A serious problems came across when examining power supplies is the availability (or nonavailability) of a suitable load.
Generally, the issue is sorted out by a lash-up of resistors which, however is not especially elegant, will allow tests to be carried out.
On the other hand, resistors using a power rating of 10 Watts and upwards can be somewhat costly and certain values difficult to acquire. In addition, this kind of load is definitely not vartable.
How the Circuit Works
Thinking about Adjustable Power Resistor Circuit referred right here can overcome these issues successfully and monetarily.
A 2N3055 transistor with a variable gain managed by an independent supply will form an ininitely variable load 'resistor'.
This circuit may have a power capability of up to 50 Watts if a appropriate heat sink is employed.
The ability to preserve a fixed load current when the power supply output voltage is diverse is an added advantage.
The utmost dissipation of the transistor ought to be borne in mind.
As diagram 2 figures out, a current of 2.5 A at 20 V is only 50 W but 2.5 A at 50 V is 125 W which might demonstrate to be slightly high for the 2N3055.
The base voltage for the transistor can be acquired via a voltage divider across an external power source.
If it is unavailable the circuit displayed in figure 3 above works extremely well.
In this instance, the BD 139 is utilized as a driver transistor to help maintain the battery supply current drain as low as possible.
The power level can surge relatively considerably with a rising voltage and consequently some indication of current and voltage levels in the circuit are necessary.
By using the graph shown in figure 2 it could be simply identified whether the maximum allowable power is being surpassed.
The Adjustable Power Resistor Circuit can also work as a current limiter.
This facility is going to be beneficial when charging batteries with a regular current.
The battery needs to be positioned in the circuit between the ammeter and the collector of the 2N3055.
This should be kept in mind to make sure that the voltage will not rise to a level so high to break the plates of the battery