Insufficient Power on my Load

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!

Have you ever studied/interested in electronics ??? You should..

the 558 is upside down - top left, you are getting the reverse gain ( ~ 7 ) instead of the fwd gain ~ >200...

Also for current >100mA you need a bigger pnp xtor ...

A few problems there....

1. closing the switch destroys Q2.
2. no bias current to Q4.
3. you are demanding about twice the maximum rated current from Q4.
4. no input or output capacitors on U1.

Brian.

yes - Q2 needs a base resistor to limit current to a few 100 uA, ditto for Q4, a few mA, Q4 E-C need swapping, the LM317 needs input and output caps to be stable - read the through the data sheet carefully ...

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.

BC558 still reversed, see post #3. If "finger" refers to touch control, the circuit will hardly work reliably. Need more sensitivity, clear on-off decision, noise suppression. Better use a capacitive touch sensor IC.

Hi,

I'm not very skilled at biasing BJTs and I think maybe you want to read up on the subject a little too

You could see if this rudimentary version suits your needs, it has a TIP30 as the PNP as that seems to be a go-to medium power BJT for this kind of thing...





I would also still consider using a voltage regulator as the switch device... Guaranteed 3.7V TO 5V out - maybe by putting a suitable PNP between the supply voltage and the regulator input pin. A regulator with an enable pin would make that all easier.

Hi,

This is basically what I meant. You can replace that circuit with the LM317 and the switch between V+ and regulator Vin. The LM317 Spice model has some fault in the script apparently so I was unable to use it, what a shame (...nor do I want to much as it has a slightly irritating "heatsink" pin and I have little inclination to learn that you need to connect a voltage equivalent to ambient or junction temperature or whatever three hours of searching online will eventually trawl up - I'm certain that pin is useful, just not for simple circuits...)

Anyway, you can use the TL431 as an error amplifier and make a simple regulator from it (plus whatever regulating device/circuit is being used). I'm sure that with a little Internet research the circuit can be improved.

Notice the much better dropout voltage by using a MOS transistor rather than a BJT. The BJT would need to be a modern part that has low equivalent RDSon, the TIP31 was useless here with only 9V available, and even then the NSS60601 (low equivalent RDSon and ~very low VCE) can't really compete with an average low VGS mosfet.