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Insufficient Power on my Load

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DarkArrow29

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Hi! I have this simple circuit that activates a load, whenever the switch is pressed (shorted). When the switch is released from being pressed, the load will power down slowly. I have already put this up on a breadboard. When the load is an LED, it works! But the actual load that I will use is a 2W MP3 Decoder. The load only receives 17.4 mW (based on my schematic diagram below) but before reaching the LM317, the power is 4.11 W. How can I make the load receive at least 2W. Please help! Thank you!

 

JimB

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The first and fundamental problem is that when you press the switch S1, you will blow the base-emitter junction of transistor Q2.

JimB
 

alec_t

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Both Q2 and Q4 need base resistances, and Q4 is the wrong way round.
Q2 base should connect to C3.
 

DarkArrow29

New Member
Just made a big change, sorry for ignorant use of devices. So my new simulation makes the LED light up at 4.17V. If I will replace the LED with an MP3 Decoder Module with 2W and 3.7 to 5V requirement, how can this circuit activate the said module? See attached file.

Forgot to explain the 'switch'. So the 'switch' is composed of a bolt and a nut on which when bridged by a finger, the "switch" closes.
 

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dknguyen

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Q3 is upside down. Conventional current has to flow in the direction of the arrow on the base-emitter symbol.

Or else Q3 also needs a base resistor to limit current or it will blow. The 9V battery will blow into Q3's collector out of the base and straight back to the battery producing a short without the base resistor.

You don't really need Q3 in this circuit. You could just place R2, R3, and LED1 in series with Q1 (place them between +9V and Q1 collector).

If you place LED1 between Q1's emitter and GND then you might be able omit the resistors because there will be some negative feedback going on there. The LED1 may run brighter/draw more current than you need it to and Q1 will dissipate the heat in place of the resistors though so you may not want that.
 
Last edited:

audioguru

Well-Known Member
Most Helpful Member
The "switch" is a 2k ohms (when sweating) to 20M ohms (when dry) finger so a logic level Mosfet should be used if there is no static electricity from the person.
 
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