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.