Schematics > Motor, light and power control > Solid State Power Controller
Solid State Power Controller
About the Circuit
The ckt is built around two 555 timer ICs. U1 and U2. U1
is wired as a variable duty cycle oscillator with a constant time period of around
0.1 second. Duty cycle can be varied from 0 to 100 per cent by R4 potentiometer.
The output of U1 (pin 3) is connected to the rest input (pin 4) of U2.
U2 is wired as a comparator with hystereis, i.e a Schmitt
trigger. Diode D6 brings the potential at control voltage (pin 5) terminal at
0.7V. The threshold (pin 6) and trigger (pin 2) terminals connected together constitute
the input. The output (pin 3) of the Schmitt trigger goes high when Vin equals
or below 0.35V and goes low when it is equals or above 0.7V.
Transformer T1 with rectifying diodes D1 and D2 delivers
unidirectional AC voltage across R1 with a peak voltage of 8.5V and 100Hz frequency.
C1 is the filtering capacitor. D3 prevents the voltage across R1 from being filtered.
Since the input of the Schmitt trigger is connected across
R1, its out put will be high when input voltage falls below 0.35V and remains
so till it exceeds 0.7V. If pin 4 of U2 is left unconnected, the triac will be
fired at the start of each half cycle of AC by a short pulse. Hence full power
will be delivered to the load. But since output of U1 is connected to the rest
input of U2, the Schmitt trigger delivers pulses to the gate of triac only when
output of U1 is high. This explains how variable duty cycle zero crossover switching
is accomplished. I have used a 5-amp triac, which is capable of switching loads
up to 1000W. Using a triac with larger current rating can also control higher
loads. Of course, size of the heat sink will have to be suitably increased.
Construction
You can build this circuit in a general purpose IC strip board. Potentiometer
R4 should be linear with a plastic shaft. It can be mounted on the front portion
of the enclosure, with a dial marked from 0 to 100 per cent power at, say 5 per
cent intervals. If a metallic enclosure is used, care must be taken to ensure
that the heat sink of triac does not touch it anywhere.
To avoid shock, do not touch any part of circuitry while in operation.
Components
U1 & U2 - NE555 timer
Q1 - 5A, 400 PIV triac (BT136)
D1-D3 - IN4001 rectifier diodes
D4-D6 - IN4148 switching diodes
R1 - 5.6K
R2 -2.2K
R3 -470 ohms
R4 - 100K linear potentiometer with plastic shaft
(all resistors ¼ watt, 5% tolerance)
C1 - 1000mfd, 12V
C2 - 1mfd, 12V
C3,C4 - 0.1mfd,50V ceramic
T1 - 220V primary 6V-0-6V secondary, 150ma
F1 - 5-amp fuse
(You will have to connect the AC line to T1 primary. I have not shown that)
Disclaimer
| Please take the greatest of care in handling
AC mains supply while constructing this project. If you have no knowledge
of mains wiring or unfamiliar with household mains supply, PLEASE DO NOT ATTEMPT
CONSTRUCTION. I take no responsibility in any personal injury or loss of life
or properties suffered by any person while undertaking the construction of
this project or using the end product by following my instructions. |
Download this project in doc format
Title: Solid State Power Controller
Source: www.electronics-lab.com
Published on: 2005-02-03
Reads: 406
Print version:  Other schematics from Motor, light and power control
Automatic 12 Volt Lamp Fader Courtesy Light Fading LEDs Triple Stroboscope LED or Lamp Pulser Infa-Red Remote Control Expandable 16 Stage LED Sequencer Automatic Room Lights IR Remote Control Jammer Auto Heat Limiter for Soldering Iron
Schematics > Motor, light and power control > Solid State Power Controller | 
Home
