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reduce the heat on the regulator

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ahgu

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I have 15V and I need a 5V and I am using a LM340 to give me the 5v. Since the voltage differential is 10v and my current usage is 0.1A. That is a lot of heat on the regulator, Very hot when you put your finger on top of it. Is there any simple way to lower to 15v to 7v and solve my heat problem. I don't want to use switcher, It will be too much extra cost and the noise it generates will affect my audio circuit.

thanks
Ahgu
 

Have you considered suitable heatsink?
You can lower regulator dissipation if you put 56ohm/1W resistor in front of regulator.
 

Hi,
You can use hi watt resistor in series before 5v reg or better use chopper circuit before 5v reg (use 555 with power transistor with small on time and long off time)
 

dual regulating

There are two more ways. One is to use another regulator in front to get 10 V out. This has the beneficial effect of reducing ripple even more. The other method is to use a BJT in front as an emitter follower from a zener. You put a 10 V zener in series with a resistor across the 15 V input. Then you put a BJt with the collector to 15 V the base to the 10 V zener and the emitter to the 5 V regulator. The BJT will have to be big enough to dissipate the 750 mW. It also produces a mild amount of ripple reduction.
 

If the current absorption is roughly constant you can draw say 50 mA with a resistor in parallel the input-output pins of the regulator and let the regulator regulate the other 50 mA.
so, for a current of 50 mA the resistor will be 10V/50mA = 200 Ohm.
The regulator will regulate the other 50 mA.
Take care not to reduce the absorption under 50 mA otherwise the regulating action will cease.

Mandi
 

2W power transistor

I guess I have to find a 2W Q . with the zener+Q method. will the heat be on the Q now?

What about put a 7.5V zener in series at the input? power zener, I guess.

so my Q will get hot instead othe reg?

Also, can I use power mosfet? Cannot get simulation to work with mosfet.
 

transistors cheaper

The heat in the zener-bjt will be in the bjt.

Power transistors like the TIP3x series are much cheaper than power zeners. You can make your own heat sinks from small squares of thick metal.
 

what difference

Then what is the difference? by having heat in reg or in Q? Both are built to be able to handle that much heat. I am using LM340. from the spec, the heat is okay. What I want is to reduce the noise by rising of temperature.

thanks
ahgu
 

it all depends

It all depends upon what parts you have available and how convenient and expensive additional parts are. It looks like you are making just one of these circuits. We gave you a variety of options which you can match with your parts availability and cost.
 

heat

My goal is to NOT have a hot board with 2W dissipated on the PCB. The Q+Zener solution will still give me the heat, right? even though the LM340 can stay below 35celcius. The Q can still get pretty hot, right?
 

stuck

Ther is no way to use a set of analog parts to reduce the voltage without generating heat. Here are some other options.

If you do not mind dumping the heat into the room, heat sink the regulator on the box wall.

Can you get into the power supply and tap off the transformer at a lower voltge to make the 5 V?

Get a 5 V supply.
 

Use PWM step down regulator. You save power but spend money.
 

Hi all
I think u consider my idea of simple fixed PWM before 5v reg
 

switcher for speaker amplifier

Can I use a 200khz switcher as the power supply for a speaker amplifier?
Will I hear a lot of noise on the speaker?

Also, can it adjust to the rapid change of current the power amplifier draws?

Also, any good cheap switcher anyone recommend? about 1A. I used switcher before and I had problem with it, it just died after sometime.
 

any simple 5v switcher? 1A?

any simple 5v switcher? 1A?

cheap and reliable. I had switchers died on me before. LM2575 I used. It just died all the sudden. Don't know why.


hehe
 

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