Jumbo dimmer

981jumbo dimmer The name jumbo dimmer points to its association with the Jumbo Display (see EE, July & August 1985), but it can, of course, also be used with other appliances such as lamps, pumps, ventilators: in short for all ap- plications where a direct voltage is to be controlled by pulse duration modulation. 5 -30V Fl 4 A TIP 147 √∑c1 output of the comparator is a rec- tangular voltage with a frequency of around 200 Hz and a pulse duration that is variable between nought and 100 per cent. The onset point of the pulses is determined by the setting of Pi. The actual control function is current of up to 5 A. provided by transistor Ti, which The supply voltage must lie between to the supply voltage. switches the relatively large display 5 V and 30 V: note that the efficiency (Sv) With reference to the diagram, At is a rectangular-wave generator: a useful by-product of this stage is the (quasi) triangular voltage at its invert- ing input. This signal is applied to the non-invertin...