School Electronics: A great site to help you with your project and exam

Transistor Driver
Darlington Driver
FET Driver
Voltage Reducer
Power Driver
Relay Output
Multi-Output

Latches
LED Blocks
Motors
PICAXE
PICAXE Inputs
PICAXE Outputs
Power Blocks
Remote Control
Sensor Blocks
Sensor Blocks 2
Sound Blocks
Switch Blocks
Timer Blocks
Touch Blocks
Alarm Example
Dice Example
Disco Example
Circuit Symbols
Handouts
Pro/Desktop
Pro/Desktop 2
Revision Notes
Links

Process: Driver Blocks Zip File ©Christopher Leigh

Here are four teaching and learning handouts in Word format which may help you in using these system modules. 2c Using System Modules, 5a Electronic Switches, 6b System Module Capacitors, and 7b System Module Astables. Check in the Handouts page for more useful handouts for teaching and learning.

Transistor Driver

A transistor driver is the simplest form of switch block. If the voltage at its input rises above about 0.6 volts, then the transistor will start to turn on. Give it a reasonable input voltage of say 2 volts and it should be turned on fully. That means that current can flow from the power supply through the load and then through the transistor and back to the power supply. The load is connected to the output side of the block. A suitable load would be an LED (Light Emitting Diode) or a buzzer. The transistor can supply about 100mA if necessary.

Darlington Driver

A "Darlington Pair" is two transistors joined together so that they make a very high gain transistor. This means in practice that the darlington driver is much easier to switch on, much more sensitve and much easier to adjust. So often it will be preferred to the ordinary transistor driver when following a sensor block. The input resistance can be quite high, but the load that can be driven is limited by the current the second transistor can supply.

FET Driver

The FET, or Field Effect Transistor, takes virtually no current from the sensor circuit so it can be very sensitive. However it usually needs a lot more voltage to turn it on than an ordinary transistor driver. This is often not a problem and since FETs can often supply more current than other transistors, a FET may be preferred. Some FETs are also called MOSFETs but they all work the same way. the 20M resistor is not absolutely necessary but is there to reduce the effect of static electric voltages which could damage the FET.

Voltage Reducer

The transistor driver block especially needs a voltage which is very nearly zero before it turns off. This isn't always easy to get so that a voltage reducer may be used. This is a bit like a volume control and can be just a variable resistor in the voltage divider arrangement so that the input voltage is reduced to the right level. Make it so that the following block is switched both on and off correctly by the preceeding block. You can use two resistors instead of the variable as shown in the PCB layout. You should not use both resistors and variable. This circuit is especially useful when using an "old" OpAmp like the 741 as a comparator since it can't get its output below about 2 volts.

Power Driver

This block is the same as the FET Driver except that it uses a high power MOSFET such as the IRF530 or BUZ51. This may, of course, need a higher voltage and current than our standard 9v PP3 can provide. The output is provided by a terminal block, with the load (motor, solenoid, bulb, etc) connected to the middle two terminals. The bottom terminal is provided so that an external power source can be connected. In this case the +ve of the external source must be connected to the top terminal of the connection block and the switch pushed over to the right to disconnect battery power. This means that you can drive a high power circuit from a PP3. This is ok for DC power but if you want to drive an ac load, then you will need to use a triac or a relay.

Relay Output

If you want to switch high power dc or any ac circuit then you probably need to use a relay. You must be very careful that your relay can cope with the voltage and current you are switching. NEVER USE MAINS ELECTRICITY. You can, however, switch 12v ac used to power a halogen bulb for a night light or disco lights.

Multi-Ouput

This block only serves as a connector. It has a 4 pin sil socket and two sets of jumper pins, one of which is arranged for many types of servo motor. The load can be connected either between 0v and the middle or signal connection, or between +ve and signal. There is a backwards diode across the +ve to signal output to guard against back emf from an inductive load such as a motor, solenoid or relay. The diode is not needed for other loads but won’t do any harm.