fringe

Firstly, thank you Kevin and hero for taking the time.... Kevin",If the load is a high impedance FET, then it can be done more easily. If the load is low impedance, you should change the circuit which generates the pulse". Yes, it does have a high impedance fet- the fet is the main driver for the chopper . Basically it chops the negative side of a generated then rectified dc voltage , thus producing a high current DC chopped output (40vpp 20khz ) Changing the Pulse drive circuit is not and option on the OEM board ... I will put up a diagram of the output circuit later today... but work must come first Hero, as for the CD4011 i will investigate the option possibly build both,

Thanks for the reply, The pulse train (20 kHz negative pulses with respect to gnd) remain constant in frequency period is 50 micro-secs' The width is automatically adjusted between 6 and 20 usec by the current PWM..Which is (completely epoxy bonded) so no change can be made at that level. 1. Firstly, I need to reduce the minimum pulse width from 6 to around 4.5 usecs to reduce to storage voltage on the chopper capacitors when the unit is in standby mode, this must be done without affecting the freq... 2. Secondly, The unit will return to normal operation and bypass the circuit I am designing when a load is applied to the chopper output..............(This part I have already designed) I have all the tools at my finger tips.... I did first try to simulate 555 pwm making VCC = VEE (0 volts) and GND = VSS (-15volts) However, multisim v11 didn

Help needed to control the pulse width of a (negative) -15vdc pulse train at 20khz.. Basically, the pulse is as described in the picture attached which is of the pulse itself all details are within picture. Pulse width is 6 micro-sec, and i want to be able to reduce increase or reduce it by around 30% of current value I will not need to vary the frequency only the pw.. I would like to use something very simple... I have been searching everywhere. However, most designs are base on negative going pulses on a +dc supply and not on a wave form that actually goes positive from a negative -15vdc supply..... please idea's would be great appreciated. Ps: The pulse train controls a fet driven NEG Dc chopper circuit (high current) Thanks to all who take the time to at least read this post.