain is less than 280mA. The current will be less than 200mA and the backlight will be slightly dim pero malinaw pa naman ang display. You can adjust the value down to 3.2 ohms kung gusto mo mas maliwanag.

Another way is to connect a diode in series with the LED backlight so that you get 4.3 to 4.4V sa backlight while 0.6 to 0.7 sa diode.

Tapos as Marce has said may current consumption pa ang ibang part ng circuit mo so talagang iinit ang 7805 mo.
Kaya lakihan mo ang heatsink. If the input to your 7805 is 12V ang drop on the 7805 will be 7V. Power dissipation will be 7 x 0.3A minimum = 2.1W minimum na. If you are connecting your LED backlight directly to 5V the power dissipation will be at least 7 x 0.5A = 3.5W na!!!

I hope this helps further.

[Mayalin22]

much better kung pwm mo ang backlight... maku-control mo pa ang contrast thru software 

[marcelino]

^ i remembered when i first committed a mistake about that power dissipation. i used an 18V supply to a 7805 din yun... so kung sabihin na din natin na 500mA yung total consumption ko. may lcd din kasi yun.

.5* (18-5) = .5 *13 = 6.5watts!!! hehehhehe... malapit na sa 10watts. di ba may soldering iron na na 10watts???

much better kung pwm mo ang backlight... maku-control mo pa ang contrast thru software 

oi, ok yan ate ah!!! naisip ko lang yung on and off... but not PWM!

[karombal]

ano ba ang load ng 8 inputs sa ADC?

yung inputs ng adc mula sa opamp circuit na may input na galing sa phototransistor.. bale puro 4.2-5V pumapasok sa mga ADC..

Are you connecting your LCD backlight directly to 5V? If yes lalong malaki ang current consumption yan. Most 20x4 LCD display modules has a LED backlight and the forward voltage drop for the LED backlight is 4.1 to 4.6V and a forward current of 280mA. The most common mistake made is to connect the LED backlight directly to 5V kasi konti lang ang difference. BUT this will draw a large current >500mA from your 5V supply and will shorten the life of your LED backlight. I hope you did not commit this mistake.

Usually I put a 4.7-ohm 2W resistor in series with the backlight to make sure the current drain is less than 280mA. The current will be less than 200mA and the backlight will be slightly dim pero malinaw pa naman ang display. You can adjust the value down to 3.2 ohms kung gusto mo mas maliwanag.

Another way is to connect a diode in series with the LED backlight so that you get 4.3 to 4.4V sa backlight while 0.6 to 0.7 sa diode.


Tapos as Marce has said may current consumption pa ang ibang part ng circuit mo so talagang iinit ang 7805 mo.
Kaya lakihan mo ang heatsink. If the input to your 7805 is 12V ang drop on the 7805 will be 7V. Power dissipation will be 7 x 0.3A minimum = 2.1W minimum na. If you are connecting your LED backlight directly to 5V the power dissipation will be at least 7 x 0.5A = 3.5W na!!!

i did connect directly connect to the 5V.. >_< ttry ko gawan ng paraan.. ano kaya mas maganda iconnect in series? yung resistor or diode?

after all that, anong kayang transformer rating ang ok sa supply ko? 220V~6V na kasi susunod nung 220V~9V eh, (and what current rating?).. kung yung 6V, aabot ba sha dun sa 5Vdc after ng bridge rectifier?

.5* (18-5) = .5 *13 = 6.5watts!!! hehehhehe... malapit na sa 10watts. di ba may soldering iron na na 10watts??? Grin Grin Grin

hahahha..   actually soldering iron na heat na rin naiisip ko nung hinahawakan ko yung 7805..  

[Mayalin22]

oi, ok yan ate ah!!! naisip ko lang yung on and off... but not PWM!

madalas ko gawin pag libre yung ccp pin. 

pwede ka rin kumuha ng power source sa incoming unregulated power supply... compute mo na lang series resistor mo. 

[marcelino]

after all that, anong kayang transformer rating ang ok sa supply ko? 220V~6V na kasi susunod nung 220V~9V eh, (and what current rating?).. kung yung 6V, aabot ba sha dun sa 5Vdc after ng bridge rectifier?

ano kaya kung bumili ka nalang nung 5V smps (1A at least) type power supply. meron sa e-gizmo.  220pesos, 5V-1500mA.
http://www.e-gizmo.com/pmaster.php?dpage=PRODUCT/ELECTRO/ADAPTER.HTM

nung nawala ang phone ng misis ko, samsung, ginamit ko na yung charger nya as power supply sa MCU circuits ko... sakto 5V kasi  (1A rating).

but for your question, using 6V transformer with fullwave rectifier configuration it will be nearly 1.414* 6V = 8.484V (may capacitor na to).