Pulse transformer issues

[Beel]

Hi. I recently had too switch brands of pulse transformer that I’m using to fire the gates on an SCR based dc drive. The new one is 200uh the old one is 100uh. I’m having issues with the trigger circuit. I changed the value of the trigger circuit capacitor but the output of the drive isn’t stable. Any thoughts ?

 

[FvM]

No. Need to consider all transformer data, e.g. series resistance, max. Vs. Do you have a schematic of the driver circuit?

 

[Beel]

No. Need to consider all transformer data, e.g. series resistance, max. Vs. Do you have a schematic of the driver circuit?

Here is the circuit

 

[FvM]

There's no indication why circuit operation would depend on transformer parameters. Some values look strange, possibly a type. I guess mF and mH means µF and µH actually.



What does "the output of the drive isn’t stable" exactly mean?

 

[Beel]

With the original 100uH pulse tx the dc output of the drive was linear and stable as the speed pot increased. With the replacement 200uh unit the drive will oscillate and eventually the dc output will significantly decrease .

 

[Easy peasy]

the 200uH one may be saturating - is it the same core size approx? ideally you would have a diode on the Tx o/p to the gate and a gate to kathode resistor ...

 

[Beel]

Hi would you be able to provide a drawing / schematic