A blocking oscillator based pulse converter

Several approximations can be used to fulfil the needs of the pulse conversion. In the past, the monostable operation of a blocking oscillator was used due to:

• Sharp rise time.
• Pulse shape parameters are straightforward dependant on circuit components.
• Needs a few components.
• Inexpensive.

What is a blocking oscillator?

A blocking oscillator consist of a BJT which is positively feed-backed by a transformer and experiences a regenerative operation. Several feed-back configurations have been considered and a study of the choosing topology can be found in our repository.

Each of the pulse parameters are related as follows:

• Pulse amplitude: tension of the desired pulse.
• Rise and fall time: turns-ratio of the transformer, switching capabilities of the BJT.
• Pulse duration and tilt: mainly affected by the magnetizing inductance of the transformer. Thanks to the inclusion of a resistor in the feed-back loop, the circuit has lower the dependence from the load.
• Overshoot, backswing, returnswing and ringing: if the turns-ratio of the transformer is close to the optimal, these effects are negligible.
• Recovery time: tension of the desired pulse and draining tension of the diode-only based net.

A technical documentation on the design of a monostable blocking oscillator can be found in our documents section

Why a monostable blocking oscillator is no longer used?

Forty years ago, the use of a blocking oscillator was a good solution. Nowadays, a simple flyback topology is better due to:

• A two-winding transformer is needed rather than a three one: much higher availability and costs reduced.
• Excellent switching capabilities.
• Easier control of the pulse shape.