design square waveform oscillator circuit/ relaxation oscillator

[dinz]

hello all .. anyone that can help me design electronic circuit ..
this is the characteristics of the circuit :
one BJT, one OPAMP UA741 and single power supply. the oscillator will connected to a transistor with collector load of 10K the available frequency is between 200Hz to 1kHz.

i hope that any one in here can help me ...
thanks ...

[Kevin Weddle]

I think a relaxation oscillator is a good job for an opamp. I prefer the opamp to always source up to about 20mA, as opposed to sink. The problem with opamp outputs is that they are prone to high voltage swings, which will destroy the transistor. I am not sure that propagating a square wave in the linear region is a good idea. Cutoff and saturation is probably best. You will need to DC couple the opamp to transistor.

[dinz]

thanks for the apply ... but what will i do to prefer the circuit with such that characteristic that given by my lecture ? it is actually for my latest mini project ..
do u have any idea to design that circuit ? please tell me more detail about it ........ :)

[dinz]

i want to know it is variable relaxation oscillator is the same as rectangular waveform circuit ?  ???

[Kevin Weddle]

An opamp output can only be operated to about 15mA DC whether the current is going in or going out. A 5Vpp output into a 2Kohm load is 2.5mApp. A 2Kohm load is optimistic for an ordinary transistor load, however. I would use good size resistors to bias the transistor, with a very low transistor current. That way you can get near at least 2Kohm load impedance. You might consider biasing the transistor at cutoff, then let the rising signal send it into saturation. This is what I meant by not using the linear region of the transistor.