symmetrical voltages from a doorbell transformer

16 R. Storn symmetrical voltages from a doorbel) transformer This circuit is of interest not merely because it uses a belt transformer with a single secondary winding to provide symmetrical voltages for low-current applications but also because the final output voltages are greater than the normai belt transformer (220 V/8 V) output. In fact the final output can be as much D4 C3 0 7 2 0SVP 19 V/150 mA 83532-1 ::3 D3 D ... D4 = 1 N4001 as twice this value. This multiplication is achieved using two voltage doublers each consisting of two diodes and two capacitors, connected head to tail. Each diode/capacitor couple takes every alternate half cycle of the sinusoidal voltage such that the output voltage U is (theoretically) equal to 2/2 Ueff., where Ueff. is the effective output voltage of the transformer. A current of 150 ... 200 mA and 1 V of ripple can be expected using the capacitor values shown here. In order to increase this current without a similar increase in ripple the value...