Hi there,

I wish to build a circuit, but without a mechanical or ssr relay.

My concept is to drive a white diffused 5mm Led diode if there is no wall dc power (5v) from the internal (5v) battery power supply.

Can someone give me some ideas?

Thank you!

Kind regards,
Viktor

 

A simple diode pair may suffice. What current does the LED draw?

 

A simple diode pair may suffice. What current does the LED draw?

Hey Alec_t,

Thank you for the fast response!

I think it's 20-30mA

 

Do you mean that the LED is on only when the wall power is off, or is it on in both cases?

 

Do you mean that the LED is on only when the wall power is off, or is it on in both cases?

Hi kubeek,

Only first case you mentioned and vice versa (like I would have a two contact standard relay).

1. LED is ON when the wall power is OFF
2. LED is OFF when the wall power is ON

Kind regards

 

Then this should work

 

Just replace the solar panel with your wall wart and a resistor to limit charging current.

 

Then this should work

Thank you, I will make it on a breadboard and report!

 

Just replace the solar panel with your wall wart and a resistor to limit charging current.

View attachment 131804

View attachment 131805

Coil?

 

I think Dick posted that into a wrong thread.

 

The solar charger is pretty simple. When there's sunlight (AKA voltage) the battery is charged. When there's insufficient sunlight the battery discharges through the LED.

 

I think Dick posted that into a wrong thread.

This is a solution to the problem presented.

The solar charger is pretty simple. When there's sunlight (AKA voltage) the battery is charged. When there's insufficient sunlight the battery discharges through the LED.

Yes, true, except when operated from a wall wart the wall wart will charge the battery.

Coil?

This circuit is the same as the Joule Thief with a little circuitry added (note the added circuitry is similar to kubeek's solution in post #6 so you know its got to be good. Any coil that will work in a joule thief will work here.

Just about anything you can get your hands on will work. Generally the higher the inductance the better.
If you aren't designing this as part of a commercial product, you have a lot of latitude in the design of the inductor. The size of the core, its permeability, and its saturation characteristic (Physical dimensions, u and Bs) determine how many amper-turns it can sustain before it saturates. If the core saturates before the IR drop from tap to collector approaches the battery voltage, the circuit will switch quickly anyway because saturating the core makes the coil look like a resistor and coupling between the collector half and the base half (the side with the 1k resistor) drops to very little, so the effect is the same as the IR drop approaching battery voltage. The wire size determines how many amps the circuit will dray (well, ok, milliamps) before the IR drop gets large enough for the circuit to switch. The inductance constant of the core (physical dimensions and u mostly) determine how man microseconds it takes the collector current to rise to the point the circuit switches off, and it also determines how long current will be delivered to the LED when the transistor is off. Nearly every inductor parameter affects the performance of this circuit.

This has been made with ferrite beads a few millimeters in diameter and toroid cores up to a few centimeters across). Here is the general relationship between core size and characteristics:

Large core: Easy to wind, lower frequency operation, higher power.

Small core: Harder to wind, higher frequency operation, lower power.

How to get started: Get a transformer core, preferably ferrite, and wind 20 turns on it. Tap by pulling a short loop of wire off to the side, then continue winding another 20 turns. Increase turns to lower frequency, decrease turns to increase frequency. I've used as little as 10 turns, center tapped (5+5) and operated this at 200 kHz. Experiment. Scroll down to the bottom of the page - the tiny ferrite core used in the #222 bulb base run at about 200 kHz.

A Common Source of Ferrite Beads

Alternative types of cores